8
Hindawi Publishing Corporation ISRN Nanotechnology Volume 2013, Article ID 497873, 7 pages http://dx.doi.org/10.1155/2013/497873 Research Article A Quick Process for Synthesis of ZnO Nanoparticles with the Aid of Microwave Irradiation Tran Thi Ha, 1 Ta Dinh Canh, 2 and Nguyen Viet Tuyen 2 1 Faculty of General Science, Hanoi University of Mining and Geology, Co Nhue, Tu Liem, Hanoi, Vietnam 2 Faculty of Physics, College of Science, VNU, 334 Nguyen Trai, anh Xuan, Hanoi 120034, Vietnam Correspondence should be addressed to Nguyen Viet Tuyen; [email protected] Received 13 February 2013; Accepted 13 March 2013 Academic Editors: K. G. Beltsios, D. Wang, and D. K. Yi Copyright © 2013 Tran i Ha et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Reaction between sodium hydroxide and zinc acetate leads to the formation of zinc hydroxide, Zn(OH) 2 . e as-prepared Zn(OH) 2 was then decomposed by using conventional heating process or with the aid of microwave irradiation. e nanoproducts of both methods were ZnO nanostructures of different size and shape, but the microwave irradiation method shows many advantages in yield and reaction time. Some surfactants such as SDS, CTAB, or PVP were then used to cap the product for studying the influence on the morphology and properties of the nanostructures. 1. Introduction Zinc oxide has been famous for a wide range of applications in the functional devices, photo-catalysts, optical materials, cosmetics, nanostructure varistors, UV absorbers, gas sen- sors, and industrial additives [15]. Until now, many different methods have been developed for the production of ZnO nanopowders [13, 610]. Mechanochemical processing, sol- gel, or hydrothermal processing methods constitute pertinent examples. However, many of these methods, or at least some of their varieties, are overly costly and constitute demonstrations of laboratory interest only. Nowadays, microwave energy has become a very efficient means of heating reactions. Chemical reactions that took long time to complete can now be accomplished in minutes with the aid of microwave [812]. Microwave assisted synthesis not only helped in implementing GREEN chemistry but also led to the revolution in organic synthesis. Microwave irradiation is well known to promote the synthesis of a variety of com- pounds, where chemical reactions are accelerated because of selective absorption of microwave by polar molecules. In this paper, we report an effective method for the prepa- ration of ZnO nanoparticles by using microwave irradiation. e microwave irradiation method considered herein is fast, mild, energy-efficient, and environment-friendly and, hence, it is not a weak substitute of the conventional method. 2. Experimental Synthesis of ZnO nanopowders was achieved by dissolving 0.1 mol zinc acetate (Merk, 99% purity) in propanol 2 to make 50 mL solution of 0.2 M Zn(CH 3 COO) 2 (Merk, 99% purity). While stirring, 50 mL of 0.3 M NaOH in propanol 2 (Merk, 99% purity) was added dropwise. e resulting solution was then heated to obtain ZnO nanoproduct. To clarify the advantages of microwave irradiation, the above solution was heated in two different ways: heating with microwave oven system (Figure 1) or normal heating with an electric cooker. For microwave heating, the mixture of precursor solution was placed in a microwave system. e microwave power was set to 150W. e reaction time was 5 minutes. During the microwave irradiation the temperature of the solution reached 82.5 C (boiling point of propanol 2). Aſter 5 minutes, a white product precipitated. In the normal heating process, the solution of precursors was heated to boiling point of propanol 2 by an electric cooker of power of 500W. e designed temperature was attained aſter 20 minutes of heating. A white precipitate was also obtained at the end of the heating process. ZnO nanopowders were prepared according to the fol- lowing equations (1), (2) and the residual sodium salt

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Page 1: A Quick Process for Synthesis of ZnO Nanoparticles with ...downloads.hindawi.com/journals/isrn.nanotechnology/... · 2 ISRNNanotechnology N2gas Cooling water Figure1:Imageofmicrowaveirradiationsystem

Hindawi Publishing CorporationISRN NanotechnologyVolume 2013 Article ID 497873 7 pageshttpdxdoiorg1011552013497873

Research ArticleA Quick Process for Synthesis of ZnO Nanoparticles withthe Aid of Microwave Irradiation

Tran Thi Ha1 Ta Dinh Canh2 and Nguyen Viet Tuyen2

1 Faculty of General Science Hanoi University of Mining and Geology Co Nhue Tu Liem Hanoi Vietnam2 Faculty of Physics College of Science VNU 334 Nguyen Trai Thanh Xuan Hanoi 120034 Vietnam

Correspondence should be addressed to Nguyen Viet Tuyen nguyenviettuyenhuseduvn

Received 13 February 2013 Accepted 13 March 2013

Academic Editors K G Beltsios D Wang and D K Yi

Copyright copy 2013 TranThi Ha et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Reaction between sodiumhydroxide and zinc acetate leads to the formation of zinc hydroxide Zn(OH)2The as-prepared Zn(OH)

2

was then decomposed by using conventional heating process or with the aid of microwave irradiation The nanoproducts of bothmethods were ZnO nanostructures of different size and shape but the microwave irradiation method shows many advantages inyield and reaction time Some surfactants such as SDS CTAB or PVP were then used to cap the product for studying the influenceon the morphology and properties of the nanostructures

1 Introduction

Zinc oxide has been famous for a wide range of applicationsin the functional devices photo-catalysts optical materialscosmetics nanostructure varistors UV absorbers gas sen-sors and industrial additives [1ndash5] Until now many differentmethods have been developed for the production of ZnOnanopowders [1ndash3 6ndash10] Mechanochemical processing sol-gel or hydrothermal processingmethods constitute pertinentexamples However many of these methods or at leastsome of their varieties are overly costly and constitutedemonstrations of laboratory interest only

Nowadays microwave energy has become a very efficientmeans of heating reactions Chemical reactions that took longtime to complete can now be accomplished in minutes withthe aid ofmicrowave [8ndash12]Microwave assisted synthesis notonly helped in implementing GREEN chemistry but also ledto the revolution in organic synthesis Microwave irradiationis well known to promote the synthesis of a variety of com-pounds where chemical reactions are accelerated because ofselective absorption of microwave by polar molecules

In this paper we report an effectivemethod for the prepa-ration of ZnO nanoparticles by using microwave irradiationThe microwave irradiation method considered herein is fastmild energy-efficient and environment-friendly and henceit is not a weak substitute of the conventional method

2 Experimental

Synthesis of ZnO nanopowders was achieved by dissolving01mol zinc acetate (Merk 99 purity) in propanol 2 tomake50 mL solution of 02M Zn(CH

3COO)

2(Merk 99 purity)

While stirring 50mL of 03M NaOH in propanol 2 (Merk99 purity) was added dropwise The resulting solutionwas then heated to obtain ZnO nanoproduct To clarifythe advantages of microwave irradiation the above solutionwas heated in two different ways heating with microwaveoven system (Figure 1) or normal heating with an electriccooker

Formicrowave heating themixture of precursor solutionwas placed in a microwave system The microwave powerwas set to 150W The reaction time was 5 minutes Duringthe microwave irradiation the temperature of the solutionreached 825∘C (boiling point of propanol 2) After 5minutesa white product precipitated

In the normal heating process the solution of precursorswas heated to boiling point of propanol 2 by an electric cookerof power of 500W The designed temperature was attainedafter 20 minutes of heating A white precipitate was alsoobtained at the end of the heating process

ZnO nanopowders were prepared according to the fol-lowing equations (1) (2) and the residual sodium salt

2 ISRN Nanotechnology

N2 gas

Cooling water

Figure 1 Image of microwave irradiation system

CH3COONa was removed by washing the sample with

absolute ethanol and distilled water for several times

Zn (CH3COO)2 +NaOH 997888rarr Zn (CH3COO) (OH)

+NaCH3COO(1)

Zn (CH3COO)OH +NaOH 997888rarr ZnO

+NaCH3COO +H

2O(2)

The washing process was repeated until the pH of thesolution was 7 Finally the product was dried to obtain ZnOnanopowder

Some different surfactants were also used to studytheir influence on the morphology and properties of thenanoproducts In case of using surfactants the weight ratiosZn2+surfactant was denoted as 119877 The as-prepared sampleswere summarized in Table 1

The particle morphologies and structures of the productswere investigated by a transmission electron microscope(TEM JEM 1010-JEOL) and X-ray diffractometer (Bruker-AXSD5005) Photoluminescence (PL) measurement at roomtemperature was carried out on a 325 nmHe-Cd laser A UV-vis spectrophotometer PU 8700 was used to record the UV-visible absorption spectra

3 Results and Discussion

Figure 2 is the powder X-ray diffraction patterns of theZnO nanoproducts prepared by two different heating pro-cesses The diffraction patterns and interplane spacings canbe well matched to the standard diffraction pattern ofwurtzite ZnO demonstrating the formation of wurtzite ZnOnanocrystals The particle diameter 119889 was calculated usingthe Debye Scherer formula [7] The (100) peak at 318∘ inFigure 2 gives the ZnO particle diameters of 32 18 nm forZnO nanoparticles prepared by conventional (sample 1) and

20 25 30 35 40 45 50 55 60 65 70

(112

)

(103

)

(110

)

(102

)

(101

)(0

02)

(b)

(a)

Inte

nsity

(au

)

(100

)

2120579 (deg)

Figure 2 X-ray diffraction patterns sample 1 (a) and sample 2 (b)

microwave assisted heating (sample 2) process respectivelyIt appears that the ZnO nanoparticles prepared with differentheating process have different sizes due to the influence oftemperature gradient and reaction time

Figure 3 shows the TEM images of ZnO nanoparticlesprepared by normal and microwave irradiation assistedheating process It is clearly seen that ordinary heating byelectric cooker leads to the formation of aggregated clustersof particles of which size distribution is quite large while thenanoparticles obtained from reactions in microwave irradi-ation field have small size of only several tens nanometerFurthermore these particles are much more uniform insize and shape compared with the products of conventionalmethod The effectiveness of microwave irradiation in thepreparation of nanoparticles can be explained by the preem-inent advantages of microwave as a means of heating Themechanism of traditional heating process is conductive heator heating by convection currents and hence this is a slowand energy inefficient process due to the energy lost at thewall of the vessel Normally the wall of the vessel absorbsheat first then heat is transferred to the liquid inside so thetemperature on the outside surface needs to be in excess of theboiling point of liquid for the temperature inside the liquidvolume to reach boiling point These disadvantages can beovercome easily by applying microwave technique becausewhen heating with microwave vessel wall is transparent toMW and solventreagent absorbs MW energy directly Thedirect in-core heating and instant on-off pulse of heat leadsto the formation of a homogenous temperature gradient andreduces the reaction time These advances in turn producesmaller particles of uniform size and shape

ZnO nanoparticles have been successfully fabricated bymicrowave irradiationmethod However after the nucleationand growth process are completed the average size ofthe particles continues to increase due to diffusion limitedcoarseningThis process reduces the quality of ZnOnanopar-ticles so restraining the particles from coarsening is a veryimportant quest We have investigated the influence of somesurfactants such as SDS CTAB and PVP on the growth of

ISRN Nanotechnology 3

Table 1 Some preparation parameters of the as-prepared sample

Sample Sample preparation method Used surfactant Morphology and size(estimated from TEM image)

S1 Normal heating No gt100 nm

S2 Microwave irradiation No Quasi-sphericalDiameter 20ndash40 nm

S3 Microwave irradiation Sodium dodecyl sulphate (SDS)119877 = 09

gt100 nm

S4 Microwave irradiationHexadecylcetyltrimethylammonium bromide

(CTAB)119877 = 09

gt100 nm

S5 Microwave irradiation Polyvinylpyrrolidone (PVP)119877 = 06

Quasi-sphericalDiameter 10ndash15 nm

S6 Microwave irradiation Polyvinylpyrrolidone119877 = 09

RodDiameter 10ndash15 nmLength 30ndash50 nm

S7 Microwave irradiation Polyvinylpyrrolidone119877 = 12

RodDiameter 20ndash30 nmLength 40ndash50 nm

200 nm

(a)

40 nm

301 nm216 nm

(b)

Figure 3 TEM images of sample 1 (a) and sample 2 (b)

ZnO nanoparticlesThese surfactants were dissolved into thesolution of sodium hydroxide before the reaction with zincsalt PVP reveals to be the most suitable surfactant to prepareZnO nanoparticles with small size and homogenous shape

500 nm

(a)

500 nm

(b)

100 nm

(c)

100 nm

(d)

Figure 4 TEM images of ZnO nanoparticles precipitated in thepresence of different surfactants (a) CTAB (S4) (b) SDS (S3) (c)PVP (S6) (d) nanoparticles precipitated in the absence of surfactant(S2)

The surfactant on the surface of ZnO plays two rolesfirstly it helps to reduce the defects in nanocrystals dur-ing nucleation and secondly it attaches to the surface ofnanoparticles so as to affect on the size of the particles TEMimages of ZnO nanoparticles with different surfactants areshown in Figure 4 It is clear that SDS and CTAB are notsuitable to produce ZnO nanoparticles because the productsare aggregated to make large particles of several hundredsnanometer In case of using PVP with 119877 = 09 (sample S6)we can see that these particles are well separated particleswith diameter of about 10 nm and length of 20ndash40 nm whilenanoparticles precipitated without using surfactants havespherical shape with diameter of 25ndash35 nm TEM images

4 ISRN Nanotechnology

320 360 400 440 480

(c)

(b)

Abso

rban

ce

Wavelength (nm)

(a)

(d)

Figure 5 Absorption spectrum of nanoparticle prepared withdifferent surfactants (a) CTAB (S4) (b) SDS (S3) (c) ZnO nanopar-ticles prepared without surfactant (S2) and (d) PVP (S6)

32 33 34 35 36 37 38

(d)

(c)

(b)

Energy (eV)

(a)

119864119892 = 341 eV

119864119892 = 34 eV

119864119892 = 333 eV

119864119892 = 335 eV

(120572ℎ)2

Figure 6 Plot of (119886ℎ120592)2 versus ℎ120592 of nanoparticle prepared withdifferent surfactants (a) CTAB (S4) (b) SDS (S3) (c) PVP (S6) and(d) without surfactant ZnO (S2)

obviously show that PVP is quite a good surfactant to reducethe size of ZnO nanoparticles

The absorption properties of ZnO nanoparticles precipi-tated in the absence of surfactant or in the presence of SDSCTAB and PVP have been also analyzed All absorptioncurves exhibit an intensive absorption in the range 200ndash370 nm with the absorption edge between 300 and 370 nmIt can be seen that there is a significant blue shift in theexcitonic absorption of the nanoparticles prepared in thepresence of PVP compared to that of the bulk ZnO (373 nm)The blue shift in the excitation absorption clearly indicatesthe quantum confinement property of nanoparticles In thequantum confinement range the band gap of the particlesincreases resulting in the shift of absorption edge to lowerwavelength as the particle size decreases All our foursamples (curves (a) to (d) Figure 5) exhibit excellent UV

30 40 50 60 70

(112

)

(103

)

(110

)

(102

)

(101

)(0

02)

Inte

nsity

(au

)

(100

)

119877 = 06 (S5)

119877 = 09 (S6)

119877 = 12 (S7)

Non capped sample (S1)

2120579 (deg)

Figure 7 X-ray diffraction patterns of ZnO nanosamples preparedwith different PVP concentrations

absorption capacity (Figure 9) and high transparency in thevisible range

From the plot of (120572ℎ120592)2 versus ℎ120592 in Figure 6 the bandgaps of our samples are estimated as 333 335 340 and341 eV for S3 S4 S2 and S6 samples respectively Thenthe average particle size in colloid can be obtained from theabsorption onset using the effectivemassmodel [6] where theband gap 119864

119892(in eV) can be approximated by

119864119892= 119864bulk119892+1205872ℎ2

21198901199032(1

119898lowast119890

+1

119898lowastℎ

) minus18119890

4120587120576120576119900119903

minus01241198903

ℎ2(4120587120576120576119900)2(1

119898lowast119890

+1

119898lowastℎ

)minus1

(3)

Due to small effective masses of ZnO (119898lowast119890= 026119898

119900

119898lowastℎ= 059119898

119900 120576 = 85 [6]) band gap enlargement gives

us the expected particle size of about 9 nm for nanoparticlesprepared without surfactant or in the presence of PVP whilein the presence of SDS CTAB the products do not show anyband gap enlargement These results imply that the particlesprecipitated in the presence of SDS and CTAB are so largethat it is not expected to observe any band gap enlargementin these samples

In order to further decrease the size of the nanoproductsvarious amounts of PVP were used to investigate the effectof this surfactant on the ZnO particle size and shape underthe same conditions of preparation Samples with differentZn2+PVP weight ratios (denoted as 119877) were prepared andchecked with X-ray diffraction absorbance and photolumi-nescence spectroscopy The X-ray diffraction patterns of thesamples with 119877 = 06 09 and 12 were shown in Figure 7All the patterns confirmed that the products were ZnO ofwurtzite structure As increasing the concentration of PVPthe width at half maximum of the diffraction lines in theX-ray patterns grows quickly which means that the particlesize is decreased under the increase of the surfactant PVP

ISRN Nanotechnology 5

The smallest value of the particle size is 9 nm attained when119877 = 06

The effect of PVP on ZnO nanoproduct was confirmeddirectly from the TEM image of the samples In Figure 8(a)119877was equal 06 and it can be seen clearly that the diameter andlength of particles are 8ndash10 nm and 35ndash45 nm respectivelyFigure 8 shows that when increasing the Zn2+PVP ratio(119877 = 12) the sizes of ZnO nanorods were increasedTheir diameters are up to 30ndash40 nm and the lengths areup to 60ndash70 nm The results demonstrate that PVP playsan important role in controlling the ZnO nanoproductsize and shape As the quantity of PVP increases the sizeof ZnO nanoparticle reduces by two or three times Thepreeminent advantages of PVP in reducing the particles sizeare understandable because PVP a bulky and highly chargedadsorbents serves as an ionic liquid which results in the so-called electrosteric stabilization The fact that PVP meets theconceptions of steric and electrostatic stabilization simulta-neously makes it a much better stabilizers than those whichonly have stabilization mechanism of steric or electrostatic[13]

Figure 10 shows the plots of (120572ℎ120592)2 versus ℎ120592 for colloidalZnO precipitated with different concentration of PVP Thelinear portion of the curves when extrapolating to 120572 = 0was an optical band gap value of the product In this studywe obtained the optical band gap of about 345 341 and338 eV at 119877 = 06 119877 = 09 and 119877 = 12 respectivelyThe obtained values of the band gap are larger than that ofbulk ZnO (330 eV) in [6] It is clear that the optical bandgap shifted to higher energy (blue shift) with increasing PVPconcentrations or decreasing the particle size

The photoluminescence spectra of the above sampleswere taken to study the influence of PVP on the opticalproperties of the nanoproducts The green band emission isattributed to the radiative recombination of photo-generatedhole with an electron belonging to a singly ionized vacancy inthe surface and subsurface The observation of strong greenband emission relative to bulk ZnO indicates the existence ofoxygen vacancies concentrated on nanoparticles surface Fornanomaterials the ratio surfacevolume is large and hence itis normal to observe a high green band compared with thepeak in the ultraviolet region

It is noted that in our samples compared with the sampleprepared without surfactant the ultraviolet peaks in thesamples using PVP as the surfactant become much moreevident On increasing the concentration of PVP the ZnOnanoparticles precipitated in the presence of PVP with 119877 =06 showed the highest ultraviolet emission and also thepeaks are blue shifted The increasing in the intensity ofthe ultraviolet compared with the visible band shows therole of PVP in passivating the trap states at the surface andreduces defects such as oxygen vacancies or Zn interstitialsThe blue shifts of these peaks (see the inset of Figure 11) areexplained by the reducing particle size as PVP concentrationreach higher value The fluorescence properties of the ZnOnanosamples prepared with PVP indicate that these samplesare of better quality than the samples prepared without usingsurfactants

50 nm

(a)

50 nm

(b)

50 nm

(c)

Figure 8 TEM images of ZnO nanoproducts with different valuesof 119877 (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c) 119877 = 12 (S7)

300 400 500 600 700 800

(c)

(b)

(a)

Abso

rptio

n

Wavelength (nm)

Figure 9 UV-vis spectra of the prepared ZnO with different valuesof 119877 (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c) 119877 = 12 (S7)

6 ISRN Nanotechnology

2 25 3 35 4 45

(c)

(b)

Energy (eV)

(a)119864119892 = 345 eV

119864119892 = 341 eV

119864119892 = 338 eV

(120572ℎ)2

Figure 10 Plots of (120572ℎ120592)2 versus ℎ120592 for ZnO nanopowder modifiedwith PVP at different 119877 values (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c)119877 = 12 (S7)

350 400 450 500 550 600

360 380 400 420

(c)

(d)

(b)

Inte

nsity

(au

)

Wavelength (nm)

(a)

Wavelength (nm)

(d)

(c)(b)(a)

Figure 11 Photoluminescence spectrum of ZnO nanoparticles (a)precipitated in the absence of surfactant (S2) and in the presence ofPVP with different values of 119877 (b) 119877 = 12 (S7) (c) 119877 = 09 (S6) (d)119877 = 06 (S5)

4 Conclusion

ZnO nanoparticles of different size and shape were success-fully fabricated by conventional and microwave methodThesample synthesis with the aid of microwave shows somepreeminent advantages compared with conventional methodand results in the formation of small ZnO nanoparticles ofuniform size and shape

Particle size of the ZnO nanoproducts prepared withmicrowave method can be further reduced by using surfac-tants Among the used surfactants PVP is the most suitableone The average diameter of the smallest ZnO particlesprepared with PVP is less than 10 nm with narrow sizedistribution The quantum confinement of the as produced

products was confirmed by the blue shift of the absorptionedge in the absorbance spectrum The increasing in the ratioof the intensity of ultravioletgreen peak in the photolumi-nescence spectra of these ZnO samples precipitated in thepresence of PVP shows that PVP not only reduces the particlesize but also the number of trap states at the surface of thenanoparticles

Acknowledgments

This work is completed with financial support by HanoiUniversity of Science Vietnam National university HanoiChina (Project TN 11 06) The authors of this paper wouldlike to thank the Center for Materials Science (CMS) Facultyof Physics College of Science VNU for permission to use itsequipments

References

[1] M R Vaezi and S K Sadrnezhaad ldquoNanopowder synthesis ofzinc oxide via solochemical processingrdquo Materials and Designvol 28 no 2 pp 515ndash519 2007

[2] Y J Kwon K H Kim C S Lim and K B Shim ldquoCharacter-ization of ZnO nanopowders synthesized by the polymerizedcomplex method via an organochemical routerdquo Journal ofCeramic Processing Research vol 3 no 3 pp 146ndash149 2002

[3] J G Lu Z Z Ye J Y Huang et al ldquoZnO quantum dotssynthesized by a vapor phase transport processrdquoApplied PhysicsLetters vol 88 no 6 Article ID 063110 3 pages 2006

[4] A D Yoffe ldquoLow-dimensional systems quantum size effectsand electronic properties of semiconductor microcrystallites(zero-dimensional systems) and some quasi-two-dimensionalsystemsrdquo Advances in Physics vol 51 no 2 pp 799ndash890 2002

[5] N F Hamedani and F Farzaneh ldquoSynthesis of nanocrystalswith hexagonal (wurtzite) structure in water using microwaveirradiationrdquo Journal of Science Islamic Republic of Iran vol 17article 231 2006

[6] Z Hu G Oskam and P C Searson ldquoInfluence of solvent on thegrowth of ZnO nanoparticlesrdquo Journal of Colloid and InterfaceScience vol 263 no 2 pp 454ndash460 2003

[7] B D Cullity Elements of X-Ray Diffractions Edition-WesleyReading Mass USA 1978

[8] G Glaspell P Dutta andAManivannan ldquoA room-temperatureandmicrowave synthesis of M-doped ZnO (M=Co Cr Fe Mnamp Ni)rdquo Journal of Cluster Science vol 16 no 4 pp 523ndash5362005

[9] N V Tuyen N N Long T T Q Hoa et al ldquoIndium-dopedzinc oxide nanometre thick disks synthesised by a vapour-phasetransport processrdquo Journal of Experimental Nanoscience vol 4no 3 pp 243ndash252 2009

[10] M Kooti and A Naghdi Sedeh ldquoMicrowave-assisted combus-tion synthesis of ZnO nanoparticlesrdquo Journal of Chemistry vol2013 Article ID 562028 4 pages 2013

[11] D K Bhat ldquoFacile synthesis of ZnO nanorods by microwaveirradiation of zinc-hydrazine hydrate complexrdquo NanoscaleResearch Letters vol 3 pp 31ndash35 2008

[12] S Cho S-H Jung and K-H Lee ldquoMorphology-controlledgrowth of ZnO nanostructures using microwave irradiationfrom basic to complex structuresrdquo The Journal of PhysicalChemistry C vol 112 pp 12769ndash12776 2008

ISRN Nanotechnology 7

[13] G Z Cao Nanostructures and Nanomaterials Synthesis Prop-erties and Applications Imperial College Press London UK2004

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Page 2: A Quick Process for Synthesis of ZnO Nanoparticles with ...downloads.hindawi.com/journals/isrn.nanotechnology/... · 2 ISRNNanotechnology N2gas Cooling water Figure1:Imageofmicrowaveirradiationsystem

2 ISRN Nanotechnology

N2 gas

Cooling water

Figure 1 Image of microwave irradiation system

CH3COONa was removed by washing the sample with

absolute ethanol and distilled water for several times

Zn (CH3COO)2 +NaOH 997888rarr Zn (CH3COO) (OH)

+NaCH3COO(1)

Zn (CH3COO)OH +NaOH 997888rarr ZnO

+NaCH3COO +H

2O(2)

The washing process was repeated until the pH of thesolution was 7 Finally the product was dried to obtain ZnOnanopowder

Some different surfactants were also used to studytheir influence on the morphology and properties of thenanoproducts In case of using surfactants the weight ratiosZn2+surfactant was denoted as 119877 The as-prepared sampleswere summarized in Table 1

The particle morphologies and structures of the productswere investigated by a transmission electron microscope(TEM JEM 1010-JEOL) and X-ray diffractometer (Bruker-AXSD5005) Photoluminescence (PL) measurement at roomtemperature was carried out on a 325 nmHe-Cd laser A UV-vis spectrophotometer PU 8700 was used to record the UV-visible absorption spectra

3 Results and Discussion

Figure 2 is the powder X-ray diffraction patterns of theZnO nanoproducts prepared by two different heating pro-cesses The diffraction patterns and interplane spacings canbe well matched to the standard diffraction pattern ofwurtzite ZnO demonstrating the formation of wurtzite ZnOnanocrystals The particle diameter 119889 was calculated usingthe Debye Scherer formula [7] The (100) peak at 318∘ inFigure 2 gives the ZnO particle diameters of 32 18 nm forZnO nanoparticles prepared by conventional (sample 1) and

20 25 30 35 40 45 50 55 60 65 70

(112

)

(103

)

(110

)

(102

)

(101

)(0

02)

(b)

(a)

Inte

nsity

(au

)

(100

)

2120579 (deg)

Figure 2 X-ray diffraction patterns sample 1 (a) and sample 2 (b)

microwave assisted heating (sample 2) process respectivelyIt appears that the ZnO nanoparticles prepared with differentheating process have different sizes due to the influence oftemperature gradient and reaction time

Figure 3 shows the TEM images of ZnO nanoparticlesprepared by normal and microwave irradiation assistedheating process It is clearly seen that ordinary heating byelectric cooker leads to the formation of aggregated clustersof particles of which size distribution is quite large while thenanoparticles obtained from reactions in microwave irradi-ation field have small size of only several tens nanometerFurthermore these particles are much more uniform insize and shape compared with the products of conventionalmethod The effectiveness of microwave irradiation in thepreparation of nanoparticles can be explained by the preem-inent advantages of microwave as a means of heating Themechanism of traditional heating process is conductive heator heating by convection currents and hence this is a slowand energy inefficient process due to the energy lost at thewall of the vessel Normally the wall of the vessel absorbsheat first then heat is transferred to the liquid inside so thetemperature on the outside surface needs to be in excess of theboiling point of liquid for the temperature inside the liquidvolume to reach boiling point These disadvantages can beovercome easily by applying microwave technique becausewhen heating with microwave vessel wall is transparent toMW and solventreagent absorbs MW energy directly Thedirect in-core heating and instant on-off pulse of heat leadsto the formation of a homogenous temperature gradient andreduces the reaction time These advances in turn producesmaller particles of uniform size and shape

ZnO nanoparticles have been successfully fabricated bymicrowave irradiationmethod However after the nucleationand growth process are completed the average size ofthe particles continues to increase due to diffusion limitedcoarseningThis process reduces the quality of ZnOnanopar-ticles so restraining the particles from coarsening is a veryimportant quest We have investigated the influence of somesurfactants such as SDS CTAB and PVP on the growth of

ISRN Nanotechnology 3

Table 1 Some preparation parameters of the as-prepared sample

Sample Sample preparation method Used surfactant Morphology and size(estimated from TEM image)

S1 Normal heating No gt100 nm

S2 Microwave irradiation No Quasi-sphericalDiameter 20ndash40 nm

S3 Microwave irradiation Sodium dodecyl sulphate (SDS)119877 = 09

gt100 nm

S4 Microwave irradiationHexadecylcetyltrimethylammonium bromide

(CTAB)119877 = 09

gt100 nm

S5 Microwave irradiation Polyvinylpyrrolidone (PVP)119877 = 06

Quasi-sphericalDiameter 10ndash15 nm

S6 Microwave irradiation Polyvinylpyrrolidone119877 = 09

RodDiameter 10ndash15 nmLength 30ndash50 nm

S7 Microwave irradiation Polyvinylpyrrolidone119877 = 12

RodDiameter 20ndash30 nmLength 40ndash50 nm

200 nm

(a)

40 nm

301 nm216 nm

(b)

Figure 3 TEM images of sample 1 (a) and sample 2 (b)

ZnO nanoparticlesThese surfactants were dissolved into thesolution of sodium hydroxide before the reaction with zincsalt PVP reveals to be the most suitable surfactant to prepareZnO nanoparticles with small size and homogenous shape

500 nm

(a)

500 nm

(b)

100 nm

(c)

100 nm

(d)

Figure 4 TEM images of ZnO nanoparticles precipitated in thepresence of different surfactants (a) CTAB (S4) (b) SDS (S3) (c)PVP (S6) (d) nanoparticles precipitated in the absence of surfactant(S2)

The surfactant on the surface of ZnO plays two rolesfirstly it helps to reduce the defects in nanocrystals dur-ing nucleation and secondly it attaches to the surface ofnanoparticles so as to affect on the size of the particles TEMimages of ZnO nanoparticles with different surfactants areshown in Figure 4 It is clear that SDS and CTAB are notsuitable to produce ZnO nanoparticles because the productsare aggregated to make large particles of several hundredsnanometer In case of using PVP with 119877 = 09 (sample S6)we can see that these particles are well separated particleswith diameter of about 10 nm and length of 20ndash40 nm whilenanoparticles precipitated without using surfactants havespherical shape with diameter of 25ndash35 nm TEM images

4 ISRN Nanotechnology

320 360 400 440 480

(c)

(b)

Abso

rban

ce

Wavelength (nm)

(a)

(d)

Figure 5 Absorption spectrum of nanoparticle prepared withdifferent surfactants (a) CTAB (S4) (b) SDS (S3) (c) ZnO nanopar-ticles prepared without surfactant (S2) and (d) PVP (S6)

32 33 34 35 36 37 38

(d)

(c)

(b)

Energy (eV)

(a)

119864119892 = 341 eV

119864119892 = 34 eV

119864119892 = 333 eV

119864119892 = 335 eV

(120572ℎ)2

Figure 6 Plot of (119886ℎ120592)2 versus ℎ120592 of nanoparticle prepared withdifferent surfactants (a) CTAB (S4) (b) SDS (S3) (c) PVP (S6) and(d) without surfactant ZnO (S2)

obviously show that PVP is quite a good surfactant to reducethe size of ZnO nanoparticles

The absorption properties of ZnO nanoparticles precipi-tated in the absence of surfactant or in the presence of SDSCTAB and PVP have been also analyzed All absorptioncurves exhibit an intensive absorption in the range 200ndash370 nm with the absorption edge between 300 and 370 nmIt can be seen that there is a significant blue shift in theexcitonic absorption of the nanoparticles prepared in thepresence of PVP compared to that of the bulk ZnO (373 nm)The blue shift in the excitation absorption clearly indicatesthe quantum confinement property of nanoparticles In thequantum confinement range the band gap of the particlesincreases resulting in the shift of absorption edge to lowerwavelength as the particle size decreases All our foursamples (curves (a) to (d) Figure 5) exhibit excellent UV

30 40 50 60 70

(112

)

(103

)

(110

)

(102

)

(101

)(0

02)

Inte

nsity

(au

)

(100

)

119877 = 06 (S5)

119877 = 09 (S6)

119877 = 12 (S7)

Non capped sample (S1)

2120579 (deg)

Figure 7 X-ray diffraction patterns of ZnO nanosamples preparedwith different PVP concentrations

absorption capacity (Figure 9) and high transparency in thevisible range

From the plot of (120572ℎ120592)2 versus ℎ120592 in Figure 6 the bandgaps of our samples are estimated as 333 335 340 and341 eV for S3 S4 S2 and S6 samples respectively Thenthe average particle size in colloid can be obtained from theabsorption onset using the effectivemassmodel [6] where theband gap 119864

119892(in eV) can be approximated by

119864119892= 119864bulk119892+1205872ℎ2

21198901199032(1

119898lowast119890

+1

119898lowastℎ

) minus18119890

4120587120576120576119900119903

minus01241198903

ℎ2(4120587120576120576119900)2(1

119898lowast119890

+1

119898lowastℎ

)minus1

(3)

Due to small effective masses of ZnO (119898lowast119890= 026119898

119900

119898lowastℎ= 059119898

119900 120576 = 85 [6]) band gap enlargement gives

us the expected particle size of about 9 nm for nanoparticlesprepared without surfactant or in the presence of PVP whilein the presence of SDS CTAB the products do not show anyband gap enlargement These results imply that the particlesprecipitated in the presence of SDS and CTAB are so largethat it is not expected to observe any band gap enlargementin these samples

In order to further decrease the size of the nanoproductsvarious amounts of PVP were used to investigate the effectof this surfactant on the ZnO particle size and shape underthe same conditions of preparation Samples with differentZn2+PVP weight ratios (denoted as 119877) were prepared andchecked with X-ray diffraction absorbance and photolumi-nescence spectroscopy The X-ray diffraction patterns of thesamples with 119877 = 06 09 and 12 were shown in Figure 7All the patterns confirmed that the products were ZnO ofwurtzite structure As increasing the concentration of PVPthe width at half maximum of the diffraction lines in theX-ray patterns grows quickly which means that the particlesize is decreased under the increase of the surfactant PVP

ISRN Nanotechnology 5

The smallest value of the particle size is 9 nm attained when119877 = 06

The effect of PVP on ZnO nanoproduct was confirmeddirectly from the TEM image of the samples In Figure 8(a)119877was equal 06 and it can be seen clearly that the diameter andlength of particles are 8ndash10 nm and 35ndash45 nm respectivelyFigure 8 shows that when increasing the Zn2+PVP ratio(119877 = 12) the sizes of ZnO nanorods were increasedTheir diameters are up to 30ndash40 nm and the lengths areup to 60ndash70 nm The results demonstrate that PVP playsan important role in controlling the ZnO nanoproductsize and shape As the quantity of PVP increases the sizeof ZnO nanoparticle reduces by two or three times Thepreeminent advantages of PVP in reducing the particles sizeare understandable because PVP a bulky and highly chargedadsorbents serves as an ionic liquid which results in the so-called electrosteric stabilization The fact that PVP meets theconceptions of steric and electrostatic stabilization simulta-neously makes it a much better stabilizers than those whichonly have stabilization mechanism of steric or electrostatic[13]

Figure 10 shows the plots of (120572ℎ120592)2 versus ℎ120592 for colloidalZnO precipitated with different concentration of PVP Thelinear portion of the curves when extrapolating to 120572 = 0was an optical band gap value of the product In this studywe obtained the optical band gap of about 345 341 and338 eV at 119877 = 06 119877 = 09 and 119877 = 12 respectivelyThe obtained values of the band gap are larger than that ofbulk ZnO (330 eV) in [6] It is clear that the optical bandgap shifted to higher energy (blue shift) with increasing PVPconcentrations or decreasing the particle size

The photoluminescence spectra of the above sampleswere taken to study the influence of PVP on the opticalproperties of the nanoproducts The green band emission isattributed to the radiative recombination of photo-generatedhole with an electron belonging to a singly ionized vacancy inthe surface and subsurface The observation of strong greenband emission relative to bulk ZnO indicates the existence ofoxygen vacancies concentrated on nanoparticles surface Fornanomaterials the ratio surfacevolume is large and hence itis normal to observe a high green band compared with thepeak in the ultraviolet region

It is noted that in our samples compared with the sampleprepared without surfactant the ultraviolet peaks in thesamples using PVP as the surfactant become much moreevident On increasing the concentration of PVP the ZnOnanoparticles precipitated in the presence of PVP with 119877 =06 showed the highest ultraviolet emission and also thepeaks are blue shifted The increasing in the intensity ofthe ultraviolet compared with the visible band shows therole of PVP in passivating the trap states at the surface andreduces defects such as oxygen vacancies or Zn interstitialsThe blue shifts of these peaks (see the inset of Figure 11) areexplained by the reducing particle size as PVP concentrationreach higher value The fluorescence properties of the ZnOnanosamples prepared with PVP indicate that these samplesare of better quality than the samples prepared without usingsurfactants

50 nm

(a)

50 nm

(b)

50 nm

(c)

Figure 8 TEM images of ZnO nanoproducts with different valuesof 119877 (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c) 119877 = 12 (S7)

300 400 500 600 700 800

(c)

(b)

(a)

Abso

rptio

n

Wavelength (nm)

Figure 9 UV-vis spectra of the prepared ZnO with different valuesof 119877 (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c) 119877 = 12 (S7)

6 ISRN Nanotechnology

2 25 3 35 4 45

(c)

(b)

Energy (eV)

(a)119864119892 = 345 eV

119864119892 = 341 eV

119864119892 = 338 eV

(120572ℎ)2

Figure 10 Plots of (120572ℎ120592)2 versus ℎ120592 for ZnO nanopowder modifiedwith PVP at different 119877 values (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c)119877 = 12 (S7)

350 400 450 500 550 600

360 380 400 420

(c)

(d)

(b)

Inte

nsity

(au

)

Wavelength (nm)

(a)

Wavelength (nm)

(d)

(c)(b)(a)

Figure 11 Photoluminescence spectrum of ZnO nanoparticles (a)precipitated in the absence of surfactant (S2) and in the presence ofPVP with different values of 119877 (b) 119877 = 12 (S7) (c) 119877 = 09 (S6) (d)119877 = 06 (S5)

4 Conclusion

ZnO nanoparticles of different size and shape were success-fully fabricated by conventional and microwave methodThesample synthesis with the aid of microwave shows somepreeminent advantages compared with conventional methodand results in the formation of small ZnO nanoparticles ofuniform size and shape

Particle size of the ZnO nanoproducts prepared withmicrowave method can be further reduced by using surfac-tants Among the used surfactants PVP is the most suitableone The average diameter of the smallest ZnO particlesprepared with PVP is less than 10 nm with narrow sizedistribution The quantum confinement of the as produced

products was confirmed by the blue shift of the absorptionedge in the absorbance spectrum The increasing in the ratioof the intensity of ultravioletgreen peak in the photolumi-nescence spectra of these ZnO samples precipitated in thepresence of PVP shows that PVP not only reduces the particlesize but also the number of trap states at the surface of thenanoparticles

Acknowledgments

This work is completed with financial support by HanoiUniversity of Science Vietnam National university HanoiChina (Project TN 11 06) The authors of this paper wouldlike to thank the Center for Materials Science (CMS) Facultyof Physics College of Science VNU for permission to use itsequipments

References

[1] M R Vaezi and S K Sadrnezhaad ldquoNanopowder synthesis ofzinc oxide via solochemical processingrdquo Materials and Designvol 28 no 2 pp 515ndash519 2007

[2] Y J Kwon K H Kim C S Lim and K B Shim ldquoCharacter-ization of ZnO nanopowders synthesized by the polymerizedcomplex method via an organochemical routerdquo Journal ofCeramic Processing Research vol 3 no 3 pp 146ndash149 2002

[3] J G Lu Z Z Ye J Y Huang et al ldquoZnO quantum dotssynthesized by a vapor phase transport processrdquoApplied PhysicsLetters vol 88 no 6 Article ID 063110 3 pages 2006

[4] A D Yoffe ldquoLow-dimensional systems quantum size effectsand electronic properties of semiconductor microcrystallites(zero-dimensional systems) and some quasi-two-dimensionalsystemsrdquo Advances in Physics vol 51 no 2 pp 799ndash890 2002

[5] N F Hamedani and F Farzaneh ldquoSynthesis of nanocrystalswith hexagonal (wurtzite) structure in water using microwaveirradiationrdquo Journal of Science Islamic Republic of Iran vol 17article 231 2006

[6] Z Hu G Oskam and P C Searson ldquoInfluence of solvent on thegrowth of ZnO nanoparticlesrdquo Journal of Colloid and InterfaceScience vol 263 no 2 pp 454ndash460 2003

[7] B D Cullity Elements of X-Ray Diffractions Edition-WesleyReading Mass USA 1978

[8] G Glaspell P Dutta andAManivannan ldquoA room-temperatureandmicrowave synthesis of M-doped ZnO (M=Co Cr Fe Mnamp Ni)rdquo Journal of Cluster Science vol 16 no 4 pp 523ndash5362005

[9] N V Tuyen N N Long T T Q Hoa et al ldquoIndium-dopedzinc oxide nanometre thick disks synthesised by a vapour-phasetransport processrdquo Journal of Experimental Nanoscience vol 4no 3 pp 243ndash252 2009

[10] M Kooti and A Naghdi Sedeh ldquoMicrowave-assisted combus-tion synthesis of ZnO nanoparticlesrdquo Journal of Chemistry vol2013 Article ID 562028 4 pages 2013

[11] D K Bhat ldquoFacile synthesis of ZnO nanorods by microwaveirradiation of zinc-hydrazine hydrate complexrdquo NanoscaleResearch Letters vol 3 pp 31ndash35 2008

[12] S Cho S-H Jung and K-H Lee ldquoMorphology-controlledgrowth of ZnO nanostructures using microwave irradiationfrom basic to complex structuresrdquo The Journal of PhysicalChemistry C vol 112 pp 12769ndash12776 2008

ISRN Nanotechnology 7

[13] G Z Cao Nanostructures and Nanomaterials Synthesis Prop-erties and Applications Imperial College Press London UK2004

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

CrystallographyJournal of

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

MaterialsJournal of

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Page 3: A Quick Process for Synthesis of ZnO Nanoparticles with ...downloads.hindawi.com/journals/isrn.nanotechnology/... · 2 ISRNNanotechnology N2gas Cooling water Figure1:Imageofmicrowaveirradiationsystem

ISRN Nanotechnology 3

Table 1 Some preparation parameters of the as-prepared sample

Sample Sample preparation method Used surfactant Morphology and size(estimated from TEM image)

S1 Normal heating No gt100 nm

S2 Microwave irradiation No Quasi-sphericalDiameter 20ndash40 nm

S3 Microwave irradiation Sodium dodecyl sulphate (SDS)119877 = 09

gt100 nm

S4 Microwave irradiationHexadecylcetyltrimethylammonium bromide

(CTAB)119877 = 09

gt100 nm

S5 Microwave irradiation Polyvinylpyrrolidone (PVP)119877 = 06

Quasi-sphericalDiameter 10ndash15 nm

S6 Microwave irradiation Polyvinylpyrrolidone119877 = 09

RodDiameter 10ndash15 nmLength 30ndash50 nm

S7 Microwave irradiation Polyvinylpyrrolidone119877 = 12

RodDiameter 20ndash30 nmLength 40ndash50 nm

200 nm

(a)

40 nm

301 nm216 nm

(b)

Figure 3 TEM images of sample 1 (a) and sample 2 (b)

ZnO nanoparticlesThese surfactants were dissolved into thesolution of sodium hydroxide before the reaction with zincsalt PVP reveals to be the most suitable surfactant to prepareZnO nanoparticles with small size and homogenous shape

500 nm

(a)

500 nm

(b)

100 nm

(c)

100 nm

(d)

Figure 4 TEM images of ZnO nanoparticles precipitated in thepresence of different surfactants (a) CTAB (S4) (b) SDS (S3) (c)PVP (S6) (d) nanoparticles precipitated in the absence of surfactant(S2)

The surfactant on the surface of ZnO plays two rolesfirstly it helps to reduce the defects in nanocrystals dur-ing nucleation and secondly it attaches to the surface ofnanoparticles so as to affect on the size of the particles TEMimages of ZnO nanoparticles with different surfactants areshown in Figure 4 It is clear that SDS and CTAB are notsuitable to produce ZnO nanoparticles because the productsare aggregated to make large particles of several hundredsnanometer In case of using PVP with 119877 = 09 (sample S6)we can see that these particles are well separated particleswith diameter of about 10 nm and length of 20ndash40 nm whilenanoparticles precipitated without using surfactants havespherical shape with diameter of 25ndash35 nm TEM images

4 ISRN Nanotechnology

320 360 400 440 480

(c)

(b)

Abso

rban

ce

Wavelength (nm)

(a)

(d)

Figure 5 Absorption spectrum of nanoparticle prepared withdifferent surfactants (a) CTAB (S4) (b) SDS (S3) (c) ZnO nanopar-ticles prepared without surfactant (S2) and (d) PVP (S6)

32 33 34 35 36 37 38

(d)

(c)

(b)

Energy (eV)

(a)

119864119892 = 341 eV

119864119892 = 34 eV

119864119892 = 333 eV

119864119892 = 335 eV

(120572ℎ)2

Figure 6 Plot of (119886ℎ120592)2 versus ℎ120592 of nanoparticle prepared withdifferent surfactants (a) CTAB (S4) (b) SDS (S3) (c) PVP (S6) and(d) without surfactant ZnO (S2)

obviously show that PVP is quite a good surfactant to reducethe size of ZnO nanoparticles

The absorption properties of ZnO nanoparticles precipi-tated in the absence of surfactant or in the presence of SDSCTAB and PVP have been also analyzed All absorptioncurves exhibit an intensive absorption in the range 200ndash370 nm with the absorption edge between 300 and 370 nmIt can be seen that there is a significant blue shift in theexcitonic absorption of the nanoparticles prepared in thepresence of PVP compared to that of the bulk ZnO (373 nm)The blue shift in the excitation absorption clearly indicatesthe quantum confinement property of nanoparticles In thequantum confinement range the band gap of the particlesincreases resulting in the shift of absorption edge to lowerwavelength as the particle size decreases All our foursamples (curves (a) to (d) Figure 5) exhibit excellent UV

30 40 50 60 70

(112

)

(103

)

(110

)

(102

)

(101

)(0

02)

Inte

nsity

(au

)

(100

)

119877 = 06 (S5)

119877 = 09 (S6)

119877 = 12 (S7)

Non capped sample (S1)

2120579 (deg)

Figure 7 X-ray diffraction patterns of ZnO nanosamples preparedwith different PVP concentrations

absorption capacity (Figure 9) and high transparency in thevisible range

From the plot of (120572ℎ120592)2 versus ℎ120592 in Figure 6 the bandgaps of our samples are estimated as 333 335 340 and341 eV for S3 S4 S2 and S6 samples respectively Thenthe average particle size in colloid can be obtained from theabsorption onset using the effectivemassmodel [6] where theband gap 119864

119892(in eV) can be approximated by

119864119892= 119864bulk119892+1205872ℎ2

21198901199032(1

119898lowast119890

+1

119898lowastℎ

) minus18119890

4120587120576120576119900119903

minus01241198903

ℎ2(4120587120576120576119900)2(1

119898lowast119890

+1

119898lowastℎ

)minus1

(3)

Due to small effective masses of ZnO (119898lowast119890= 026119898

119900

119898lowastℎ= 059119898

119900 120576 = 85 [6]) band gap enlargement gives

us the expected particle size of about 9 nm for nanoparticlesprepared without surfactant or in the presence of PVP whilein the presence of SDS CTAB the products do not show anyband gap enlargement These results imply that the particlesprecipitated in the presence of SDS and CTAB are so largethat it is not expected to observe any band gap enlargementin these samples

In order to further decrease the size of the nanoproductsvarious amounts of PVP were used to investigate the effectof this surfactant on the ZnO particle size and shape underthe same conditions of preparation Samples with differentZn2+PVP weight ratios (denoted as 119877) were prepared andchecked with X-ray diffraction absorbance and photolumi-nescence spectroscopy The X-ray diffraction patterns of thesamples with 119877 = 06 09 and 12 were shown in Figure 7All the patterns confirmed that the products were ZnO ofwurtzite structure As increasing the concentration of PVPthe width at half maximum of the diffraction lines in theX-ray patterns grows quickly which means that the particlesize is decreased under the increase of the surfactant PVP

ISRN Nanotechnology 5

The smallest value of the particle size is 9 nm attained when119877 = 06

The effect of PVP on ZnO nanoproduct was confirmeddirectly from the TEM image of the samples In Figure 8(a)119877was equal 06 and it can be seen clearly that the diameter andlength of particles are 8ndash10 nm and 35ndash45 nm respectivelyFigure 8 shows that when increasing the Zn2+PVP ratio(119877 = 12) the sizes of ZnO nanorods were increasedTheir diameters are up to 30ndash40 nm and the lengths areup to 60ndash70 nm The results demonstrate that PVP playsan important role in controlling the ZnO nanoproductsize and shape As the quantity of PVP increases the sizeof ZnO nanoparticle reduces by two or three times Thepreeminent advantages of PVP in reducing the particles sizeare understandable because PVP a bulky and highly chargedadsorbents serves as an ionic liquid which results in the so-called electrosteric stabilization The fact that PVP meets theconceptions of steric and electrostatic stabilization simulta-neously makes it a much better stabilizers than those whichonly have stabilization mechanism of steric or electrostatic[13]

Figure 10 shows the plots of (120572ℎ120592)2 versus ℎ120592 for colloidalZnO precipitated with different concentration of PVP Thelinear portion of the curves when extrapolating to 120572 = 0was an optical band gap value of the product In this studywe obtained the optical band gap of about 345 341 and338 eV at 119877 = 06 119877 = 09 and 119877 = 12 respectivelyThe obtained values of the band gap are larger than that ofbulk ZnO (330 eV) in [6] It is clear that the optical bandgap shifted to higher energy (blue shift) with increasing PVPconcentrations or decreasing the particle size

The photoluminescence spectra of the above sampleswere taken to study the influence of PVP on the opticalproperties of the nanoproducts The green band emission isattributed to the radiative recombination of photo-generatedhole with an electron belonging to a singly ionized vacancy inthe surface and subsurface The observation of strong greenband emission relative to bulk ZnO indicates the existence ofoxygen vacancies concentrated on nanoparticles surface Fornanomaterials the ratio surfacevolume is large and hence itis normal to observe a high green band compared with thepeak in the ultraviolet region

It is noted that in our samples compared with the sampleprepared without surfactant the ultraviolet peaks in thesamples using PVP as the surfactant become much moreevident On increasing the concentration of PVP the ZnOnanoparticles precipitated in the presence of PVP with 119877 =06 showed the highest ultraviolet emission and also thepeaks are blue shifted The increasing in the intensity ofthe ultraviolet compared with the visible band shows therole of PVP in passivating the trap states at the surface andreduces defects such as oxygen vacancies or Zn interstitialsThe blue shifts of these peaks (see the inset of Figure 11) areexplained by the reducing particle size as PVP concentrationreach higher value The fluorescence properties of the ZnOnanosamples prepared with PVP indicate that these samplesare of better quality than the samples prepared without usingsurfactants

50 nm

(a)

50 nm

(b)

50 nm

(c)

Figure 8 TEM images of ZnO nanoproducts with different valuesof 119877 (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c) 119877 = 12 (S7)

300 400 500 600 700 800

(c)

(b)

(a)

Abso

rptio

n

Wavelength (nm)

Figure 9 UV-vis spectra of the prepared ZnO with different valuesof 119877 (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c) 119877 = 12 (S7)

6 ISRN Nanotechnology

2 25 3 35 4 45

(c)

(b)

Energy (eV)

(a)119864119892 = 345 eV

119864119892 = 341 eV

119864119892 = 338 eV

(120572ℎ)2

Figure 10 Plots of (120572ℎ120592)2 versus ℎ120592 for ZnO nanopowder modifiedwith PVP at different 119877 values (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c)119877 = 12 (S7)

350 400 450 500 550 600

360 380 400 420

(c)

(d)

(b)

Inte

nsity

(au

)

Wavelength (nm)

(a)

Wavelength (nm)

(d)

(c)(b)(a)

Figure 11 Photoluminescence spectrum of ZnO nanoparticles (a)precipitated in the absence of surfactant (S2) and in the presence ofPVP with different values of 119877 (b) 119877 = 12 (S7) (c) 119877 = 09 (S6) (d)119877 = 06 (S5)

4 Conclusion

ZnO nanoparticles of different size and shape were success-fully fabricated by conventional and microwave methodThesample synthesis with the aid of microwave shows somepreeminent advantages compared with conventional methodand results in the formation of small ZnO nanoparticles ofuniform size and shape

Particle size of the ZnO nanoproducts prepared withmicrowave method can be further reduced by using surfac-tants Among the used surfactants PVP is the most suitableone The average diameter of the smallest ZnO particlesprepared with PVP is less than 10 nm with narrow sizedistribution The quantum confinement of the as produced

products was confirmed by the blue shift of the absorptionedge in the absorbance spectrum The increasing in the ratioof the intensity of ultravioletgreen peak in the photolumi-nescence spectra of these ZnO samples precipitated in thepresence of PVP shows that PVP not only reduces the particlesize but also the number of trap states at the surface of thenanoparticles

Acknowledgments

This work is completed with financial support by HanoiUniversity of Science Vietnam National university HanoiChina (Project TN 11 06) The authors of this paper wouldlike to thank the Center for Materials Science (CMS) Facultyof Physics College of Science VNU for permission to use itsequipments

References

[1] M R Vaezi and S K Sadrnezhaad ldquoNanopowder synthesis ofzinc oxide via solochemical processingrdquo Materials and Designvol 28 no 2 pp 515ndash519 2007

[2] Y J Kwon K H Kim C S Lim and K B Shim ldquoCharacter-ization of ZnO nanopowders synthesized by the polymerizedcomplex method via an organochemical routerdquo Journal ofCeramic Processing Research vol 3 no 3 pp 146ndash149 2002

[3] J G Lu Z Z Ye J Y Huang et al ldquoZnO quantum dotssynthesized by a vapor phase transport processrdquoApplied PhysicsLetters vol 88 no 6 Article ID 063110 3 pages 2006

[4] A D Yoffe ldquoLow-dimensional systems quantum size effectsand electronic properties of semiconductor microcrystallites(zero-dimensional systems) and some quasi-two-dimensionalsystemsrdquo Advances in Physics vol 51 no 2 pp 799ndash890 2002

[5] N F Hamedani and F Farzaneh ldquoSynthesis of nanocrystalswith hexagonal (wurtzite) structure in water using microwaveirradiationrdquo Journal of Science Islamic Republic of Iran vol 17article 231 2006

[6] Z Hu G Oskam and P C Searson ldquoInfluence of solvent on thegrowth of ZnO nanoparticlesrdquo Journal of Colloid and InterfaceScience vol 263 no 2 pp 454ndash460 2003

[7] B D Cullity Elements of X-Ray Diffractions Edition-WesleyReading Mass USA 1978

[8] G Glaspell P Dutta andAManivannan ldquoA room-temperatureandmicrowave synthesis of M-doped ZnO (M=Co Cr Fe Mnamp Ni)rdquo Journal of Cluster Science vol 16 no 4 pp 523ndash5362005

[9] N V Tuyen N N Long T T Q Hoa et al ldquoIndium-dopedzinc oxide nanometre thick disks synthesised by a vapour-phasetransport processrdquo Journal of Experimental Nanoscience vol 4no 3 pp 243ndash252 2009

[10] M Kooti and A Naghdi Sedeh ldquoMicrowave-assisted combus-tion synthesis of ZnO nanoparticlesrdquo Journal of Chemistry vol2013 Article ID 562028 4 pages 2013

[11] D K Bhat ldquoFacile synthesis of ZnO nanorods by microwaveirradiation of zinc-hydrazine hydrate complexrdquo NanoscaleResearch Letters vol 3 pp 31ndash35 2008

[12] S Cho S-H Jung and K-H Lee ldquoMorphology-controlledgrowth of ZnO nanostructures using microwave irradiationfrom basic to complex structuresrdquo The Journal of PhysicalChemistry C vol 112 pp 12769ndash12776 2008

ISRN Nanotechnology 7

[13] G Z Cao Nanostructures and Nanomaterials Synthesis Prop-erties and Applications Imperial College Press London UK2004

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

CrystallographyJournal of

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

MaterialsJournal of

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Page 4: A Quick Process for Synthesis of ZnO Nanoparticles with ...downloads.hindawi.com/journals/isrn.nanotechnology/... · 2 ISRNNanotechnology N2gas Cooling water Figure1:Imageofmicrowaveirradiationsystem

4 ISRN Nanotechnology

320 360 400 440 480

(c)

(b)

Abso

rban

ce

Wavelength (nm)

(a)

(d)

Figure 5 Absorption spectrum of nanoparticle prepared withdifferent surfactants (a) CTAB (S4) (b) SDS (S3) (c) ZnO nanopar-ticles prepared without surfactant (S2) and (d) PVP (S6)

32 33 34 35 36 37 38

(d)

(c)

(b)

Energy (eV)

(a)

119864119892 = 341 eV

119864119892 = 34 eV

119864119892 = 333 eV

119864119892 = 335 eV

(120572ℎ)2

Figure 6 Plot of (119886ℎ120592)2 versus ℎ120592 of nanoparticle prepared withdifferent surfactants (a) CTAB (S4) (b) SDS (S3) (c) PVP (S6) and(d) without surfactant ZnO (S2)

obviously show that PVP is quite a good surfactant to reducethe size of ZnO nanoparticles

The absorption properties of ZnO nanoparticles precipi-tated in the absence of surfactant or in the presence of SDSCTAB and PVP have been also analyzed All absorptioncurves exhibit an intensive absorption in the range 200ndash370 nm with the absorption edge between 300 and 370 nmIt can be seen that there is a significant blue shift in theexcitonic absorption of the nanoparticles prepared in thepresence of PVP compared to that of the bulk ZnO (373 nm)The blue shift in the excitation absorption clearly indicatesthe quantum confinement property of nanoparticles In thequantum confinement range the band gap of the particlesincreases resulting in the shift of absorption edge to lowerwavelength as the particle size decreases All our foursamples (curves (a) to (d) Figure 5) exhibit excellent UV

30 40 50 60 70

(112

)

(103

)

(110

)

(102

)

(101

)(0

02)

Inte

nsity

(au

)

(100

)

119877 = 06 (S5)

119877 = 09 (S6)

119877 = 12 (S7)

Non capped sample (S1)

2120579 (deg)

Figure 7 X-ray diffraction patterns of ZnO nanosamples preparedwith different PVP concentrations

absorption capacity (Figure 9) and high transparency in thevisible range

From the plot of (120572ℎ120592)2 versus ℎ120592 in Figure 6 the bandgaps of our samples are estimated as 333 335 340 and341 eV for S3 S4 S2 and S6 samples respectively Thenthe average particle size in colloid can be obtained from theabsorption onset using the effectivemassmodel [6] where theband gap 119864

119892(in eV) can be approximated by

119864119892= 119864bulk119892+1205872ℎ2

21198901199032(1

119898lowast119890

+1

119898lowastℎ

) minus18119890

4120587120576120576119900119903

minus01241198903

ℎ2(4120587120576120576119900)2(1

119898lowast119890

+1

119898lowastℎ

)minus1

(3)

Due to small effective masses of ZnO (119898lowast119890= 026119898

119900

119898lowastℎ= 059119898

119900 120576 = 85 [6]) band gap enlargement gives

us the expected particle size of about 9 nm for nanoparticlesprepared without surfactant or in the presence of PVP whilein the presence of SDS CTAB the products do not show anyband gap enlargement These results imply that the particlesprecipitated in the presence of SDS and CTAB are so largethat it is not expected to observe any band gap enlargementin these samples

In order to further decrease the size of the nanoproductsvarious amounts of PVP were used to investigate the effectof this surfactant on the ZnO particle size and shape underthe same conditions of preparation Samples with differentZn2+PVP weight ratios (denoted as 119877) were prepared andchecked with X-ray diffraction absorbance and photolumi-nescence spectroscopy The X-ray diffraction patterns of thesamples with 119877 = 06 09 and 12 were shown in Figure 7All the patterns confirmed that the products were ZnO ofwurtzite structure As increasing the concentration of PVPthe width at half maximum of the diffraction lines in theX-ray patterns grows quickly which means that the particlesize is decreased under the increase of the surfactant PVP

ISRN Nanotechnology 5

The smallest value of the particle size is 9 nm attained when119877 = 06

The effect of PVP on ZnO nanoproduct was confirmeddirectly from the TEM image of the samples In Figure 8(a)119877was equal 06 and it can be seen clearly that the diameter andlength of particles are 8ndash10 nm and 35ndash45 nm respectivelyFigure 8 shows that when increasing the Zn2+PVP ratio(119877 = 12) the sizes of ZnO nanorods were increasedTheir diameters are up to 30ndash40 nm and the lengths areup to 60ndash70 nm The results demonstrate that PVP playsan important role in controlling the ZnO nanoproductsize and shape As the quantity of PVP increases the sizeof ZnO nanoparticle reduces by two or three times Thepreeminent advantages of PVP in reducing the particles sizeare understandable because PVP a bulky and highly chargedadsorbents serves as an ionic liquid which results in the so-called electrosteric stabilization The fact that PVP meets theconceptions of steric and electrostatic stabilization simulta-neously makes it a much better stabilizers than those whichonly have stabilization mechanism of steric or electrostatic[13]

Figure 10 shows the plots of (120572ℎ120592)2 versus ℎ120592 for colloidalZnO precipitated with different concentration of PVP Thelinear portion of the curves when extrapolating to 120572 = 0was an optical band gap value of the product In this studywe obtained the optical band gap of about 345 341 and338 eV at 119877 = 06 119877 = 09 and 119877 = 12 respectivelyThe obtained values of the band gap are larger than that ofbulk ZnO (330 eV) in [6] It is clear that the optical bandgap shifted to higher energy (blue shift) with increasing PVPconcentrations or decreasing the particle size

The photoluminescence spectra of the above sampleswere taken to study the influence of PVP on the opticalproperties of the nanoproducts The green band emission isattributed to the radiative recombination of photo-generatedhole with an electron belonging to a singly ionized vacancy inthe surface and subsurface The observation of strong greenband emission relative to bulk ZnO indicates the existence ofoxygen vacancies concentrated on nanoparticles surface Fornanomaterials the ratio surfacevolume is large and hence itis normal to observe a high green band compared with thepeak in the ultraviolet region

It is noted that in our samples compared with the sampleprepared without surfactant the ultraviolet peaks in thesamples using PVP as the surfactant become much moreevident On increasing the concentration of PVP the ZnOnanoparticles precipitated in the presence of PVP with 119877 =06 showed the highest ultraviolet emission and also thepeaks are blue shifted The increasing in the intensity ofthe ultraviolet compared with the visible band shows therole of PVP in passivating the trap states at the surface andreduces defects such as oxygen vacancies or Zn interstitialsThe blue shifts of these peaks (see the inset of Figure 11) areexplained by the reducing particle size as PVP concentrationreach higher value The fluorescence properties of the ZnOnanosamples prepared with PVP indicate that these samplesare of better quality than the samples prepared without usingsurfactants

50 nm

(a)

50 nm

(b)

50 nm

(c)

Figure 8 TEM images of ZnO nanoproducts with different valuesof 119877 (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c) 119877 = 12 (S7)

300 400 500 600 700 800

(c)

(b)

(a)

Abso

rptio

n

Wavelength (nm)

Figure 9 UV-vis spectra of the prepared ZnO with different valuesof 119877 (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c) 119877 = 12 (S7)

6 ISRN Nanotechnology

2 25 3 35 4 45

(c)

(b)

Energy (eV)

(a)119864119892 = 345 eV

119864119892 = 341 eV

119864119892 = 338 eV

(120572ℎ)2

Figure 10 Plots of (120572ℎ120592)2 versus ℎ120592 for ZnO nanopowder modifiedwith PVP at different 119877 values (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c)119877 = 12 (S7)

350 400 450 500 550 600

360 380 400 420

(c)

(d)

(b)

Inte

nsity

(au

)

Wavelength (nm)

(a)

Wavelength (nm)

(d)

(c)(b)(a)

Figure 11 Photoluminescence spectrum of ZnO nanoparticles (a)precipitated in the absence of surfactant (S2) and in the presence ofPVP with different values of 119877 (b) 119877 = 12 (S7) (c) 119877 = 09 (S6) (d)119877 = 06 (S5)

4 Conclusion

ZnO nanoparticles of different size and shape were success-fully fabricated by conventional and microwave methodThesample synthesis with the aid of microwave shows somepreeminent advantages compared with conventional methodand results in the formation of small ZnO nanoparticles ofuniform size and shape

Particle size of the ZnO nanoproducts prepared withmicrowave method can be further reduced by using surfac-tants Among the used surfactants PVP is the most suitableone The average diameter of the smallest ZnO particlesprepared with PVP is less than 10 nm with narrow sizedistribution The quantum confinement of the as produced

products was confirmed by the blue shift of the absorptionedge in the absorbance spectrum The increasing in the ratioof the intensity of ultravioletgreen peak in the photolumi-nescence spectra of these ZnO samples precipitated in thepresence of PVP shows that PVP not only reduces the particlesize but also the number of trap states at the surface of thenanoparticles

Acknowledgments

This work is completed with financial support by HanoiUniversity of Science Vietnam National university HanoiChina (Project TN 11 06) The authors of this paper wouldlike to thank the Center for Materials Science (CMS) Facultyof Physics College of Science VNU for permission to use itsequipments

References

[1] M R Vaezi and S K Sadrnezhaad ldquoNanopowder synthesis ofzinc oxide via solochemical processingrdquo Materials and Designvol 28 no 2 pp 515ndash519 2007

[2] Y J Kwon K H Kim C S Lim and K B Shim ldquoCharacter-ization of ZnO nanopowders synthesized by the polymerizedcomplex method via an organochemical routerdquo Journal ofCeramic Processing Research vol 3 no 3 pp 146ndash149 2002

[3] J G Lu Z Z Ye J Y Huang et al ldquoZnO quantum dotssynthesized by a vapor phase transport processrdquoApplied PhysicsLetters vol 88 no 6 Article ID 063110 3 pages 2006

[4] A D Yoffe ldquoLow-dimensional systems quantum size effectsand electronic properties of semiconductor microcrystallites(zero-dimensional systems) and some quasi-two-dimensionalsystemsrdquo Advances in Physics vol 51 no 2 pp 799ndash890 2002

[5] N F Hamedani and F Farzaneh ldquoSynthesis of nanocrystalswith hexagonal (wurtzite) structure in water using microwaveirradiationrdquo Journal of Science Islamic Republic of Iran vol 17article 231 2006

[6] Z Hu G Oskam and P C Searson ldquoInfluence of solvent on thegrowth of ZnO nanoparticlesrdquo Journal of Colloid and InterfaceScience vol 263 no 2 pp 454ndash460 2003

[7] B D Cullity Elements of X-Ray Diffractions Edition-WesleyReading Mass USA 1978

[8] G Glaspell P Dutta andAManivannan ldquoA room-temperatureandmicrowave synthesis of M-doped ZnO (M=Co Cr Fe Mnamp Ni)rdquo Journal of Cluster Science vol 16 no 4 pp 523ndash5362005

[9] N V Tuyen N N Long T T Q Hoa et al ldquoIndium-dopedzinc oxide nanometre thick disks synthesised by a vapour-phasetransport processrdquo Journal of Experimental Nanoscience vol 4no 3 pp 243ndash252 2009

[10] M Kooti and A Naghdi Sedeh ldquoMicrowave-assisted combus-tion synthesis of ZnO nanoparticlesrdquo Journal of Chemistry vol2013 Article ID 562028 4 pages 2013

[11] D K Bhat ldquoFacile synthesis of ZnO nanorods by microwaveirradiation of zinc-hydrazine hydrate complexrdquo NanoscaleResearch Letters vol 3 pp 31ndash35 2008

[12] S Cho S-H Jung and K-H Lee ldquoMorphology-controlledgrowth of ZnO nanostructures using microwave irradiationfrom basic to complex structuresrdquo The Journal of PhysicalChemistry C vol 112 pp 12769ndash12776 2008

ISRN Nanotechnology 7

[13] G Z Cao Nanostructures and Nanomaterials Synthesis Prop-erties and Applications Imperial College Press London UK2004

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

CrystallographyJournal of

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

MaterialsJournal of

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Page 5: A Quick Process for Synthesis of ZnO Nanoparticles with ...downloads.hindawi.com/journals/isrn.nanotechnology/... · 2 ISRNNanotechnology N2gas Cooling water Figure1:Imageofmicrowaveirradiationsystem

ISRN Nanotechnology 5

The smallest value of the particle size is 9 nm attained when119877 = 06

The effect of PVP on ZnO nanoproduct was confirmeddirectly from the TEM image of the samples In Figure 8(a)119877was equal 06 and it can be seen clearly that the diameter andlength of particles are 8ndash10 nm and 35ndash45 nm respectivelyFigure 8 shows that when increasing the Zn2+PVP ratio(119877 = 12) the sizes of ZnO nanorods were increasedTheir diameters are up to 30ndash40 nm and the lengths areup to 60ndash70 nm The results demonstrate that PVP playsan important role in controlling the ZnO nanoproductsize and shape As the quantity of PVP increases the sizeof ZnO nanoparticle reduces by two or three times Thepreeminent advantages of PVP in reducing the particles sizeare understandable because PVP a bulky and highly chargedadsorbents serves as an ionic liquid which results in the so-called electrosteric stabilization The fact that PVP meets theconceptions of steric and electrostatic stabilization simulta-neously makes it a much better stabilizers than those whichonly have stabilization mechanism of steric or electrostatic[13]

Figure 10 shows the plots of (120572ℎ120592)2 versus ℎ120592 for colloidalZnO precipitated with different concentration of PVP Thelinear portion of the curves when extrapolating to 120572 = 0was an optical band gap value of the product In this studywe obtained the optical band gap of about 345 341 and338 eV at 119877 = 06 119877 = 09 and 119877 = 12 respectivelyThe obtained values of the band gap are larger than that ofbulk ZnO (330 eV) in [6] It is clear that the optical bandgap shifted to higher energy (blue shift) with increasing PVPconcentrations or decreasing the particle size

The photoluminescence spectra of the above sampleswere taken to study the influence of PVP on the opticalproperties of the nanoproducts The green band emission isattributed to the radiative recombination of photo-generatedhole with an electron belonging to a singly ionized vacancy inthe surface and subsurface The observation of strong greenband emission relative to bulk ZnO indicates the existence ofoxygen vacancies concentrated on nanoparticles surface Fornanomaterials the ratio surfacevolume is large and hence itis normal to observe a high green band compared with thepeak in the ultraviolet region

It is noted that in our samples compared with the sampleprepared without surfactant the ultraviolet peaks in thesamples using PVP as the surfactant become much moreevident On increasing the concentration of PVP the ZnOnanoparticles precipitated in the presence of PVP with 119877 =06 showed the highest ultraviolet emission and also thepeaks are blue shifted The increasing in the intensity ofthe ultraviolet compared with the visible band shows therole of PVP in passivating the trap states at the surface andreduces defects such as oxygen vacancies or Zn interstitialsThe blue shifts of these peaks (see the inset of Figure 11) areexplained by the reducing particle size as PVP concentrationreach higher value The fluorescence properties of the ZnOnanosamples prepared with PVP indicate that these samplesare of better quality than the samples prepared without usingsurfactants

50 nm

(a)

50 nm

(b)

50 nm

(c)

Figure 8 TEM images of ZnO nanoproducts with different valuesof 119877 (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c) 119877 = 12 (S7)

300 400 500 600 700 800

(c)

(b)

(a)

Abso

rptio

n

Wavelength (nm)

Figure 9 UV-vis spectra of the prepared ZnO with different valuesof 119877 (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c) 119877 = 12 (S7)

6 ISRN Nanotechnology

2 25 3 35 4 45

(c)

(b)

Energy (eV)

(a)119864119892 = 345 eV

119864119892 = 341 eV

119864119892 = 338 eV

(120572ℎ)2

Figure 10 Plots of (120572ℎ120592)2 versus ℎ120592 for ZnO nanopowder modifiedwith PVP at different 119877 values (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c)119877 = 12 (S7)

350 400 450 500 550 600

360 380 400 420

(c)

(d)

(b)

Inte

nsity

(au

)

Wavelength (nm)

(a)

Wavelength (nm)

(d)

(c)(b)(a)

Figure 11 Photoluminescence spectrum of ZnO nanoparticles (a)precipitated in the absence of surfactant (S2) and in the presence ofPVP with different values of 119877 (b) 119877 = 12 (S7) (c) 119877 = 09 (S6) (d)119877 = 06 (S5)

4 Conclusion

ZnO nanoparticles of different size and shape were success-fully fabricated by conventional and microwave methodThesample synthesis with the aid of microwave shows somepreeminent advantages compared with conventional methodand results in the formation of small ZnO nanoparticles ofuniform size and shape

Particle size of the ZnO nanoproducts prepared withmicrowave method can be further reduced by using surfac-tants Among the used surfactants PVP is the most suitableone The average diameter of the smallest ZnO particlesprepared with PVP is less than 10 nm with narrow sizedistribution The quantum confinement of the as produced

products was confirmed by the blue shift of the absorptionedge in the absorbance spectrum The increasing in the ratioof the intensity of ultravioletgreen peak in the photolumi-nescence spectra of these ZnO samples precipitated in thepresence of PVP shows that PVP not only reduces the particlesize but also the number of trap states at the surface of thenanoparticles

Acknowledgments

This work is completed with financial support by HanoiUniversity of Science Vietnam National university HanoiChina (Project TN 11 06) The authors of this paper wouldlike to thank the Center for Materials Science (CMS) Facultyof Physics College of Science VNU for permission to use itsequipments

References

[1] M R Vaezi and S K Sadrnezhaad ldquoNanopowder synthesis ofzinc oxide via solochemical processingrdquo Materials and Designvol 28 no 2 pp 515ndash519 2007

[2] Y J Kwon K H Kim C S Lim and K B Shim ldquoCharacter-ization of ZnO nanopowders synthesized by the polymerizedcomplex method via an organochemical routerdquo Journal ofCeramic Processing Research vol 3 no 3 pp 146ndash149 2002

[3] J G Lu Z Z Ye J Y Huang et al ldquoZnO quantum dotssynthesized by a vapor phase transport processrdquoApplied PhysicsLetters vol 88 no 6 Article ID 063110 3 pages 2006

[4] A D Yoffe ldquoLow-dimensional systems quantum size effectsand electronic properties of semiconductor microcrystallites(zero-dimensional systems) and some quasi-two-dimensionalsystemsrdquo Advances in Physics vol 51 no 2 pp 799ndash890 2002

[5] N F Hamedani and F Farzaneh ldquoSynthesis of nanocrystalswith hexagonal (wurtzite) structure in water using microwaveirradiationrdquo Journal of Science Islamic Republic of Iran vol 17article 231 2006

[6] Z Hu G Oskam and P C Searson ldquoInfluence of solvent on thegrowth of ZnO nanoparticlesrdquo Journal of Colloid and InterfaceScience vol 263 no 2 pp 454ndash460 2003

[7] B D Cullity Elements of X-Ray Diffractions Edition-WesleyReading Mass USA 1978

[8] G Glaspell P Dutta andAManivannan ldquoA room-temperatureandmicrowave synthesis of M-doped ZnO (M=Co Cr Fe Mnamp Ni)rdquo Journal of Cluster Science vol 16 no 4 pp 523ndash5362005

[9] N V Tuyen N N Long T T Q Hoa et al ldquoIndium-dopedzinc oxide nanometre thick disks synthesised by a vapour-phasetransport processrdquo Journal of Experimental Nanoscience vol 4no 3 pp 243ndash252 2009

[10] M Kooti and A Naghdi Sedeh ldquoMicrowave-assisted combus-tion synthesis of ZnO nanoparticlesrdquo Journal of Chemistry vol2013 Article ID 562028 4 pages 2013

[11] D K Bhat ldquoFacile synthesis of ZnO nanorods by microwaveirradiation of zinc-hydrazine hydrate complexrdquo NanoscaleResearch Letters vol 3 pp 31ndash35 2008

[12] S Cho S-H Jung and K-H Lee ldquoMorphology-controlledgrowth of ZnO nanostructures using microwave irradiationfrom basic to complex structuresrdquo The Journal of PhysicalChemistry C vol 112 pp 12769ndash12776 2008

ISRN Nanotechnology 7

[13] G Z Cao Nanostructures and Nanomaterials Synthesis Prop-erties and Applications Imperial College Press London UK2004

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

CrystallographyJournal of

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

MaterialsJournal of

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Page 6: A Quick Process for Synthesis of ZnO Nanoparticles with ...downloads.hindawi.com/journals/isrn.nanotechnology/... · 2 ISRNNanotechnology N2gas Cooling water Figure1:Imageofmicrowaveirradiationsystem

6 ISRN Nanotechnology

2 25 3 35 4 45

(c)

(b)

Energy (eV)

(a)119864119892 = 345 eV

119864119892 = 341 eV

119864119892 = 338 eV

(120572ℎ)2

Figure 10 Plots of (120572ℎ120592)2 versus ℎ120592 for ZnO nanopowder modifiedwith PVP at different 119877 values (a) 119877 = 06 (S5) (b) 119877 = 09 (S6) (c)119877 = 12 (S7)

350 400 450 500 550 600

360 380 400 420

(c)

(d)

(b)

Inte

nsity

(au

)

Wavelength (nm)

(a)

Wavelength (nm)

(d)

(c)(b)(a)

Figure 11 Photoluminescence spectrum of ZnO nanoparticles (a)precipitated in the absence of surfactant (S2) and in the presence ofPVP with different values of 119877 (b) 119877 = 12 (S7) (c) 119877 = 09 (S6) (d)119877 = 06 (S5)

4 Conclusion

ZnO nanoparticles of different size and shape were success-fully fabricated by conventional and microwave methodThesample synthesis with the aid of microwave shows somepreeminent advantages compared with conventional methodand results in the formation of small ZnO nanoparticles ofuniform size and shape

Particle size of the ZnO nanoproducts prepared withmicrowave method can be further reduced by using surfac-tants Among the used surfactants PVP is the most suitableone The average diameter of the smallest ZnO particlesprepared with PVP is less than 10 nm with narrow sizedistribution The quantum confinement of the as produced

products was confirmed by the blue shift of the absorptionedge in the absorbance spectrum The increasing in the ratioof the intensity of ultravioletgreen peak in the photolumi-nescence spectra of these ZnO samples precipitated in thepresence of PVP shows that PVP not only reduces the particlesize but also the number of trap states at the surface of thenanoparticles

Acknowledgments

This work is completed with financial support by HanoiUniversity of Science Vietnam National university HanoiChina (Project TN 11 06) The authors of this paper wouldlike to thank the Center for Materials Science (CMS) Facultyof Physics College of Science VNU for permission to use itsequipments

References

[1] M R Vaezi and S K Sadrnezhaad ldquoNanopowder synthesis ofzinc oxide via solochemical processingrdquo Materials and Designvol 28 no 2 pp 515ndash519 2007

[2] Y J Kwon K H Kim C S Lim and K B Shim ldquoCharacter-ization of ZnO nanopowders synthesized by the polymerizedcomplex method via an organochemical routerdquo Journal ofCeramic Processing Research vol 3 no 3 pp 146ndash149 2002

[3] J G Lu Z Z Ye J Y Huang et al ldquoZnO quantum dotssynthesized by a vapor phase transport processrdquoApplied PhysicsLetters vol 88 no 6 Article ID 063110 3 pages 2006

[4] A D Yoffe ldquoLow-dimensional systems quantum size effectsand electronic properties of semiconductor microcrystallites(zero-dimensional systems) and some quasi-two-dimensionalsystemsrdquo Advances in Physics vol 51 no 2 pp 799ndash890 2002

[5] N F Hamedani and F Farzaneh ldquoSynthesis of nanocrystalswith hexagonal (wurtzite) structure in water using microwaveirradiationrdquo Journal of Science Islamic Republic of Iran vol 17article 231 2006

[6] Z Hu G Oskam and P C Searson ldquoInfluence of solvent on thegrowth of ZnO nanoparticlesrdquo Journal of Colloid and InterfaceScience vol 263 no 2 pp 454ndash460 2003

[7] B D Cullity Elements of X-Ray Diffractions Edition-WesleyReading Mass USA 1978

[8] G Glaspell P Dutta andAManivannan ldquoA room-temperatureandmicrowave synthesis of M-doped ZnO (M=Co Cr Fe Mnamp Ni)rdquo Journal of Cluster Science vol 16 no 4 pp 523ndash5362005

[9] N V Tuyen N N Long T T Q Hoa et al ldquoIndium-dopedzinc oxide nanometre thick disks synthesised by a vapour-phasetransport processrdquo Journal of Experimental Nanoscience vol 4no 3 pp 243ndash252 2009

[10] M Kooti and A Naghdi Sedeh ldquoMicrowave-assisted combus-tion synthesis of ZnO nanoparticlesrdquo Journal of Chemistry vol2013 Article ID 562028 4 pages 2013

[11] D K Bhat ldquoFacile synthesis of ZnO nanorods by microwaveirradiation of zinc-hydrazine hydrate complexrdquo NanoscaleResearch Letters vol 3 pp 31ndash35 2008

[12] S Cho S-H Jung and K-H Lee ldquoMorphology-controlledgrowth of ZnO nanostructures using microwave irradiationfrom basic to complex structuresrdquo The Journal of PhysicalChemistry C vol 112 pp 12769ndash12776 2008

ISRN Nanotechnology 7

[13] G Z Cao Nanostructures and Nanomaterials Synthesis Prop-erties and Applications Imperial College Press London UK2004

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

CrystallographyJournal of

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

MaterialsJournal of

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Page 7: A Quick Process for Synthesis of ZnO Nanoparticles with ...downloads.hindawi.com/journals/isrn.nanotechnology/... · 2 ISRNNanotechnology N2gas Cooling water Figure1:Imageofmicrowaveirradiationsystem

ISRN Nanotechnology 7

[13] G Z Cao Nanostructures and Nanomaterials Synthesis Prop-erties and Applications Imperial College Press London UK2004

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ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

CrystallographyJournal of

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

MaterialsJournal of

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Page 8: A Quick Process for Synthesis of ZnO Nanoparticles with ...downloads.hindawi.com/journals/isrn.nanotechnology/... · 2 ISRNNanotechnology N2gas Cooling water Figure1:Imageofmicrowaveirradiationsystem

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

CrystallographyJournal of

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

MaterialsJournal of

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials