NANO EXPRESS Open Access

Influence of Mg Doping on ZnONanoparticles for Enhanced PhotocatalyticEvaluation and Antibacterial AnalysisK. Pradeev raj1,2, K. Sadaiyandi3, A. Kennedy1, Suresh Sagadevan4,6*, Zaira Zaman Chowdhury5*,Mohd. Rafie Bin Johan5, Fauziah Abdul Aziz6, Rahman F. Rafique7, R. Thamiz Selvi8 and R. Rathina bala2

Abstract

In this research, a facile co-precipitation method was used to synthesize pure and Mg-doped ZnO nanoparticles(NPs). The structure, morphology, chemical composition, and optical and antibacterial activity of the synthesizednanoparticles (NPs) were studied with respect to pure and Mg-doped ZnO concentrations (0–7.5 molar (M) %).X-ray diffraction pattern confirmed the presence of crystalline, hexagonal wurtzite phase of ZnO. Scanning electronmicroscope (SEM) images revealed that pure and Mg-doped ZnO NPs were in the nanoscale regime with hexagonalcrystalline morphology around 30–110 nm. Optical characterization of the sample revealed that the band gap energy(Eg) decreased from 3.36 to 3.04 eV with an increase in Mg2+ doping concentration. Optical absorption spectrum ofZnO redshifted as the Mg concentration varied from 2.5 to 7.5 M. Photoluminescence (PL) spectra showed UV emissionpeak around 400 nm. Enhanced visible emission between 430 and 600 nm with Mg2+ doping indicated the defectdensity in ZnO by occupying Zn2+ vacancies with Mg2+ ions. Photocatalytic studies revealed that 7.5% Mg-doped ZnONPs exhibited maximum degradation (78%) for Rhodamine B (RhB) dye under UV-Vis irradiation. Antibacterial studieswere conducted using Gram-positive and Gram-negative bacteria. The results demonstrated that doping with Mg ionsinside the ZnO matrix had enhanced the antibacterial activity against all types of bacteria and its performance wasimproved with successive increment in Mg ion concentration inside ZnO NPs.

Keywords: Mg-doped ZnO nanoparticles, Structural study, Optical study, Photocatalytic evaluation, Antibacterial study

BackgroundNanoparticles exhibit novel properties which depend ontheir size, shape, and morphology which enable them tointeract with plants, animals, and microbes [1]. Nano-particles of commercial importance are being synthe-sized directly from metal or metal salts, in the presenceof some organic material or plant extract. The creepersand many other plants exude an organic material, prob-ably a polysaccharide with some resin, which helpsplants to climb vertically or through adventitious rootsto produce nanoparticles of the trace elements present,so that they may be absorbed [2]. Nanosize inorganic

compounds have shown remarkable antibacterial activityat very low concentration due to their high surface areato volume ratio and unique chemical and physical fea-tures [3]. In addition, these particles are also more stableat high temperature and pressure [4]. Some of them arerecognized as non-toxic and even contain mineral ele-ments which are vital for the human body [5]. It hasbeen reported that the most antibacterial inorganic ma-terials are metallic nanoparticles and metal oxide nano-particles such as silver, gold, copper, titanium oxide, andzinc oxide [6, 7]. Zinc is an essential trace element forthe human system without which many enzymes such ascarbonic anhydrase, carboxypeptidase, and alcohol de-hydrogenase become inactive, while the other two mem-bers, cadmium and mercury belonging to the samegroup of elements having the same electronic configur-ation, are toxic [8]. For biosynthesis of nanoparticles, dif-ferent parts of a plant are used as they contain

* Correspondence: drsureshnano@gmail.com; zaira.chowdhury76@gmail.com4Centre for Nanotechnology, AMET University, Kanathur, Chennai, Tamil Nadu602 105, India5Nanotechnology and Catalysis Research Centre, University of Malaya, KualaLumpur 50603, MalaysiaFull list of author information is available at the end of the article

© The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made.

Pradeev raj et al. Nanoscale Research Letters (2018) 13:229 https://doi.org/10.1186/s11671-018-2643-x

metabolites such as alkaloids, flavonoids, phenols, terpe-noids, alcohols, sugars, and proteins which act as redu-cing agents to produce nanoparticles. They also act ascapping agent and stabilizer for them. They are used inmedicine, agriculture, and many other fields as well astechnologies. The attention is therefore focused on allplant species which have either aroma or color in theirleaves, flowers, or roots for the synthesis of nanoparti-cles because they all contain such chemicals as will re-duce the metal ions to metal nanoparticles [9]. Recently,nanoparticles have started gaining interest because oftheir unique mechanical, optical, magnetic, electrical,and other properties [10]. These emergent characteris-tics make them a promising candidate for use in elec-tronics, medicine, and other fields. It has been observedthat nanomaterials have a greater surface to volume ratiocompared with their conventional forms [11]. This is thereason why nanomaterials show greater chemical re-activity. Basically at nanoscale, the quantum effect ismore pronounced to determine their end characteristicsleading to novel optical, magnetic, and electrical behav-ior. Among the various metal oxide semiconductornanostructures, ZnO nanostructures have attracted con-siderable interest because of their low cost, high chem-ical stability, and mass production [12]. ZnO researchonly makes up a reasonable bit of the current nano-lookinto; however, all factors considered it is one of the im-portant materials which will presume an expanding partof the nanotechnology without bounds. ZnO is one ofthe most generally connected topical drugs ever. It isutilized in most sunscreens and discovers its way intonumerous treatments for anguish and itching alleviation[13]. It will be seen on the function of photocatalysis, es-sentially on ZnO and doped ZnO; there is a large clusterof potential chemical, photochemical, and electrochem-ical responses that can happen on the photocatalyst sur-face [14]. ZnO has won much consideration in thedegradation and total mineralization of environmentalcontaminations [15]. The best-preferred point of view ofZnO is the capacity to attract an extensive variety ofsolar-powered light range and more light quanta thansome semiconducting metal oxides. ZnO has developedas the main material and a proficient and promising can-didate in green ecology management structure due to itsnovel attributes [16].Basically two factors, namely surface area and surface

defects, are the most important variables to determine thephotocatalytic activity of semiconductor metal oxides.Due to its high surface activity, crystalline nature, mor-phological features, and texture; ZnO nanoparticles areconsidered as the most favorable catalyst for the degrad-ation of organic pollutants [17]. Recent literature reportedthat Mg-doped ZnO nanostructures can exhibit excellentproperties for device application [18]. Investigation on

doping Group II elements with ZnO showed that the dop-ants can alter the band gap energy (Eg) with an increase inthe UV-Visible luminescence intensity [19].Doping of Mg into ZnO is expected to modify the ab-

sorption, physical, and chemical properties of ZnO [20].Metal ion-doped ZnO nanostructures are the most prom-ising catalyst for the degradation of various pollutants be-cause of its enhancement in its optical properties [21].Different types of infectious diseases caused by bacteriapose a severe menace towards the public health world-wide. To enhance the antibacterial activity of ZnO, differ-ent types of physiochemical properties such as particlesize, crystallinity index, and optical properties should bemodified by doping with metal or non-metal [22].By inducing more defects over the surface of ZnO, the

optical adsorption properties can be enhanced. Basicallyminute amounts of dopants are sufficient to act as do-nors or acceptors inside the semiconductor crystal latticewhich will significantly alter the properties of the semi-conductor up to a greater extent. The size quantizationmakes variation in the energy gap between the conduc-tion band electrons and valence band holes which resultin change in optical properties of the doped metal oxidenanostructures [23]. Earlier literature reported that ZnOnanoparticles can resist bacterium and they have theability to shield ultraviolet radiations [24]. Zinc oxideNPs have the ability to disrupt the gram-negative cellmembrane structure of Escherichia coli [25, 26]. It wasreported also that nanoparticles with a positive chargecould bind the gram-negative cell membrane using elec-trostatic attraction [27]. ZnO NPs doped with differentmetal ions were evaluated against E. coli, and Staphylo-coccus aureus showed the antibacterial activity increas-ing with crystallite size [28].Various physical andchemical techniques have been adopted by researchersto synthesize pure and doped ZnO NPs like the vaportransport process [29], spray pyrolysis [30], thermal de-composition [31], electrochemical method [32], sol-gelmethod [33], hydrolysis [34], chemical precipitation [35],and hydrothermal method [36] in order to tailor itsmorphology and size. Among all these methods,co-precipitation method is relatively simple and inex-pensive. Furthermore, it can give high yield at roomtemperature for the synthesis of pure and doped ZnONPs [37].Here, we have investigated the preparation and

characterization of ZnO nanoparticles with different con-centrations of Mg dopants by using a simple chemicalco-precipitation method. The effects of Mg2+ ion concen-tration inside the ZnO lattice have been evaluated interms of structural, morphological, optical, and photocata-lytic studies. Further, the effect of Mg2+ ions on the anti-bacterial activity were studied against (Gram-positive andGram-negative) S. aureus, E. coli, and Proteus cultures.

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MethodsAll the reagents of analytical grade were purchased fromSigma-Aldrich and used as received without furtherpurification. The flow chart (Fig. 1) describes the prepar-ation method of the pure and Mg-doped ZnO NPs. Inthis method, 1 M of sodium hydroxide (NaOH) solutionis added to 1 M of zinc chloride (ZnCl2) solution. Thefinal solution is kept under constant stirring for 6 h. Thealkaline solution of sodium hydroxide helps in the pre-cipitation of the transition metal hydroxides. It acceler-ates the reduction process, thereby causing theformation of ZnO and Mg-doped ZnO nanoparticles.Furthermore, sodium hydroxide converts ZnCl2 to Zn(OH)2 which after heating yields ZnO nanoparticles.After the precipitation, the beaker is taken out and suffi-cient time is given to settle the final product. The prod-uct obtained is filtered and washed several times withdeionized water and acetone. Finally, the samples aredried at 100 °C for 5 h and then converted to a finepowder by grinding in an agate mortar. The powdersthus obtained are calcined at 300 °C for 4 h to yieldnano-sized ZnO particles.To synthesize Mg-doped ZnO, molar ratios of ZnCl2

and MgCl2 were measured as Zn1 − x Mg xO (where x =0.025, 0.050, and 0.075) and the same procedures were

repeated. The chemical equation for the synthesis ofpure and Mg-doped ZnO are shown in Eqs. (1–4)

ZnCl2 þ 2NaOH→Zn OHð Þ2 þ 2NaCl aqð Þ ð1ÞZn OHð Þ2→Sintering→Mg‐doped ZnOþH2O ð2Þ

MgCl2 þ ZnCl2 þ 2NaOH→ZnMg OHð Þ2þ 2NaCl aqð Þ ð3Þ

ZnMg OHð Þ2→Sintering→Mg‐doped ZnOþH2O ð4Þ

In the electrochemical series, Mg is more reactive thanZn and hence it undergoes reduction to occupy the Znlattice.

CharacterizationThe crystal structures of the samples were investigated byX-ray diffraction (XRD) Bruker D8 advanced X-ray dif-fractometer) with Cukα radiation (λ = 1.54 Å) and surfacemorphology features were studied by field emission scan-ning electron microscope (FESEM, ZEISS). Optical ab-sorption spectra of the samples were recorded with adouble beam UV-Visible spectrophotometer using HitachiU-3900H in the range 200–1200 nm. Photoluminescence

Fig. 1 Flow chart describing the synthesis of Mg-doped ZnO NPs

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(PL) emission studies were carried out by means of a spec-trometer (JOB HR800 IN Yoon Horbe) using a He-Cdlaser source with a wavelength of 325 nm. The antibacter-ial activity of the synthesized samples was tested towardsdifferent organisms by agar disc diffusion technique.

Measurement of Photocatalytic ActivityExperiments were carried out in a photocatalytic quartzreactor having a capacity of 150 ml. The reactor had fa-cilities for water circulation to ensure a constanttemperature. The UV irradiation was carried out byusing 125 W (311 nm) medium pressure Hg arc lamp(SAIC, INDIA). One hundred fifty milliliters of desiredinitial concentration (20 ppm) of RhB dye solution wasmixed with a fixed amount ZnO NPs (50 mg/L) at nat-ural pH (6.2). The solution was placed under UV illu-mination and was magnetically stirred. The sample fromthe photoreactor was withdrawn at different time inter-vals and centrifuged. The supernatants were analyzed forits absorption maximum (554 nm) using UV-Vis spec-trophotometer. Similar procedure was adopted for Mgdopants (2.5, 5, and 7.5%)-ZnO NPs using RhB dye solu-tion. Percentage of RhB degraded by the catalyst surfacewas calculated from the following equation:

Percentage of degradation¼ C0−Ctð Þ=C0 � 100% ð5Þ

where C0 represents the initial time of absorption andCt represents the absorption after various intervals oftime (0, 30, 60, 90, and 120 min).

Antibacterial StudiesE. coli (Gram-negative), S. aureus (Gram-positive), andProteus (Gram-negative strains) were maintained at 4 °Con broth media before use. Nutrient agar medium wasprepared and sterilized at 121 °C for 15 min. Twenty-fivemilliliters of nutrient agar was poured into sterile Petridishes and setting was allowed. In each Petri dish wasspread 0.2 ml of different bacterial species (E. coli, S.aureus, and Proteus). A disc was prepared and placed inthe plates with the help of a sterile loop, and two discsper plates were made into the set agar containing thebacterial culture.

Results and DiscussionStructural StudiesFigure 2 illustrates the X-ray diffraction (XRD) patternsfor the pure and Mg-doped ZnO samples. In the figure,seven major peaks are seen at 31.8°, 34.5°, 36.3°, 47.5°,56.7°, 62.9°, and 68° which can be consigned to diffrac-tion from (100), (002), (101), (102), (110), (103), and(112) planes respectively for a lattice constant of a = b =3.24 Å and c = 5.2066 Å [38]. The XRD pattern clearly

reflects the presence of the hexagonal wurtzite phasecrystal structure for pure ZnO nanoparticles (JCPDS:36-1451) [39]. Also from the diffraction, it is noted thatno further secondary phases are observed with Mg dop-ant into ZnO crystal lattice and no significant changesare observed in the XRD pattern of the Mg-doped ZnONPs. It is also noted that the intensity of the XRD peakdecreases with increase in Mg doping concentration(shown in Fig. 2a–d) which confirms the slender loss intheir crystallinity due to distortion of lattice. Due to Mgions doping inside the periodic crystal lattice of ZnO, asmall amount of strain is persuaded. This results in theswap of the lattice which consecutively leads to changethe regularity of crystal. However, very careful inferencesindicate that the peak position shifts towards the lowerangle values as observed with higher doping of Mg intoZnO matrix. Especially for the peak located at (101)plane 35°.84, it is found that it does shift towards lowervalue with increase in doping concentration, which canbe attributed to the replacement of Zn2+ ions by Mg2+

ions [40]. It is well reported in the literature that the lat-tice characteristics of the host materials get changed dueto the incorporation of dopant materials. This happensdue to their variance in the atomic radii. Furthermore,the dopant ions may replace Zn ions in the host lattice(Mg ions) [41]. Thus the basic structure of ZnO NPs isunaltered and they retain their original wurtzite struc-ture. This indicates that most of the Mg2+ ions go intothe lattice as substitution ions to replace the Zn2+ ionsand do not enter the void spaces. Since the ionic radiusof the substituted Mg2+ (RMg

2+ = 0.057 nm is 0.57 Å) issmaller than that of Zn2+ (RZn

2+ = 0.06 nm is 0.60 Å)[42], it is observed that the shift corresponds to a smallamount of lattice strain on the account of Mg2+ intoZnO environment.The mean crystallite size is calculated by using Scherrer

formula [43].

d ¼ 0:89λβ cosθ

ð6Þ

where λ is the wavelength of the radiation (1.54056 Å), βis the full width at half maximum intensity, and θ is thediffraction angle. From the calculated values, it is ob-served that the mean crystallite size increases with an in-crease in Mg doping concentration (Table 1).

Effect of Doping on Lattice ParametersThe crystallite size, lattice parameters, atomic packingfraction (APF), lattice strain, and volume show the phys-ical properties of pure and doped ZnO NPs [44]. For awurtzite phase, the lattice parameters are calculated byusing the Eq. (7–9) where, a = b, and c are the lattice

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parameters, dhkl is the interplanar distance correspond-ing to its Miller indices (hkl).

1dhkl

¼ h2 þ k2� �

a2þ l2

c2ð7Þ

a ¼ λffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi3 sinθ100

p ð8Þ

c ¼ λsinθ002

ð9Þ

D ¼ 1A:P:F

The calculated lattice parameters are listed in Table 1.It is observed from Table 1 that there is an alteration inits lattice parameter values as Mg2+ ion substitutes Zn2+

ion in the lattice. As the doping concentration increases,the dopant atom incorporated occupies the substitu-tional lattice site. It is also observed from Table 1 that

the crystallite size (D) varies inversely with the atomicpacking fraction (APF) as shown in Eq. (10).Strain induced is calculated using Eq. (10).

ε ¼ βhkl cosθ=4 ð10Þ

Furthermore, it is noted that there is a decrease in itslattice strain due to Mg2+ ions doping inside the ZnOmatrix (Table 1), which causes the local distortion of thecrystal structure. This is evident and noted earlier alsoin the literature for the difference in their atomic radiias well as in their doping concentration [45].

Field Emission Scanning Electron Microscope (FESEM) andEDS AnalysisFigure 3a–d illustrates the morphology of Mg-dopedZnO NPs at different Mg molar concentrations. Fromthe FESEM images, it is observed that most of the grainsfall in the nanoscale regime. It is also noted that the par-ticles get aggregated on their surface. Aggregation of

Fig. 2 XRD pattern for pure and Mg-ZnO NPs. a Pure ZnO NPs. b 2.5% Mg-ZnO NPs. c 5% Mg- ZnO NPs. d 7.5% Mg- ZnO NPs

Table 1 Lattice parameters of pure and Mg-ZnO NPs

Sample Crystallite size (D) Lattice parameter Atomicpackingfraction(APF) %

Volume(nm3)

Strain

nm a (Å) c (Å) c/a ratio No unit

ZnO NPs 24 3.2621 5.2256 1.603 75.84 48.21 1.995 × 10− 3

2.5% Mg-ZnO NPs 42 3.2618 5.2203 1.602 75.65 48.32 1.552 × 10− 3

5% Mg-ZnO NPs 61 3.2585 5.2181 1.602 75.47 48.41 1.201 × 10−3

7.5% Mg-ZnO NPs 90 3.2541 5.1999 1.599 75.22 48.50 1.043 × 10−3

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particles on the surface might have originated from thehigh surface energy of the synthesized NPs [46]. It is in-teresting to note that for a doping concentration of 5 M% and 7.5 M % some hexagonal crystal-shaped andwell-distributed nanostructured grains are observed indi-cating the influence of higher doping Mg on the surfaceof ZnO matrix. With increased concentration of Mg ionsinside the ZnO matrix, the grain size of the final

particles was increasing from 30 to 110 nm. Figure 3c, dis in accordance with the crystallite size obtained by theXRD analysis.Figure 4a–d displays the chemical compositional ana-

lysis of pure and Mg-doped ZnO nanoparticles carriedout using EDS. From the obtained EDS spectra, thepresence of various elements such as Zn, Mg, and O areobserved. Figure 4c, d clearly shows the intensity of Mg

Fig. 3 FESEM photographs of pure and Mg-doped ZnO NPs. a Pure ZnO NPs. b 2.5% Mg-ZnO NPs. c 5% Mg-ZnO NPs. d 7.5% Mg- ZnO NPs

Fig. 4 Energy-dispersive X-ray (EDS) spectra. a Pure ZnO NPs. b 2.5% Mg-ZnO NPs. c 5% Mg-ZnO NPs. d 7.5% Mg-ZnO NPs

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slightly increasing with the injecting of Mg into ZnO en-vironment. The incorporation of Mg ions had a signifi-cant effect on the structural and optical properties. Itwas also concluded from the EDS spectrum that noother foreign elements were present in the synthesizedsamples.

Optical StudiesThe UV-Vis absorption spectra of pure and Mg-dopedZnO NPs as a function of wavelength for the range of200 to 1200 nm are illustrated by Fig. 5a. From the fig-ure, it is noted that the absorption peak increases withthe doping concentration. The increase in absorbancemay be due to various factors like particle size, oxygendeficiency, and defects in grain structure [47]. Thestrong absorbance is found for the wavelength below380 nm for Mg-doped ZnO nanoparticles while a verylow absorbance is observed in the visible region as ob-served from Fig. 5a. This is attributed to greater

absorption of incident photon energy by the moleculespresent in the lower energy state getting excited to thehigher energy levels.It is observed that the absorption edge of Mg-doped

ZnO NPs is shifted to the longer wavelength (redshift)as Mg content is changed from 2.5 to 7.5 M %. Thismight be due to the small amount of lattice strainpresent in the sample as a result of Mg dopant towardsZnO. This redshift behavior is expected to decrease inits band gap (Eg) value. The optical bandgap (Eg) is de-termined from a Tauc-plot from the following relation(11).

α ¼ A hν−Eg� �1=2

hvð11Þ

where α is absorption coefficient, h is Plank’s constant, νis the frequency of light radiation, and Eg is the bandgap energy, where “n” takes the value of ½ for alloweddirect transition [48]. Plots of (αhν) 2 versus (hν) aremade for pure and Mg-doped ZnO NPs. The band gapenergy (Eg) is obtained from the extrapolation of the lin-ear portions of the plots onto the x-axis.From Fig. 5b, it is found that the band gap energy (Eg)

for pure ZnO NPs is around 3.36 eV and decreases withMg dopant (3.36 to 3.04 eV). The band gap is decreaseddue to strong quantum confinements and enhancementin their surface area to volume ratio [49]. Enhancementof redshift and decrease in band gap energy (Eg) confirmthe presence of Mg2+ inside the Zn2+ site of the ZnOlattice.

Photoluminescence StudiesFigure 6 illustrates the photoluminescence spectra for thepure and Mg2+-doped ZnO NPs at the wavelength of325 nm. A relatively sturdy UV emission band around400 nm and broad bands at 450 to 620 nm are observedin the visible spectrum region. Strong UV emission is at-tributed to the radiative recombination of excitons

Fig. 5 a Optical absorption and b band gap energy (Eg) for pureand Mg-doped ZnO NPs Fig. 6 Photoluminescence spectrum of pure and Mg-ZnO NPs

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(exciton emission) [50]. The origin of the broad visibleemission band at 450 to 620 nm is due to the surfaceanion vacancies [51]. This may be due to the tunneling ofsurface-bound electrons through pre-existing trappedholes [52]. It is also observed that the intensity of emissionbands observed at 390 and 525 nm is decreased withhigher doping of Mg content (7.5%). Higher doping per-centages inside the ZnO NPs are preventing the recom-bination of photo-generated electrons and holes.Moreover, Mg (7.5%) ions produce additional active defectsites inside the ZnO lattice resulting in further visible lightadsorption through these active defect sites [53].

Photocatalytic StudiesThe photocatalytic degradation study of pure andMg-doped ZnO with Rhodamine B (Rh B) dye solutionwas studied under different intervals of time (0–120 min). The optical absorption spectra of RhB dye so-lution at different time intervals (0–120 min) were re-corded and the same is illustrated by Fig. 7. It isobserved that with the lapse of time the peak height de-creases indicating greater degradation of Rhodamine Bdue to the photocatalytic activity of ZnO. A negligibleamount of the dye has been degraded using pure ZnOafter 120 min, whereas the 7.5% Mg-doped sampleshowed higher degradation efficiency. This is anticipated

due to presence of defects and oxygen vacancies createdby Mg doping inside the ZnO matrix [54]. Figure 8shows the percentage of degradation for pure andMg-doped ZnO NPs. It is observed that 7.5% Mg-dopedZnO has exhibited a maximum degradation of 78% com-pared with the other doping concentrations (Table 2). Itis also noted that a higher Mg (10% or more) dopingconcentration into ZnO will reduce the photocatalyticactivity. This is understandable due to the physical de-fects as well as the increased oxidation states of cations.This phenomenon was observed earlier in the literaturewhich described that excess cations produced during thedoping process will act as trapping sites for the holesand electrons. Subsequently, this will stimulate the re-combination of photo-generated charged species. Thisgradually impedes the generation of •OH (hydroxyl) andO•2

− (oxygen) superoxide radicals. This phenomenonwill reduce the photocatalytic activity. Similar resultshave been reported by Lee et al. [55] and Yousefi et al.[56]. Further, in our co-precipitation technique, thethermodynamic solubility is less for higher doping con-centration of Mg into ZnO. Similar to such results havebeen reported by Javed Iqbal et al [57].It seems that Mg-doped ZnO NPs act similar to electron

sink, which consequently can enhance significantly theseparation of the photo-generated electron−hole pairs and

Fig. 7 Absorption spectral decrement of Rhodamine B dye aqueous solution degraded from (0–120 min)

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inhibit their recombination resulting in improved photo-catalytic activity [58].The reaction kinetics can be observed by plotting linear

curves for the concentration ratio, ln(C/Co), against the ir-radiation time “t”. From the graph (Fig. 9a), it is evidentlyvisible that the existence of Mg ions from 2.5 to 7.5% insidethe ZnO matrix has in fact activated the photocatalyticprocess. From Fig. 9b, the RhB degradation rate constant kwas evaluated and it was 1.09 × 10− 3, 2.76 × 10− 3, 5.72 ×10− 3, and 1.26 × 10− 2 and for the pure ZnO NPs, 2.5%Mg-ZnO NPs, 2.5% Mg-ZnO NPs, and 2.5% Mg-ZnO NPs,respectively. Among them, the 7.5% Mg-ZnO NPs have ex-hibited the highest degradation rate constant (k) value,which has quite significantly increased compared with thatof pure ZnO NPs (Table 2). The findings of this photocata-lytic experiment clearly reveal that the doping of Mg ionsup to a certain limit can effectively enhance the photocata-lytic activity of ZnO photocatalyst.The reason behind the enhanced photocatalytic activity

for Mg-doped ZnO NPs is enlarged surface area with thepresence of surface oxygen vacancies [59]. The photocata-lytic mechanism of semiconductor materials proceedsthrough the formation of electron–hole pair (e−, h+) alongwith the subsequent separation as well as the recombin-ation of electrons and holes [60]. Photocatalytic activity forpure ZnO is attributed both to the donor states caused by a

large number of defect sites such as oxygen vacancies andinterstitial zinc atoms and to the acceptor states which arisefrom zinc vacancies and interstitial oxygen atoms [61]. Butfor Mg-doped ZnO NPs for the degradation of RhB underUV-Visible irradiation, initially electron–hole pairs are cre-ated and then the species such as •OH and •O− 2 areformed as shown in the equation.

ZnOþ hν→ZnO eCB þ hVBð Þ ð12Þ

The photo-induced electrons are easily trapped byelectronic acceptors like adsorbed (O2), in order to pro-duce a superoxide radical anion (O•− 2) Eq. (13)

eCB þ O2→O•−2 ð13Þ

Further, the photo-induced holes are easily trapped bynegative OH− ions to errand the production of hydroxylradical species (OH•) Eq. (14)

Fig. 8 Photodegradation of Rhodamine B under pure and IZ-NPs

Fig. 9 (a) Evolution of the relative concentration of RhB as afunction of the time for pure and Mg-ZnO NPs (b) The reactionkinetics of RhB dye degradation for pure and Mg-ZnO NPs

Table 2 Catalytic degradation with band gap energy:(pure andMg-doped ZnO NPs)

Sample Band gap(Eg) eV

Degradation(%) at 120 min

Degradationrate constant (k)

ZnO NPs 3.36 13.18 1.09 × 10−3

2.5% Mg-ZnO NPs 3.27 30.76 2.76 × 10− 3

5% Mg-ZnO NPs 3.13 56.04 5.72 × 10− 3

7.5% Mg-ZnO NPs 3.04 78.02 1.26 × 10−2

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OH− þ hþ→OH • ð14ÞThus produced OH− radical and superoxide radical

anion will carry out the total photocatalytic reaction.However, •OH radical is a particularly strong oxidantwhich can cause fractional or complete mineralization oforganic molecules. The high oxidative potential of thehole in the valence band causes the oxidation of organiccompounds to form some reactive intermediates [62] asshown by Eq. (15–16).

O•−2 þ RhB degradation productsþ CO2

þ H2O ð15Þ

OH• þ RhB degradation productsþ CO2

þ H2O ð16ÞThus, it is necessary to prevent the recombination of

electron–hole pairs to have better photocatalytic activityof semiconductor based NPs. Controlled doping of Mgover the ZnO NPs up to a certain limit can enhance thephotocatalytic activities. All the Mg-doped ZnO NPs showa significant enhancement of the photo-degradation of

RhB dye compared with the pure ZnO NPs. In this re-search, 7.5% Mg-doped ZnO NPs show better photocata-lytic properties after 120 min compared with pure ZnOsample. This might be due to the change in their particlesize and band gap effects [63].

Antibacterial StudiesThe zone of inhibition by using Mg-doped ZnO NPs for E.coli (Gram-negative), S. aureus (Gram-positive bacteria),and Proteus (Gram-negative strains) is displayed by Fig. 10.It was carried out using disc diffusion method to observetheir ability as a potential antimicrobial agent. The preparedNPs were highly reactive due to their high surface to vol-ume ratio. From Fig. 10, it is clear that the Mg2+-dopedZnO NPs inhibit the growth of both Gram-negative andGram-positive bacteria. It was observed that the zone of in-hibition is proportional with the amount of Mg doping inZnO NPs. The results obtained to show the effect of Mgdoping in ZnO NPs are illustrated in Table 3. This mightbe attributed to the reduction in their band gap values. Dueto reduction in the band gap, there is a possibility of excitongeneration. Overall, this enhances the photocatalyst

Fig. 10 Zones of Inhibition of ZnO and Mg-doped ZnO NPs against the given bacteria

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activities for improved bactericidal activity of Mg-dopedZnO NPs [64]. Furthermore, due to the varioussurface-interface characteristics may have differentchemical-physical, adsorption-desorption abilities in thedirection towards bacteria, make sure in different antibac-terial performances [65].The interaction between the NPs and the cell wall of

bacteria was changed due to doping of Mg. The growthof S. aureus and the other two bacteria was more com-mendably affected by Mg2+-doped ZnO nanostructurescompared with pure ZnO NPs. From Table 3, it is notedthat Gram-negative and Gram-positive have different in-hibition zones. This difference in the antibacterial activ-ity of Mg-doped ZnO nanostructures against Gram-negative and Gram-positive bacterial strains may be dueto the difference in cell wall structure of those respectivebacteria. It was also reported earlier that various bacter-ial strains had considerably different infectivity and tol-erance levels towards the different agents includingantibiotics [66]. Also differences in the antibacterial ac-tivity might be due to different particle dissolution.Basically, the antibacterial efficiency of pure and

Mg-doped ZnO NPs is mainly dependent on the in-creased levels of reactive oxygen species (ROS), mostlyhydroxyl radicals (OH) and singlet oxygen [67]. This ismainly due to the enlarged surface area which causes in-crease in oxygen vacancies as well as the diffusion cap-acity of the reactant molecules inside the NPs [68]. Thereactive oxygen group contains superoxide radical andhydrogen peroxide. Both of them can damage the DNAand cellular protein leading to cell death [69]. Moreover,the presence or addition of the nanostructures on thesurface or cytoplasm of the bacteria can cause the dis-ruption of cellular function as well as disorganization ofthe cell membranes [70]. The doping of Mg with ZnOmay lead to the variation in grain size, morphology, andsolubility of Zn2+ ions. All these factors combined to-gether have a robust impact on the antibacterial activityof ZnO [71, 72]. The results have revealed that

Mg-doped ZnO nanostructures will be a promising can-didate to be used for potential drug delivery systems tocure some significant infections in the near future.

ConclusionsTo conclude, pure and Mg-doped ZnO structures weresuccessfully synthesized by co-precipitation method. TheXRD patterns revealed the wurtzite structure for all thenanosamples and no impurity phase was noted. The max-imum crystallite size obtained from XRD was less than100 nm. FE-SEM studies confirmed that the crystallite sizeincreased with increase in Mg content. The UV-Visible re-sults revealed that absorption underwent a redshift withMg into ZnO as compared to pure ZnO exhibiting strongquantum confinement effects. Optical band gap energywas found to decrease from 3.36 to 3.04 eV with Mg dop-ing, resulting in the increment in their crystallite size as aresult of Mg doping. PL results confirmed the enhancedvisible emissions with Mg-doped ZnO leading to the in-crease in delocalization of electron-hole pairs. Photocata-lytic measurements revealed the increase in Mg doping inthe ZnO nanoparticles that caused higher photocatalyticactivity. The antibacterial activities of the synthesizednanosamples were tested against E. coli (Gram-negative),S. aureus (Gram-positive bacteria), and Proteus (Gram-ne-gative strains).

AcknowledgementsThe authors are also grateful to the authorities concerned for providingthem the testing facilities of IIT Madras-Chennai, India, Anna University, andDepartment of Chemistry, L.R.G. Govt Arts College, Tiruppur, TN, India. Oneof the authors (Suresh Sagadevan) acknowledges the honor, namely the“Visiting fellow” at the Department of Physics, Center for Defence FoundationStudies, National Defence University of Malaysia, Kem Sg. Besi, 57000 KualaLumpur, Malaysia. The author wishes to place on record his heartfelt thanksthat are due to the authorities concerned.

FundingThe authors are thankful to the authorities concerned for the fundingprovided from the Grant No. RP044C-17AET and RP044D-17AET from theUniversity of Malaya, Malaysia.

Availability of Data and MaterialsAll relevant data are within the paper.

Authors’ ContributionsKPr, KS, and AK conceived and designed the experiments; KPr hadperformed the experiments; SS, ZZC, MRBJ, FAA, and RFR analyzed the data;KS, AK, RTS, and RRb had contributed reagents/materials/analysis tools. KPr,SS, and ZZC had written the paper. All authors read and approved the finalmanuscript.

Competing InterestsThe authors declare that they have no competing interests.

Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims inpublished maps and institutional affiliations.

Author details1Department of Physics, CSI College of Engineering, Ooty 643215, India.2Research and Development Centre, Bharathiar University, Coimbatore

Table 3 Average diameter values of Zones of Inhibition (ZOI)for pure and Mg-doped ZnO NPs (2.5–7.5 M %)

S.No

Samples Zone of inhibition (mm)

Gram-negativestrains

Gram-negativestrains

Gram-positivestrains

Proteus Escherichia coli Staphylococcusaureus

1 ZnO NPs 6 ± 0.7 9 ± 0.7 9 ± 0.6

2 2.5% Mg-ZnONPs

9 ± 0.4 10 ± 0.4 13 ± 0.4

3 5% Mg-ZnONPs

12 ± 0.3 14 ± 0.5 16 ± 0.3

4 7.5% Mg-ZnONPs

15 ± 0.4 16 ± 0.5 19 ± 0.3

Pradeev raj et al. Nanoscale Research Letters (2018) 13:229 Page 11 of 13

641046, India. 3Department of Physics, Government Arts College for Women,Nilakkottai, Dindigul 624202, India. 4Centre for Nanotechnology, AMETUniversity, Kanathur, Chennai, Tamil Nadu 602 105, India. 5Nanotechnologyand Catalysis Research Centre, University of Malaya, Kuala Lumpur 50603,Malaysia. 6Department of Physics, Center for Defence Foundation Studies,National Defence University of Malaysia, Kuala Lumpur, Malaysia. 7RutgersCooperative Extension Water Resources Program, Rutgers, The StateUniversity of New Jersey, New Brunswick, USA. 8Department of Chemistry,LRG Government Arts College for Women, Tiruppur 641 604, India.

Received: 29 May 2018 Accepted: 26 July 2018

References1. Siddiqi KS, Husen A, Rao RAK (2018) A review on biosynthesis of silver

nanoparticles and their biocidal properties. J Nanobiotechnol 16:142. Husen A, Siddiqi KS (2014) Photosynthesis of nanoparticles: concept,

controversy and application. Nanoscale Res Lett 9:2293. Rai M, Yadav A, Gade A (2009) Silver nanoparticles as a new generation of

antimicrobials. Biotechnol Adv 27:76–834. Sawai J (2003) Quantitative evaluation of antibacterial activities of metallic

oxide powders (ZnO, MgO and CaO) by conductimetric assay. J MicrobiolMethods 54:177–182

5. Roselli M, Finamore A, Garaguso I, Britti MS, Mengheri E (2003) Zinc oxideprotects cultured enterocytes from the damage induced by Escherichia coli.J Nutr 133:4077–4082

6. Husen A (2017) Gold nanoparticles from plant system: synthesis,characterization and their application. In: Ghorbanpourn M, Manika K, VarmaA (eds) Nanoscience and plant–soil systems Vol.–48. Springer InternationalPublishing, Cham, pp 455–479

7. Chaudhry Q, Scotter M, Blackburn J, Ross B, Boxall A, Castle L, Aitken R,Watkins R (2008) Applications and implications of nanotechnologies for thefood sector. Food Add Cont: Part A R 25:241–258

8. Siddiqi KS, Rahman A, Tajuddin, Husen A (2008) Properties of zinc oxidenanoparticles and their activity against microbes. Nanoscale Res Lett 13:141

9. Siddiqi KS, Husen A (2017) Recent advances in plant-mediated engineeredgold nanoparticles and their application in biological system. J Trace ElemMed Biol 40:10–23

10. Shah AH, Basheer Ahamed M, Manikandan E, Chandramohan R, Iydroose M(2013) Magnetic, optical and structural studies on Ag doped ZnOnanoparticles. J Mater Sci Mater Electron 24:2302–2308

11. Ramrakhiani M (2012) Nanostructures and their applications. Recent Res SciTechnol 4:14–19

12. Li JH, Chu XY, Xu MZ, Li X, Fang X, Wei ZP, Wang XH, Zhai YJ (2015)Photocatalytic performance in oxide nanomaterials. Integr Ferroelectr167:1–16

13. Lohani A, Verma A, Joshi H, Yadav N, Karki N (2014) Nanotechnology-basedcosmeceuticals. ISRN Dermatolog 2014:1–14. https://doi.org/10.1155/2014/843687

14. Baruah S, Samir PK, Dutta J (2012) Nanostructured zinc oxide for watertreatment. Nanosc Nanotechnol Asia 2:90–102

15. Poulios I, Makri D, Prohaska X (1999) Photocatalytic treatment of olivemilling waste water: oxidation of protocatechuic acid. Global Nest: Int J 1:55–62

16. Agarwal H, Kumar SV, Kumar SR (2017) A review on green synthesis ofzinc oxide nanoparticles—an eco-friendly approach. Resour EfficTechnol 3:406–413

17. Khataee A, Kirans M¸ Karaca S, Arefi-oskoui S, Long MC, Hu NT, Zhang, Yu YF(2015) Preparation and characterization of ZnO/MMT nanocomposite forphotocatalytic ozonation of a disperse dye. Turk J Chem 40:546–564

18. Tripathi P, Ashraf SSZ, Naqvi AH, Azam A, Ahmed S (2015) Band gapengineering and enhanced photoluminescence of Mg doped ZnOnanoparticles synthesized by wet chemical route. J Lumin 161:275–280

19. Ivetića TB, Dimitrievskaa MR, Finčurb NL, Đačanina LJR, Gútha IO,Abramovićb BF, Lukić-Petrovića SR (2014) Effect of annealing temperatureon structural and optical properties of Mg-doped ZnO nanoparticles andtheir photocatalytic efficiency in alprazolam degradation. Ceram Int 40:1545–1552

20. Abed C, Bouzidi C, Elhouichet H, Gelloz B, Mokhtar F Mg doping inducedhigh structural quality of sol–gel ZnO nanocrystals: Application inphotocatalysis. Appl Surf Sci 15:855–863

21. Arshad M, Ansari MM, Ahmed AS, Tripathi P, Ashraf SS, Naqvi AH, Azam A(2015) Band gap engineering and enhanced photoluminescence of Mgdoped ZnO nanoparticles synthesized by wet chemical route. J Lumin 161:275–280

22. Sirel khatim A, Azman SM, Haida SN, Kaus M, Chuo L, Khadijah AS, BakhoriSK, Hasan H, Mohamad D (2015) Review on zinc oxide nanoparticles:antibacterial activity and toxicity mechanism. Nano-Micro Lett 7:219–242

23. Kalele S, Gosavi SW, Urban J, Kulkarni SK (2006) Nanoshell particles:synthesis, properties and applications. Curr Sci 91:1038–1052

24. Kathirvelu S, D’Souz L, Dhurai B (2009) UV protection finishing of textilesusing ZnO nanoparticles. Indian J Fibre Text Res 34:267–273

25. Sirelkhatim A, Mahmud S, Seeni A, Haida N, Kaus M, Chuo L, Khadijah AS,Bakhori M, Hasan H, Mohamad D (2005) Review on zinc oxide nanoparticles:antibacterial activity and toxicity mechanism. Nano Micro Letters 7:219–242

26. C Karthikeyan, A Parveez, Ahamed, N Thajuddin, NS Alharbi, SA Alharbi, GRavi, Abdulrahman, Syedahamed Haja Hameed (2016) In vitro antibacterialactivity of ZnO and Nd doped ZnO nanoparticles against ESBL producingEscherichia coli and Klebsiella pneumoniae. Sci Rep 6:1–11

27. Gopinath K, Karthia V, Sundaravadivelan C, Gowri S, Arumugam A (2015)Mycogenesis of cerium oxide nanoparticles using Aspergillus niger culturefiltrate and their applications for antibacterial and larvicidal activities. J ofNanostruct Chem 5:295–303

28. Mahmud S, Seeni A, Kaus NHM, Ann LC, Bakhori SKM, Hasan H, SirelkhatimDMA (2015) Review on zinc oxide nanoparticles: antibacterial activity andtoxicity mechanism. Nano-Micro Lett 7:219–242

29. Ozgur U, Morkoc H (2009) Zinc Oxide: Fundamentals, Materials and DeviceTechnology. Wiley, pp 365–370. https://doi.org/10.1002/9783527623945

30. Ghaffarian HR, Saiedi M, Sayyadnejad MA (2011) Synthesis of ZnOnanoparticles by spray pyrolysis method. Iran J Chem Chem Eng 30:1–6

31. Lin CC, Li YY (2015) Synthesis of ZnO nanowires by thermal decompositionof zinc acetate dihydrate. Mater Chem Phys 113:334–337

32. Anand V, Srivastav VC (2015) Zinc oxide nanoparticles synthesis byelectrochemical method: optimization of parameters for maximization ofproductivity and characterization. J Alloys Compd 636:288–292

33. Alwan RM, Kadhim QA, Sahan KM, Ali RA, Mahdi RJ, Kassim NA, Jassim AN(2015) Synthesis of zinc oxide nanoparticles via sol–gel route and theircharacterization. Appl Surf Sci 5:1–6

34. Vasudevan A, Jung S, Ji T (2011) Synthesis and characterization of hydrolysisgrown zinc oxide nanorods. ISRN Nanotechnol 2011:1–7. https://doi.org/10.5402/2011/983181.

35. Lang J, Wang J, Zhang Q, Li X, Han Q, Wei M, Sui Y, Wang D, Yang J(2016) Chemical precipitation synthesis and significant enhancement inphotocatalytic activity of Ce-doped ZnO nanoparticles. Ceram Int 42:14175–14181

36. Maryanti E, Damayanti D, Gustian I, Yudha SS (2014) Synthesis of ZnOnanoparticles by hydrothermal method in aqueous rinds extracts ofSapindus rarak DC. Mater Lett 118:96–98

37. Bagabas A, Alshammari A, Aboud MFA, Kosslick H (2013) Room-temperaturesynthesis of zinc oxide nanoparticles in different media and theirapplication in cyanide photodegradation. Nanoscale Res Lett 8:1–10

38. Joshi R, Kumar P, Gaur A, Asokan K (2014) Structural, optical andferroelectric properties of V doped ZnO. Appl Nanosci 4:531–536

39. Hoggas K, Nouveau C, Djelloul A, Bououdina M (2015) Structural,microstructural, and optical properties of Zn1−xMgxO thin films grown ontoglass substrate by ultrasonic spray pyrolysis. Applied Physics A 120:745–755

40. Chandrasekaran K, Seemaisamy S, Venugopal SK, Kumaresan S, Ravi G,Hameed ASH (2013) Impact of alkaline metal ions Mg2+, Ca2+, Sr2+ and Ba2+

on the structural, optical, thermal and antibacterial properties of ZnOnanoparticles prepared by the co-precipitation method. Mater Chem B1:5950–5962

41. Boggs S (2009) Petrology of Sedimentary Rocks. 2nd edition, University ofOregon, Cambridge University Press. https://doi.org/10.1017/CBO9780511626487

42. Vipin Kumar P, Sahare D (2013) Optical and magnetic properties of cu-doped ZnO nanoparticles. Int J Innov Technol Explor Eng 3:2278–3075

43. Talam S, Karumuri SR, Gunnam N (2012) Synthesis, characterization andspectroscopic properties of ZnO nanoparticles. ISRN Nanotechnol 2012:1–6.https://doi.org/10.5402/2012/372505

44. Huse VR, Patle LB, Chaudhari AL, Sonawane GH, Labhane PK (2015)Synthesis of cu doped ZnO nanoparticles: crystallographic, optical, FTIR,morphological and photocatalytic study. J Mater Sci Chem Eng 3:1–12

Pradeev raj et al. Nanoscale Research Letters (2018) 13:229 Page 12 of 13

45. Lakshmana Perumal S, Hemalatha P, Alagara M, Navaneetha Pandiyaraj K(2015) Investigation of structural, optical and photocatalytic properties of Srdoped Zno nanoparticles. Int J Chem Phys Sci 4:1–13

46. He Q, Zhong C, Wu JW (2008) Magnetic iron oxide nanoparticles: synthesisand surface functionalization strategies. Nanoscale Res Lett 3:397–415

47. Mir FA, Batoo KM (2016) Effect of Ni and Au ion irradiations on structuraland optical properties of nanocrystalline Sb-doped SnO2 thin films. ApplPhys A 122:418. https://doi.org/10.1007/s00339-016-9948-3

48. Kaur P, Kumar S, Negi NS, Rao SM (2015) Enhanced magnetism in Cr-dopedZnO nanoparticles with nitrogen co-doping synthesized using sol–geltechnique. Appl Nanosci 5:367–372

49. Khajuri S, Sanotra S, Lado J, Sheikh HN (2015) Synthesis, characterization andoptical properties of cobalt and lanthanide doped CdS nanoparticles. JMater Sci Mater Electron 26:7073–7080

50. Manna B, Chowdhury A, Layek A (2012) Carrier recombination dynamicsthrough defect states of ZnO nanocrystals. Chem Phys Lett 539:133–138

51. Padmavathy N, Vijayaraghavan R (2008) Enhanced bioactivity of ZnOnanoparticles—an antimicrobial study. Sci Technol Adv Mater 9:1–7

52. Wang LS, Li X (2000) Clusters and nanostructure interfaces. In: Jena P,Khanna SN, Rao BK (eds) . World Scientific, River Edge, pp 300–310

53. Nur O, Sadaf JR, Qadir MI, Zaman S, Zainelabdin A, Bano N, Willander IHM(2010) Luminescence from zinc oxide nanostructures and polymers andtheir hybrid devices. Materials 3:2643–2667

54. Snega S, Ravichandran K, Jabena Begum N, Thirumurugan K (2013) Enhancementin the electrical and antibacterial properties of sprayed ZnO films bysimultaneous doping of Mg and F. J Mater Sci Mater Electron 24:135–141

55. Lee KM, Lai CW, Ngai KS, Juan JC (2016) Recent developments of zinc oxide basedphotocatalyst in water treatment technology: a review. Water Res 88:428–448

56. Yousefi R, Sheini FJ, Cheraghizade M, Gandomani SK, Sáaedi A, Huang NM,Jefrey Basirun W, Azarang M (2015) Enhanced visible-light photocatalyticactivity of strontium-doped zinc oxide nanoparticles. Mater Sci SemicondProcess 32:152–159

57. Iqbal J, Jan T, Ismail M, Ahmad N, Arif A, Khan M, Adil M, Haq S, Arshad A (2014)Influence of Mg doping level on morphology, optical, electrical properties andantibacterial activity of ZnO nanostructures. Ceram Int 40:7487–7493

58. Sun Y, Chen L, Bao Y, Zhang Y, Wang J, Fu M, Wu J, Ye D (2016) Theapplications of morphology controlled ZnO in catalysis. Catalysts 6:1–44

59. Tan YN, Wong CL, Mohamed AR (2011) An Overview on the PhotocatalyticActivity of Nano-Doped-TiO2 in the Degradation of Organic Pollutants. ISRNMater Sci 2011:1–18. https://doi.org/10.5402/2011/261219

60. Girish Kumar S, Koteswara Rao KSR (2014) Zinc oxide based photocatalysis:tailoring surface-bulk structure and related interfacial charge carrierdynamics for better environmental applications. RSC Adv 5:3306–3351

61. Ramachandra Rao MS, T Okada (2013) ZnO Nanocrystals and AlliedMaterials. Springer Science & Business Media 180:278–279. https://doi.org/10.1007/978-81-322-1160-0

62. Kharisov BI, Kharissova OV, Ortiz-Mendez U (2016) CRC ConciseEncyclopedia of Nanotechnology. Boca Raton: CRC Press, Taylor & FrancisGroup p. 980

63. Maji TK, Bagchi D, Kar P, Karmakar D, Pala SK (2017) Enhanced chargeseparation through modulation of defect-state in wide band-gapsemiconductor for potential photocatalysis application: ultrafastspectroscopy and computational studies. J Photochem Photobiol A Chem332:391–398

64. Shahtahmasebia N, Kompany A, Mashreghi M, Maddahi P (2013) Dopantinduced changes in physical properties of ZnO:Mg nanosuspensions: studyof antibacterial activity. Scientia Iranica F 20:2375–2381

65. Suresh Kumar P, Mangalaraj D, Ponpandian N, Viswanathan C, Sonia S,Jayram ND (2014) Effect of NaOH concentration on structural, surface andantibacterial activity of CuO nanorods synthesized by direct sonochemicalmethod. Superlattice Microst 66:1–9

66. Nicole J, Binata R, Koodali TR, Adhar CM (2008) Antibacterial activity of ZnOnanoparticles suspensions on a broad spectrum of microorganisms. FEMSMicrobiolLett 279:71–76

67. Mahendra S, Lyon DY, Brunet L, Liga MV, Dong L, Li Q (2008) Antimicrobialnanomaterials for water disinfection and microbial control: potentialapplications and implications. Water Res 42:4591–4602

68. Vijaya Kumar P, Karthikeyan M, Jafar Ahamed A (2016) Synthesis, structural andantibacterial properties of Mg doped ZnO. J Environ Nanotechnol 5:11–16

69. Jha AB, Dubey RS, Pessarakli M, Sharma P (2012) Reactive oxygen species,oxidative damage, and Antioxidative defense mechanism in plants understressful conditions. J Bot:1–26

70. Storz G, Imlayt JA (1999) Oxidative stress. Curr Opin Microbiol 2:188–19471. Yamamoto O (2001) Influence of particle size on the antibacterial activity.

Int J Inorg Mater 3:643–64672. Seyedeh MA, Monir D, Nasrin T (2013) Controllable synthesis of ZnO

nanoparticles and their morphology-dependent antibacterial and opticalproperties. J Photochem Photobiol B: Biol 120:66–73

Pradeev raj et al. Nanoscale Research Letters (2018) 13:229 Page 13 of 13