Study of the Preparation of Mesoporous Magnetic Microspheres

and Their Applications

M å r t e n E r i c s o n

Master of Science ThesisStockholm 2009

Mårten Ericson

STUDY OF THE PREPARATION OF MESOPOROUS MAGNETIC MICROSPHERES

AND THEIR APPLICATIONS

PRESENTED AT

INDUSTRIAL ECOLOGY ROYAL INSTITUTE OF TECHNOLOGY

www.ima.kth.se

Master of Science Thesis

STOCHOLM 2009

Examiner: Per Olof Persson, Industrial Ecology

TRITA-IM 2009:25 ISSN 1402-7615 Industrial Ecology, Royal Institute of Technology www.ima.kth.se

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Abstract Treatment of wastewater using magnetic technology is a rising field. In this thesis, the latest

research on the subject is reviewed and several adsorbents with different coatings, which

impart them unique properties, are discussed. Separation of particles from aqueous solution

using magnetic technology is more convenient compared to conventional techniques, such as

filtration and centrifugation. The adsorbents described in this thesis are effective for

adsorption of several types of contaminants, such as heavy metals and different types of dyes.

Magnetic microspheres were synthesised using porous polystyrene microspheres as

template. The microspheres were first sulfonated using chlorosulfonic acid followed by

stirring in the presence of ferrous chloride which then was oxidised and magnetic

nanoparticles were formed on the surface.

The sulfonated microspheres had a surface area of 420 m2/g and the magnetic 175 m2/g,

indicative of Fe3O4 nanoparticles were successfully formed in the pores. The weight fraction

of the Fe3O4 nanoparticles in the magnetic microspheres was 33 %.

Adsorption and desorption studies of the cationic dye, methylene blue, using mesoporous

magnetic microspheres were performed. The results show that the mesoporous magnetic

microspheres have good ability to adsorb methylene blue at low concentrations. In a cycle

study the adsorption efficiency were nearly 100 % throughout the study. Using a 6/4

EtOH/H2O with saturated KCl solution the desorption efficiency in the cycle study were

about 95 %.

The microspheres were used as carriers for TiO2 in order to overcome the problem with the

separation of TiO2 from solution. The TGA results show that the microspheres contained

about 12 % of TiO2. The TiO2 coated microspheres were used for the photocatalytic

degradation of phenol. However, the TiO2 microspheres did not work. This was a result from

that the phenol had too little contact with the TiO2. A possible way of solving this problem

could be to decrease the size of the microspheres, thus increase the surface area.

Lysozyme was adsorbed and separated using the porous microspheres. The lysozyme

adsorption worked best at pH 9.6, which is the pI for lysozyme. The lysozyme could be

extracted from the microspheres by using a pH 13 buffer. Also, by using MeOH/H2O and

EtOH/H2O solutions with saturated KCl the lysozyme could be desorbed. An adsorption and

desorption mechanism was also presented.

Keywords: Adsorption, bioseparation, magnetic adsorbents, magnetic microspheres,

magnetic separation, photocatalyst, wastewater

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IV

Sammanfattning

Vattenrening med magnetisk teknologi är en ny och alltmer uppmärksammad teknik.

Magnetisk separation är ett enkelt och snabbt sätt att separera något från en lösning.

Magnetisk separation är mer lätthanterligt jämfört med traditionell separationsteknik såsom

centrifugering och filtrering.

Med porösa polystyren mikrosfärer som mall, syntetiserades magnetiska mikrosfärer. Först

så sulfonerades mikrosfärerna med klorosulfonisk syra, följt av att de rördes om i en

järnkloridlösning. Magnetiska nanopartiklar bildades i porerna och på ytan av mikrosfärerna.

Sulfonerade mikrosfärerna hade en specifik ytarea på 420 m2/g och de magnetiska 175 m2/g, detta indikerar att Fe3O4-nanopartiklar bildades på ytan och i porerna. Massfraktionen

av Fe3O4 var 33 %.

Adsorption- och desorptionsstudier på de magnetiska mikrosfärerna utfördes. Färgämnet

metylblått användes i studien. Resultaten visade att magnetiska mikrosfärerna hade en bra

adsorptionsförmåga vid låga koncentrationer av metylblått. Cykelstudier visade att

adsorptionsverkningsgraden var nära 100 % under flera adsorptionscykler. Desorptionsförsök

med olika lösningsmedel visade att en mättad KCl 6/4 EtOH/H2O lösning gav en desorptions-

verkningsgrad på ca 95 %.

Mikrosfärerna användes som mall och kärna för att syntetisera en TiO2-fotokatalysator, detta

för att överkomma problemet som finns med separation av rent TiO2 pulver från lösning. TGA

resultaten visade att mikrosfärerna innehöll ca 12 % TiO2. De syntetiserade TiO2-

mikrosfärerna användes till att bryta ner fenol fotokatalytiskt. Dock fungerade inte detta

experiment. En anledning var att fenolen hade för lite kontakt med TiO2. En lösning på detta

problem är att använda mikrosfärer med högre specifik ytarea.

Proteinet lysozym användes som modellprotein för försök att separera proteiner från lösning

genom att använda porösa mikrosfärer. Resultatet visade att lysozym kunde adsorberas vid

pH 9.6. Med en pH 13 buffer kunde lysozymet sedan extraheras från mikrosfärerna. En

mekanism för adsorptionen och desorptionen på mikrosfärerna presenterades.

Nyckelord: Adsorption, magnetiska adsorbenter, bioseparation, magnetiska mikrosfärer, fotokatalys

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Table of Contents Chapter 1: Introduction .............................................................................................................. 1

1.1 Aims and Objectives ........................................................................................................ 2 1.2 Methods ............................................................................................................................ 2 1.3 Limitations ....................................................................................................................... 2

Chapter 2: Background ............................................................................................................... 3

2.1 Updated Research Progress in Magnetic Adsorbents ...................................................... 3 2.1.1 Mesoporous Magnetic Adsorbents ............................................................................ 3 2.1.2 Coated Magnetic Nano-Adsorbents .......................................................................... 6 2.1.3 Magnetic Carbon Adsorbents .................................................................................. 10 2.1.4 Other Magnetic Adsorbents .................................................................................... 11 2.1.5 Conclusions ............................................................................................................. 12

2.2 Updated Research Progress in Magnetic Photoocatalyst ............................................... 14 2.2.1 Different Preparation Techniques and Magnetic Carriers ....................................... 14 2.2.2 Degradation of Organic Pollutants by Magnetic Photocatalysts ............................. 16 2.2.3 Conclusions ............................................................................................................. 18

2.3 Updated Research Progress in Bioseparation Using Magnetic Technology .................. 19 2.3.1 Bioseparation ........................................................................................................... 19 2.3.2 Conclusions ............................................................................................................. 20

Chapter 3: Magnetic Microspheres for Removal of Methylene Blue From Wastewater ......... 21

3.1 Experimental .................................................................................................................. 21 3.1.1 Materials .................................................................................................................. 21 3.1.2 Preparation .............................................................................................................. 21 3.1.3 Characterisation ....................................................................................................... 22 3.1.4 Adsorption and Desorption Optimisation ............................................................... 22

3.2 Results and Discussion ................................................................................................... 23 3.2.1 Preparation of Magnetic Microspheres ................................................................... 23 3.2.2 Characterisation ....................................................................................................... 24 3.2.3 Adsorption and Desorption Study of Methylene Blue ............................................ 25 3.2.4 Adsorption and Desorption Mechanism .................................................................. 27

3.3 Conclusions .................................................................................................................... 30 Chapter 4: Mesoporous Microspheres with Photocatalytic Ability ......................................... 33

4.1 Experimental .................................................................................................................. 33 4.1.1 Materials .................................................................................................................. 33 4.1.2 Preparation of Photocatalytic Microspheres ........................................................... 33 4.1.3 Characterisation ....................................................................................................... 33 4.1.4 Photocatalytic Degradation of Phenol ..................................................................... 33

4.2 Results & Discussion ..................................................................................................... 34 4.2.1 Preparation of Photocatalytic Microspheres ........................................................... 34 4.2.2 Characterisation ....................................................................................................... 34 4.2.3 Photocatalytic Degradation of Phenol ..................................................................... 35

4.3 Conclusions .................................................................................................................... 37

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VII

Chapter 5: Mesoporous Microspheres for Bioseparation ......................................................... 39

5.1 Experimental .................................................................................................................. 39 5.1.1 Material ................................................................................................................... 39 5.1.2 Separation of Lysozyme .......................................................................................... 39

5.2 Results & Discussion ..................................................................................................... 40 5.2.1 Separation of Lysozyme .......................................................................................... 40 5.2.2 Adsorption and Desorption Mechanism .................................................................. 42

5.3 Conclusions .................................................................................................................... 43 Chapter 6: Conclusions ............................................................................................................ 45

References ................................................................................................................................ 47

Chapter 1 .............................................................................................................................. 47 Chapter 2 .............................................................................................................................. 48 Chapter 3 .............................................................................................................................. 55 Chapter 4 .............................................................................................................................. 56 Chapter 5 .............................................................................................................................. 56 Chapter 6 .............................................................................................................................. 56

Publications .............................................................................................................................. 57

Acknowledgment ..................................................................................................................... 57

End Note ................................................................................................................................... 57

1

CHAPTER 1: INTRODUCTION It is important to develop new techniques for the treatment of wastewater but also to

improve the existing ones. In most of all industry there are non-environmentally friendly

chemicals in the effluents. There is a need to remove these substances but also to recycle and

reuse them, which is beneficial from an economical point of view.

Today there are several techniques available for removal of pollutants from effluents. A few

worth to mention are chemical oxidation, biological treatment, nanofiltration, and adsorption

[1.1-1.4]. There has been a lot of research in the field of adsorption. Prominent among

recently studied adsorbents are zeolites, hydrogels, nanotubes, waste materials, and active

carbon [1.5-1.11]. Active carbon is the most commonly used adsorbent because it adsorbs a

variety of substances and possesses a great adsorption capacity [1.12]. However, active

carbon is generally difficult to separate from aqueous solutions. One approach to solve this

problem has been to incorporate magnetic particles [1.13], a technique which has drawn much

attention lately.

One of the main applications for photocatalysts is the degradation of pollutants from waste

water. This technique is becoming increasingly important, especially for removing low trace

contaminants but also for bacteria and viruses [1.14, 1.15]. Some of the advantages with

photocatalytic decomposition are, low costs, complete mineralisation thus, no waste disposal

problem [1.16]. The photocatalysts have the same problems as many adsorbents, due to the

size they are difficult to separate from aqueous solutions. Also within this field magnetic

particles have been incorporated with the photocatalysts, thus making the separation easy and

convenient [1.17].

Bioseparation is a growing field and with the increasing research proteomics, new and better

separation techniques is required in order to meet the demands of high selectivity, efficiency

etc. [1.18]. One technique that has recently got much attention is to use magnetically

separable particles with tailored coatings, which can adsorb different types of proteins [1.19].

This technique fulfils the high demands that are required for the separation of proteins.

The applications for the porous polymer microspheres are numerous, for example, ion

exchange, liquid chromatography, adsorption, purification, and catalyst [1.20-1.24]. Some of

the reasons for their extensive applications are that the microspheres show high physical

endurances, temperature durability, inertness, and low degradability. Hence, integrating

magnetic particles in the microspheres opens for applications in new areas, such as

environmental remediation.

In this thesis, we focus on the latest research progress of magnetic adsorbents for

wastewater treatment. Different coatings of the magnetic particles and their applications,

including their adsorption abilities are discussed. Further, adsorption, desorption, and

separation studies using porous magnetic microspheres were performed. Then, TiO2 coated

2

microspheres were synthesised and used for the photocatalytic degradation of phenol. Finally,

the porous microspheres were used for separation of protein.

This was the final degree project work in the education of Master of Science in Chemical

Engineering at The Royal Institute of Technology (KTH). The work has been executed at the

State Key Laboratory of Chemical Engineering, Department of Chemical Engineering and

Biological Engineering, Zhejiang University, China.

1.1 AIMS AND OBJECTIVES

The aims of this thesis were to review and increase the knowledge about the recent studies

in wastewater treatment using magnetic technology. Following, implement the knowledge

gained from the literature study in similar cases and develop new ideas for future advances in

the waste water treatment. The objectives were to study the methods in the treatment of

wastewater using magnetic technology and to improve/develop strategies for separation and

removal of pollutants from wastewater. Further, to explore the possibility of using the

microspheres as carriers for photocatalysts. Finally, by using the porous microspheres perform

a bioseparation.

1.2 METHODS

The thesis started with an extensive literature study in the recent research progress on the

applications of magnetic adsorbents in the treatment of wastewater, which resulted in an

article later to be published in a scientific journal.

Weekly seminars where the research group presented recent published articles in contiguous

fields. This was to keep everyone updated on the recent research in various fields and to gain

new ideas to implement in the research.

The experimental work was done at the State Key Laboratory of Chemical Engineering,

Zhejiang University. The work included: repeating previous work done by others, this to

familiarise with the methods and techniques. Then to design, develop, improve, and evaluate

applications for magnetic microspheres based on the previous work.

UV/Vis-spectrophotometry, XRD, TGA, and N2-sorption have been used to the evaluate

results from different experiments that were carried out.

1.3 LIMITATIONS

The research was performed under a short period of time, therefore the limitations were the

time frame. However, new inspiring ideas have been formed during this work which could be

fundamental for further research.

3

CHAPTER 2: BACKGROUND

2.1 UPDATED RESEARCH PROGRESS IN MAGNETIC ADSORBENTS

The areas of application for magnetic particles are numerous, for example data-storage,

cancer treatment, drug release, nuclear waste, and magnetic resonance imaging [2.1-2.5].

Adsorbents with incorporated magnetic particles have proved to be useful for removal of

different contaminants, such as heavy metals and dyes [2.6, 2.7] and the magnetic adsorbents

show great ability for regeneration and reuse [2.8].

Separating and removing particles using magnetic technology have shown to be more

efficient and selective compared to other methods such as centrifugation and filtration.

Magnetic adsorbents have also shown to be efficient for rapid separation of large volume

samples and in suspended systems [2.9-2.11].

There are some differences between nano- and micro-sized magnetic adsorbents. For one,

the nano-sized adsorbents have no internal diffusion resistance. The internal diffusion

resistance may cause slow adsorption and desorption rates. Also, the nano-sized adsorbents

have greater specific surface area compared to the micro-sized. This reduces the amount of

adsorbent needed to achieve satisfactory results [2.12, 2.13]. The magnetic force acting on

particles in a field gradient is direct proportional to the particle volume. If the magnetic

adsorbent is too small no separation will occur when applying a magnetic force. This is due to

the force will not be strong enough to overcome the Brownian motion [2.10].

Fe3O4 is the most commonly used material in the field for synthesising magnetic adsorbents.

The nano-sized Fe3O4-particles show superparamagnetic properties in room temperature and

can be attracted by a magnet. However, the particles do not retain the magnetism after the

magnet is removed. This is due to their superparamagnetic properties. Also, the magnetic

nano-particles do not cluster and an easy separation using an external magnetic field can be

achieved [2.6].

2.1.1 MESOPOROUS MAGNETIC ADSORBENTS

Mesoporous materials have applications in many areas, such as separation, catalysis, and

adsorption [2.14]. Incorporating Fe3O4-particles in mesoporous materials is of great interest

for the development of high quality adsorbents combined with convenient separation using an

external magnetic field. However, poor magnetic response in the magnetic adsorbents has

been a problem. The underlying cause has been found to be structure irregularities and low

Fe3O4 mass fraction [2.15-2.17].

Recently Liu et al. [2.6] have prepared mesoporous magnetic microspheres using

macroporous polydivinylbenzene (PDVB) microspheres with a diameter of 350-450 µm as a

template. The PDVB microspheres were first sulfonated with chlorosulfonic acid.

Subsequently, the sulfonated microspheres were stirred in the presence of ferrous chloride and

4

magnetic Fe3O4 nano-particles (MNPs) were formed and distributed all over the pore wall. A

scheme of the process is given in Figure 2.1.

: Magnetic particle

SO3-

Na+ -O3S

SO3-

-O3S

+Na

Na+

+Na

Magneticmicrosphere

Polystyremicrosphere

CH2Cl2

SO3H

HO3S

SO3H

HO3S

Sulfonatedmicrosphere

Fe2+SO3

-

-O3SSO3

-

-O3S

Fe2+

NaOH

H2O2

FeCl2SO3HCl

Figure 2.1 Scheme for preparing mesoporous magnetic microspheres [2.6]

The synthesised mesoporous magnetic microspheres were used for removal of the dyes

methyl violet (MV) and basic fuchsin (BF) (Figure 2.2) from an aqueous solution. The

sulfonic groups distributed over the pore walls are advantageous for adsorption of cationic

dyes. The results showed that the microspheres had good adsorption abilities, and 99.1 % of

BF and 92.8 % of MV were adsorbed from the solution. The mesoporous magnetic

microspheres had a specific surface area of 239 m2/g and a Fe3O4 weight-fraction of 25 wt%.

It was stated that the Fe3O4 weight fraction could be improved by additional cycles of stirring

in the presence of ferrous chloride. Noteworthy, the magnetisation curves showed that the

magnetic microspheres had ferromagnetic properties at 5 K. However at 300 K, the

microspheres have superparamagnetic properties. As desorbent, anhydrous ethanol was used,

which made recycling and reusage of the microspheres possible. After the fourth cycle, 91.8

% BF and 86.3 % MV were removed [2.6]. Maintaining good adsorption abilities is important

from an economical point of view.

NCH3H3C

NHN CH3

CH3H3C

NHH

NH2H2N

CH3

Methyl violet Basic fuchsin

Cl- Cl-

Figure 2.2 Molecular structures of methyl violet and basic fuchsin [2.6]

5

Mesoporous silica-coated MNPs were synthesised by Wu et al. [2.18]. MNPs with a

diameter of <5 µm were coated with a thin layer of silica followed by addition of cetyl-

trimethyl-ammonium chloride (CTAC). The magnetic particles were collected by separation

using a magnet and then mixed with tetraethyl orthosilicate (TEOS) [2.18]. The products were

then calcinated in presence of N2 and to improve the silanation reaction with mercapto-

propyl-trimethoxy-silane (MPTS) the products were steamed [2.19]. A detailed scheme of the

synthesis is presented in Figure 2.3. Dong et al. [2.19] demonstrates that the silica-coated

MNPs are effective for adsorbing mercury. With a mercury loading capacity of 14 mg/g, the

silica-coated magnetic particles show great potential for removing mercury and can be used in

industries with high mercury concentrations in the wastewater discharge. A high loading

capacity reduces the amount of adsorbent needed and also the amount of waste.

Figure 2.3. Scheme for preparation of mesoporous silica-coated magnetic particles [2.19]

The mesoporous magnetic microspheres synthesised by Liu et al. were discovered to only

be able to adsorb cationic species. To solve this problem, Zubieta et al. treated a silica

lamellar mesoporous material with chitosan using a similar synthesis route as Wu et al. [2.18],

and succeeded to remove an anionic- and a cationic dye, Tectilon Blue and Rhodamine B

[2.20]. However, Zubieta et al. did not utilise magnetic separation. Nevertheless, it is likely

that the technique could be adapted on the mesoporous magnetic microspheres. This might be

of great interest for further research.

Deng et al. [2.21] have prepared mesoporous magnetic microspheres (~500 nm) with a

Fe3O4@SiO2 core. Initially, Fe3O4-particles were coated with a thin layer of silica followed by

templating with cetyltrimethylammonium bromide (CTAB) and finally, the templates were

removed with acetone. The procedure is shown in Figure 2.4. Deng et al. [2.21] have removed

different species of microcystins using the mesoporous magnetic microspheres. Microcystins

are toxic molecules with high molecular weight (about 1000 Daltons) which are produced in

cyano-bacterial blooms [2.22]. Three different species of microcystins were used in the

experiment; MC-RR, MC-YR, and MC-LR. Within one minute, 95.4 % MC-RR, 97.2 % MC-

YR, and 97.5 % MC-LR had been adsorbed from the aqueous solution. Worth to mention is

that only 0.05 mg/µg-microcystins of the microspheres were needed for removal of the

microcystins. Acetonitril was used as desorbent and after eight cycles the removal efficiency

was 90 % [2.21]. These results indicate that the method could have a high commercial value.

6

Figure 2.4. Scheme for preparing mesoporous magnetic microspheres with a Fe3O4@SiO2 core [2.21]

2.1.2 COATED MAGNETIC NANO-ADSORBENTS

The preparation of polyacrylic acid (PAA)-coated MNPs has been developed by Liao et al

[2.23]. The binding of PAA onto MNPs were performed by initially sonicate MNP in a pH 6

buffer followed by addition of carbodiimide. PAA-solution was added and bound to the

MNPs which then were recovered from the solution using a magnet. Figure 2.5 step I shows a

scheme of the synthesis of PAA-coated MNPs. From this point, there were two existing

synthesis routes for functionalising the PAA-coated MNPs. Mak et al. [2.24] have treated the

PAA-coated MNPs with sulfanilic acid as shown in Figure 2.5 step II. Huang et al [2.25] have

prepared amino-functionalised PAA-coated MNPs using diethylenetriamine via activation

with carbodiimide as shown in the scheme in Figure 2.5 step III. By altering the surface of the

PAA-coated MNPs, different types of contaminants could be adsorbed. The three different

adsorbents described above have been proved to be useful for adsorption of cationic dyes,

multivalent metal ions, and enzymes [2.8, 2.24-2.26].

PAA

Carbodiimide

HN

NH2

H2N C

C

O

O

N

N NH

HN

H

H

NH2

NH2

Fe3O4

C

O

N

H

SO3H

C

O

N

H

SO3HNH2

HO3S

Carbodiimide

CarbodiimideFe3O4-PAA

COOH

COOH

II.

III.

I.

Figure 2.5. Scheme for preparing PAA-coated magnetic nano-particles, sulfonated-PAA-coated magnetic nano-

particles, and amino-functionalised PAA-coated magnetic nano-particles [2.24, 2.25] Mak et al. [2.8] have studied adsorption of the cationic dye methylene blue (MB) (Figure

2.6) using PAA-coated MNPs. The results showed that the PAA-coated MNPs were an

effective adsorbent for this particular dye and the adsorption was performed in approximately

2 minutes. By using acetic acid in methanol solution, 80 % of the dye was desorbed and after

3 desorption steps all of the MB was desorbed from the adsorbent. Chen et al. [2.26] have

performed a separation of the enzyme bromelain via adsorption by magnetic PAA-coated

7

MNPs. Also here the adsorption process was rapid. In approximately 1 minute the bromelain

present in the solution was adsorbed. The adsorptions were quick due to the absence of

internal diffusion. [2.8, 2.26]

Figure 2.6. Molecular structure of methylene blue

As demonstrated by Mak et al., [2.8] PAA-coated MNPs can be very useful for removal of

cationic dyes. Unfortunately, it is not as easy for anionic dyes to be adsorbed onto PAA-

coated MNPs and they also show a low ability for adsorption of heavy metal ions [2.27]. Mak

et al. [2.24] have used the sulfonated PAA-coated MNPs for adsorption of multivalent cation

metal ions from aqueous solutions. The result and a comparison of adsorption of multivalent

cation metal ions from aqueous solutions are shown in Table 2.1. The results were found to be

satisfying. The sulfonated PAA-coated MNPs adsorbed nearly 100 % of the multivalent metal

ions, in comparison with the PAA-coated MNPs which only adsorbed approximately 30-40 %

of the metal ions in the study [2.24].

Table 2.1. Comparison of recovery of metal cations using either sulfonated magnetic nano-particles or PAA-

coated magnetic nano-particles, with initial concentration of 100 mg/L for each metal specie [2.24]

Recovery (%)

Cation Sulfonated magnetic nano-particles PAA-coated magnetic nano-particle

Co2+ ~100 30.5

Al3+ ~100 34.5

Ni2+ ~100 37.1

Cu2+ 97.2 38.3

Ag+ ~100 78.5

Sulfonated PAA-coated MNPs do not adsorb anionic metals or substances. To circumvent

this problem and to get a magnetic nano-adsorbent for both anionic and cationic species,

Huang et al. [2.25] have used the amino-functionalised PAA-coated MNPs. The results in

Table 2.2 confirm that amino-functionalised MNPs have good adsorption abilities, both for

cationic and anionic species. The recovery was nearly 100 % for all the different metal ions.

This demonstrates the high feasibility of the method and also its superiority compared to

sulfonated PAA-coated MNPs and PAA-coated MNPs. The adsorption rate was fast, and

equilibrium was achieved in only a few minutes [2.25].

Humic acid (HA) coated MNPs have recently been synthesised by Liu et al. [2.28]. Ferric

chloride and ferrous sulphate were dissolved in water followed by the addition of ammonium

hydroxide and HA-sodium salt. The precipitate was the HA-coated MNPs and without further

8

treatment they could be used for removal of Cd(II), Cu(II), Hg(II), and Pb(II) from the

aqueous solution. Both HA and Fe3O4 are naturally abundant [2.29, 2.30], so they possess a

minimal treat for the environment. Also, for the preparation of HA-coated MNPs

environmentally friendly salts and solvents were used [2.28]. The feasibility of the HA-coated

MNPs for removal of heavy metals from water is shown in Table 2.3.

Table 2.2. Comparison of recovery of metal ions using either amino-functionalised magnetic nano-particles, or PAA-coated magnetic nano-particles, with initial concentration of 100 mg/L [2.25]

Recovery (%)

Metal ions Amino-functionalised magnetic

nano-particles

PAA-coated magnetic

nano-particles

Fe3+ 100 82.3

Ag+ 100 41.0

Cu2+ ~100 34.7

Co2+ ~100 32.3

Fe2+ 98.7 30.1

Ni2+ 100 18.6

Cd2+ 100 8.5

AuCl4- ~100 -

PdCl4- 100 -

HCrO4- 96 -

The removal efficiency is pH-dependent, and as a result the adsorption efficiency can differ

up to 20 % for Cu and about 7 % for Cd in unfavourable conditions. The study showed that

there was no interference in adsorption of the four metal species related to adsorption of other

natural abundant metals in water, such as calcium. Further, the influence of dissolved organic

matter on adsorption of heavy metal onto HA-coated MNPs was minimal. This concludes that

the HA-coated MNP s selectively adsorb heavy metals.

Table 2.3. Comparison of removal (%) of heavy metals from water from different sources, with initial concentration C in mg/L [2.28]

Hg Pb Cd Cu

Matrix pH C Removal C Removal C Removal C Removal

Tap water 7.8 1.011 99.8 1.006 99.4 1.001 96.8 1.077 86.0

Ground water 6.4 1.012 99.8 1.005 99.5 1.002 92.1 1.005 99.7

River water 7.6 1.011 99.9 1.005 99.4 1.001 92.3 1.008 86.0

Lake water 7.2 1.011 99.2 1.006 99.4 1.001 91.7 1.011 82.4

Sea water 7.7 1.013 99.9 1.20 99.0 1.009 99.0 1.040 79.3

Chang et al. [2.27] have coated MNPs with carboxymethyl chitosan, via activation by

carbodiimide followed by addition of a carboxymethyl chitosan solution. Chitosan have many

9

amino-groups that can serve as chelation sites, and this makes it prominent to adsorb several

metal cations, [2.31-2.33] fluoride and numerous types of dyes [2.27, 2.34-2.36]. Chitosan is a

natural polysaccharide which is a non-toxic and biodegradable polymer product produced by

deacetylation of chitin. There are many applications for chitosan in various fields, such as

biomedicine, drug delivery, and paper industry [2.37-2.39]. In a study by Chang et al. [2.34] Co(II) was adsorbed from aqueous solution using the chitosan MNPs. The adsorption rate

proved to be fast, and equilibrium was reached in approximately 1 minute. In previous

reports, Chang et al. have used the chitosan MNPs for removal of Cu(II) ions. The results

showed that the maximum adsorption capacity was 21.5 mg/g and that the adsorption rate was

fast. Also here the equilibrium was achieved in approximately 1 minute [2.35]. Recovering

metals from effluents is not only important from an environmental aspect, but also from an

economical point of view, due to high raw material costs.

Two acid dyes, acid green 25 and crocein orange g (Figure 2.7) have been used in an

adsorption study by Chang et al. [2.27]. The adsorption abilities were high for both of the

dyes, 1883 mg/g for crocein orange g and 1471 mg/g for acid green 25. This was due to the

large specific surface area of the MNPs. However, acid dyes have a strong affinity to chitosan

which causes problems in the desorption step. The maximum desorption achieved for crocein

orange g was 83.6 % and for acid green 66.1 %. Desorption efficiency is as important as

adsorption efficiency.

Figure 2.7. Molecular structures of acid green 25 and crocein orange g [2.27]

With low desorption percentage the economy of the method becomes lower. It has been

suggested that multiple desorption steps could improve desorption percentage, but no further

research has been done. Figure 2.8 shows the adsorption mechanism of the acid dyes onto the

amino-groups of chitosan [2.27]. Chitosan MNPs can be used not merely for adsorption of

cationic species, but also for anionic species as shown in this case.

Figure 2.8. The mechanism of adsorption of acid dyes where R’(SO3

-)2: acid green 25 and R’’SO3-: crocein orange g [2.27]

10

Low concentrations of fluoride in drinking water have beneficial effects on dental health,

however higher concentrations have negative effects on human health [2.40, 2.41]. Several

methods for removing fluoride from water have been developed, such as reverse osmosis, and

nanofiltration [2.42, 2.43]. The drawbacks of the methods have often been high operational

costs. Wei et al. [2.36] have studied the adsorption of fluoride on chitosan MNPs, and also the

surface structure. Groups of NH, NH2, NH3, and Fe-O, create an amorphous surface on the

chitosan MNPs. As mentioned earlier these groups work as chelation sites, on which the

fluoride ions can be disposed. The results showed that the initial adsorption rate was 2.08

mg/g min. The high adsorption efficiency of fluoride using chitosan MNPs gives the method

great commercial value.

2.1.3 MAGNETIC CARBON ADSORBENTS

Active carbon is a good adsorbent with a high specific surface area. Due to the good

adsorption ability, active carbon has often been used over the years for removal of all types of

pollutants [2.44-2.47]. It has been reported by Long et al. [2.48] that carbon nanotubes

(CNTs) are more efficient in adsorbing dioxins in comparison with active carbon. Active

carbon is generally very difficult to separate from aqueous solution [1.13]. Incorporating the

CNTs with MNPs makes it easy to separate adsorbent from solution by utilising the magnetic

properties. Hence, overcoming the problem caused by their size which occurs when using

conventional separation techniques, such as filtration or centrifugation for the separation of

nano-sized particles [2.34].

Peng et al. [2.49] have prepared the CNTs by catalytic pyrolysis of a mixture containing

propylene and hydrogen with Ni as catalyst. The MNPs were incorporated by initially

dissolving the catalyst particles in nitric acid and hydrofluoric acid. Finally, ferric chloride

and ferrous sulphate were mixed with the CNTs under nitrogen, and NaOH was added. The

CNTs with incorporated MNPs can be used for adsorption of heavy metals and dyes from

aqueous solution [2.49-2.51]. By chemical oxidation, the CNTs improve their metal

adsorption due to progression of the number of oxygen-containing groups on the surface. In

the study by Peng et al., [2.49] the adsorption of Pb(II) and Cu(II) using the magnetic CNTs

were nearly 100 %, with a CNT recovery rate of approximately 98 %. Attempts of removing

dyes from water using magnetic CNTs have been executed by Qu et al. [2.50] and Gong et al.

[2.51]. Three different dyes were examined in these studies, MB, neutral red (NR), and

brilliant cresyl blue (BCB) (Figure 2.6, 2.9). The results showed that the CNTs possess high

adsorption abilities for these specific dyes, 99.2% MB, 98.3 % NR, and 98.8% BCB were

adsorbed [2.51].

From rice husk based activated carbon (RHC) Yang et al. [1.13] have synthesised

mesoporous MNPs. The MNPs were used for adsorption of MB from aqueous solution. A

scheme of the preparation and adsorption of the MNPs is shown in Figure 2.10. The RHC-

11

Fe3O4 particles have a specific surface area of 770 m2/g and an adsorption capacity of 321

mg/g for MB in aqueous solution. Yang et al. show an environmentally friendly way of

removing contaminants.

Figure 2.9. Molecular structure of neutral red and brilliant cresyl blue

As mentioned earlier, Fe3O4 is the most commonly used material for magnetic adsorbents.

However, in one study Gorria et al [2.52] have synthesised active carbon with incorporated

nickel nano-particles. To prevent leakage of Ni, sucrose was used in the synthesis which

proved to protect the Ni-particles from acid corrosion in a low pH-environment. It was

discovered that the synthesis of active carbon with integrated Ni was cost-effective and easy

to produce due to inexpensive materials, easily available chemicals, and a simple synthesis

procedure.

RHC Modif ied-RHC RHC-Fe3O4 MB-RHC-Fe3O4

HNO3 COOH AdsorptionCOOH Fe(NO3)3

Figure 2.10. Scheme for the preparation of magnetic rice husk based activated carbon and the adsorption of MB [1.13]

2.1.4 OTHER MAGNETIC ADSORBENTS

A more original method of adsorbing heavy metals from aqueous solution has been

presented by Wang et al [2.53]. Gellan gel beads were prepared with MNPs, thus giving them

magnetic properties. The magnetic gellan gel beads were then used for adsorbing Pb2+, Cr3+,

and Mn2+ from aqueous solution. Parameters such as temperature, pH, adsorbent dosage, and

initial concentration were investigated. Interestingly, it was noticed that with increasing

temperature, starting from 10 °C to 30 °C the Pb2+ adsorption decreased approximately 10 %

and adsorption of Cr3+ and Mn2+ were almost constant. When raising the temperature to 60

°C, the adsorption of Pb2+ decreased with nearly 40 % and Mn2+ with 10 %. However,

adsorption of Cr3+ increased with approximately 35%. This shows the importance of

controlling the physical parameters when adsorbing contaminants from aqueous solution.

Rocher et al. [2.54] have prepared alginate beads containing active carbon and MNPs for

removal of the cationic and anionic dyes, MB and methyl orange (MO) (Figure 2.6, 2.11).

The adsorption to magnetic alginate beads containing active carbon was compared with active

carbon without alginate beads and the results showed that the magnetic alginate beads were

more efficient in removing MB. The maximum adsorption capacity for alginate beads was

38.9 mmol/g active carbon compared to 0.62 mmol/g active carbon for the active carbon

12

without alginate beads. The adsorption capacity for MO proved to be quite similar in both

cases, 1.32 mmol/g active carbon for alginate beads and respectively 0.86 mmol/g active

carbon for the active carbon without alginate beads. These results show that it is possible to

use environmental friendly and also cost-effective methods for removing organic compounds

from aqueous solutions [2.54]. Lim et al. have synthesised a magnetic calcium-alginate

adsorbent and experiments were performed for adsorption of arsenic and copper ions. The

maximum adsorption capacity for arsenic and copper respectively, was found to be 6.75 mg/g

and 60.24 mg/g, which is higher than the commercial adsorbents presently available [2.55].

Figure 2.11. Molecular structure of methyl orange

Due to the functional groups of bismuthiol, -SH- and -NH-, it serves as a good complex

binder for heavy metals, such as Pb, Cu, and Cd [2.56, 2.57]. Suleiman et al. [2.58] have

prepared bismuthiol-silica coated MNPs for adsorption of heavy metals. The adsorption

abilities were good. ~98% Pb, ~99% Cu, and ~99% Cr were adsorbed from the aqueous

solution. It was found that this method was useful for rapid adsorption of the metals in the

study and also good for adsorbing metals from large volumes.

An important environmental application has been reported by Machado et al. [2.59]. A

magnetic adsorbent based on polymer coated vermiculite, used for adsorbing contaminants

spilled on water. The adsorbent is hydrophilic and floats on water, thus making it useful for

adsorption of spilled oil.

2.1.5 CONCLUSIONS

In this chapter, a number of different adsorption techniques have been discussed. One

difficulty, but possibly also an advantage, is that the adsorbents are specific and do not adsorb

several kinds of contaminants. This can be advantageous in separation processes. The

progress in this field has been very remarkable over the last few years. New types of

adsorbents have been successfully synthesised when it proved that the previous ones were not

sufficient. It is very likely that adsorption and separation using magnetic technology will

improve further, generating a powerful tool for removal of hazardous matter and also for

recycling waste.

To the best of my knowledge, there are no full scale attempts of implementing magnetic

adsorbents. One of the reasons for this is that the industry tends to rely on existing technique

and not try new methods. However, it is most likely that this technique will be in operation in

the future. A possible full scale setup for treatment of waste water using magnetic adsorbents

is presented in Figure 2.12. In step 1. unprocessed water is introduced in the process, for

example dyeing of textiles, the waste water is transferred to a balance tank (4.) that works as a

13

buffer tank and from there the waste water is brought to the adsorption and desorption tank (5.)

and mixed with the magnetic adsorbents via mechanical stirring. The concentration pollutant

in the waste water can be measured via online monitoring with UV/Vis spectroscopy, this to

control that the sufficient adsorption is achieved and then a magnetic separation of adsorbent

and waste water using an electromagnet can be performed. After several adsorption cycles the

adsorbent must be regenerated, a desorption solution is added in step 6 with the same

procedure as with the adsorption. After the desorption, the product can be reused in process to

minimise material costs and waste (8.). There are no fundamental differences in the structure

layout of the complete process compared to conventional techniques.

Balacingtank

Process

Wastewater

Recycling

1.2.

3.

4.

5.

6.

7.

8. Figure 2.12. Flow chart for a possible setup for the treatment of waste water using magnetic adsorbents

The textile industry is one of the major big industries that affects both economics and

environment and consumes high quantity of water and chemicals, sometimes hazardous

chemicals, in the process of dyeing textile. Therefore, strategies of reducing emissions from

this industry and also reducing raw material are of high importance, both in economically and

environmentally terms. The magnetic adsorbents can provide the strategy for reducing the

economics and environmental effects.

Several of the commercial adsorbents use stationary packed beds to perform the adsorption,

also moving beds are sometime used. However there are some disadvantages with packed

beds. One is the pressure drop that occurs when pumping a fluid through a packed bed. If the

flow is high then it would require a big pump which is environmentally and economically

disadvantageous. Further, packed beds do not provide the fast adsorption and separation of

adsorbent. Therefore, a fluidised bed could be a more proper method. Also fluidised beds

have different kinetics than the fixed bed which could be more advantageous for the magnetic

adsorbents. However, fluidised beds also require a high load of energy input which affects the

economy. Conventional stirring may be applied for the adsorption process. The exact method

for every individual magnetic adsorbent must be evaluated and tested in small and big scale.

14

2.2 UPDATED RESEARCH PROGRESS IN MAGNETIC PHOTOCATALYST Since the discovery of the photocatalytic properties of TiO2 in 1972 by Fujishima and

Honda [2.60], many new types of applications for TiO2 have been discovered, such as

photovoltaics [2.61]. Photocatalytic reactions have recently drawn much attention due

potential of producing hydrogen from water using solar light [2.62-2.64]. One of the main

applications for photocatalysts is the degradation of pollutants from waste water. This

technique is becoming increasingly important, especially for removing low trace contaminants

but also for bacteria and viruses [1.14, 1.15, 2.65-2.68]. The photocatalysts have the same

problems as many adsorbents, due to the size they are difficult to separate from aqueous

solutions. [1.17].

The size of the TiO2 particles have found to be important for the photocatalytic efficiency,

when decreasing TiO2 particle size the specific surface area increases, thus the contact area

increases which results in an increase of efficiency [2.69]. However, separation and recovery

of the TiO2 particles is difficult due to the small particle size. Therefore, incorporating TiO2 in

magnetic carriers is of great interest due to the effective separation and recovery that can be

achieved by magnetic separation. Further, the carriers can be fluidised by an external

magnetic field [2.70]. Several different types of magnetic carriers have recently been

investigated, such as barium ferrite [2.71], Fe2O3/SiO2 [2.72], magnetite [2.73], and magnetic

poly(methyl methacrylate) microspheres (mPMMA) [2.74].

In this chapter, several different types of magnetic carriers and the preparation of

photocatalysts using these carriers are discussed. Also, the degradation of different organic

contaminants using the magnetic photocatalysts is discussed. The sol-gel technique is the

most commonly used technique for the preparation of semi-conducting photocatalysts. There

are several articles and reviews addressing this technique. Therefore, in this chapter we focus

on alternative synthesis route for the preparation of photocatalysts.

2.2.1 DIFFERENT PREPARATION TECHNIQUES AND MAGNETIC CARRIERS Magnetic Fe2O3/SiO2/TiO2 nanoparticles were synthesised by Wang et al. [2.72]. The

synthesis route is presented in Figure 2.13. Fe3O4 particles were dispersed in water followed

by addition of tetraethyl orthosilicate (TEOS) at high pH. Subsequently, the Fe3O4/SiO2

particles were transferred to an autoclave and dispersed in hexane, water, and TBOT solution

and the autoclave was heated. The product was then calcinated under high temperature and

the Fe3O4 particles were transferred into Fe2O3.

Figure 2.13Scheme for the preparation of Fe2O3/SiO2/TiO2 magnetic photocatalyst catalyst [2.72]

15

Xuan et al. [2.70] successfully synthesised hollow Fe3O4/TiO2 spheres by using a

poly(styrene-acrylic acid) (PSA) core. First, PSA-spheres with a diameter of 270 nm were

dispersed in ethanol followed by addition of aqueous FeCl3. Second, the pH was adjusted to

9-10 using aqueous NH3 followed by addition of Na2SO3. Fe3O4 particles were formed on the

PSA surface. The PSA/Fe3O4 particles were dispersed in a mixture of butanol, ethanol, and

TBOT and stirred overnight to get a saturated adsorption of TBOT on the spheres.

Subsequently, water was added to hydrolyse the TBOT into amorphous titania. The

PSA/Fe3O4/TiO2 particles were dispersed in THF, this to dissolve the PSA and then

transferred to an autoclave. The amorphous titania was transformed to anastase form by

solvothermal heating with hexane in the autoclave. A scheme for this procedure is presented

in Figure 2.14.

Figure 2.14 Scheme for the preparation of hollow Fe3O4/SiO2 magnetic photocatalyst catalyst [2.70]

The preparation of black sand based magnetic photocatalyst was developed by Luo et al.

[2.74, 2.75]. Black sand (BS), a natural magnetic material, was used as magnetic core in the

preparation of magnetic photocatalyst. BS was dispersed in water with TEOS and was stirred

for a short while following by addition of ammonium hydroxide. The formed particles were

dried and then the BS/SiO2 was dispersed in a mixture of propanol and Titanium tetra-

isopropoxide (TPOT) followed by stirring and heating. The product was then calcinated in

order to transfer the TiO2 into crystalline phase. The synthesis process of BS/SiO2/TiO2 is

shown in Figure 2.15.

Figure 2.15. Scheme for the preparation of black sand/SiO2/TiO2 magnetic photocatalyst catalyst [2.74, 2.75]

TiO2 coated mPMMA microspheres were prepared by Chen et al. [2.76]. The magnetic

particles were oleic acid coated (OMP) and introduced with the PMMA microspheres via

modified suspension polymerisation. Described shortly, the OMP were mixed with

divinylbenzene, methyl methacrylate, benzoyl peroxide, and hexane and was let reacted under

heating. Then the formed mPMMA was magnetically separated from the solution.

Subsequently, the mPMMA was mixed with TiO2 powder and heated close to the glass

transition temperature of PMMA which resulted in a soft surface that the TiO2 could be

adhered to. The process is shown in Figure 2.16.

16

polymerisation TiO2

mPMMA/TiO2mPMMAOMP

Figure 2.16. Scheme for the preparation of mPMMA/TiO2 magnetic photocatalyst catalyst [2.76]

2.2.2 DEGRADATION OF ORGANIC POLLUTANTS BY MAGNETIC PHOTOCATALYSTS The general photocatalytic process is illustrated in Figure 2.17 and by equations 1-6. When

the TiO2 photocatalyst is irradiated with light, an electron in the valence band can be excited

to the conduction band and a hole in the valence band is generated (equation 1). The back

reaction (equation 1*) produces heat. Further, the free electron reacts with the oxygen and

forms the super oxide anion (equation 2). The hole in the valence band take one electron from

the water and H+ and ·OH is formed (equation 3). The super oxide anion combines with H+

and forms the ·HO2 (equation 4). The ·HO2 reacts with H+ and forms hydrogen peroxide which

then dissociates into hydroxyl radicals (equation 5, 6). [2.77]

Wang et al. [2.72] used the Fe2O3/SiO2/TiO2 for photocatalytic degradation of MB. After 80

min, 80 % of the 50 mL 25 mg/L MB was degraded using 0.1 g photocatalyst. The results

showed that the prepared photocatalyst had nearly the same photocatalytic ability compared

with TiO2 powder. This indicates that the SiO2 layer prevented the electrons from transferring

to the Fe2O3 that would reduce the photocatalytic ability.

Rhodamine B was photocatalytic degraded using hollow Fe3O4/TiO2 spheres prepared by

Xuan et al. [2.70]. In the experiment, 25 mg photocatalyst was used for the degradation of 60

mL 0.3 mg/L rhodamine B. After 80 min nearly 100 % of the dye was degradated. This

concludes that the hollow Fe3O4/TiO2 spheres are an excellent photocatalyst.

Photocatalytic degradation of p-phenylenediamine using TiO2-coated magnetic PMMA

microspheres was performed by Chen et al. [2.76]. Experiments using different concentrations

of p-phenylenediamine were performed. The experiments showed that the TiO2-coated

magnetic PMMA microspheres were excellent for removing low concentration contaminants.

17

After 90 min using 3.7 g photocatalyst, 100 % of 3.7 L 3.5 mg/L of p-phenylenediamine were

removed and in 240 min, 70% of 3.7 L 332 mg/L was removed. Also, the efficiencies were

similar to what could be obtained with TiO2 powder.

TiO2

h+

e-

hv

O2

H2O

Magneticcarrier

OH

O2-

H+

HO2

H2O2

OH-

OH

H+

H+

OrganicpollutantO2

-OHOH-

HO2 CO2 H2O

Figure 2.17. Mechanism for the photocatalytic induced reactive groups and the degradation process of organic pollutants [2.76]

The TiO2/CoFe2O4 prepared by Fu et al. [2.78] was used for photocatalytic degradation of

the dye Procion Red MX-5B. The experiment was carried out using 4 mg of the photocatalyst

in 50 mL 10mg/L Procion Red MX-5B solution. The prepared photocatalyst had different

weight ratio of TiO2, 10, 50, 70, and 90%. Obviously, with higher content follows higher

efficiency. However, at very low concentrations of Procion Red MX-5B the difference

between 70 and 90 % was very little. In about 250 min nearly 100% of the dye was degraded

using the photocatalyst with 70 and 90 % content of TiO2. In comparison, with TiO2 powder

the dye was completely degraded after 175 min.

Lee et al. [2.71] used TiO2 with a BaFe2O4 core for the degradation of Procion Red MX-5B.

The experiment was carried out using 30 mg of the photocatalyst in 50 mL 10mg/L Procion

Red MX-5B solution. After 350 min 80 % of the dye was decomposed. The results were not

as good compared to the photocatalyst with CoFe2O4 core.

Luo et al. [2.74, 2.75] used black sand as magnetic core coated with TiO2 for degradation of

several different types of dyes and organic compounds. For the degradation of phenol, 0.2 g

photocatalyst was dispersed in 75 mL phenol solution with the concentration of 20 mg/L.

About 10 % phenol was degraded after 120 min of irradiation as compared to the TiO2 powder

which degraded about 40 % under the same conditions. For the degradation of different dyes,

0.3 g photocatalyst was dispersed in 200 mL dye with the concentration of 60 mg/L. About 8

% of the dye rose bengal, 12 % of orange II, and 10% of eosin b was degraded after 120 min

of irradiation.

To enhance the photocatalytic performance Xu et al [2.77] dope the TiO2/SiO2/Fe3O4

photocatalyst doped with silver. It was found that this photocatalyst had better photocatalytic

efficiency, about 30 % higher efficiency, in the degradation of orange II as compared to TiO2

18

powder. After 20 min using 50 mg photocatalyst, 90 % of 0.1 L 17.5 mg/L orange II was

removed. In comparison with TiO2 powder were 70 % was removed after 20 min. The process

can be described with equation 1-8. Compared to the un-doped photocatalyst reaction 7 and 8

do not take place. The formation of extra super oxide anion boosts the photocatalytic

degradation.

2.2.3 CONCLUSIONS

In this chapter, several different magnetic carriers for the TiO2 photocatalyst have been

reviewed. The magnetic carriers provide an effective way of the separation of TiO2 which

otherwise is very difficult and expensive to separate. However, the photocatalyst need to be

more efficient and more research has to be put in the field before they will have industrial

applications. The photocatalyst have high potential for providing a cheap and efficient way of

removing pollutants from effluents.

19

2.3 UPDATED RESEARCH PROGRESS IN BIOSEPARATION USING MAGNETIC

TECHNOLOGY The magnetic technology has many applications in several areas. Biotechnology is perhaps

the most prominent field for the magnetic technology. The magnetic technology can be used

for drug delivery, enzyme immobilisation, protein separation and isolation [2.79, 2.80].

In this chapter, a brief review of the recent progress on the magnetic technology for

bioseparation is presented.

2.3.1 BIOSEPARATION

Ding et al. [2.81] and Shamim et al. [2.82] used magnetic particles covered by

thermosensitive polymer for adsorption of human serum albumin (HSA) and bovine serum

albumin (BSA). The results showed that by increasing the temperature the magnetic particles

decreased in size and could adsorb more protein. Also, it was found that with increasing pH

the adsorption decreased. This was attributed to the electrostatic forces between the protein

and adsorbent. The protein could be desorbed from the magnetic particles by decreasing the

temperature. This was a result from the structure change on the surface. It was found that the

protein could be deformed in the adsorption process due to interaction with the polymer. The

deformed protein could not be easily desorbed by changing temperature and therefore the

efficiency of the adsorbent decreased when it was reused. A scheme of the adsorption and

desorption process is shown in Figure 2.18

Figure 2.18 Scheme for the separation of HSA by magnetic particle coated with thermosensitive polymer [2.81] BSA was separated from aqueous solution using surface functionalised magnetic

poly(styrene-divinylbenzene-glycidyl methacrylate) microspheres [2.83]. The microspheres

had a size of 6 µm. The adsorption capacity were high, about 80 mg/g and with a desorption

efficiency of 94 % using a NaSCN solution.

Li et al. [2.84] use magnetic beads with Env protein covalently linked to magnetic beads in

the process of separation of antibodies used in the neutralisation of HIV-1. This shows the

usability and importance of the magnetic technology in the biotechnology field.

Lipase is an enzyme which generally breaks down fats and is used in food industry and

pharmaceutical industry [2.85, 2.86]. Wu et al [2.87] use magnetic Fe3O4 nanoparticles coated

with chitosan for the adsorption, immobilisation, and oxidation of lipase. It was found that by

adding glutaraldehyde the enzyme maintain the activity even after desorption as to if not

glutaraldehyde was added the enzyme lost up to 60 % of the activity. This phenomenon can

20

be used for controlling processes in the food industry and pharmaceutical industry more

accurate.

Recently, Luo et al [2.88] prepared cellulose microspheres with fabricated Fe3O4 particles in

the cellulose pores. The synthesised microspheres were used for adsorption with controlled

release of BSA. The release of BSA from the microspheres could be controlled by changing

pH. At pH 7.4, which is close to the pH in the human body, nearly 100 % of the BSA could be

released. However, the process was very slow, about 500 h. This could be exploited for slow

drug delivery which releases the active substance slowly.

Lin et al. [2.89] use amino-functionalised magnetic nanoparticles with trypsin immobilised

on the surface. These particles were used for digestion of BSA, myoglobin, and cytochrome c.

After the digestion the microspheres could easily be removed by magnetic separation and the

samples could be analysed. This is an interesting way of studying the digestion of proteins

and to be able to investigate the process without interference of the enzyme in the analysis.

Chiang [2.90] use Fe3O4 particles coated with glycidyl methacrylate-iminodiacetic acid for

extraction of protein from a specific fluorescent modified protein from E-coli bacteria. The

result shows that the magnetic particles were specific and were effective in adsorbing and

extracting this specific protein.

2.3.2 CONCLUSIONS

In this chapter, we have shown that the magnetic technology can be used not only for

environmental purpose but also in the field of biotechnology. By altering the coatings of the

magnetic particles different kinds of bio-molecules can be separated which can be exploited

when there is a need to separate in a moiety of bio-molecules. Without doubt, the magnetic

technology can provide the fast, specific, and efficient separation which is important in this

field.

21

CHAPTER 3: MAGNETIC MICROSPHERES FOR REMOVAL OF

METHYLENE BLUE FROM WASTEWATER Most dyes used in industries are considered hazardous, so, it is necessary to remove these

from effluents. Organic dyes show low biodegradability, hence, other methods than the

biological treatment is required for removing dyes from effluents [3.4]. Also, other

conventional techniques such as reverse osmosis and chemical coagulation have problems

with removing the colour completely [3.5].

Methylene blue (MB) is a cationic dye and is used in many areas, such as medicine and

biotechnology [3.6, 3.7]. Several materials have recently been studied to remove MB from

wastewater such as carbon nano-tubes, fly ash, red mud, and vermiculite [3.8-3.12]. However,

these methods do not provide an easy and quick separation process.

In this study, mesoporous magnetic microspheres have been synthesised and used for the

adsorption of MB. MB is a model dye and been used extensively in adsorption studies, hence

make a comparison between other methods convenient. The chemical structure of MB is

shown in Figure 2.6. Liu et al. [3.13] reported that the mesoporous magnetic microspheres

have good ability to adsorb the cationic dyes methyl violet and basic fuchsin. Further,

magnetic separation makes the reusage of the adsorbent convenient.

3.1 EXPERIMENTAL

3.1.1 MATERIALS

Porous polystyrene microspheres with a diameter of ~200 µm which were prepared in house

were used in this study. Chlorosulfonic acid and ferrous chloride were purchased from

Jingshanting Chemical Corporation of Shanghai, China. Dichloromethane, sodium hydroxide,

potassium chloride, anhydrous ethanol, and hydrogen peroxide were purchased from Lanling

Chemical Corporation of Linan in Zhejiang, China. Methylene blue was purchased from

Shanghai San’aisi Chemical Company, China. All the chemicals were used without further

treatment.

3.1.2 PREPARATION

3.1.2.1 PREPARATION OF SULFONATED MICROSPHERES

The porous magnetic microspheres were prepared according to the previous reported

method by Liu et al [3.13]. Into a 250 ml 3-neck round bottom flask 75 ml dichloromethane

and 5.78 g polystyrene microspheres were added. The solution was cooled using an ice bath,

subsequently, 0.8 ml chlorosulfonic acid in 75 ml dichloromethane was added dropwise into

the stirring solution. The solution was kept stirring for 24 h. The products were then filtrated

and washed with dichloromethane followed by drying in a vacuum oven for 12 h. Finally, the

microspheres were washed with deionised water and again dried in a vacuum oven.

22

3.1.2.2 PREPARATION OF MAGNETIC MICROSPHERES

Into a 250 ml 3-neck round bottom flask with a mechanical stirrer and argon inlet, 2.11 g of

the sulfonated microspheres as synthesised, were added with 80 ml 1 M FeCl2 solution. The

solution was kept stirring for 24 h. The products were then filtrated and washed three times

with deionised water and then transferred to another 3-neck round bottom flask with a

mechanical stirrer and a condenser, 20 ml deionised water and 80 ml 2 M NaOH was added.

The mixture was heated using an oil bath, when the temperature reached 75 °C, 20 ml 30 %

H2O2 was added dropwise into the mixture and the solution was kept stirring at 75 °C for 2 h.

The products were filtrated and washed three times with deionised water, one time with

anhydrous ethanol, and then dried in a vacuum oven.

3.1.3 CHARACTERISATION

Optical microscope photos were taken using a NOVEL XS-2100 microscope instrument

connected to a Canon powershot A630 with a Canon 640 52 mm objective. TGA were carried

out on a Perkin Elmer TGA-7 apparatus with a heating rate of 10 °C/min, starting from room

temperature to 700 °C. The surface areas were determined by nitrogen sorption porosimetry

on a micromeritics ASIC-2 apparatus. A 5.2 × 5.2 × 2.8 cm Fe-SrBr magnet was used for the

magnetic separation.

3.1.4 ADSORPTION AND DESORPTION OPTIMISATION

The adsorption optimisation was performed by varying pH and sonication time (contact

time adsorbent/MB) as shown in Table 3.1. In principle, into a small vial 0.2 g magnetic

microspheres were added with 4 mL of 1×10-6 M MB solution and then the solution was

sonicated for 2 min. The pH value of the system was regulated by using a specific pH buffer.

Subsequently, the magnetic microspheres were separated using a magnet and the solution was

collected and the adsorption efficiency were determined using an UNICO 3802 UV/Vis

spectrophotometer.

Table 3.1.4 Different parameters for the optimisation of the adsorption of MB onto magnetic microspheres

Run (pH, 0.2 g, 2min)

A01

pH 6

A02

pH 7

A03

pH 8

A04

pH 9

A05

pH 10

A06

pH 11

A07

pH 12

Run (Time, 0.2 g, pH 7)

A11

1 min

A12

2 min

A13

3 min

A14

4 min

A15

5 min

The desorption optimisation was performed by varying the parameters of EtOH/H2O

volume ratio, salt type, salt concentration, and sonication time, as shown in Table 3.2. In

principle, into a small vial 0.2 g magnetic microspheres were added with 4 mL of the

23

desorption solution and then the solution was sonicated for 2 min. Subsequently, the magnetic

microspheres were separated using a magnet and the solution was collected and the adsorption

optimisation efficiency were determined using a UV751GW UV/Vis spectrophotometer.

Table 3.2.5 Different parameters for the optimisation of the desorption of MB from microspheres

Run (E/W, 0.2 g, 2min) EW01 EW02 EW03 EW04 EW05

E/W(v/v) 2/8 4/6 6/4 8/2 10/0

Run (1 M salt, 0.2 g, 2min) EW11 EW12 EW13

E/W (0/10) NaCl KCl MnCl2

Run (1 M salt, 0.2 g, 2min) EW21 EW22 EW23

E/W (4/6) NaCl KCl MnCl2

Run (1 M salt, 0.2 g, 2min) EW31 EW32 EW33

E/W (6/4) NaCl KCla MnCl2

Run (KCl, 0.2 g, 2min) EW41 EW42 EW43 EW44

E/W (4/6) 0.1 M 0.5 M 1 M Saturated

Run (KCl, 0.2 g, 2min) EW51 EW52 EW53

E/W (6/4) 0.1 M 0.5 M Saturated

Run (Time, 0.2 g, Sat. KCl)

E/W (6/4)

EW61

1 min

EW62

2 min

EW763

3 min

EW64

4 min

EW65

5 min a Saturated KCl

3.2 RESULTS AND DISCUSSION

3.2.1 PREPARATION OF MAGNETIC MICROSPHERES

The porous polystyrene microspheres used in this study were prepared by free radical

suspension polymerisation with toluene as porogen according to the routes proposed by Liu et

al. [3.14]. The synthesised microspheres used for the preparation of the magnetic

microspheres had a diameter of ~200 µm.

First, the polystyrene microspheres were sulfonated in the presence of chlorosulfonic acid

and -SO3H were formed on the surface and on the pore walls. The sample was labelled as PS-

SO3H. Subsequently, the sulfonated microspheres were stirred in the presence of ferrous

chloride for 24 h to ensure full ion exchange. Finally, the ferrous ions were oxidised using

hydrogen peroxide and Fe3O4 particles were formed on the surface and in the pores of the

microspheres. A scheme of this process is shown in Figure 3.1. The weight fraction of Fe3O4

in the microspheres was very low, so the microspheres showed little magnetic response.

Therefore, the process described above was repeated. After each cycle, a sample was

collected and labelled as Mag 1 and Mag 2.

24

SO3-

SO3-

SO3-

SO3-

SO3-

+Na

+Na

+Na

+Na

+Na

SO3-

SO3-

SO3-

SO3-

SO3-

+H

+H

+H+H

+H

Fe2+CH2Cl2

SO3HCl FeCl2 NaOH

H2O2

SO3-

SO3-

SO3-

SO3-

SO3-

Fe2+

Fe2+

SO3-+H SO3

-SO3

- +Na

: Fe3O4 nano particles Figure 3.1. Scheme for the preparation of magnetic microspheres

3.2.2 CHARACTERISATION

A magnetic response comparison between PS-SO3H and Mag 2 is presented in Figure 3.2.

The PS-SO3H microspheres show no attraction towards the magnet. The Mag 2 microspheres

show a strong attraction to the magnet. After the removal of the magnet, the microspheres did

not agglomerate nor retained magnetic properties. This indicates that microspheres are

superparamagnetic and that it is the Fe3O4-nanoparticles which are responsible for the

attraction to the magnet.

Figure 3.2. Comparison of magnetic response between a) PS-SO3H b) Mag 2

Optical microscope images of the PS-SO3H, Mag 1, and Mag 2 are presented in Figure 3.3.

The sulfonated microspheres are a slightly transparent, however the magnetic microspheres

are less transparent, and this is a result of the Fe3O4 nanoparticles on the surface and in the

pore walls of the microspheres. The magnetic microspheres became almost completely

opaque after two repetition of the process described in chapter 3.1.2. Also, the microspheres

maintain the spherical shape after sulfonation and magnetisation and are of uniform size.

Figure 3.3. Optical microscope images of a) PS-SO3H b) Mag 1 c) Mag 2

25

The results from the TGA are presented in Figure 3.4, and shows that the major

decomposition region of the polystyrene microspheres is from 400 to 600 °C. The weigh-loss

between room temperature and 100 °C was attributed to the microspheres containing a small

amount of water. According to the results Mag 1 and Mag 2 had a weight fraction of Fe3O4-

nanoparticles of 23 % and 33 % respectively. However, Liu et al. [3.13] reported a weight

fraction Fe3O4-nanoparticles of Mag 1 to 9 % and Mag 4 to 25 %. The difference may be a

result from insufficient washing of the microspheres in the preparation of the microspheres.

0 100 200 300 400 500 600 7000

10

20

30

40

50

60

70

80

90

100

Wei

ght

(%)

Temperature (°C)

PS-SO3H

Mag 1 Mag 2

A

a) TGA

-

1 10 100 1000

0,0

0,2

0,4

0,6

0,8

1,0

1,2

b) Pore size distribution

macromesomicro

Log

diff

ere

ntal

vol

um

e (c

m3/g

)

Pore diameter (nm)

PS-SO3H

Mag 1 Mag 2

Figure 3.4. a) TGA and b) pore size distribution curves for PS-SO3H, Mag 1, and Mag 2

From the N2-sorption analysis the specific surface area of the PS-SO3H, Mag 1, and Mag 2

were calculated to 420 m2/g, 243 m2/g, and 175 m2/g respectively. Figure 3.4 b) shows the

pore size distribution for PS-SO3H, Mag 1, and Mag 2. The PS-SO3H had some micropores,

however, these pores were unavailable or closed in Mag 1 and 2, indicating that Fe3O4-

nanoparticles were formed in these pores. The average pore diameter of PS-SO3H was

calculated to 4.9 nm, for Mag 1: 5.9 nm, and for Mag 2: 6 nm. Further the average pore

volume decreases from 0.50 cm3/g to 0.36 cm3/g and 0.26 cm3/g for the magnetic

microspheres compared with the PS-SO3H microspheres. Indicating, Fe3O4-nanoparticles

were successfully formed in all of the pores of the microspheres.

3.2.3 ADSORPTION AND DESORPTION STUDY OF METHYLENE BLUE

An adsorption and desorption study using the porous magnetic microspheres for the removal

of MB were performed. This was to evaluate the performance of removing cationic dyes using

magnetic microspheres. In this experiment, the microspheres were adsorbing 4 mL 1×10-6 M

MB-solution under sonication at 80 % for 2 minutes at 22-25 °C. Liu et al. [3.13] reported

that a 4/6 MeOH/H2O with saturated KCl were effective as desorption solution for the

desorption of methyl violet and basic fuchsin. The same desorption solution was used in this

study. The adsorption and desorption efficiencies were evaluated by UV-spectrophotometer at

26

the wavelength 665 nm which was the most suitable peak as seen in Figure 3.6 a). A scheme

of the adsorption, desorption, and separation process is presented in Figure 3.5.

Figure 3.5. Scheme of the adsorption and desorption process of MB with the magnetic separation

200 300 400 500 600 700 800

a)

0.3

0.1

0

0.2

Abs

Wavelength (nm)

UV-spectrum of methylene blue

0.4

0,0 2,0x10-6 4,0x10-6 6,0x10-6 8,0x10-6 1,0x10-50,0

0,2

0,4

0,6

0,8

1,0

1,2

b)

Standard curve for methylene blue

Abs

Concentration (M)

Standard solutions Linear fit

R2=0.99799

y = 0.01666 + 120596.99x

Figure 3.6. a) UV-spectrum of methylene blue, b) standard curve for methylene blue

The result from the adsorption and desorption study is presented in Figure 3.7. The

adsorption efficiency was 75-80 % throughout the study and the desorption efficiency was 80-

90 %. The adsorption and desorption efficiency was not decreasing dramatically during the

cycles, indicating that the microspheres is a robust method for removing cationic dyes.

However, Liu et al reports an adsorption efficiency of 99.1 % for basic fuchsin and 92.7 % for

methyl violet. This concludes that the adsorption and desorption efficiency for MB can be

improved.

27

1 2 3 4 5 6 7 8 9 100

20

40

60

80

100

a)

Ad

sorp

tion

effi

cie

ncy

(%)

Adsorption cycle

Adsorption of methylene blue over several cycles

1 2 3 4 5 6 7 8 9 100

20

40

60

80

100

b) Desorption of methylene blue over several cycles

Des

orp

tion

eff

icie

ncy

(%)

Desorption cycle

Figure 3.7. Adsorption a) and desorption b) efficiencies of methylene blue [1×10-6 M] over several cycles. Sonication time 2 min at 80 %, 22-25 °C. MeOH/H2O 40/60 saturated KCl solution was used as desorbing solution. 3.2.4 ADSORPTION AND DESORPTION MECHANISM

The proposed adsorption and desorption mechanisms are presented in Figure 9 and 10. The

affinity of MB to –SO3- is higher than for Na+. The MB has a Cl- group which interacts with

the Na+ and forms Na+-Cl, i.e. an ion exchange is achieved. In the case of the desorption, an

ion exchange is also performed. However, using the co-solvent EtOH/H2O/KCl the process

can be speed up. The EtOH/H2O/KCl interfere the electrostatic interaction between MB and

-SO3-, thus the counterions are changed and the dye is desorbed from the microspheres.

Figure 3.8. Proposed mechanism for the adsorption of MB onto magnetic microspheres

Figure 3.9. Proposed mechanism for the desorption of MB from magnetic microspheres

28

3.2.5 ADSORPTION OPTIMISATION AND DESORPTION OPTIMISATION

The result from the adsorption optimisation is presented in Figure 3.10. The adsorption

efficiency is most likely pH-dependent. This is attributed to the change of charge and

ionisation that appear with pH change. The pH was changed in the range of pH 6-12. The

result from the study is shown in Figure 3.10 a). The result shows that there is no significant

change in adsorption efficiency between pH 6-12. However, with increasing pH a slight

faster adsorption rate was detected. The results show that the magnetic microspheres can be

used in a broad pH range which is important for industrial use where the pH might fluctuate

with time. Unfortunately, in acid environment, pH 1~3, the Fe3O4 particles start to dissolve.

Therefore should acid environment be avoided. However, after short exposure of strong acid

the microspheres retain the magnetic properties. It was found adsorption time is what affects

the adsorption efficiency the most. After 5 minutes of adsorption nearly 100 % of the MB was

adsorbed.

6 7 8 9 10 11 1290

92

94

96

98

100

A07

A06

A05A04

A03

A02

A01

a)

Ad

sorp

tion

effi

cie

ncy

(%)

pH

Adsorption at different pH

1 2 3 4 570

80

90

100b)

A15A14

A13

A12

A11

Adsorption time

Ad

sorp

tion

effi

cie

ncy

(%)

Adsorption time (min)

Figure 3.10. Result from the adsorption optimisation of pH a) and sonication time b)

The results from the desorption optimisation is presented in Figure 3.11 a)-g). In the

optimisation of the desorption, several types of salts, salt concentrations, and EtOH/H2O-

ratios were examined. As seen in Figure 3.11 a) the EtOH/H2O 10/0 had the highest

desorption efficiency. However, the efficiency was only about 40 % so further optimisation

was required. The dye is adsorbed ion exchange between the dye and the -SO3- and there are

two major ways of breaking this interaction. One is through polarity differences of the co-

solvent and the other one is ion exchange. Therefore was salts introduced to the desorption

solution. However, most salts are insoluble in EtOH so it was necessary to use an EtOH/H2O

ratio with H2O ≠ 0 to dissolve the salts.

29

2/8 4/6 6/4 8/2 10/00

10

20

30

40

50

EW05

EW04EW03

EW01

Des

orp

tion

eff

icie

ncy

(%)

EtOH/H2O ratio

Different EtOH/H2O ratios

EW02

a)

NaCl KCl MnCl0

10

20

30

40

50

EW13

EW12

EW11

2

EtOH/H2O 0/10 + 1 M salt

Des

orp

tion

eff

icie

ncy

(%)

Type of salt

b)

NaCl KCl MnCl0

20

40

60

80

100

c)

EW23

EW22

EW21

2

EtOH/H2O 4/6 + 1 M salt

De

sorp

tion

eff

icie

ncy

(%

)

Type of salt

NaCl KCl MnCl0

20

40

60

80

100

d)

EW33

EW32EW31

De

sorp

tion

eff

icie

ncy

(%

)

Type of salt

EtOH/H2O 6/4 + 1 M salt

Note: Saturated KCl

2

0,1 0,5 Saturated0

20

40

60

80

100

e)

EW43EW42

EW41

EtOH/H2O 6/4 + KCl

Des

orpt

ion

effic

ienc

y (%

)

KCl concentration (M)

0,1 0,5 1 Saturated0

20

40

60

80

100

f)

EW54EW53EW52

EW51

EtOH/H2O 4/6 + KCl

Des

orpt

ion

effic

ienc

y (%

)

KCl concentration (M)

30

1 2 3 4 50

20

40

60

80

100

g)

EW65EW64EW63EW62EW61

Desorption time

De

sorp

tion

eff

icie

ncy

(%

)

Desorption time (min)

Figure 3.11. Result from the desorption optimisation a) EtOH/H2O ratio b) salt type c) 4/6 EtOH/H2O ratio with different types of salt d) 6/4 EtOH/H2O ratio with different types of salt e) 6/4 EtOH/H2O ratio with salt

concentration f) 4/6 EtOH/H2O ratio with salt concentration f) desorption time In the optimisation study many different salts were examined besides the ones mentioned

above, NH4Cl, LiCl, CaCl2, NaSCN, NaNO3, KI, NaHCO3. However, it was found that these

salts interacted and changed the structure of the dye or affected the following adsorption step.

Nevertheless, it cannot be ruled out that some of these salts enhance the desorption rate, but

due to the difficulties to measure this, and KCl show good ability to increase the desorption

rate, no further research was made.

3.3 CONCLUSIONS

After the adsorption and desorption optimisation, another adsorption/desorption cycle study

were performed. The result is presented in Figure 3.12. The adsorption efficiency of MB was

approximately 100 % throughout the study and the desorption was about 95 %. Interesting

noticing, after several desorption cycles the desorption efficiency was over 100 %, this can be

attributed to that some of the MB was still in the microspheres after every desorption cycle.

This study confirms that the magnetic microspheres are an excellent adsorbent for cationic

dyes.

A small deterioration of the microspheres was detected after some time, this due to the

physical stress that occurs in the sonication. However, no noticeable reduction in performance

was detected. This concludes that the magnetic microspheres prepared by this route are very

robust and are suitable for reuse and regeneration, i.e. the microspheres have high potential

for industrial use.

One of the drawbacks with the magnetic microspheres is that the Fe3O4 dissolves in harsh

environment. Down to pH 4 there is no visual detection of the leakage, however UV results

show a slight increment of dissolved iron. In strong acid environment, pH 0-1, there is a

noticeable leakage of Fe3O4 from the microspheres and the magnetic response of

31

microspheres is affected. Magnetic microspheres that endure acid environment are of interest

for further research.

1 2 3 4 5 6 7 8 9 100

20

40

60

80

100

a) Adsorption of methylene blue over several cycles

Ad

sorp

tion

effi

cie

ncy

(%

)

Adsorption cycle

1 2 3 4 5 6 7 8 9 100

20

40

60

80

100

b) Desorption of methylene blue over several cycles

De

sorp

tion

effi

cie

ncy

(%

)

Desorption cycle

Figure 3.12. Adsorption a) and desorption b) efficiencies of methylene blue [1×10-6 M] over several cycles. Sonication time 5 min at 80 %, 27-30 °C. EtOH/H2O 60/40 with saturated KCl was used as desorbing solution

Adsorption via electrostatic interactions, as used in microspheres in this report, is a more

selective adsorption method compared to the chemical adsorption of active carbon. This can

be made use of in separation of a mixture of dyes, thus make the separation and recovery

easier. Also, chemical adsorption is generally more difficult to desorb and regenerate

compared to adsorption via electrostatic interactions.

32

33

CHAPTER 4: MESOPOROUS MICROSPHERES WITH PHOTOCATALYTIC

ABILITY In this chapter, TiO2 coated microspheres for the photocatalytic degradation of phenol are

studied. Phenol is a commonly used chemical in the industry and agriculture and is a common

pollutant. Therefore, phenol was chosen as a model pollutant in order to evaluate the

photocatalytic performance. To the best of my knowledge, this is the first time to use

polystyrene microspheres as carriers for TiO2.

4.1 EXPERIMENTAL

4.1.1 MATERIALS

Anhydrous ethanol, n-butanol, titanium butoxide (TBOT), and phenol were purchased from

Sinopharm Chemical Reagent Co., Ltd. All the chemicals were used without further

treatment.

4.1.2 PREPARATION OF PHOTOCATALYTIC MICROSPHERES

The TiO2 coated microspheres were prepared according to the previous reported method by

Xuan et al. [2.70]. Into a 100 mL 3-neck round bottom flask with a mechanical stirrer and

argon inlet, 1 g PS-SO3H was mixed with 50 mL n-butanol and 5 mL ethanol. In 10 mL

ethanol, 2 mL of TBOT was dissolved and added to the mixture. The solution was stirred

overnight. Following, 10 mL of aqueous ethanol was added and the mixture was aged for 12

h. The synthesised microspheres were washed three times with ethanol and three times with

deionised water. One fraction of the prepared microspheres was heated to 300 °C and the

other to 500 °C for 2 h.

4.1.3 CHARACTERISATION

TGA were carried out on a Perkin Elmer TGA-7 apparatus with a heating rate of 10 °C/min,

starting from room temperature to 700 °C. XRD pattern was determined on a D/max-rA XRD

instrument using a copper X-ray source. The surface areas were determined by nitrogen

sorption porosimetry on a micromeritics ASIC-2 apparatus.

4.1.4 PHOTOCATALYTIC DEGRADATION OF PHENOL

First, 90 mL of phenol solution with a concentration of 60 mg/L was prepared. Then, in

three 50 mL beakers 30 mL phenol was added. The photocatalytic degradation was performed

according to Table 4.1. In one beaker, 0.5 g of heat treated TiO2 coated microspheres was

added and in the other, 0.5 g of the TiO2 microspheres with no heat treatment was added and

in the last beaker heat treated SO3H microspheres was added. The solution was stirred in the

dark for 2 h in order to ensure establishment of the adsorption equilibrium. Then the solution

34

was exposed to UV irradiation using three 50 W Hg lamps. Samples were collected every

hour to measure the degradation efficiency by UV/Vis spectrophotometry.

Table 4.16 Different parameters in the photocatalytic degradation of phenol study

Run (type)

P01

SO3Ha

P02

TiO2-SO3H

P03

TiO2-SO3Ha

a Heat treated samples (300 °C)

4.2 RESULTS & DISCUSSION

4.2.1 PREPARATION OF PHOTOCATALYTIC MICROSPHERES

First, the PS-SO3H microspheres were stirred with TBOT in order to get a full adsorption of

TBOT on the surface. Subsequently, water was added which hydrolysed the TBOT into

Ti(OH)x. Last, the prepared microspheres were heated in an oven, this to transfer the titanium

from anastase to crystalline form. The sample that was heated to 500 °C was completely

burned out. A scheme of the preparation of TiO2-coated microspheres is shown in Figure 4.1.

500 C

2 h

TBOT H2O

PS-SO3H/TBOT PS-SO3H/Ti(OH)x PS-SO3H/TiO2PS-SO3H Figure 4.1. Scheme for the preparation of TiO2 coated microspheres

4.2.2 CHARACTERISATION

Optical images of TiO2-SO3H and heat treated TiO2-SO3H are presented in Figure 4.2 a)-b).

Figure 4.2 a) shows that the microspheres were successfully coated with TiO2 and b) that the

microspheres were decomposed and carbon was formed on the surface hence the black

surface.

The result from the TGA is presented in Figure 4.3 a) and shows a comparison between the

thermal decomposition of SO3H, TiO2-SO3H, and heat treated TiO2-SO3H microspheres. The

results shows that the weight percent of TiO2 in the heat treated TiO2-SO3H microspheres was

12 % and without heat treatment 8 %. The difference of the TiO2 weight percent is attributed

to decomposition of the polystyrene in the heat treatment.

The XRD results presented in Figure 4.3 b) shows that there is no crystalline form of TiO2

in the TiO2-SO3H microspheres. In the TiO2-SO3H microspheres that were heated to 300 °C

little crystalline TiO2 can be discernible. The TiO2-SO3H microspheres that were heated to

500 °C the characteristic peaks for crystalline TiO2 are clearly visible. However, these

microspheres were almost completely burned out thus giving a strong signal to noise ratio.

The pore size distribution results are shown in Figure 4.3 c). When the microspheres are

heat treated the pore size distribution becomes narrower. The micro and the high end

mesoporous are burned out.

35

Figure 4.2. Optical microscope images of a) TiO2-SO3H b) heat treated TiO2-SO3H

0 100 200 300 400 500 600 7000

10

20

30

40

50

60

70

80

90

100TGA

We

igh

t %

Temperature °C

PS-SO3H

TiO2-SO

3H

ΔTiO2-SO

3H

a)

10 20 30 40 50 60 70 80

TiO2-SO

3H

Δ300 °C TiO2-SO

3H

Δ500 °C TiO2-SO

3H

XRD

Re

lativ

e in

ten

sity

(a

.u.)

2θ degree

b)

1 10 100 1000

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

macromesomicro

c) Pore size distribution

PS-SO3H

ΔTiO2-SO

3H

TiO2-SO

3H

Lo

g d

iffe

ren

tal v

olu

me

(cm

3 /g)

Pore diameter (nm)

Figure 4.3 a) TGA curves for SO3H, TiO2-SO3H, and heat treated TiO2-SO3H b) XRD results for TiO2-SO3H, heat treated 300°C TiO2-SO3H, and heat treated 500°C TiO2-SO3H microspheres

4.2.3 PHOTOCATALYTIC DEGRADATION OF PHENOL The photocatalytic degradation of phenol processes is explained by Figure 4.4 and 4.5. In

Figure 4.4 a simplified scheme for the formation of the reactive species that reacts with the

phenol is presented. In Figure 4.5 a possible and simplified mechanism for the photocatalytic

degradation of phenol is presented. The complete and exact pathway for the degradation is

36

very complicated and has many steps and intermediates. However, the end products are water

and carbon dioxide.

TiO2

h+

e-

hv

O2

H2O

Mesoporousmicrosphere

OH

O2-

H+

O2- HO2

H2O2

OH-

OH

H+

H+

Figure 4.4. Simplified scheme for the photocatalytic induced formation of reactive species [2.76]

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OHOpen ringfragments

CO2H2O

OHOH-

Figure 4.5. Simplified mechanism of the photocatalytic degradation of phenol [4.16]

A scheme for the setup used for the photocatalytic degradation of phenol is presented in

Figure 4.6. The UV-lamps produce heat so the beaker was cooled down in a water bath to

ensure constant temperature in the study.

hv

Figure 4.6. Scheme of the setup used for the degradation of phenol using TiO2 coated microspheres

The results from the study of the photocatalytic degradation of phenol are presented in

Figure 4.7 a)-c). As shown in Figure 4.7 a) it is obvious that the microspheres adsorb the

phenol. This phenomenon could be used for other purposes. Unfortunately, the photocatalytic

degradation of phenol using the TiO2 coated microspheres did not work. In Figure 4.7 b) there

is a noticeable increase of absorbance in time. This was attributed to that TiO2 was leaking

37

from the microspheres, which concludes that the interaction between the microspheres and

TiO2 were not strong. However, the heat treated microspheres showed no leakage of TiO2

from the microspheres.

200 250 3000,0

0,5

1,0

1,5

2,0

2,5

3,0

Ab

s

Wavelength (nm)

original after adsorption 1h 2h 3h

a) ΔSO3H

200 250 3000,0

0,5

1,0

1,5

2,0

2,5

3,0

Ab

s

Wavelength (nm)

original after adsorption 1h 2h 3h

b) SO3H-TiO

2

200 250 3000,0

0,5

1,0

1,5

2,0

2,5

3,0ΔTiO

2-SO

3H

Ab

s

Wavelength

original after adsorption 2h 4h 6h 8h

c)

Figure 4.7. Results from the photocatalytic degradation of phenol by a) heat treated sulfonated microspheres, b) TiO2 coated microspheres c) heat treated TiO2coated microspheres

4.3 CONCLUSIONS

Several different methods were examined for the preparation of photocatalytic magnetic

microspheres. The methods were the following: sol-gel technique, physical deposition of TiO2

by heat treatment, and the method described above. The methods were tried under different

conditions such as temperature and molar ratio. However, neither of them worked. The

magnetic microspheres could not be coated with TiO2, however the sulfonated microspheres

were successfully coated with TiO2. The Fe3O4-particles should not interfere with the TiO2-

coating. According to the literature, Fe3O4-particles can be coated with TiO2. The magnetic

microspheres have R-SO3Na groups on the surface and the sulfonated microspheres have R-

SO3H groups. This is probably the main reason why the magnetic microspheres could not be

38

coated with TiO2. Several attempts of replacing the Na with H were executed. However, only

strong acids at low pH (pH 0-2) were able to change the Na to H, at pH 3-4 there was no

change. Unfortunately, the Fe3O4 dissolves in strong acid environment and the magnetic

microspheres lose their magnetic ability. However, after treatment with acid the microspheres

could be coated with TiO2. This concludes that if the Fe3O4-particles can be protected from

the acid, TiO2 coated magnetic microspheres could be synthesised. There are several possible

ways of protecting the Fe3O4, for example to coat the particles with oleic acid or SiO2.

Another possibility is to synthesise magnetic microspheres using another method that the

Fe3O4-particles are on the inside of the microspheres and not on the surface as with the

method used in this thesis.

There are several possible reasons why the photocatalytic degradation of phenol did not

work. The microspheres were too large to disperse in the phenol solution and because of that

there was too little contact between the TiO2 and phenol. This could be solved by using nano-

sized microspheres which easily disperse in solution and have much greater surface area. The

setup used for the photocatalytic degradation was very simple. If a photo reactor would have

been used, the results would perhaps been successful. Also, using a glass beaker was not

optimal, a beaker made of quarts would have been better because then the solution could have

been exposed to more UV-light thus having higher efficiency.

The heat treated TiO2 microspheres were also used for photocatalytic degradation of the

anionic dye creosol red. The dye was pH and temperature sensitive and it was difficult to

stabilise these parameters so the dye was changes to phenol. However, the microspheres

showed quite good ability to adsorb this anionic dye and it could be desorbed using

EtOH/H2O 6/4 with saturated KCl. One interesting idea is to heat treat the magnetic

microspheres under N2 atmosphere thus making magnetic microspheres with active carbon

surface.

39

CHAPTER 5: MESOPOROUS MICROSPHERES FOR BIOSEPARATION Recently, all the genes in the human DNA was determined and identified in the HUGO-

project. The HUGO-project was completed ahead of the time schedule. This was a result of

the technological advances which took place during this time [5.1]. At present, the human

proteomes are being investigated and catalogued [5.2]. Again, the technological advances

probably make this work go faster and easier than planned. Quick, selective, and effective

separation techniques in the biotechnology field are of high importance in order to study and

fully understand the proteomes and the different processes in which the proteomes take part.

Mass spectrometry is the most used instrument for the characterisation of proteins.

However, many samples cannot be directly analysed and there is a need for purification and

preconcentration. For example in the enzymatic digestion of proteins were the digested

intermediates and product are in small quantities there is a need for selective adsorption in

order to investigate the process [5.3].

One promising separation technique is to use magnetic adsorbents in the separation of

proteomes [5.3-5.5].

Lysozyme (Figure 5.1) is used in this as a model protein for the separation of proteins using

magnetic microspheres.

Figure 5.1. Three dimensional structure of lysozyme [5.6]

5.1 EXPERIMENTAL

5.1.1 MATERIAL

Lysozyme was purchased from Sigma-Aldrich Co. H3BO3, NaOH, KCl, ethanol, methanol,

citric acid, were purchased from Sinopharm Chemical Reagent Co., Ltd. All chemicals were

used as received.

5.1.2 SEPARATION OF LYSOZYME

A 50 mL lysozyme solution (0.7 g/L) was prepared in a pH 9.6 buffer, which is near the pI

for lysozyme. Into a vial, 0.2 g microspheres and 4 mL of lysozyme solution were added. The

mixture was shaken for 30 min and then separated. The lysozyme was extracted from the

microspheres by adding a pH 13 buffer and again shaken for 30 min. The adsorption and

extraction efficiencies were determined using a UNICO 3802 UV/Vis spectrophotometer.

The adsorption and desorption process was optimised according to Table 5.1 and 5.2.

Parameters such as pH and amount of adsorbent were evaluated.

40

Table 5.17 Different parameters for the optimisation of the adsorption of lysozyme

Run (type, pH 9.6, 30 min)

L01

Mag 2

L02

PS-SO3H

Run (pH, 30 min)

L21

pH 4

L22

pH 6

L23

pH 8

L24

pH 9.6

L25

pH 11

Table 5.28 Different parameters for the optimisation of the desorption of lysozyme

Run (pH, 30 min)

M01

pH 4

M02

pH 6

M03

pH 10

M04

pH 11

M05

pH 13

Run (E/W 6/4, pH 7, 30 min)

Sat. KCl

M11

Run (M/W 4/6, pH 7, 30 min)

Sat. KCl

M21

5.2 RESULTS & DISCUSSION

5.2.1 SEPARATION OF LYSOZYME

The results from the adsorption and desorption study of lysozyme is presented in Figure 5.2

a)-g). The magnetic microspheres did not adsorb lysozyme and the sulfonated microspheres

showed quite low ability to adsorb the lysozyme as shown in Figure 5.2 a). This may be due

to the pore volume and pore size, the lysozyme is too big to enter the pores and therefore the

low adsorption capacity. At pH 4 the lysozyme did not adsorb any UV light and also at pH 11

the spectrum looks different compared with the other (Figure 5.2 b) and e)). This can be

attributed to structural changes in the protein or denaturation of the protein. The adsorption

efficiencies at pH 6 and 8 the adsorption were very low. This concludes that it is mainly the

electrostatic interaction between the SO3- group in the microspheres and the positive charge

density in the protein that is responsible for the adsorption. For the extraction of the protein

several different solution were used. By varying the pH the protein could be extracted from

the microspheres. However, it seems that only at pH 13 the protein could be extracted (Figure

5.2 f)). The MeOH/H2O 4/6 with saturated KCl showed nearly the same extraction efficiency

as the pH 13 buffer (Figure 5.2 g)).

41

200 250 3000,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

Ab

s

Wavelength (nm)

Original Magnetic microspheres Sulfonated microspheres

a) Adsorption of lysozyme

200 250 3000,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

Abs

Wavelength (nm)

original

pH 4b)

200 250 3000,0

0,5

1,0

1,5

2,0

2,5

Ab

s

Wavelength (nm)

original adsorption

Adsorption at pH 6c)

200 250 3000,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

Ab

s

Wavelength (nm)

original adsorption

Adsorption at pH 8d)

200 250 3000,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

Ab

s

Wavelength (nm)

original adsorption

Adsorption at pH 11e)

200 250 3000,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5Lysozyme desorption at different pH

Abs

Wavelength (nm)

original adsorption ph4 ph6 ph10 ph11 ph13

f)

42

200 250 3000,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

Ab

s

Wavelenth (nm)

original adsorption MeOH/H2O KCl pH 13

Adsorption and desorption of lysozymeg)

Figure 5.2. a) comparison between the adsorption of lysozyme using magnetic and sulfonated microspheres,

adsorption at b) pH 4 c) pH 6 d) pH 8 e) pH11 f) desorption efficiency at different pH g) desorption efficiency using a 4/6 MeOH/H2O solution with saturated KCl

5.2.2 ADSORPTION AND DESORPTION MECHANISM A proposed mechanism for the adsorption and desorption of lysozyme onto the

microspheres are shown in Figure 5.3 and 5.4. Lysozyme has a positive charge density at pH

9.6 and this can be exploited in the separation of different proteins. By changing the pH in the

solution the proteins can be extracted from the microspheres as shown in Figure 5.6.

Figure 5.3. Scheme for the adsorption of Lysozyme

Figure 5.4 Scheme for the extraction of Lysozyme

43

5.3 CONCLUSIONS

The approach presented herein for the separation of protein could be very useful for sample

preconcentration and purification. However, the adsorption and desorption efficiency is quite

low. However, the efficiency can most likely be improved by decreasing the size of the

microspheres, thus increasing the surface area and optimise the pore size and volume. The

size of lysozyme is 4.5 × 3.5 × 3.5 nm [5.7] and the pore diameter distribution of the

microspheres is from 1-100 nm, however the majority of the pores lie in the region of 1-10

nm [3.14]. The adsorbed lysozyme probably blocks the pores thus the theoretical maximum

efficiency decreases. However, by increasing the pore diameter this phenomenon could be

avoided. Liu et al. [3.14] reports that by using 1-chlorodecane as a porogen instead of toluene,

the pore size increases.

44

45

CHAPTER 6: CONCLUSIONS

In this thesis, we have shown several possible applications for the porous polystyrene

microspheres, both environmental and biotechnological applications. The magnetic

microspheres showed great capacity of adsorbing cationic dyes. Also, by using the magnetic

microspheres the problem with separating adsorbent from the effluent was easily solved by

applying an external magnetic field. The porous polystyrene microspheres were successfully

coated with TiO2. Unfortunately, the magnetic microspheres could not be coated with TiO2,

however, the non-magnetic microspheres provide a much easier separation compared with

when TiO2 is used without being embedded in a carrier. The TiO2 coated microspheres were

not able to be used for photocatalytic degradation. One possible reason for that was that there

were no or very little contact between the TiO2 and the pollutant. This could perhaps be

solved by decreasing the size of the microspheres thus increasing the surface area and make

the microspheres disperse more easily in the solution. Suzuki et al. [6.1] solves this problem

by incorporating TiO2 in DNA. The DNA interacts easily with many compounds thus giving a

great contact between the TiO2 and pollutant. Finally, the microspheres were used for

separation of protein from aqueous solution. The results show that it is possible to use these

microspheres for separation of proteins. However, it would require further and more extensive

research in the mechanisms and how the proteins get affected by the adsorption process. This

separation method could be interesting using in lab scale were the microspheres can be altered

in order to be more specific and efficient. The applications for the microspheres will probably

increase in the future thus extensive research is being put in this field.

46

47

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57

PUBLICATIONS

Ericson M., Wang L., Recent research progress on application of magnetic adsorbents in

the treatment of wastewater, submitted to Adsorption

Ericson M., Wang L., Liu Q., Removal of methylene blue from wastewater by magnetic

microspheres, submitted to Journal of Magnetism and Magnetic Materials

Ericson M., Wang L., Liu Q., Porous polystyrene microspheres for the separation of

lysozyme from aqueous solution, submitted to Adsorption Science & Technology

Liu Q., Wang L., Xiao A., Yu H., Huo J., Ericson M., Templated preparation of

mesoporous magnetic microspheres for removal of cationic dyes from water, submitted to

Journal of Hazardous Materials

Liu Q., Wang L., Xiao A., Yu H., Huo J., Ericson M., Regeneration research of porous magnetic microspheres during treatment of wastewater containing cationic dyes, submitted to Separation Science and Technology

ACKNOWLEDGMENT I would like to thank all those people who helped me with this work, without them, I could

not have completed this project. In no specific order, Professor Wang Li, Liu Qingquan, Per-

Olof Persson, He Yingfang. Also, I would like to thank the group members at Zhejiang

University for the good working environment and helping me in the laboratory.

END NOTE All cited text in this thesis has been credited to the original authors. All data is my original

and have not been manipulated and can be repeated. All figures have been made by me.

TRITA-IM 2009:25 ISSN 1402-7615 Industrial Ecology, Royal Institute of Technology www.ima.kth.se