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Environmental Nanotechnology, Monitoring & Management 1–2 (2014) 36–49

Contents lists available at ScienceDirect

Environmental Nanotechnology, Monitoring &Management

jou rn al hom epage: www.elsev ier .com/ locat e/enmm

eview

agnetic composite an environmental super adsorbent for dyeequestration – A review

. Sivashankar, A.B. Sathya, K. Vasantharaj, V. Sivasubramanian ∗

epartment of Chemical Engineering, National Institute of Technology Calicut, India

r t i c l e i n f o

rticle history:eceived 6 February 2014eceived in revised form 7 June 2014ccepted 21 June 2014iero Gardinali

eywords:orption

a b s t r a c t

Adsorption is the most extensively used technique for dye sequestration. Magnetic separation of toxicpollutant is becoming a potential method in waste water purification and found to have predominantsignificance in the removal of dyes more effectively compared to conventional method of treatments.Numerous natural and synthetic adsorbents were used, out of which magnetic composites (MCs) andmagnetic nanocomposites (MNCs) have gained much attention presently in the removal of dyes fromaqueous solution. Abundant references are existing pertaining to synthesis of various magnetic compos-ites and its application in adsorption of dyes. This report displays the exploitation of MCs and MNCs for

yesagnetic compositesagnetic nanocomposites

eaction kinetics

adsorption of dyes, hazards posed by dyes, sorption mechanism, preparation methods, magnetic behaviorand characteristics of magnetized particles with the relevant literature on the basic principle of adsorp-tion using MCs and MNCs for separation of dyes under optimum physicochemical condition. Adsorptionreaction model, diffusion model and isotherms which facilitate in understanding the reaction mechanismbetween adsorbent and adsorbate are concisely discussed.

© 2014 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/3.0/).

ontents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372. Industrial dye stuffs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373. Hazards of dyes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374. Sorption and its mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375. Preparation techniques involved in synthesis of MCs/MNCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386. Magnetic behavior of magnetized particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387. Characteristic features of magnetized particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398. Magnetic Composites (MCs) as dye adsorbent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409. Magnetic Nanocomposites (MNCs) as dye adsorbent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4210. Advantages of MNCs over MCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4511. Adsorption reaction model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

11.1. Pseudo-first-order rate equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4611.2. Pseudo-second-order rate equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

12. Adsorption diffusion models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4612.1. Liquid film diffusion model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4612.2. Intraparticle diffusion model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

13. Adsorption isotherm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

14. Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

∗ Corresponding author. Tel.: +91 4952285406; fax: +91 4952287250.E-mail address: siva@nitc.ac.in (V. Sivasubramanian).

ttp://dx.doi.org/10.1016/j.enmm.2014.06.001215-1532/© 2014 Published by Elsevier B.V. This is an open access article under the CC B

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

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Y-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

ology

1

isfcswtftritmstfipMtcteamgra2t(shfmtah2puiw

t

R. Sivashankar et al. / Environmental Nanotechn

. Introduction

The land consists of 75% water, but only 3% is fresh water out oft and 1% is available for people to use (Ragunath, 2006). Waterupports life for man, animals and plants. Yet the provision ofresh water available to humanity is shrinking. One of the primaryauses of this is the polluting of many freshwater resources. Theoils, lakes and rivers has become polluted with an assortment ofaste, including untreated or partially treated municipal sewage,

oxic industrial effluents, harmful chemicals, and ground watersrom agricultural activities. Polluted water not only determineshe water availability, but also invests millions at risk of water-elated diseases (WPNWAC, 2003). Oil and gasoline from petroleumndustry, sewage and solid waste, discharge of nuclear materials,oxic chemicals from industrial plants, fertilizers and pesticides are

ajor sources of water pollution (Dozier, 2005). Fig. 1 illustrates theources of water contamination. In certain conditions, water pollu-ion is caused by nature itself, but frequently, human actions are aptor the pollutants that go in the water (Carneiro et al., 2010). Dyes one of the most important pollutants in the effluents of textile,aper, plastic, food and cosmetic industries (Rafatullah et al., 2010).any of the industrial dyes are toxic, carcinogenic, mutagenic and

eratogenic (Mekkawy et al., 1998; Oxspring et al., 1996). It is cal-ulated that, over 100,000 commercially available dyes with morehan 7 × 105 tonne of dyestuff are produced per year (McMullant al., 2001; Pearce et al., 2003; Lee et al., 2006). Therefore, there is

huge quantity of colored waste water is generated from theseanufactures. Recently, the removal of dyes from effluent has

iven much consideration in controlling water pollution. Among aange of techniques available for dye removal from effluent, such asdsorption, flocculation, oxidation and electrolysis (Wawrzkiewicz,012; Crini, 2003), adsorption turns to be uncomplicated, effec-ive and economical technique applied for wastewater treatmentShuang et al., 2012). In general, adsorbent used are smaller in sizeince smaller size adsorbents have increased surface area leading toighest adsorption capacity. But it would be really hard to sort them

rom water after reaching saturated adsorption. In such conditions,agnetic separation of adsorbents has been one of the promising

echniques for wastewater treatment, since no contaminants suchs flocculants are produced and large quantity of effluent can beandled within a diminutive period (Rocher, 2008; Luo and Zhang,009). Magnetic separation technique using MCs (magnetic com-osites) and MNCs (magnetic nanocomposites) has attained widese in sequestration of dyes due to its stupendous significance

n accelerating separation speed and improvising the efficiency of

ater treatment (Qadri et al., 2009).

This review is to provide a summary of information bearing onhe use of MCs and MNCs as adsorbents for removal of dyes from

Fig. 1. Sources of water contamination.

, Monitoring & Management 1–2 (2014) 36–49 37

aqueous solution. The competence of MCs and MNCs are discussedwith their operational parameters. Further, overview of few MCsand MNCs used for adsorption and its performances over removal ofdyes are discussed separately. The adsorption kinetic, diffusion andisotherm models which influence the equilibrium time required forsolute uptake from liquid phase are also surveyed.

2. Industrial dye stuffs

Dyes are colored organic compounds that are applied to impartcolor to various substrates including paper, leather, fur, hair, drugs,cosmetics, waxes, greases, plastics and textile materials (Amithet al., 2007; Samanta and Agarwal, 2009; Monash and Pugazhenthi,2009). The main role of dyes is in the cloth industry, despitesubstantial quantities are consumed for coloring, such diversematerials as leather, paper, plastics, crude oil products and intellec-tual nourishment. Generally, the dyes used in the textile industryare basic dyes, acid dyes, reactive dyes, direct dyes, azo dyes, mor-dant dyes, vat dyes, disperse dyes and sulfur dyes (Demirbas, 2009),where azo derivatives are the major class of dyes, used in the indus-tries (Forgacs et al., 2004). Dyes can be classified into cationic,anionic and nonionic dyes. Cationic dyes are basic dyes while theanionic dyes include direct, acid and reactive dyes (Mishra andTripathy, 1993). General classification of colorants is shown inFig. 2.

3. Hazards of dyes

The dye materials are not only possesses harmful effects, butalso aesthetically unpleasant in water. The dyes used in the tex-tile industries include several structure varieties such as acidic,reactive, basic, disperse, azo, diazo, anthraquinone based and metalcomplex dyes (Banat et al., 1996). It puts up have more or less harm-ful effects. Intense exposure to dyes leads to have increased heartrate, vomiting, shock, Heinz body formation, cyanosis, jaundice,quadriplegia, and tissue necrosis in humans (Vadivelan and Kumar,2005). Dyes like Metanil Yellow also have a tumor-producing effect(Ramachandani et al., 1997) and can produce enzyme disorders inthe human body (Das et al., 1997). However, it is not mutagenic butcan alter the gene expression (Gupta et al., 2003). On oral consump-tion, it causes toxic methaemoglobinaemia (Sachdeva et al., 1992)and cyanosis (Chandro and Nagaraja, 1987) in humans, while skincontact results in allergic dermatitis (Hausen, 1994). The oral feed-ing or intraperitoneal and intratesticular administration of dyesin animal produces testicular lesions due to which seminiferoustubules suffer damage and rate of spermatogenesis is decreased(Tiwari, 2012).

4. Sorption and its mechanism

Sorption is one of the processes, being widely used for dyeremoval and has wide applicability in wastewater treatment. Theterm sorption refers to a process wherein a material is centered ata solid surface from its liquid or gaseous environment. In universal,two classes of sorption processes are available, if the draw betweenthe firm surface and the adsorbed molecules is physical in nature,the adsorption is referred to as physical adsorption (physisorp-tion) and if the attraction forces are due to chemical bonding,the adsorption process is called desorption. Frequently, in physi-cal adsorption, the attractive forces between adsorbed moleculesand the solid surface are Van der-Waals forces of attraction and

reversible adsorption occurs when they are weak in nature and incase of chemisorptions, the higher intensity of the bonding resultsin difficulty to remove chemisorbed adsorbate from the solid sur-face (Gupta and Suhas, 2009; Yadla et al., 2012).

38 R. Sivashankar et al. / Environmental Nanotechnology, Monitoring & Management 1–2 (2014) 36–49

Va

Phthacyan

Pigments

at

Malo -nin e Minera l

Azoic

Oxidatdye

Miner

Colourant s

Ingraindyes

tives

ral

Basic

Direc t

Sy

water soluble

R

Dy

yntheti c

Acid

Reactiv e

Optical

win

ye stuffs

wate r nsoluble

S

Di

Na

Vat

ulphur

isperse

atu ral

ssifica

tepietaamndwteptt2M

5M

oed22ah

Fig. 2. General cla

The essential characteristic of an adsorbent is that, the quan-ity of adsorbate accumulated on adsorbent which is generallystimated from the adsorption isotherms. The adsorbent shouldossess few basic qualities such as porous in structure (resulting

n high surface area), smaller in size and time taken for adsorptionquilibrium should be as depressed as possible with the purposehat it can be used to remove dye wastes in a short period (Guptand Suhas, 2009; Nguyen and Juang, 2013). Tailoring of naturallyvailable adsorbents as MCs/MNCs provides an excellent propertyakes them to be well recovered by magnetic separation tech-

ology after adsorption or regeneration, which sweeps over theisadvantage of separation (Solis et al., 2012). By impregnationith a magnet, the adsorbents could be easily told apart from solu-

ions under an external magnetic field (Yang et al., 2009; Phamt al., 2011; Slunjski, 2000). Investigation of other factors such asH, activators & depressants, adsorbent & adsorbate concentra-ions, temperature, agitation, etc. are desirable in understandinghe adsorption of dyes on magnetic composites (Salleh et al.,011). Fig. 3 explains the overview of adsorption processes usingCs/MNCs.

. Preparation techniques involved in synthesis ofCs/MNCs

Several preparation methods were described for synthesisf magnetic nanoparticles which includes co-precipitation (Wuat al., 2011; Drbohlavova et al., 2009; Zhao et al., 2008), thermalecomposition (Daengsakul et al., 2009), solvothermal (Li et al.,

013a), microemulsion (Drmota, 2012), sonochemical (Wu et al.,007), chemical vapor deposition (Morales et al., 2013), microwavessisted (Safarik et al., 2013), polyol process (Karipoth et al., 2013),ydrothermal (Nejati et al., 2012), photolysis (Nkosi et al., 2012),

Identification of suitable adsorbent material for

colour removal

Synthesis and preparation of ferro

fluid

Magnetic separation of MCs/MNCs and elution

of aqueous solution

Desorption of colourants from adsorbent used

Fig. 3. Overview of adsorption p

wwhitener s

tion of colorants.

Sol–Gel (Xu et al., 2007), electrochemical (Starowicz et al., 2011),electrodeposition (Banerjee et al., 2000), laser pyrolysis methods(Sabino et al., 2004) have been reported for synthesis of MNCs. Par-ticle size distribution, particle size control, crystallinity and crystalstructure, shape control, alignment (Rao, 2007; Hyeon, 2003) arethe key issues in synthesizing MNCs. These methods assist inpreparing magnetic composites, which are stable at ambient tem-perature, uniform size, regular shape, high level of monodispersity,non-aggregate, etc. Fig. 4 presents the classification of magneticcomposites synthesizing techniques.

6. Magnetic behavior of magnetized particles

External magnetic field applied to materials determines theproperty of magnetic particles. Descriptions of orientations of themagnetic moments in a material aid to identify different formsof magnetism observed in nature. Five basic types of magnetismcan be described: diamagnetism, paramagnetism, ferromagnetism,antiferromagnetism and ferrimagnetism (Akbarzadeh et al., 2012).Diamagnetism is a central attribute of all atoms (atoms), and themagnetization is very small and opposed to the applied magneticfield direction. Many materials exhibit paramagnetism, where amagnetization develops parallel to the applied magnetic field as theorbit is increased from zero, however, the effectiveness of the mag-netization is small. Ferromagnetism is the belongings of those stuffswhich are inherently magnetically ordered and which developspontaneous magnetization without the need to utilize a field. Adisparity on ferromagnetism is ferrimagnetism, where different

atoms possess different moment strengths, but at that state is stillan ordered state below a certain critical temperature. The magneticmaterial can be sorted based on their susceptibility, i.e., diamagnet(� < 0), paramagnet (� > 0), ferromagnet (� � 0). It has been proven

Magnetic modification of adsorbent material

using ferro fluid (MCs/MNCs)

MCs/MNCs added to analyte (dye solution) for adsorption of dyes

on to MCs/MNCs

Regenration and reuse of MCs/MNCs for next

cycle of adsorption process

rocess using MCs/MNCs.

R. Sivashankar et al. / Environmental Nanotechnology, Monitoring & Management 1–2 (2014) 36–49 39

Synthe sis of Magnetic Compo sites

Solid Phase Synthesis

Combustion

Annealing

Gas Phase Synthesi s

Chemical vopour depostion

Arc di scharg e

Laser pyrolysis

Liquid Pha se Synthe sis

Co-precipitation

Microemulsion

Thermal Decomposition

Solvothermal

Chemicalreduction

Sonochemical redu

Microwave ass isted

Protection Method

Organic coating

Inorganiccoating

ques o

tbSscMjMvrcZpdmvitm1i

7

mbaagtbscb2

amWstta

where h is the Planck constant (6.626 × 10−27 erg/s); is Univer-sal constant (9.274 × 10−21 Erg/G); � is frequency (9.707 × 109 Hz)and Hr a resonance of magnetic field (G). These values will be an

Fig. 4. General classification of techni

hat many of the unique magnetic properties of nanoparticles cane ascribed to their high surface-to-volume ratio (Frey et al., 2009;ingamaneni et al., 2011). Saturation magnetism (Ms) varies withize until it passes a threshold size beyond which magnetization isonstant and is close to the bulk value. The linear dependence ofs on size below this threshold has been shown in various sub-

ect areas. Research on the effect of shape influence the property ofCs and MNCs in volume or related size parameter. The anisotropy

alue (Magnetic anisotropy is the directional dependence of a mate-ial’s magnetic properties) for spherical nanoparticles is higher thanubic nanoparticles of the same volume (Noh et al., 2012; Song andhang, 2004; Salgueiro et al., 2013; Ardisson et al., 2008). Com-osition is the most commonly cited parameter responsible foretermining the specific magnetic properties of a material. Theseagnetic properties arise in the presence or absence of unpaired

alence electrons located on the metal atoms or metal ions foundn MNPs (Zhen et al., 2011; Williams et al., 1982). The orientation ofhe magnetic moment, �, associated with the electrons defines the

agnetic behavior. Using the magnetic moment of a single electron,.73 Bohr magnetons (BM), we can calculate the magnetic moment

n MCs and MNCs (West, 1999; Kolkhatkar et al., 2013).

. Characteristic features of magnetized particles

Magnetic adsorbents have been prepared extensively usingetal oxide as a backing material for natural and synthetic adsor-

ents. Adsorbent/catalyst like magnetic metal oxide compositend magnetic metal oxide supported adsorbents possesses highdsorption capacity and catalytic activity toward organic and inor-anic waste water coming out from coal and steel industries,extile and dyeing industries etc. The magnetic modified adsor-ents can be generally classified according to difference of theupport of magnetic particles such as magnetic particle modifiedarbon adsorbent, magnetic particles modified clay mineral adsor-ent, magnetic particle modified biopolymer adsorbent, etc. (Jiuhui,008).

Magnetic metal oxide composite adsorbent (powder CuFe2O4nd MnO–Fe2O3) was first prepared by a simple co-precipitationethod from environmental friendly and low cost materials byu et al. (2004, 2005). This nanocomposites have a relatively high

urface area, a smaller particle size, and porous structure. In par-icular, the excellent magnetic property of the powder makes themo be easily recovered by magnetic separation technology afterdsorption or regeneration, which overcomes the disadvantage of

ction

f synthesizing magnetic composites.

separation difficulty of common powdered adsorbents. Wu alsostudied the adsorption performance of the magnetic compositesusing azo dye, namely, Acid red-B (ARB) as a model compound.The results demonstrated that both the CuFe2O4 and MnO–Fe2O3adsorbents had high adsorption rate and the maximal adsorptioncapacities for ARB are 86.8 and 105.3 mg/g, respectively.

The presence of ferrofluids in the magnetically modified adsor-bents can be investigated with an electron spin resonance (ESR)spectrophotometer. Microscopic observation facilitates in char-acterizing magnetic modified adsorbents. The application of anoutside magnetic field may bring forth an inner magnetic field in thesample which will add to or deduct from the external field (Karaand Demirbel, 2012; Yavuz et al., 2006). The local magnetic fieldgenerated by the electron magnetic moment will add vectorially tothe external magnetic field (Hext) to present an effective field (Heff)(Eq. (1)).

Heff = Hext + Hlocal, (1)

Yavuz et al. (2006) developed a magnetically modified yeast cellsfor the absorption of mercury. The relative intensity magnetic mod-ified yeast cell is found to be 100. This value indicates that the yeastcell structure has a local magnetic field because of ferrofluid in itsconstruction. The g factor can be considered as quantity character-istic of the molecules in which the unpaired electrons are turnedup, and it is calculated from Eq. (2). The mensuration of the g factorof an unknown signal can be a valuable help in the identification ofa signal. In the literature the g factor for Fe3+ is determined between1.4–3.1 for low spin and 2.0–9.7 for high spin complexes (Swartz,1997). The g factor was found to be 3.8 for magnetically modifiedyeast cell structure.

g = h�

ˇHr, (2)

important design parameter for a magnetically stabilized fluidizedbed or for magnetic filtration. The value of this magnetic field is apart of the flow velocity, particle size and magnetic susceptibilityof solids to be removed (Swartz, 1997; Akgol and Denizli, 2004).

40 R. Sivashankar et al. / Environmental Nanotechnology, Monitoring & Management 1–2 (2014) 36–49

Table 1Summary of adsorption capacity of magnetic composites for dyes.

Adsorbent Adsorbate Adsorptioncapacity (mg/g)

pH Temp. (◦C) Kinetic model Isotherm Reference

Glutamic acid modified chitosanmagnetic composite

Crystal violet 375.4 7 20 Pseudo 2nd order Langmuir Yan et al. (2013)

Glutamic acid modified chitosanmagnetic composite

Light yellow 7GL 217.3 7 20 Pseudo 2nd order Langmuir Yan et al. (2013)

Monoamine modified magnetic silica Acid orange 10 61.33 3 25 Pseudo 2nd order Langmuir Atia et al. (2009)Epichlorohydrin magnetic alginate

beadsMethyl orange 6.54 7.5 – Pseudo 2nd order Langmuir Rocher et al. (2010)

Magnetic chitosan/poly (vinyl alcohol)hydrogel beads

Congo red 470.1 – 25 Pseudo 2nd order Langmuir Zhu et al. (2012)

Magnetic graphene oxide(impregnation method)

Reactive Black 5 164 3 25 Pseudo 2nd order Langmuir Kyzas et al. (2013)

Magnetic graphene oxide(co-precipitation method)

Reactive Black 5 188 3 25 Pseudo 2nd order Langmuir Kyzas et al. (2013)

Organosilane functionalized Fe3O4

compositeBrilliant blue FCF 241 mmol/kg 6.5 <50 – Langmuir Wu et al. (2006)

Magnetic cellulose Fe3O4 activatedcarbon composite

Congo red 66.09 4 25 Pseudo 2nd order Langmuir Zhu et al. (2011)

Magnetic �-Fe2O3 crosslinked chitosancomposite

Methyl orange 29.83 4 – Pseudo 2nd order – Zhu et al. (2010)

Magnetic porous covalenttriazine-based framework

Methyl orange 291 – 25 Pseudo 2nd order – Zhang et al. (2011)

8

roppscamttparad

gdbaitPvat

hftmwfrat

u

compositesMagnetic powder MnO–Fe2O3 Acid red ARB 105.3

. Magnetic Composites (MCs) as dye adsorbent

MCs have been widely used with adsorption process in envi-onmental purification. The main advantage of MCs is that a massf wastewater can be disposed in a very short period of time androduce no contaminants. Most commercially available magneticarticles are rather expensive and cannot be applied to large-cale processes (Safarik et al., 2012). Magnetic modification of lowost adsorbents could lead to materials suitable for biotechnologynd environmental applications (Safarik and Safarikova, 2010). Theagnetic separation provides a desirable path for online separa-

ion, where particles with affinity to target species are merged withhe heterogeneous solution. Upon merging with the solution, thearticles tag the target species. The external magnetic field is thenpplied to separate the tagged particles from the solution. Table 1eveals the maximum adsorption capacity of magnetic compositest optimum pH and temperature and models fit toward a range ofyes.

Safarik et al. (2012) used magnetically modified spent coffeerounds (discharged from food industries) for adsorption of fewyes crystal violet, malachite green, amido black 10B, congo red,ismarck brown Y, acridine orange and safranin O. The maximumdsorption capacity reached 73.4 mg/g of dried magnetically mod-fied coffee grounds for acridine orange. The existence of iron alonghe magnetic modified coffee grounds was detected using adaptederl’s staining procedure. The outcomes of the batch experimentisibly exhibit that the spent coffee grounds can be effortlesslyltered into a magnetic form by magnetic fluid treatment for poten-ial removal of selected dyes.

Safarik and Safarikova (2010) applied ferrofluid modified peanutusks (FMMPH) for the sequestration of water soluble organic dyes

rom aqueous solution. FMMPH was used as an absorbent to studyhe binding of several water soluble dyes (acridine orange, bis-

arck brown, crystal violet and safranin-O). Maximum adsorptionas achieved up to 95.3 mg/g, 86.1 mg/g, 80.9 mg/g and 71.4 mg/g

or bismarck brown, safranin-O, crystal violet and acridine orangeespectively. The langmuir isotherm fits well with equilibrium

dsorption data. Therefore, this low cost adsorbent could be poten-ially used for removal of dyes.

Yan et al. (2013) prepared biodegradable magnetic adsorbentsing glutamic acid modified chitosan by a one-step method.

3.5 – Pseudo 2nd order Langmuir Wu et al. (2005)

The construction of the glutamic acid modified chitosan magneticcomposite microspheres (CS-Glu-MCMs) was characterized byFourier transform infrared spectroscopy (FTIR), thermogravimetricanalysis (TGA), vibrating-sample magnetometer (VSM), scanningelectron microscope (SEM), and equilibrium swelling experiment.CS-Glu-MCM was used as adsorbent for elimination of cationicdyes, methylene blue (MB), crystal violet (CV) and light yellow7GL (7GL), from aqueous solution and the adsorption capacity wasfound to be 180 mg/g for MB, 375.4 mg/g for CV and 217.3 mg/g for7GL. CS-Glu-MCM shows the highest dye uptake rate on compar-ing with chitosan magnetic composite microspheres (CS-MCMs)without modification. This may be due to the size of the mag-netic atom. The diameter of CSGlu-MCM (∼90 �m) is lesser thanthat of CS-MCM (∼120 �m), exhibiting a larger surface area forCS-Glu-MCM and therefore an improved adsorption performancewas achieved. Further, carboxyl groups on glutamic acid in CS-Glu-MCM play a major chore in the adsorption of dyes. The adsorptionof dyes by both CS-MCM and CS-Glu-MCM ensures the homo-geneous monolayer chemisorption mechanism. Desorption wasperformed at room temperature. The dyes loaded magnetic adsor-bents were recovered using 0.1 mol dm3 HCl aqueous solutions andconsequently activated for regeneration using 0.1 mol dm3 NaOHaqueous solution to pH 8.0.

Safarikova et al. (2005) synthesized magnetically modifiedBrewer’s yeast cells (Saccharomyces cerevisiae) using water basedmagnetic fluid for adsorption of various water soluble dyes.The adsorption capacity was found to be 228.0 mg/g, 93.1 mg/g,46.6 mg/g, 41.7 mg/g, 11.6 mg/g for aniline blue, congo red,safranine-O, crystal violet, naphthol blue respectively. The quan-tity of the heat treatment during the preparation process was setup to cause a minor influence on the adsorption capacity. Theexperiment fits well with Freundlich isotherm describing a het-erogenous adsorption. The maximum adsorption was achieved foraniline blue, could be induced by the bearing of two aromatic ringswith sulfonic group.

Atia et al. (2009) synthesized monoamine modifiedmagnetic silica (MAMMS) using precipitation method and

compared the adsorption efficiency of MAMMS and MAMPS(magnetic free silica). The particles were immobilized with 3-aminopropyltriethoxysilane and characterized by FTIR and X-raydiffraction (XRD). The Gibbs free energy (�G◦) indicates the

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pontaneity of adsorption was found to be −26.52 and28.49 kJ/mol at 25 ◦C for MAMPS and MAMMS, respectively.he adsorption depending on pH was brought away to advanceia the electrostatic attraction between the positively chargedrotonated amino groups on the silica surface ( NH3+) and theegatively charged sulfonate groups (SO3−) of the dyestuff. Theigher adsorption capacity was recognized for MAMMS in spiteAMPS possesses a higher surface area and pore volume. This may

e ascribable to the formation of thin films of silica on magnetitene particles that facilitates the interaction between dye withhe active sites of silica and inaccessibility of the dye ions forntraparticle diffusion in MAMPS. Desorption was performed usingn aqueous solution of 10pH and 98% recovery was achieved afterhree adsorption/desorption cycles.

Epichlorohydrin magnetic alginate beads (EpiMAB) were madesing extrusion technique and crosslinked with epichlorohy-rin by Rocher et al. (2010). EpiMAB served as biosorbent forhe removal of the dyes methyl orange (MO) and methylenelue (MB). The Langmuir equation fits well the adsorption dataith maximum adsorption capacities of 0.02 mmol/g for MO and

.7 mmol/g for MB. The issue of pH of the solution on adsorptions also tested and found effective at 7.5 and <7 for MB and MOespectively.

Zhu et al. (2012) prepared a novel magnetic chitosan/polyvinyl alcohol) hydrogel beads (m-CS/PVA HBs) by an instantaneouselation method and characterized by XRD, VSM and TGA. Thedsorption capacity of congo red on m-CS/PVA HBs was found to be70.1 mg/g. Positive value of enthalpy change (�H◦) (13.32 kJ/mol)

ndicates that the adsorption was endothermic and physical inature. The values of Gibbs free energy change (�G◦) were foundo be 3.321 kJ/mol at 25 ◦C for m-CS/PVA HBs, indicating the spon-aneity of congo red adsorption.

Magnetic graphene oxide (mGO) has been tested for adsorptionn Reactive Black 5 (RB5) by Kyzas et al. (2013). The synthesis ofGO was achieved in both impregnation (mGOi nanoparticles) and

o-precipitation method (mGOp nanoparticles). Characterizationith various techniques (SEM, FTIR, XRD and VSM) reveals manyossible interactions/forces of dye-composite system. The adsorp-ion evaluation of the magnetic nanoparticles obtained higherdsorption capacity of mGOp derivative (188 mg/g) and lower ofGOi (164 mg/g).Wu et al. (2006) produced organosilane-functionalized Fe3O4

omposite particles by reacting organosilane precursor, bis(3-trimethoxysilyl) propyl]-ethylenediamine (TSPED) on Fe3O4

agnetic particles. The adsorption and desorption properties ofhe composites were tested against brilliant blue FCF (BBF) and thexperimental results confirm equilibrium time for adsorption andesorption was achieved within 15 min. The composites present aoccule form and therefore sequestration from the solution with aagnet is effortless. The equilibrium adsorption amount is found to

ncrease with increasing initial dye concentration and diminishedith the increasing ionic strength. Hydrogen bonding, electrostatic

nd hydrophobic attractions are found to be the driving forces forhe adsorption of BBF. In addition, anion exchange exhibits a sub-tantial role during adsorption. NaOH solution appears to be a morefficient desorption medium than NaCl solution.

Magnetic cellulose/Fe3O4/activated carbon composites (m-ell/Fe3O4/ACCs) were successfully synthesized and used fordsorption of congo red by Zhu et al. (2011). Characterizationsf m-Cell/Fe3O4/ACCs were carried out using XRD, BET, TGA, SEMnd VSM. The initial dye concentration, contact time, temperature,dsorbent dosage and pH played a major role in the dye adsorp-

ion on m-Cell/Fe3O4/ACCs. The maximum adsorption capacityf CR on m-Cell/Fe3O4/ACCs was found to be 66.09 mg/g. Theseudo-second-order model fitted well with experimental data andangmuir isotherm equation could better describe the adsorption.

, Monitoring & Management 1–2 (2014) 36–49 41

Negative values of free energy change indicated that adsorptionwas spontaneous.

Zhu et al. (2010) created novel magnetically separableadsorbent magnetic �-Fe2O3 crosslinked chitosan composites (M�-Fe2O3/CSCs) by miroemulsion process and characterized by XRD,FTIR, TGA, DSC, SEM and VSM (Vibrating Sample Magnetometer).M�-Fe2O3/CSCs was tested for adsorption of methyl orange (MO)from aqueous solution. Adsorption results showed that both adsor-bents with a weight ratio of �-Fe2O3 to chitosan of 1:10 and 2:5exhibited higher adsorption capacities and attained adsorptionequilibrium in a shorter time compared with crosslinked chitosan.The intraparticle diffusion was found to be the rate-controllingstep for adsorption using crosslinked chitosan. Boundary layerdiffusion found to act as a substantial role in adsorption usingM�-Fe2O3/CSCs. After adsorption, M�-Fe2O3/CSCs were effectivelyseparated from the reaction solution in 10 seconds by applying anadscititious magnetic field.

A magnetic porous carbonaceous polymeric material, cova-lent triazine-based framework (CTF), CTF/Fe2O3 composite hasbeen synthesized by Wang Zhang in 2011 using facile microwave-enhanced high-temperature iono-thermal method. The resultingsamples were characterized by the XRD, XPS, SEM, TEM, VSMand N2 sorption–desorption isotherms. The CTF/Fe2O3 compos-ites were applied to get rid of organic dye from aqueous solutionby selecting methyl orange and both high adsorption capacity(291 mg/g) and fast adsorption kinetics (kads = 4.31 m2/mg/min)were observed (Zhang and Kong, 2011).

Rongcheng et al. (2005) employed magnetic powderedMnO–Fe2O3 composites for the removal of an azo-dye, acid redB (ARB) from water. The adsorption and regeneration of adsor-bents containing ARB by catalytic combustion were studied. Thesepowder adsorbents showed excellent adsorption toward ARB underacidic conditions, adsorption rate was observed and could be welldescribed by the pseudo-second order kinetic model. The adsorp-tion capacity increased with increasing Fe content and surface areaof the adsorbent, and the highest adsorption capacity of 105.3 mg/gwas obtained at pH 3.5. The presence of Cl− does not affect adsorp-tion, but was significantly impressed by SO2−

4 .Xiao et al. (2013) synthesized magnetic porous carbons (MPCs)

from an iron-based metal-organic framework (MOF) by a novelmicrowave-enhanced high temperature iono-thermal method.Structure, morphology and magnetic property, as well as poros-ity of the MPCs were studied by powder XRD, X-ray photoelectronspectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface areamethod, TGA, VSM, SEM, and high resolution TEM. Their adsorptionproperties were preliminarily tested by the adsorptive removal ofMB dye from aqueous solution. The products exhibit high surfaceareas (up to 800 m2/g) with different magnetic separation per-formance (MS = 4.12–19.54 emu/g), and possess high adsorptioncapacity toward methylene blue (303.95 mg/g). MPCs also found tobe recoverable and recyclable, super-adsorbents for removal andrecovery of pollutants. Table 2 provides the information about theadsorption capacity of MCs toward a range of dye.

Ai et al. (2011) developed a novel adsorbent montmorillonite/CoFe2O4 composite with the magnetic separation potential in afacile, one-step low-temperature refluxing route. The structure,morphology and magnetic properties of the synthesized compositewere characterized by XRD, SEM and VSM. Adsorption character-istics of the composite were examined by using methylene blue(MB) as an adsorbate. The outcomes indicated that the adsorp-tion isotherm data were fitted well to the Langmuir isothermand followed the pseudo-second-order kinetic model. Adsorptionmechanism was found to be pH dependent. Most silanol and alu-minol groups on edges are protonated at pH <4. Hence, adsorption

capacity found lower at lower pH, and increases with increasingpH.

42 R. Sivashankar et al. / Environmental Nanotechnology, Monitoring & Management 1–2 (2014) 36–49

Table 2Comparison of adsorption capacity of magnetic composites for range of dyestuffs.

Adsorbate Adsorbent Adsorption capacity (mg/g) Isotherm Reference

Acridine Orange magnetically modified spent coffee grounds 73.4 Langmuir Safarik et al. (2012)Amido black 10B magnetically modified spent coffee grounds 1.24 Freundlich Safarik et al. (2012)Bismark brown magnetically modified spent coffee grounds 69.2 Langmuir Safarik et al. (2012)Congo red magnetically modified spent coffee grounds 9.43 Langmuir Safarik et al. (2012)Crystal red magnetically modified spent coffee grounds 68.1 Langmuir Safarik et al. (2012)Malachite green magnetically modified spent coffee grounds 43.0 Langmuir Safarik et al. (2012)Safranin-O magnetically modified spent coffee grounds 59.0 Langmuir Safarik et al. (2012)Bismarck brown Ferrofluid modified peanut husks 95.3 Langmuir Safarik and Safarikova (2010)Safranin-O Ferrofluid modified peanut husks 86.1 Langmuir Safarik and Safarikova (2010)Crystal violet Ferrofluid modified peanut husks 80.9 Langmuir Safarik and Safarikova (2010)Acridine orange Ferrofluid modified peanut husks 71.4 Langmuir Safarik and Safarikova (2010)Methylene blue Glutamic acid modified chitosan magnetic composite 180 Langmuir Yan et al. (2013)Aniline blue Magnetically modified yeast 228 Freundlich Safarikova et al. (2005)Congo red Magnetically modified yeast 93.1 Freundlich Safarikova et al. (2005)Safranine-O Magnetically modified yeast 46.6 Freundlich Safarikova et al. (2005)Crystal violet Magnetically modified yeast 41.7 Freundlich Safarikova et al. (2005)Naphthol blue Magnetically modified yeast 11.6 Freundlich Safarikova et al. (2005)Methylene blue Epichlorohydrin magnetic alginate beads 229.18 Langmuir Rocher et al. (2010)

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. Magnetic Nanocomposites (MNCs) as dye adsorbent

The emergence of tailored nanoparticles with magnetic prop-rties and high adsorption competence for an extended mixturef compounds, offer a novel tool to deal with waste water purifi-ation (Qu et al., 2013). The functionalized magnetic nanoparticlesave recently been examined as a promising platform for detectionnd separation application (Jung et al., 2011). Table 3 furnishes thenformation about the use of the MNCs for adsorption of toxic dyeollutant with its competence toward toxic dyes.

Zhou et al. (2011) investigated ethylenediamine-modified mag-etic chitosan nanoparticles (EMCN) for adsorption of acid orange

(AO7) and acid orange 10 (AO10) from aqueous solution. Thedsorption experiments indicated that the maximum adsorptionapacity occurred at pH 4.0 for AO7 and pH 3.0 for AO10, respec-ively. Equilibrium experiments fitted well with the Langmuirsotherm model, and the maximum adsorption capacity of theMCN at 298 K was determined to be 3.47 mmol/g for AO7 and.25 mmol/g for AO10, respectively. The mechanisms of the adsorp-ion process of the acid dyes on the EMCN are expected to be theonic interactions of the colored dye ions with the amino groups ofhe EMCN. Desorption of dyes from EMCN were carried out usingH4OH/NH4Cl solution at pH 10. The % recovery of desorption

ound to be 81.1% and 87.8% for AO7 and AO10 respectively.Zhang and Kong (2011) synthesized magnetic Fe3O4/C

ore–shell nanoparticles by a simple strategy and used as adsorbentor removal of organic dyes from aqueous solution. The resultingroducts are characterized by SEM, energy dispersive X-ray spec-rometry (EDX), XPS, XRD, and FTIR. Adsorption performances ofhe Super paramagnetic Fe3O4/C nanoparticles with average size50 nm was tested with removal of methylene blue (MB) andresol red (CR) from aqueous solution. The adsorption capacitiesor MB and CR in the concentration range studied are 44.38 mg/gnd 11.22 mg/g respectively. The higher adsorption capacity forB was recognized to those functional groups (such as OH, CO)

n the composite surface and the negative potential of the mag-etic nanocomposites that provide weak electrostatic interactionetween the cationic dye and the nanomaterials.

Xie et al. (2011) prepared iron oxide nanoparticles on the hal-oysite nanotube (HNT) to create a magnetic sorbent HNT–Fe3O4,

nvestigated for adsorption for three dyes namely methylene blueMB), neutral red (NR) and methyl orange (MO). HNT–Fe3O4as characterized by TEM, FTIR, XRD and TGA. Magneticroperties illustrated that HNT–Fe3O4 was superparamagnetic

5.95 – Xiao et al. (2013)7.75 Langmuir Ai et al. (2011)

with a saturation magnetization (27.91 emu/g). The magneticHNT–Fe3O4 exhibited better adsorption on MB (18.44 mg/g) thanNR (13.62 mg/g), while the adsorption of MO (0.65 mg/g) was verylittle.

Magnetite nanoparticles coated with an anionic biopolymerpoly (c-glutamic acid) (PGA-MNPs) were synthesized by Inbaraj(2011). Both bare and dye-loaded PGA-MNPs were characterized byFTIR, TEM and VSM measurements. Redlich–Peterson and Langmuirmodels precisely described the isotherm and the maximum adsorp-tion capacity was 78.67 mg/g. A pseudo-second-order equation bestpredicted the kinetics with a maximum adsorption attained within5 min. Desorption was performed by turning down the pH of deion-ized water from 5 to 1, the percentage of dye recovery rose from17.6 to 100 with 91.0% recovery.

Magnetic nanoparticles with iron oxides and N-benzyl-O-carboxymethylchitosan, an amphiphilic chitosan derivative, wereprepared through the incorporation method by Debrassi et al.(2012a). The characterization of MNCs was performed by FTIR,TGA, TEM, Mossbauer spectroscopy, and magnetization measure-ments. The material was used to adsorb three cationic dyes[MB, CV, and malachite green (MG)] from aqueous solution. TheLangmuir–Freundlich equation was the best isotherm model, andthe maximum adsorption capacities were 223.58, 248.42, and144.79 mg/g for MB, CV, and MG, respectively. Desorption exper-iments were performed with HCl solution in order to reuse theadsorbent. The dye adsorption capacity found to be decreasedslowly with increasing the number of cycles.

Singh et al. (2011) developed and characterized a novel mag-netic carbon-iron oxide nanocomposite (MCIONC) for adsorptionof crystal violet (CV) dye from water. A four-factor central compos-ite design (CCD) combined with response surface modeling (RSM)was used for maximizing CV removal from aqueous solution by theMNCs based on 30 different experimental data obtained in a batchstudy. The Langmuir adsorption capacity of the adsorbent wasdetermined as 81.70 mg/g. The model predicted maximum adsorp-tion of 113.31 mg/g under the optimum conditions of variables(dye concentration 240 mg/l; temperature 50 ◦C; pH 8.50; dose1 g/l), which was very close to the experimental value (111.80 mg/g)determined in batch experiment.

Fei Ge modified magnetic nanoparticles (MNPs) with 3-

aminopropyltriethoxysilane and copolymers of acrylic acid andcrotonic acid for removal of cationic dyes crystal violet (CV), methy-lene blue (MB) and alkali blue 6B (AB 6B) from water solution.Characterization was performed using TEM, XRD, infrared spectra

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43

Table 3Comparison of adsorption capacity of adsorbents (MNCs) for dyes.

Adsorbent Adsorbate Adsorption capacity(mg/g)

pH Temp. (◦C) Kinetic model Isotherm Reference

Maghemite (�-Fe2O3) nanoparticles Methyl orange 4.5 × 10−3 mmol/g 7 – Pseudo 2nd order Langmuir Luo and Zhang (2009)Magnetic nanoparticles (�Fe2O3) Acridine orange 59 4 24 Pseudo 2nd order Freundlich Qadri et al. (2009)Ethylenediamine-modified magnetic chitosan nanoparticles Acid orange 7 1214 3 25 Pseudo 2nd order Langmuir Zhou et al. (2011)Ethylenediamine-modified magnetic chitosan nanoparticles Acid orange 10 1017 3 25 Pseudo 2nd order Langmuir Zhou et al. (2011)Magnetic Fe3O4/C core–shell nanoparticles Cresol red 11.22 3 – – – Zhang and Kong (2011)Halloysite nanotube – Fe3O4 magnetic nanoparticles Neutral red 13.62 – – – – Xie et al. (2011)Halloysite nanotube – Fe3O4 magnetic nanoparticles Methyl orange 0.65 – – – – Xie et al. (2011)Iron oxides/N-benzyl-O-carboxy-methyl chitosan magnetic

nanoparticlesCrystal violet 248.42 7 – Pseudo 2nd order Langmuir Debrassi et al. (2012a)

Iron oxides/N-benzyl-O-carboxy-methyl chitosan magneticnanoparticles

Malachite green 114.79 7 – Pseudo 2nd order Langmuir Debrassi et al. (2012a)

Magnetic carbon-iron oxide nanocomposite Crystal violet 111.8 8.5 50 – Langmuir Singh et al. (2011)Polymer modified magnetic nanoparticles Crystal violet 208.3 7.5 – Pseudo 2nd order Langmuir Ge et al. (2012)Polymer modified magnetic nanoparticles Alkali blue 6B 22 7.5 – Pseudo 2nd order Langmuir Ge et al. (2012)Magnetic Zn Fe2O4 nanoparticles Acid red 88 111.1 3.2 20 Pseudo 2nd order Langmuir Konicki et al. (2013)Starch functionalized magnetic MWCNT Methyl orange 135.6 – – – – Chang et al. (2011)Magnetic Fe3o4 @ graphene Congo red 33.06 – – Pseudo 2nd order Langmuir Yao et al. (2012)Magnetic ferrite nanoparticle alginate composite Basic Blue 9 106 8 – Pseudo 2nd order Temkin Mahmoodi (2013)Magnetic ferrite nanoparticle alginate composite Basic Blue 41 25 8 – Pseudo 2nd order Langmuir Mahmoodi (2013)Magnetic ferrite nanoparticle alginate composite Basic Red 18 56 8 – Pseudo 2nd order Langmuir Mahmoodi (2013)Magnetic graphene oxide orange G 20.85 3.5 – Pseudo 2nd order Langmuir Deng et al. (2013)Super para-magnetic rectorite nanocomposite Neutral red 16.0 – – Pseudo 2nd order Freundlich Wu et al. (2011)Super para-magnetic rectorite nanocomposite Methyl orange 0.36 – – Pseudo 2nd order Freundlich Wu et al. (2011)Biodegradable hollow zein nanoparticles Reactive blue 19 1016 9 – – Langmuir Xu et al. (2013)PANI/Co1−xMgx–Fe2O4 Bromopyrogallol red dye 0.4908 – – – – Farghali et al. (2010)Magnetic N-lauryl chitosan nanocomposite Remazol red 198 267 – – Pseudo 2nd order Langmuir & Freundlich Debrassi et al. (2012b)Magnetic zeolite/iron oxide nanocomposite Reactive Orange 16 1.1 – 25 ± 2 Pseudo 2nd order Langmuir Fungaro et al. (2011)Magnetic zeolite/iron oxide nanocomposite Indigo Carmine 0.58 2 25 ± 2 Pseudo 2nd order Langmuir Fungaro et al. (2011)Magnetic MWCNT composite Neutral red 9.77 2 35 Pseudo 2nd order Freundlich Gonga et al. (2009)Magnetic MWCNT composite Brilliant cresyl blue 6.28 2 35 Pseudo 2nd order Freundlich Gonga et al. (2009)Magnetic polymer MWCNT orange II 67.57 2 25 Pseudo 2nd order Langmuir Gao et al. (2013)Magnetic polymer MWCNT Sunset yellow FCF 85.47 2 25 Pseudo 2nd order Langmuir Gao et al. (2013)Magnetic polymer MWCNT Amaranth 47.39 2 25 Pseudo 2nd order Langmuir Gao et al. (2013)Magnetic-modified MWCNT Crystal violet 227.7 7 – – Langmuir Madrakiana et al. (2011)Magnetic-modified MWCNT Thionine 36.4 7 – – Langmuir Madrakiana et al. (2011)Magnetic-modified MWCNT Janus green 250 7 – – Langmuir Madrakiana et al. (2011)Magnetic Fe3o4 @ GPTMS and Gly Orange I 45 1.5 – Pseudo 2nd order Langmuir Zhang et al. (2013)Magnetic Fe3o4 @ GPTMS and Gly Acid red 18 49 2 – Pseudo 2nd order Langmuir Zhang et al. (2013)Magnetic Fe3o4 @ GPTMS and Gly Azure I 123 12 – Pseudo 2nd order Langmuir Zhang et al. (2013)Magnetic Fe3o4 @ GPTMS and Gly Methyl Blue 158 2 – Pseudo 2nd order Langmuir Zhang et al. (2013)Magnetic Fe3o4 @ GPTMS and Lys Orange I 83 2 – Pseudo 2nd order Langmuir Zhang et al. (2014)Magnetic Fe3o4 @ GPTMS and Lys Acid red 18 71 2 – Pseudo 2nd order Langmuir Zhang et al. (2014)Magnetic Fe3o4 @ GPTMS and Lys Azure I 190 13 – Pseudo 2nd order Langmuir Zhang et al. (2014)Magnetic Fe3o4 @ GPTMS and Lys Methyl Blue 185 2 – Pseudo 2nd order Langmuir Zhang et al. (2014)Aminoguanidine modified MNPs Acid green 25 95.2 1 – Pseudo 2nd order Langmuir Li et al. (2013b)Aminoguanidine modified MNPs Acid violet 43 137 1 – Pseudo 2nd order Langmuir Li et al. (2013b)Aminoguanidine modified MNPs Acid orange 20 120 1 – Pseudo 2nd order Langmuir Li et al. (2013b)Aminoguanidine modified MNPs Acid red 27 83.3 1 – Pseudo 2nd order Langmuir Li et al. (2013b)Aminoguanidine modified MNPs Methyl blue 165 1 – Pseudo 2nd order Langmuir Li et al. (2013b)Graphene-Fe3O4 nanocomposite Pararosaniline 198.23 3–5 25 Pseudo 2nd order Langmuir Wu et al. (2013)Chitosan suppoted CNT-MNPs Acid red 18 809.9 6.5 50 Pseudo 2nd order Redlich–Peterson Wang et al. (2014)

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4 R. Sivashankar et al. / Environmental Nanotechn

IRS) and TGA. The cationic dyes were quickly withdrawn fromater solution with high efficiency at pH 5–12. The adsorption

apacity of MNPs was found to be 208.3 mg/g, 128.7 mg/g and2 mg/g for CV, MB, and AB 6B respectively. Desorption was per-ormed with methanol and acetic acid and adsorption capacity ofdsorbent after 4 adsorption/desorption cycle was found to be 90%Ge et al., 2012).

Konicki et al. (2013) synthesized magnetic ZnFe2O4 (MNZnFe)y microwave assisted hydrothermal method for the removalf acid dye Acid Red 88 (AR88) from aqueous solution. Theffects of various parameters such as initial AR88 concentration10–56 mg/L) pH solution (3.2–10.7), and temperature (20–60 ◦C)ere investigated. Prepared magnetic ZnFe2O4 was characterized

y XRD, SEM, TEM, AES, BET, FTIR, and measurements of the mag-etic susceptibility. Thermodynamic parameters, �G◦, �H◦ andS◦ indicate that the adsorption of AR88 onto MNZnFe was spon-

aneous and exothermic in nature. Desorption efficiency of AR88rom MNZnFe in acetone and methanol was found to be 63% and1%, respectively.

Soluble starch-functionalized magnetic multiwall carbon nano-ube composites (MWCNT-starch) were prepared by synthesizingron oxide nanoparticles at the surface of MWCNT-starch tomprove the hydrophilicity and biocompatibility of MWCNTsChang et al., 2011). Characterization studies were performed byTIR, UV–vis spectroscopy, XRD, TEM and TG showed that thetarch component (about 14.3 wt%) was covalently grafted onto theurface of MWCNT. MWCNT-starch-iron oxide exhibits superpara-agnetic properties with a saturation magnetization (23.15 emu/g)

nd better adsorption for anionic methyl orange (MO) and cationicethylene blue (MB) dyes than MWCNT-iron oxide.The adsorption of methylene blue (MB) from an aqueous solu-

ion by Polyacrylic acid-bound iron oxide magnetic nanoparticlesas studied by Sou-Yee Mak. In the aqueous solution of MB at

5 ◦C, the adsorption data fit with the Langmuir equation with maximum adsorption amount of 0.199 mg/mg and a Langmuirdsorption equilibrium constant of 10.1 mL/mg. The adsorptionapacity increased with increase in solution pH (2–10) and thedsorption process was endothermic in nature with an enthalpyhange (�H) of 30.9 kJ/mol between 10 and 40 ◦C (Mak and Chen,004). Table 4 affords the adsorption capability of various MNCsoward MB dye.

Yao et al. (2012) described the synthesis of magnetice3O4@graphene composite (FGC) and its use in dye removal of MBnd CR from aqueous media. The structure, surface, and magneticharacteristics were investigated by SEM, TEM, ED, X-ray spectrom-ter, XRD, FTIR, and TGA. Through a chemical deposition method,e3O4 nanoparticles in a size of 30 mm were homogeneously dis-ersed onto graphene sheets. The maximum adsorption capacitiesf MB and CR on FGC were found to be 45.27 and 33.66 mg/g, respec-ively.

Magnetic ferrite nanoparticle (nickel–zinc ferrite)MFN)–alginate composite was synthesized and characterizedy Mahmoodi (2013). The dye removal ability of MFN–alginaterom single and binary systems was studied. The characteristicsf MFN–alginate were studied using XRD, SEM and FTIR. Basiclue 9 (BB9), Basic Blue 41 (BB41) and Basic Red 18 (BR18) weresed as model dyes. The maximum dye adsorption capacity (Q0) ofFN–alginate was 106 mg/g, 25 mg/g, and 56 mg/g for BB9, BB41

nd BR18, respectively.Deng et al. (2013) used magnetic graphene oxide (MGO) as

n adsorbent for simultaneous removal of Cd (II) and ionic dyes,ncluding methylene blue (MB) and orange G (OG). MGO adsorbent

as characterized by TEM, SEM, XRD and XPS. In mono-componentystem, the maximum sorption capacities in ultrapure water ford (II), MB and OG were 91.29 mg/g, 64.23 mg/g and 20.85 mg/g,espectively. The sorption capacity suppressed for Cd (II) with

, Monitoring & Management 1–2 (2014) 36–49

increasing MB concentration and almost was not affected for MBby increasing Cd (II) concentration in Cd (II)–MB binary system. Intap water samples, the sorption capacity for Cd(II) was 65.39% ofthat in ultrapure water.

Wu et al. (2011) synthesized superparamagnetic Fe3O4nanoparticles on the rectorite (REC) to develop an adsorbent(REC-Fe3O4) which was explored to adsorb three dyes, namelymethylene blue (MB), neutral red (NR) and methyl orange (MO).Characterization of REC-Fe3O4 by FTIR, TEM and XRD showed thatREC was attached with clusters of Fe3O4 nanoparticles. Magneticproperties revealed that REC-Fe3O4 was superparamagnetic witha saturation magnetization (19.14 emu/g). The adsorption behav-ior of the REC and REC-Fe3O4 illustrated that it exhibited goodadsorption for MB and NR, while the adsorption of MO was verylittle.

�-Carrageenan coated magnetic iron oxide nanoparticles (NPs)were produced by Salgueiro et al. (2013) and tested for the mag-netically assisted removal of methylene blue (MB) from aqueoussolutions. The resulting composite NPs were superparamagneticand contained ca. 12 wt% carrageenan. The MB uptake ability wasfound to deviate with the pH solution and was larger in alka-line conditions. Both pseudo-first-order and pseudo-second-orderequations predicted well the dynamics with the maximum adsorp-tion achieved very fast, within 5 min. The MB adsorption has shownan unusual Z-type isotherm, which proposes the generation of newadsorbing sites with increasing MB initial concentration.

Xu et al. (2013) developed biodegradable hollow zein nanopar-ticles (HZN) with diameters less than 100 nm to remove reactivedyes from simulated post-dyeing wastewater with remarkablyhigh efficiency. HZN showed higher adsorption for Reactive Blue19 than solid structures, and the adsorbed amount increased asthe temperature decreased, pH decreased or initial dye concen-tration increased. At pH 6.5 and pH 9.0, increasing electrolyteconcentration could improve dye adsorption significantly. Underthe simulated post-dyeing condition with 50.0 g/L salts and pH 9.0,maximum adsorption of 1016.0 mg dye per gram zein nanoparticlescould be obtained.

Magnetic nanoparticles (MNPs) were developed and modi-fied with 3-glycidoxypropyltrimethoxysilane (GPTMS) and glycine(Gly) by Zhang et al. (2013). The characterization was performed byTEM, XRD, IR and TGA. The MNPs were employed for the removalof both anionic and cationic dyes in highly acidic and strong alka-line environment. The experimental data fit well with pseudosecond order kinetics and adsorption behavior is reliable to Lang-muir isotherm. Reusability of adsorbents was effectively done usingethanol and HCl or NaOH.

Zhang et al. (2014) developed a glycidoxypropyltrimethoxysi-lane (GPTMS) and Lysine (Lys) modified MNPs for sequestration ofanionic and cationic dyes. MNPs was characterized by TEM, XRD, IRand TGA. The presence of the more amine group not only improvesthe maximum adsorption capacities for anionic dyes, but also effi-ciently removes cationic dyes. The experimental data follow pseudosecond order kinetics and adsorption behavior is consistent withLangmuir isotherm. Desorption was performed with ethanol andHCl or NaOH.

Li et al. (2013b) produced aminoguanidine (AG) modified MNPsand characterized by TEM, XRD, VSM and IR. The nanocomposite istested for adsorption of different acid dyes and maximum adsorp-tion was achieved at pH 1.3–2.5. Adsorption kinetics are describedby pseudo second order model and adsorption behavior fit wellwith Langmuir isotherm. Further, the Dubinin–Radushkevich (D–R)isotherm model describes the participation of chemical adsorp-

tion. Since maximum adsorption occurred at pH not beyond 4,desorption was excellently carried out using NH4OH/NH4Cl at pH10. Adsorption capacity of nanocomposites remains excellent afterthree cycles of reusability.

R. Sivashankar et al. / Environmental Nanotechnology, Monitoring & Management 1–2 (2014) 36–49 45

Table 4Comparison of adsorption capacity of various MNCs for the removal of methylene blue dye.

Adsorbent Adsorptioncapacity (mg/g)

pH Temp. (◦C) Kinetic model Isotherm Reference

Magnetic Fe3O4/C core–shell nanoparticles 44.38 10 – – – Zhang and Kong (2011)Halloysite nanotube – Fe3O4 magnetic

nanoparticles18.44 – – – – Xie et al. (2011)

Anionic biopolymer coated magneticnanoparticles

78.67 6 28 Pseudo 2nd order Langmuir andRedlich Peterson

Inbaraj (2011)

Iron oxides/N-benzyl-O-carboxy-methylchitosan magnetic nanoparticles

223.58 7 – Pseudo 2nd order Langmuir Debrassi et al. (2012a)

Polymer modified magnetic nanoparticles 128.7 7.5 – Pseudo 2nd order Langmuir Ge et al. (2012)Starch functionalized magnetic MWCNT 93.7 – – – – Chang et al. (2011)Polyacrylic acid-bound iron oxide magnetic

nanoparticles199 9 25 – Langmuir Mak and Chen (2004)

Magnetic Fe3o4 @ grapheme 45.27 – – Pseudo 2nd order Langmuir Yao et al. (2012)Magnetic MWCNT composite 11.86 2 35 Pseudo 2nd order Freundlich Gonga et al. (2009)Magnetic graphene oxide 64.23 10 – Pseudo 2nd order Langmuir Deng et al. (2013)Super para-magnetic rectorite nanocomposite 18.6 – – Pseudo 2nd order Freundlich Wu et al. (2011)�-Carrageenan coated magnetic iron oxide

nanocomposite185.3 9 23 Pseudo 1st & 2nd order Z-type Salgueiro et al. (2013)

Magnetic Fe3O4 -activated carbonnanocomposite

321 – 25 – Langmuir Yang et al. (2008)

Magnetic-modified MWCNT 48.1 7 – – Langmuir Madrakiana et al. (2011)Magnetic Fe3o4 @ GPTMS and Gly 357 12.5 – Pseudo 2nd order Langmuir Zhang et al. (2013)Magnetic chitosan and graphene oxide nano

composite179.6 10 – Pseudo 2nd order Langmuir Fan et al. (2012)

EDTAD modified magnetic chitosan 113.26 – – Pseudo 2nd order Sipss Xia et al. (2013)

alcssisasop

mpwopaln

twsmrf

duSwtTpna

Magnetic bioadsorbent was synthesized with magnetic chitosannd graphene oxide and employed for the removal of methy-ene blue dye from aqueous solution by Fan et al. (2012). Theomposite material was characterized by SEM, FTIR and XRD mea-urements. The nano composite was tested against MB dye. Highurface area of nanocomposite enhanced adsorption active sites ast offered a beneficial state for drawing in additional target sub-tances around the sites and equally improved the absorption ratend adsorption capacities. The experimental data pursue pseudoecond order kinetic and Langmuir isotherm. Maximum adsorptionf 179.6 mg/g for initial concentration of 10 mg/L was achieved atH 10.

Graphene-Fe3O4 nanocomposite was synthesized by solvother-al method and analyzed for the adsorption of organic dye

ararosaniline (Wu et al., 2013). The dye adsorption rate increasedith increasing pH from 3 to 5 and found no considerable change

ver 5 pH. The pseudo second order model and Langmuir isothermrecisely describe the experimental adsorption data. The Langmuirdsorption capacity for the maximum removal of pararosani-ine found to be 198.23 mg/g. Desorption ratio was 92% and theanocomposites were regenerated using ethanol at pH 3.

Chitosan supported carbon nanotube (CS/CNT) was synthesizedhrough “surface deposition-crosslinking” method and implantedith MNP by Wang et al. (2014). The nanocomposite examined for

equestration of anionic azo dye Acid red 18 (AR 18). The maxi-um adsorption capacity of 809.9 mg/g was reached at 50 ◦C. The

eusability and desorption of nanocomposite found to be consistentor ten successive cycles.

Xia et al. (2013) constructed a ethylenediaminetetraaceticianhydride (EDTAD)-modified magnetic Chitosan (EMC) complexsing glutaraldehyde as a cross-linking agent and exemplified usingEM, XRD, potentiometric titration, and FTIR. The nano compositeas tested for adsorption of MB dye and the maximum adsorp-

ion capacity of 113.26 mg/g was reached at optimum condition.

he adsorption process was well described by Sips isotherm andseudo second order model. The efficiency ratio of regeneration ofanocomposite and recovery of MB was deliberated to be 82.82%nd 80.72%, respectively.

10. Advantages of MNCs over MCs

Nanotechnology is currently engaged in an extended range offields, including environmental and water treatment technology(Mak and Chen, 2004). The application of metal oxides Fe2O3,Fe3O4, TiO2 and Al2O3 as an adsorbent in singular or composite formbecome the first generation of nanoscale environmental cleanuptechnology (Xiao et al., 2013; Yao et al., 2012). Comparing to con-ventional natural or synthetic adsorbents at macro size, the MNCspossesses a very good compensation because of its reduced size,promising greater surface area and its high specific surface reac-tivity. In addition, the MNCs can be tailored to specific adsorbentsequestration by modifying the functional group of the adsorbentor by changing the ionic strength of the solution or by alteringthe active sites of the MNCs (Zhou et al., 2011; Zhang and Kong,2011; Inbaraj, 2011; Debrassi et al., 2012a; Konicki et al., 2013).The recovery and regeneration of the adsorbent become ease andreusability of nanocomposites for the successive cycles, shows anexcellent efficiency after 3–10 adsorption–desorption cycles (Wuet al., 2013; Wang et al., 2014; Xia et al., 2013). The temperatureneeded for regeneration of MNCs is very low, the energy eatenup for regeneration is >50% of other technologies, low operatingpressure, low pressure drop, the performance has no restrictionby orientation and resistance to vibration, i.e., high flexibility anddurability, compact size, possesses rapid adsorption kinetics, donot generate contamination, can be completely saturated and com-pletely recovered without any damage (Singh et al., 2011; Mak andChen, 2004; Yao et al., 2012; Mahmoodi, 2013; Deng et al., 2013;Xu et al., 2013; Wu et al., 2013; Xia et al., 2013). The high surfacearea to volume ratios results in MNCs to have higher adsorptioncapacities relative to macroscopic adsorbents, MCs. The high sur-face area produces rapid adsorption kinetics and thus relativelyshort contact time. Furthermore, these nanocomposites are mag-netic, as they can be well separated from aqueous streams using

an external magnetic field. On the whole, the unique attributesof magnetic nanocomposites and their overlap with current treat-ment technologies becoming a revolutionizing tool for wastewatertreatments.

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1

mesweas

1

dott

wart2

l

w

l

cebwa2

1

ldacassle

q

w

wt

6 R. Sivashankar et al. / Environmental Nanotechn

1. Adsorption reaction model

Concerning adsorption, the adsorption reaction model deter-ines the adsorption performance and mechanism, i.e., the

quilibrium time required for the uptake of dyes from a liquidolution, the time required for completion of adsorption reactionhich determines the solute uptake rate (Qiu et al., 2009; Shankar

t al., 2012). Various kinetic models have been proposed for andsorption process, in which pseudo-first order kinetics and pseudoecond order kinetics are primarily discussed.

1.1. Pseudo-first-order rate equation

Lagergren (1898) introduced a first-order rate equation toescribe the kinetic process of liquid-solid phase adsorption ofxalic acid and malonic acid onto charcoal, which is consideredo be the earliest model pertaining to the adsorption rate based onhe adsorption capacity. It can be constructed as follows:

dqt

dt= kp1(qe − qt), (3)

here qe and qt (mg/g) are the adsorption capacities at equilibriumnd time t (min), respectively. kp1 (min−1) is the pseudo-first-orderate constant for the kinetic model. Integrating above equation withhe boundary conditions of qt = 0 at t = 0 and qt = qt at t = t, yields (Ho,004).

nqe

qe − qt= kp1t, (4)

hich can be rearranged to:

og(qe − qt) = log qe − kp1t

2.303(5)

To distinguish kinetic equations based on the adsorptionapacity from solution concentration, Lagergren’s first order ratequation has been called pseudo first order. In recent years, it haseen widely used to describe the adsorption of pollutants fromastewater in different fields, such as the adsorption of dyes from

queous solution by natural and synthetic adsorbents (Qiu et al.,009; Lagergren, 1898; Crini, 2005).

1.2. Pseudo-second-order rate equation

In 1998, Ho described a kinetic process of the adsorption of diva-ent metal ions onto peat, in which the chemical bonding amongivalent metal ions and polar functional groups on peat, such asldehydes, ketones, acids, and phenolics are responsible for theation-exchange capacity of the peat. The principal assumptionsre, the adsorption may be second-ordered, and the rate limitingtep may be chemical adsorption involving valent forces throughharing or the interchange of electrons between the peat and diva-ent metal ions. In summation, the adsorption follows the Langmuirquation (Ho and McKay, 2000). It can be presented as a possibility

dqt

dt= kp2(qe − qt)

2 (6)

Integrating the above equation with the boundary conditions oft = 0 at t = 0 and qt = qt at t = t, yields

1qe − qt

= 1qe

+ kp2t (7)

hich can be rearranged to:

t 1 t

qt=

kp2q2e

+qe

(8)

here kp2q2e (mg/(g min)) means the initial adsorption rate, and

he constants can be determined experimentally by plotting of t/qt

, Monitoring & Management 1–2 (2014) 36–49

against t. Similarly, Ho’s second-order rate equation has been calledpseudo-second-order rate equation to distinguish kinetic equa-tions based on the adsorption capacity for concentration of solution.This equation has been successfully applied to the adsorption ofdyes from aqueous solutions (Qiu et al., 2009; Ho, 2006; Chenget al., 2008).

12. Adsorption diffusion models

In general, the liquid–solid adsorption involves diffusion andfound that, it predominantly controls the kinetic process of adsorp-tion i.e., one of the processes should be the rate limiting step.Adsorption diffusion models are invariably made on the founda-tion of three consecutive steps (Qiu et al., 2009; Lazaridis andAsouhidou, 2003): (1) diffusion across the liquid film surroundingthe adsorbent particles, i.e., external diffusion or film diffusion; (2)diffusion in the liquid contained in the pores and/or along the porewalls, which is so-called internal diffusion or intra-particle diffu-sion; and (3) adsorption and desorption between the adsorbent andactive sites, i.e., mass action. However, adsorption reaction modelsoriginating from chemical reaction kinetics are based on the wholeprocess of adsorption without considering these steps mentionedabove.

12.1. Liquid film diffusion model

The film diffusion mass transfer rate equation (Boyd et al., 1947)presented as

ln(

1 − qt

qe

)= −R1t (9)

Rl = 3Dle

r0�r0k(10)

where Rl (min−1) is the liquid film diffusion constant, Dle (cm2/min)

is effective liquid film diffusion coefficient, r0 (cm) is radius ofadsorbent beads, �r0 (cm) is the thickness of liquid film, and k is theequilibrium constant of adsorption. A plot of should be a straightline with a slope – Rl, if the film diffusion is the rate determiningstep. Then the corrected liquid film diffusion coefficient Dl

e can bejudged according to linear driving force rate law as below (Cooney,1999),

∂q

∂t= kf s0(C − Ci) (11)

where kf is film mass transfer coefficient, s0 is the ratio betweenthe particle surface area per unit particle volume, Ci and C denotethe concentration of solute at the particle/liquid interface and in thebulk of the liquid far from the surface. The film diffusion mass trans-fer rate equation has been successfully applied to model severalliquid/solid adsorption processes (Ho et al., 2000).

12.2. Intraparticle diffusion model

Weber and Morris (1962) theorized that the rate of intraparticlediffusion varies proportionally with the half power of time and isexpressed as:

qt = Kid(t1/2) + C, (12)

where qt is adsorbate uptake at time t, (mg/g), Kid is the rate con-stant of intra-particle transport, (mg/g−t1/2). The value of intercept,C is related to the boundary layer thickness, i.e., the larger the value

of the intercept, the greater is the boundary layer effect (Kannanand Rengasamy, 2005). According to Weber and Morris, if the ratelimiting step is intraparticle diffusion, a plot of solute adsorbedagainst the square root of the contact time should yield a straight

ology

lp2

1

belaLa(

l

wcsht

ea

R

woe

geba

ee

�

�

want

1

pdmjlwlimua

R. Sivashankar et al. / Environmental Nanotechn

ine passing through the origin. Besides, the rate constant for intra-article diffusion is obtained from the incline of the curve (Ho et al.,000).

3. Adsorption isotherm

Two important physico-chemical aspects for evaluation of theiosorption process as a unit operation are the kinetics and thequilibria of adsorption (Pandey et al., 2007). Modeling of the equi-ibrium data has been performed using the Langmuir, Freundlichnd Redlich–Peterson isotherms (Zhu and Alexandratos, 2005). Theangmuir and Freundlich isotherms are represented as follows (13)nd (14), respectively.

1qe

)=

(1

qmax

)+

[1

qbmax

](1Ce

), (13)

n qe = 1n

(ln Ce) + ln KF , (14)

here b is the Langmuir isotherm constant, KF is the Freundlichonstant, and n is the Freundlich exponent. 1/n is a measure of theurface heterogeneity ranging between 0 and 1, becoming moreeterogeneous as its value gets closer to zero. The ratio of Qo giveshe theoretical monolayer saturation capacity of adsorbent.

The essential characteristic of the Langmuir equation can bexpressed in terms of dimension factor, RL, which was defined (Hond McKay, 1998) as:

L = 1(1 + KLC0)

, (15)

here C0 is the highest initial metal concentration (mg/L). The valuef RL indicates the nature of adsorption as unfavorable (RL > 1), lin-ar (RL = 1), favorable (0 < RL < 1) or irreversible (RL = 0).

The Redlich–Peterson equation describes adsorption on hetero-eneous surfaces, as it contains the heterogeneity factor ˇ. Thisquation has three parameters, A, B and ˇ. Parameter rangesetween 0 and 1. It can be reduced the Langmuir equation as ˇpproaches 1. A, B and were determined by curve fitting.

Ce

Qe=

(B

A

)+

(1A

)Cˇ

e , (16)

Thermodynamic parameters such as free energy (�G0),nthalpy (�H0) and entropy (�S0) changes in the process can bestimated using the following equations:

G0 = −RT ln b, (17)

G0 = −H0 − T�S0, (18)

here b is Langmuir constant. The plot of ln b versus 1/T for thedsorption process determines the change in free energy and theegative change in free energy (�G0 < 0) indicated that the adsorp-ion process a thermodynamically favorable.

4. Perspectives

The adsorption of dyes using MCs and MNCs had been com-iled and reviewed in this paper. From the literature, adsorption ofyes using MCs and MNCs is predicted to have enhanced perfor-ance. However, the comparison between the two composites is

ust a guideline. From this reassessment, we would wish to high-ight that, low production cost with high adsorption efficiency as

ell as a multipurpose adsorbent suitable for all forms of pol-utants should be chosen, since the choice of the adsorbent is an

mportant event in deciding an appropriate adsorbent to be imple-

ented in large scale. This review discloses that MCs and MNCssed for the dye adsorption involve ease of preparation methodnd inexpensive chemical reagents. However, economic feasibility

, Monitoring & Management 1–2 (2014) 36–49 47

should be enhanced by examining the effectiveness of regen-eration of magnetic composites, since regeneration studies willdetermine the reusability of the magnetic composite. The kineticstudies, isotherms and diffusion models were employed widelyfor fitting kinetic data for understanding the interaction betweenadsorbate and adsorbent, rate of adsorption and efficiency and fea-sibility of adsorbent to uptake solute molecules. On the other hand,many new effective softwares are developed to solve complexdata and mathematical models which are expected to depict moreaccurately and helps in understanding the insight of mechanism.Further, the use of scanning electron microscope (SEM), energy dis-persive X-ray spectroscopy (EDX), X-ray diffraction (XRD) analysis,electron spin resonance (ESR), X-ray photoelectron spectroscopy(XPS), and thermogravimetric analysis (TGA) are extremely recom-mended for characterization studies.

15. Conclusion

This review indicates that adsorption using MCs and MNCs isbecoming a promising option to replace conventional adsorbentsin removing dyes. This review also indicates that these mag-netic composites have an equivalent or even more adsorption andregeneration capacity to locally available adsorbents and activatedcarbon. And wholly the same, difficulty stands high in comparingdifferent adsorbent, since different parameters are taken into con-sideration in evaluating the overall performance of the adsorbent.However, adsorbents coming out at long last with high adsorptionefficiency for the handling of waste water containing dyes will besuccessfully commercialized as a beneficiary to society.

References

Ai, L., Zhou, Y., Jiang, J., 2011. Removal of methylene blue from aqueous solutionby montmorillonite/CoFe2O4 composite with magnetic separation performance.Desalination 266, 72–77.

Akbarzadeh, A., Samiei, M., Davaran, S., 2012. Magnetic nanoparticles: preparation,physical properties, and applications in biomedicine. Nanoscale Res. Lett. 7, 144.

Akgol, S., Denizli, A., 2004. Novel metal-chelate affinity sorbents for reversible usein catalase adsorption. J. Mol. Catal. B: Enzymatic 28, 7.

Amith, B., Sivanesan, D., Kannan, K., Tapan, C., 2007. Kinetics of decolorization andbiotransformation of Direct Black 38 by C. hominis and P. stutzeri. Appl. Microbiol.Biotechnol. 74, 1145–1152.

Ardisson, J.D., Macedo, W.A.A., Mikhaylova, M., Muhammed, M., et al., 2008. Cubicversus spherical magnetic nanoparticles: The role of surface anisotropy. J. Am.Chem. Soc. 130, 13234–13239.

Atia, A.A., Donia, A.M., Al-Amrani, W.A., 2009. Adsorption/desorption behavior ofacid orange 10 on magnetic silica modified with amine groups. Chem. Eng. J.150, 55–62.

Banat, I.M., Nigam, P., Singh, D., Marchant, R., 1996. Microbial decolorization oftextile-dye containing effluents: a review. Boiresour. Technol. 58, 217–227.

Banerjee, S., Roy, S., Chen, J.W., Chakravorty, D., 2000. Magnetic properties ofoxide-coated iron nanoparticles synthesized by electrodeposition. Journal ofMagnetism and Magnetic Materials 219, 45–52.

Boyd, G.E., Adamson, A.W., Myers, L.S., 1947. The exchange adsorption of ions fromaqueous solutions by organic zeolites, II, Kinetics. J. Am. Chem. Soc. 69 (11),2836–2848.

Carneiro, P.A., Umbuzeiro, G.A., Oliveira, D.P., Zanoni, M.V.B., 2010. Assessment ofwater contamination caused by a mutagenic textile effluent/dyehouse effluentbearing disperse dyes. J. Hazard. Mater. 174, 694–699.

Chandro, S.S., Nagaraja, T., 1987. A food-poisoning outbreak with chemical dye. Aninvestigation report. Med. J. Armed Forces Ind. 43, 291–300.

Chang, P.R., Zheng, P., Liu, B., Anderson, D.P., Yu, J., Ma, X., 2011. Characterizationof magnetic soluble starch-functionalized carbon nanotubes and its applicationfor the adsorption of the dyes. J. Hazard. Mater. 186, 2144–2150.

Cheng, W., Wang, S.G., Lu, L., Gong, W.X., Liu, X.W., Gao, B.Y., Zhang, H.Y., 2008.Removal of malachite green (MG) from aqueous solutions by native and heat-treated anaerobic granular sludge. Biochem. Eng. J. 39 (3), 538–546.

Cooney, D.O., 1999. Adsorption Design for Wastewater Treatment. Lewis Publishers,Boca Raton.

Crini, G., 2003. Studies on adsorption of dyes on beta-cyclodextrin polymer. Biore-

sour. Technol. 90, 193–198.

Crini, G., 2005. Recent developments in polysaccharide-based materials used asadsorbents in wastewater treatment. Prog. Polym. Sci. 30, 38–70.

Daengsakul, S., Mongkolkachit, C., Thomas, C., Siri, S., Thomas, I., Amornkitbam-rung, V., Maensiri, S., 2009. A simple thermal decomposition synthesis, magnetic

4 ology

D

D

D

D

D

D

D

D

F

F

F

F

F

G

G

G

G

G

H

H

H

H

H

H

H

I

J

J

K

K

8 R. Sivashankar et al. / Environmental Nanotechn

properties, and cytotoxicity of La0.7Sr0.3MnO3 nanoparticles. Appl. Phys. A 96,691–699.

as, M., Ramchandani, S., Upreti, R.K., Khanna, S.K., 1997. MetanilYellow: a biofunc-tional inducer of hepatic phase I and phase II xenoblastic-metabolising enzymes.Food Chem. Toxicol. 35, 835–838.

ebrassi, A., Correa, A.F., Baccarin, T., Nedelko, N., Slawska-Waniewska, A., Sobczak,K., Dluzewski, P., Greneche, J.-M., Rodrigues, C.A., 2012a. Removal of cationicdyes from aqueous solutions using N-benzyl-O-carboxymethylchitosan mag-netic nanoparticles. Chem. Eng. J. 183, 284–293.

ebrassi, A., Baccarin, T., Demarchi, C.A., Nedelko, N., Slawska-Waniewska, A.,Dhuzewski, P., Bilska, M., Rodrigues, C.A., 2012b. Adsorption of Remazol Red198 onto magnetic N-lauryl chitosan particles: equilibrium, kinetics, reuse andfactorial design. Environ. Sci. Pollut. Res. 19, 1594–1604.

emirbas, 2009. Agricultural based activated carbons for the removal of dyes fromaqueous solutions: a review. J. Hazard. Mater. 167, 1–9.

eng, J.-H., Zhang, X.-R., Zeng, G.-M., Gong, J.-L., Niu, Q.-Y., Liang, J., 2013. Simul-taneous removal of Cd (II) and ionic dyes from aqueous solution usingmagnetic graphene oxide nanocomposite as an adsorbent. Chem. Eng. J. 226,189–200.

ozier, M.C., 2005. What is water pollution, Water and Me Series, SCS-2005-02.In: Soil and Crop Sciences Communications. Texas A&M University Systemhttp://waterandme.tamu.edu/WaterPollution/waterpollution.pdf

rbohlavova, J., Hrdy, R., Adam, V., Kizek, R., Schneeweiss, O., Hubalek, J., 2009.Preparation and properties of various magnetic nanoparticles. Sensors 9,2352–2362.

rmota, A., Drofenik, M., Koselj, J., Znidarsic, A., 2012. In: Najjar, R. (Ed.), Microemul-sion Method for Synthesis of Magnetic Oxide Nanoparticles, Microemulsions –An Introduction to Properties and Applications. , ISBN 978-953-51-0247-2.

an, L., Luo, C., Sun, M., Li, X., Lu, F., Qiu, H., 2012. Preparation of novel magneticchitosan/graphene oxide composite as effective adsorbents toward methyleneblue. Bioresour. Technol. 114, 703–706.

arghali, A.A., Moussa, M., Khedr, M.H., 2010. Synthesis and characterizationof novel conductive and magnetic nano-composites. J. Alloys Compd. 499,98–103.

orgacs, Cserháti, T., Oros, G., 2004. Removal of synthetic dyes from wastewaters: areview. Environ. Int. 30, 953–971.

rey, N.A., Peng, S., Cheng, K., Sun, S., 2009. Magnetic nanoparticles: Synthesis,functionalization, and applications in bioimaging and magnetic energy storage.Chem. Soc. Rev. 38, 2532–2542.

ungaro, A., Yamaura, M., Carvalho, T.E.M., 2011. Adsorption of anionic dyes fromaqueous solution on zeolite from fly ash-iron oxide magnetic nanocomposite. J.At. Mol. Sci. 2 (4), 305–316.

ao, H., Zhao, S., Cheng, X., Wang, X., Zheng, L., 2013. Removal of anionic azo dyesfrom aqueous solution using magnetic polymer multi-wall carbon nanotubenanocomposite as adsorbent. Chem. Eng. J. 223, 84–90.

e, F., Ye, H., Li, M.-M., Zhao, B.-X., 2012. Efficient removal of cationic dyes fromaqueous solution by polymer-modified magnetic nanoparticles. Chem. Eng. J.198–199, 11–17.

onga, J.-L., Wanga, B., Zenga, G.-M., Yanga, C.-P., Niua, C.-G., Niua, Q.-Y., Zhoua, W.-J.,Liang, Y., 2009. Removal of cationic dyes from aqueous solution using magneticmulti-wall carbon nanotube nanocomposite as adsorbent. J. Hazard. Mater. 164,1517–1522.

upta, V.K., Suhas, 2009. Application of low-cost adsorbents for dye removal – areview. J. Environ. Manage. 90, 2313–2342.

upta, S., Sundarrajan, M., Rao, K.V.K., 2003. Tumour promotion by metanil yellowand malachite green during rat hepatocarcinogenesis is associated with dys-regulated expression of cell cycle regulatory proteins. Teratogen. Carcin. Mut.(Suppl. 1), 301–312.

ausen, B.M., 1994. A case of allergic contact dermatitis due to metanil yellow.Contact Dermat. 31, 117–118.

o, Y.S., 2004. Citation review of Lagergren kinetic rate equation on adsorptionreactions. Scientometrics 59 (1), 171–177.

o, Y.S., 2006. Review of second-order models for adsorption systems. J. Hazard.Mater. 136 (3), 103–111.

o, Y.S., McKay, G., 1998. Sorption of dye from aqueous solution by peat. Chem. Eng.J. 70 (2), 115–124.

o, Y.S., McKay, G., 2000. The kinetics of sorption of divalent metal ions onto sphag-num moss peat. Water Res. 34 (3), 735–742.

o, Y.S., Ng, J.C.Y., McKay, G., 2000. Kinetics of pollutant sorption by biosorbents:review. Sep. Purif. Methods 29 (2), 189–232.

yeon, T., 2003. Chemical synthesis of magnetic nanoparticle. Chem. Commun.,927–934.

nbaraj, S., Chen, B.H., 2011. Dye adsorption characteristics of magnetite nanoparti-cles coated with a biopolymer poly (�-glutamic acid). Bioresour. Technol. 102,8868–8876.

iuhui, Q.U., 2008. Research progress of novel adsorption processes in water purifi-cation: A review. J. Environ. Sci. 20, 1–13.

ung, J.H., Lee, J.H., Shinkai, S., 2011. Functionalized magnetic nanoparticles aschemosensors and adsorbents for toxic metal ions in environmental and bio-logical fields. Chem. Soc. Rev. 40, 4464–4474.

annan, N., Rengasamy, G., 2005. Comparison of cadmium ion adsorption on various

activated carbons. Water Air Soil Pollut. 163, 185–201.

ara, A., Demirbel, E., 2012. Kinetic, isotherm and thermodynamic analysis onadsorption of Cr(IV) ions from aqueous solution by synthesis and characteriza-tion of magnetic-poly(divinylbenzene-vinyllimidazole) microbeads. Water AirSoil Pollut. 223 (5), 2387–2403.

, Monitoring & Management 1–2 (2014) 36–49

Karipoth, P., Thirumurugan, A., Justin Joseyphus, R., 2013. Synthesis and magneticproperties of flower-like FeCo particles through a one pot polyol process. J.Colloids Interface Sci. 404, 49–55.

Kolhatkar, A.G., Jamison, A.C., Litvinov, D., Willson, R.C., Randall Lee, T., 2013. Tuningthe magnetic properties of nanoparticles. Int. J. Mol. Sci. 14, 15977–16009.

Konicki, W., Sibera, D., Mijowska, E., Lendzion-Bielun, Z., Narkiewicz, U., 2013. Equi-librium and kinetic studies on acid dye Acid Red 88 adsorption by magneticZnFe2O4 spinel ferrite nanoparticles. J. Colloids Interface Sci. 398, 152–160.

Kyzas, G.Z., Travlou, N.A., Kalogirou, O., Deliyanni, E.A., 2013. Magnetic grapheneoxide: Effect of preparation route on reactive Black 5 adsorption. Materials 6,1360–1376.

Lagergren, S., 1898. About the theory of so-called adsorption of soluble substances.Kungliga Svenska Vetenskapsakademiens Handlingar 24 (4), 1–39.

Lazaridis, N.K., Asouhidou, D.D., 2003. Kinetics of sorptive removal of chromium (VI)from aqueous solutions by calcined Mg–Al–CO3 hydrotalcite. Water Res. 37 (12),2875–2882.

Lee, J.W., Choi, S.P., Thiruvenkatachari, R., Shim, W.G., Moon, H., 2006. Evaluationof the performance of adsorption and coagulation processes for the maximumremoval of reactive dyes. Dyes Pigments 69, 196–203.

Li, C., Wei, Y., Liivat, A., Zhub, Y., Zhu, J., 2013a. Microwave-solvothermal synthesisof Fe3O4 magnetic nanoparticles. Mater. Lett. 107, 23–26.

Li, D.-P., Zhang, Y.-R., Zhao, X.-X., Zhao, B.-X., 2013b. Magnetic nanoparticles coatedby aminoguanidine for selective adsorption of acid dyes from aqueous solution.Chem. Eng. J. 232, 425–433.

Luo, X., Zhang, L., 2009. High effective adsorption of organic dyes on magnetic cel-lulose beads entrapping activated carbon. J. Hazard. Mater. 171, 340–347.

Madrakiana, T., Afkhamia, A., Ahmadia, M., Bagheri, H., 2011. Removal of somecationic dyes from aqueous solutions using magnetic-modified multi-walledcarbon nanotubes. J. Hazard. Mater. 196, 109–114.

Mahmoodi, N.M., 2013. Magnetic ferrite nanoparticle–alginate composite: synthe-sis, characterization and binary system dye removal. J. Taiwan Inst. Chem. Eng.44, 322–330.

Mak, S.Y., Chen, D.-H., 2004. Fast adsorption of methylene blue on polyacrylic acid-bound iron oxide magnetic nanoparticles. Dyes Pigments 61, 93–98.

McMullan, G., Meehan, C., Conneely, A., Kirby, N., Robinson, T., Nigam, P., Banat, I.M.,Marchant, R., Smyth, W.F., 2001. Microbial decolourisation and degradation oftextiles dyes. Appl. Microbiol. Biotechnol. 56, 81–87.

Mekkawy, H.A., Ali, M.O., El-Zawahry, A.M., 1998. Toxic effect of synthetic and nat-ural food dyes on renal and hepatic functions in rats. Toxicol. Lett. 95, 155–161.

Mishra, G., Tripathy, M., 1993. A critical review of the treatment for decolorizationof textile effluent. Colourage 40, 35–38.

Monash, P., Pugazhenthi, G., 2009. Adsorption of crystal violet dye from aqueoussolution using mesoporous materials synthesized at room temperature. Adsorp-tion 15, 390–405.

Morales, N.J., Goyanes, S., Chiliotte, C., Bekeris, V., Candal, R.J., Rubiolo, G.H.,2013. One-step chemical vapor deposition synthesis of magnetic CNT–hercynite(FeAl2O4) hybrids with good aqueous colloidal stability. Carbon 61, 515–524.

Nejati, K., Zabihi, R., 2012. Preparation and magnetic properties of nano size nickelferrite particles using hydrothermal method. Nejati Zabihi Chem. Cent. J. 6, 23.

Nguyen, T.A., Juang, R.S., 2013. Treatment of waters and wastewaters containingsulfur dyes: A review. Chem. Eng. J. 219, 109–117.

Nkosi, S.S., Mwakikunga, B.W., Sideras-Haddad, E., Forbes, A., 2012. Nanotechnology.Sci. Appl. 5, 27–36.

Noh, S.H., Na, W., Jang, J.T., Lee, J.H., Lee, E.J., Moon, S.H., Lim, Y., Shin, J.S., Cheon,J., 2012. Nanoscale magnetism control via surface and exchange anisotropy foroptimized ferromagnetic hysteresis. Nano Lett. 12, 3716–3721.

Oxspring, D.A., Mc Mullan, G., Smyth, W.F., Marchant, R., 1996. Decolourisation andmetabolism of the reactive textile dye, Remazol Black B, by an immobilizedmicrobial consortium. Biotechnol. Lett. 18, 527–530.

Pandey, P.K., Choubey, S., Verma, Y., Pandey, M., Kalyan Kamal, S.S., Chandrashekhar,K., 2007. Biosorption removal of Ni (II) from wastewater and industrial effluent.Int. J. Environ. Res. Public Health 4 (4), 332–339.

Pearce, C.I., Lloyd, J.R., Guthrie, J.T., 2003. The removal of color from textiles waste-water using whole bacterial cells: a review. Dyes Pigments 58, 179–196.

Pham, H.L., Do, H.M., Tran, D.L., Le, V.H., Nguyen, X.P., Nguyen, A.T., Nguyen,T.N., Vu, A.T., 2011. Magnetic nanoparticles: study of magnetic heating andadsorption/desorption for biomedical and environmental applications. Int. J.Nanotechnol. 8, 399–413.

Qadri, S., Ganoe, A., Haik, Y., 2009. Removal and recovery of acridine orange fromsolutions by use of magnetic nanoparticles. J. Hazard. Mater. 169, 318–323.

Qiu, H., Lv, L., Pan, B.-C., Zhang, Q., Zhang, W.-M., Zhang, Q.-X., 2009. Critical reviewin adsorption kinetic models. J. Zhejiang Univ. Sci. A 10 (5), 716–724.

Qu, X., Pedro, J.J., Qilin Li, A., 2013. Applications of nanotechnology in water andwastewater treatment. Water Res. 47, 3931–3946.

Rafatullah, M., Sulaiman, O., Hashim, R., Ahmad, A., 2010. Adsorption of methyleneblue on low-cost sorbents: a review. J. Hazard. Mater. 177, 70–80.

Ragunath, H.M., 2006. Hydrology Principles, Analysis Design. New Age International(P) Limited, India.

Ramachandani, S., Das, M., Joshi, A., Khanna, S.K., 1997. Effect of oral and parentaladministration of metanil yellow on some hepatic and intestinal biochemicalparameters. J. Appl. Toxicol. 17, 85–91.

Rao, C.N.R., Thomas, P.J., Kulkarni, G.U., 2007. Nanocrystals: synthesis, properties andapplications. Materials Science, vol. 95. Springer, Berlin/Heidelberg/New York,pp. 1–182.

Rocher, V., 2008. Removal of organic dyes by magnetic alginate beads. Water Res.42 (4–5), 1290–1298.

ology

R

R

S

S

S

S

S

S

S

S

S

S

S

S

S

S

S

S

S

ST

V

W

W

W

W

W

W

W

W

W

R. Sivashankar et al. / Environmental Nanotechn

ocher, V., Bee, A., Siaugue, J.M., Cabuil, V., 2010. Dye removal from aqueous solutionby magnetic alginate beads crosslinked with epichlorohydrin. J. Hazard. Mater.178, 434–439.

ongcheng, W., Jiuhui, Q., Yongsheng, C., 2005. Magnetic powder MnO–Fe2O3 com-posite – A novel material for the removal of azo-dye from water. Water Res. 39,630–638.

abino, V.-V., Morales, M.P., Bomati-Miguel, O., Bautista, C., Zhao, X., Bonville, P., deAlejo, R.P., Ruiz-Cabello, J., Santos, M., Tendillo-Cortijo, F.J., Ferreiros, J., 2004.Colloidal dispersions of maghemite nanoparticles produced by laser pyrolysiswith application as NMR contrast agents. Phys. D: Appl. Phys. 37, 2054.

achdeva, S.M., Mani, K.V., Adval, S.K., Jalpota, V.P., Rasela, K.C., Chadha, D.S., 1992.Acquired toxic methaemoglobinaemia. J. Assoc. Phys. Ind. 40, 239–240.

afarik, I., Safarikova, M., 2010. Magnetic fluid modified peanut husks as an adsor-bent for organic dyes removal. Phys. Proc. 9, 274–278.

afarik, I., Horska, K., Svobodova, B., Safarikova, M., 2012. Magnetically modifiedspent coffee grounds for dyes removal. Eur. Food Res. Technol. 234, 345–350.

afarik, I., Horska, K., Pospiskova, K., Maderova, Z., Safarikova, M., 2013. Microwaveassisted synthesis of magnetically responsive composite materials. IEEE Trans.Magn. 49, 1.

afarikova, M., Ptackova, L., Kibrikova, I., Safarık, I., 2005. Biosorption of water-soluble dyes on magnetically modified Saccharomyces cerevisiae subsp. uvarumcells. Chemosphere 59, 831–835.

algueiro, A.M., Daniel-da-Silva, A.L., Girao, A.V., Pinheiro, P.C., Trindade, T., 2013.Unusual dye adsorption behavior of �-carrageenan coated superparamagneticnanoparticles. Chem. Eng. J. 229, 276–284.

alleh, M.A.M., Mahmoud, D.K., Karim, W.A.W.A., Idris, A., 2011. Cationic and anionicdye adsorption by agricultural solid wastes: a comprehensive review. Desalina-tion 280, 1–13.

amanta, A.K., Agarwal, P., 2009. Application of natural dyes on textiles. Indian J.Fibre Text. Res. 34, 384–399.

hankar, D.S., Sreenivasa, R.B., 2012. Kinetic models in adsorption – a review. AsianJ. Res. Chem. 5 (1), 8–13.

huang, C.D., Li, P.H., Li, A.M., Zhou, Q., Zhang, M.C., Zhou, Y., 2012. Quaternizedmagnetic microspheres for the efficient removal of reactive dyes. Water Res. 46,4417–4426.

ingamaneni, S., Bliznyuk, V.N., Binek, C., Tsymbal, E.Y., 2011. Magnetic nanopar-ticles: recent advances in synthesis, self-assembly and applications. J. Mater.Chem. 21, 16819–16845.

ingh, K.P., Gupta, S., Singh, A.K., Sinha, S., 2011. Optimizing adsorption of crys-tal violet dye from water by magnetic nanocomposite using response surfacemodeling approach. J. Hazard. Mater. 186, 1462–1473.

lunjski, M., Cadee, K., Tattersall, J., MIEX, 2000. Resin Water Treatment Process.Aquatech Amsterdam, Netherlands.

olis, M., Solis, A., Perez, H.I., Manjarrez, N., Flores, M., 2012. Microbial decolourationof azo dyes: a review. Process Biochem. 47, 1723–1748.

ong, Q., Zhang, Z.J., 2004. Shape control and associated magnetic properties of spinelcobalt ferrite nanocrystals. J. Am. Chem. Soc. 126, 6164–6168.

tarowicz, M., Starowicz, P., Zukrowski, J., Przewoznik, J., Lemanski, A., Kapusta, C.,Banas, J., 2011. Electrochemical synthesis of magnetic iron oxide nanoparticleswith controlled size. J. Nanopart. Res. 13, 7167–7176.

wartz, H.M., Bolton, J.R., Borg, D.C., 1997. Borg. Wiley, New York.iwari, H., 2012. Assessment of teratogenecity and embryo toxicity of dye waste-

water untreated sludge from sanganer on swiss albino mice when administeredduring growth period of gestation. Water Res. Dev. 2, 48–53.

adivelan, V., Kumar, K.V., 2005. Equilibrium, kinetics, mechanism, and processdesign for the sorption of methylene blue onto rice husk. J. Colloids InterfaceSci. 286, 90–100.

ang, S., Zhai, Y.-Y., Gao, Q., Luo, W.-J., Xia, H., Zhou, C.-G., 2014. Highly efficientremoval of Acid Red 18 from aqueous solution by magnetically retrievable chi-tosan/carbon nanotube: batch study, isotherms, kinetics, and thermodynamics.Chem. Eng. Data 59, 39–51.

awrzkiewicz, M., 2012. Anion exchange resins as effective sorbents for acidic dyeremoval from aqueous solutions and wastewaters. Solvent Extr. Ion Exch. 30,507–523.

eber, W.J., Morris, C.J., 1962. Advances in Water Pollution Research: Removalof Biologically Resistant Pollutants From Waste Water by Adsorption. PaperPresented at Proceedings of International Conference on Water Pollution Sym-posium, vol. 2. Pergamon Press, Oxford, pp. 231–266.

est, A., 1999. Basic Solid State Chemistry. John Wiley & Sons, Ltd., Chichester, WestSussex, UK, pp. 100–109.

illiams, A.R., Moruzzi, V.L., Gelatt, C.D., Kubler, J., Schwarz, K., 1982. Aspects oftransition-metal magnetism. J. Appl. Phys. 53, 2019–2023.

ater Pollution, National Water Awareness Campaign, Gaia Atlas of Planet Man-agement, The Guardian. 2003, August.

u, R.C., Qu, J.H., He, H., 2004. Removal of azo-dye Acid Red B (ARB) by adsorptionand combustion using magnetic CuFe2O4 powder. Appl. Catal. B 48, 49–56.

u, R.C., Qu, J.H., Chen, Y.S., 2005. Magnetic powder MnOFe2O3 – a novel materialfor the removal of azo-dye from water. Water Res. 39, 630–638.

u, Z., Wu, J., Xiang, H., Chun, M.S., Lee, K., 2006. Organosilane-functionalized Fe3O4

composite particles as effective magnetic assisted adsorbents. Colloids Surf. A:Physicochem. Eng. Aspects 279, 167–174.

, Monitoring & Management 1–2 (2014) 36–49 49

Wu, W., He, Q., Chen, H., Tang, J., Nie, L., 2007. Sonochemical synthesis, structureand magnetic properties of air-stable Fe3O4/Au nanoparticles. Nanotechnology18, 145609.

Wu, D., Zheng, P., Chang, P.R., Ma, X., 2011. Preparation and characterization of mag-netic rectorite/iron oxide nanocomposites and its application for the removal ofthe dyes. Chem. Eng. J. 174, 489–494.

Wu, Q., Feng, C., Wang, C., Wang, Z., 2013. A facile one-pot solvothermal methodto produce superparamagnetic graphene–Fe3O4 nanocomposite and its appli-cation in the removal of dye from aqueous solution. Colloids Surf. B: Biointerf.101, 210–214.

Wua, S., Suna, A., Zhai, F., Wang, J., Xua, W., Zhang, Q., Volinsky, A.A., 2011.Fe3O4 magnetic nanoparticles synthesis from tailings by ultrasonic chemicalco-precipitation. Mater. Lett. 65, 1882–1884.

Xia, Y., Dai, X., Huang, S., Tian, X., Yang, H., Li, Y., Liu, Y., Zhao, M., 2013. Fast andhighly efficient removal of methylene blue by a novel EDTAD-modified magneticchitosan material. Desalin. Water Treat. 51, 7586–7595.

Xiao, J.D., Qiu, L.G., Jiang, X., Zhu, Y.J., Ye, S., Jiang, X., 2013. Magnetic porous car-bons with high adsorption capacity synthesized by a microwave-enhanced hightemperature ionothermal method from a Fe-based metal-organic framework.Carbon 59, 372–382.

Xie, Y., Qian, D., Wu, D., Ma, X., 2011. Magnetic halloysite nanotubes/iron oxidecomposites for the adsorption of dyes. Chem. Eng. J. 168, 959–963.

Xu, J., Yang, H., Fu, W., Du, K., Sui, Y., Chen, J., Zeng, Y., Li, M., Zou, G., 2007. Preparationand magnetic properties of magnetite nanoparticles by sol–gel method. J. Magn.Magn. Mater. 309, 307–311.

Xu, H., Zhang, Y., Jiang, Q., Reddy, N., Yang, Y., 2013. Biodegradable hollow zeinnanoparticles for removal of reactive dyes from wastewater. J. Environ. Manage.125, 33–40.

Yadla, S.V., Sridevi, V., Chandana Lakshmi, M.V.V., 2012. A review on adsorption ofheavy metals from aqueous solution. J. Chem. Biol. Phys. Sci. 2 (3), 1585–1593.

Yan, H., Li, H., Yang, H., Li, A., Cheng, R., 2013. Removal of various cationic dyesfrom aqueous solutions using a kind of fully biodegradable magnetic compositemicrosphere. Chem. Eng. J. 223, 402–411.

Yang, N., Zhu, S., Zhang, D., Xu, S., 2008. Synthesis and properties of magneticFe3O4-activated carbon nanocomposite particles for dye removal. Mater. Lett.62, 645–647.

Yang, H., Yuan, B., Lu, Y.B., Cheng, R.S., 2009. Preparation of magnetic chitosanmicrospheres and its applications in wastewater treatment. Sci. China Ser. B52, 249–256.

Yao, Y., Miao, S., Liu, S., Ma, L.P., Sun, H., Wang, S., 2012. Synthesis, characterization,and adsorption properties of magnetic Fe3O4@graphene nanocomposite. Chem.Eng. J. 184, 326–332.

Yavuz, H., Denizli, A., Gungunes, H., Safarikova, M., Safarik, I., 2006. Biosorp-tion of mercury on magnetically modified yeast cells. Sep. Purif. Technol. 52,253–260.

Zhang, Z., Kong, J., 2011. Novel magnetic Fe3O4@C nanoparticles as adsorbentsfor removal of organic dyes from aqueous solution. J. Hazard. Mater. 193,325–329.

Zhang, W., Liang, F., Li, C., Qiu, L.-G., Yuan, Y.-P., Peng, F.-M., Jiang, X., Xie, A.-J.,Shen, Y.H., Zhu, J.-F., 2011. Microwave-enhanced synthesis of magnetic porouscovalent triazine-based framework composites for fast separation of organic dyefrom aqueous solution. J. Hazard. Mater. 186, 984–990.

Zhang, Y.-R., Wang, S.-Q., Shen, S.-L., Zhao, B.-X., 2013. A novel water treatmentmagnetic nanomaterial for removal of anionic and cationic dyes under severecondition. Chem. Eng. J. 233, 258–264.

Zhang, Y.-R., Shen, S.-L., Wang, S.-Q., Huang, J., Su, P., Wang, Q.-R., Zhao, B.-X., 2014.A dual function magnetic nanomaterial modified with lysine for removal oforganic dyes from water solution. Chem. Eng. J. 239, 250–256.

Zhao, Y., Qiu, Z., Huang, J., 2008. Preparation and analysis of Fe3O4 magnetic nanopar-ticles used as targeted-drug carriers. Chin. J. Chem. Eng. 16 (3), 451–455.

Zhen, G., Muir, B.W., Moffat, B.A., Harbour, P., Murray, K.S., Moubaraki, B., Suzuki,K., Madsen, I., Agron-Olshina, N., Waddington, L., et al., 2011. Comparativestudy of magnetic behavior of spherical and cubic superparamagnetic iron oxidenanoparticles. J. Phys. Chem. C 115, 327–334.

Zhou, L., Jin, J., Liu, Z., Liang, X., Shang, C., 2011. Adsorption of acid dyes from aqueoussolutions by the ethylenediamine-modified magnetic chitosan nanoparticles. J.Hazard. Mater. 185, 1045–1052.

Zhu, X., Alexandratos, S.D., 2005. Affinity and selectivity of immobilized N-Methyl-D-glucamine for mercury(II) ions. Ind. Eng. Chem. Res. 44, 8605.

Zhu, H.Y., Jiang, R., Xiao, L., Li, W., 2010. A novel magnetically separable�-Fe2O3/crosslinked chitosan adsorbent: Preparation, characterization andadsorption application for removal of hazardous azo dye. J. Hazard. Mater. 179,251–257.

Zhu, H.Y., Fu, Y.Q., Jiang, R., Jiang, J.H., Xiao, L., Zeng, G.M., Zhao, S.L., Wang, Y., 2011.Adsorption removal of congo red onto magnetic cellulose/Fe3O4/activated car-bon composite: Equilibrium, kinetic and thermodynamic studies. Chem. Eng. J.

173, 494–502.

Zhu, H.Y., Fu, Y.Q., Jiang, R., Yao, J., Xiao, L., Zeng, G.M., 2012. Novel magneticchitosan/poly(vinyl alcohol) hydrogel beads: Preparation, characterization andapplication for adsorption of dye from aqueous solution. Bioresour. Technol.105, 24–30.