G

A

I(

Sa

b

a

ARRAA

KCRNP

1

faccpaothrfrtfidw

isC

0h

ARTICLE IN PRESS Model

PSUSC-25996; No. of Pages 6

Applied Surface Science xxx (2013) xxx– xxx

Contents lists available at SciVerse ScienceDirect

Applied Surface Science

j ourna l ho me page: www.elsev ier .com/ locate /apsusc

nfluence of growth and photocatalytic properties of copper selenideCuSe) nanoparticles using reflux condensation method

. Soniaa, P. Suresh Kumarb, D. Mangalaraja,∗, N. Ponpandiana, C. Viswanathana

Department of Nanoscience and Technology, Bharathiar University, Coimbatore 641046, IndiaThin Film and Nanomaterials Laboratory, Department of Physics, Bharathiar University, Coimbatore 641046, India

r t i c l e i n f o

rticle history:eceived 19 April 2013eceived in revised form 24 June 2013ccepted 6 July 2013vailable online xxx

a b s t r a c t

Influence of reaction conditions on the synthesis of copper selenide (CuSe) nanoparticles and their photodegradation activity is studied. Nearly monodispersed uniform size (23–44 nm) nanoparticles are synthe-sized by varying the reaction conditions using reflux condensation method. The obtained nanoparticlesare characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electronmicroscopy and UV–visible absorption spectroscopy. The X-ray diffraction analysis of the sample shows

eywords:uSeeflux condensationanoparticleshoto degradation

the formation of nanoparticles with hexagonal CuSe structure. The result indicates that on increasing thereaction time from 4 to 12 h, the particle size decreases from 44 to 23 nm, but an increase in the reac-tion temperature increases the particle size. The calculated band gap Eg is ranging from 2.34 to 3.05 eVwhich is blue shifted from the bulk CuSe (2.2 eV). The photocatalytic degradation efficiency of the CuSenanoparticles on two organic dyes Methylene blue (MB) and Rhodamine-B (RhB) in aqueous solution

ated a

under UV region is calcul

. Introduction

In recent decades, hazardous environmental problems, arisesrom industries and modernization of the living hoods which glob-lly affects the reusage of water and increases the demand forlean water. Among many wastewater treatment methods espe-ially for the removal of organic contaminants, heterogeneoushotocatalytic process using different nanostructures has received

considerable attention because of its low-cost and inert naturef the catalyst [1]. It is well known that the photocatalytic reac-ion on the surface of a semiconductor is initiated by electron andole generation that produce hydroxyl (•OH) and superoxide (•O2-)adicals for decomposition of organic pollutant in water. So far dif-erent Nanostructured materials like ZnO, TiO2, SnO2, and CuO haveeceived considerable attention due to its increase in surface areashan that of bulk materials and have been significantly investigatedor both energy and environmental applications. The semiconduct-ng photocatalysts are environmental catalysts that can efficientlyegrade hazardous chemicals which have been extensively usedorldwide to solve environmental issues [2–6].

As an important p-type semiconductor, Copper selenide (CuSe)

Please cite this article in press as: S. Sonia, et al., Influence of growth and phreflux condensation method, Appl. Surf. Sci. (2013), http://dx.doi.org/10.10

s a unique metal chalcogenide that found in many phases andtructural forms with different stoichiometries such as CuSe, Cu2Se,u2Sex, CuSe2, �-Cu2Se, Cu3Se2, Cu5Se4 and Cu7Se4 as well with

∗ Corresponding author. Tel.: +91 422 2425458; fax: +91 422 2422387.E-mail address: dmraj800@yahoo.com (D. Mangalaraj).

169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.apsusc.2013.07.022

s 76 and 87% respectively.© 2013 Elsevier B.V. All rights reserved.

non-stoichiometric form such as Cu2–xSe and can be constructedinto several crystallographic forms (monoclinic, cubic, tetragonaland hexagonal). Therefore, considerable progress on the studyof CuSe has been made in recent years due to its fascinatingproperties and wide applications in solar cells, gas sensors, ther-moelectric converters etc. Metal chalcogenide materials such asZnSe, CuS, CuS/ZnS and CuSe modified TiO2 have been directlyused as photocatalysts due to their fascinating properties [7–10].Among these, Cu2–xSe nanocrystals show efficient photocatalyticactivity (50% with irradiation time of 2 h) towards the photodegra-dation of RhB aqueous solution under visible light due to its widebandgap [11]. Among the assorted metal chalcogenides, CuSe is ap-type semiconductor with wide range of stoichiometric as well asnon-stoichiometric compositions and also with various crystallo-graphic forms for each of these compositions [12]. The synthesis ofdifferent nanostructures has been depicted in different methodsincluding SILAR process, solution growth technique, brush elec-troplating, chemical bath deposition, chemical vapor deposition,pulsed laser deposition, thermal evaporation, solid state reaction,galvanic synthesis, solution phase synthesis and electrospinningmethod [13–23]. Recently, nanodendrites, nanocrystals, hollownanostructures and nanoplates of metal chalcogenides have beensynthesized by environmental friendly solvothermal method, one-pot solution, and aqueous solution method respectively [24–27].

otocatalytic properties of copper selenide (CuSe) nanoparticles using16/j.apsusc.2013.07.022

Hydrothermal or solvothermal synthesis is a well-known low-temperature wet chemical process and it promises the directpreparation of advanced nanostructures. But the reflux condensa-tion method provides highly crystalline materials with high purity,

IN PRESSG Model

A

2 face Science xxx (2013) xxx– xxx

nwraM

2

(ooiThmdaspaird(wwtcor

C

S

puUbmmwdwir

3

3

n(t2(CJipsb

20 30 40 50 60 70 80

2θ (degree)

JCPDS # 34-0171

12 hrs

8 hrs

50oC

Inte

ns

ity

(a

rb.u

nit

s)

4 hrs

12hrs

8 hrs

4 hrs

70oC

12 hrs

8 hrs

4 hrs

(20

8)

(11

6)

(10

8)

(11

0)

(00

6)

(10

2)

90oC

(10

1)

ARTICLEPSUSC-25996; No. of Pages 6

S. Sonia et al. / Applied Sur

arrow size distribution, high surface area and low aggregationhich enhance the photocatalytic activity [28]. In this paper we

eport the preparation of copper selenide (CuSe) nanoparticlesnd their photocatalytic activity on two organic dyes, viz., such asethylene blue (MB) and Rhodamine B (RhB).

. Experimental procedure

An aqueous solution of copper chloride dyhydride (CuCl2•2H2O0.1 mol)) was mixed with 20 ml of ethylene glycol under vig-rous stirring till it was converted to a clear solution. The pHf the resultant solution was set to 12 to make the hydroxylons offer stabilizing effect for the II–VI semiconductors [29].hen 0.1 mol of selenium metal powder was dissolved in 10 ml ofydrazine hydrate and was mixed with the above solution. Theoment selenide solution entered, the colourless solution sud-

enly changed to dark brown colour. The hydrazine hydrate acteds a reducing and complexing agent and also simultaneously a goodolvent for selenium. Also, hydrazine was added to reduce any sul-hite formation during the reaction. The molar ratio among Cu, Send the stabilizer (ethylene glycol) was initially set to 1:1:2 accord-ng to the ingredients adopted in the preparations of CuSe. Theesultant and final solution was refluxed in an atmospheric con-ition for various duration time (4, 8 and 12 h) and temperature50 ◦C, 70 ◦C and 90 ◦C) respectively. The obtained precipitate wasashed three times with hot double distilled water and one timeith ethanol (AR grade 99.99% purity) and dried in an oven at 60 ◦C

o remove remnants or side products. The obtained ultra fine parti-les were used for further investigations. The temperature and timef reactions were tuned to obtain different sized nanoparticles. Theeaction mechanism is as follows:

uCl2aquous−→ Cu2+ + 2Cl−

eReduction Ethylene Glycol/Hydrazine Hydrate−→ Se2−

Se2− + Cu2+ → CuSePhase purity, crystal structure and the crystallinity of the sam-

les were analyzed by recording the X-ray diffraction (XRD) patternsing a Panalytical X’Pert Pro with Cu–K� radiation (1.5406 A). TheV–vis absorption and of the CuSe nanoparticles were recordedy the Perkin Elmer LS 55 fluorescence spectrometer. The surfaceorphology of the samples was investigated by a scanning electronicroscope (SEM) (FEI Quanta-250) and the chemical compositionas examined using EDAX attached with the FESEM. Also, an in-epth analysis of the morphologies of the prepared nanoparticlesas done by a transmission electron microscope (TEM). The TEM

mage and selected area electron diffraction (SAED) pattern wereecorded using a 120 KV Tecnai Sprit TEM instrument.

. Results and discussion

.1. Structural analysis

Fig. 1 shows the XRD pattern of the as-synthesized CuSeanoparticles prepared at different reaction conditions such as time4, 8 and 12 h) and temperature (50 ◦C, 70 ◦C and 90 ◦C) respec-ively. All the samples shows the sharp diffraction peaks at 26.45◦,8.15◦, 31.23◦, 45.92◦, 50.02◦, 56.51◦ and 70.17◦ can be index to101), (102), (006), (110), (108), (116) and (208) planes of hexagonaluSe and the intensities are very well matching with the standard

CPDS # 34-0171. No characteristic impurity peak is detected which

Please cite this article in press as: S. Sonia, et al., Influence of growth and phreflux condensation method, Appl. Surf. Sci. (2013), http://dx.doi.org/10.10

ndicates the formation of pure CuSe. All the samples show theure hexagonal structure of CuSe with strong and sharp inten-ity in (102) peaks which demonstrate the better crystallizationehaviour. The estimated average lattice constants are a = 3.96 A

Fig. 1. XRD spectra of CuSe nanoparticles refluxed at different reaction temperatureand time.

and c = 17.23 A, which are consistent with previously reported dataand standard JCPDS value. The crystallite sizes of CuSe samples arecalculated using Debye–Scherer formula as shown below in Eq. (1)

D = 0.89�

cos �(1)

where D is the crystallite size, � is the wavelength (1.5406 A forCu–K�), is the full-width at half-maximum (FWHM) of mainintensity peak after subtraction of the equipment broadening and� is the diffraction angle. It is interesting to note that the aver-age crystallite size decreases by increasing the reaction time from∼44.73 (for 4 h) to ∼23.73 nm (for 12 h) and no appreciable changein crystallite size is noticed in the reaction time of 12 h and atthe reaction temperatures of 50, 70 and 90 ◦C. The reaction timeplays an important role in determining the surface structure of thenanoparticles. When the reaction time increases, faster growth rateof the nanoparticles can reduce the surface defects of the nanopar-ticles, but lower reaction time would reduce the reaction speedwhich in turn may adversely influence the quality of the nanopar-ticles [30]. Generally, the monomer reactivity was a function ofreaction temperature. Therefore, it was understood that the reac-tion temperature could affect the reactivity of Se and, thereby,the nucleation process of NPs. When the temperature was low,the reactivity of Se was not high enough to support the reactionwith Cu. When the temperature is high the diffraction peaks show

otocatalytic properties of copper selenide (CuSe) nanoparticles using16/j.apsusc.2013.07.022

high crystallinity of CuSe nanoparticles compared to the growth ofnanoparticles at low temperatures due to the high reactivity of Sewith Cu [31].

ARTICLE IN PRESSG Model

APSUSC-25996; No. of Pages 6

S. Sonia et al. / Applied Surface Science xxx (2013) xxx– xxx 3

F ◦C (c)t

3

wsmststapbefcaassp

Topgss

ig. 2. SEM image of CuSe refluxed at different reaction temperature (a) 50 ◦C (b) 70emperature of 90◦c for 12 h.

.2. Surface and compositional analysis

The surface morphology of the prepared CuSe nanoparticlesere analyzed by scanning electron microscopy (SEM). The sample

ynthesized at lower reaction temperature (50 ◦C) shows the for-ation of irregular structures upto 2 �m (Fig. 2(a)) whereas the

ample refluxed at higher temperature of 70 ◦C typically showshe porous CuSe nanoparticles as shown in inset Fig. 2(b) withize ranging from 1 to 1.5 �m which aggregate into bunch of clus-ers (Fig. 2(b)). The morphology of these samples reveals that thegglomeration of nanocrystals leads to the formation of individualarticles or grains, which are expected to contribute more grainoundary effects. Further increase in reaction temperature (90 ◦C)vidently shows the spherical CuSe nanoparticle with size rangesrom 200 nm to 1 �m (Fig. 2(c)). These spherical particles are highlyrystalline in nature. The EDAX spectrum shows the presence of Cund Se elements alone in the sample, confirming the absence ofny other impurity. The atomic percentage of Cu and Se elementsample is 53.43 and 46.57, respectively are shown in Fig. 2(d). Thetoichiometric ratio calculated from the EDAX is 1:1 shows theresence of pure CuSe.

The size and shape of the CuSe nanoparticles are depicted in theEM image (Fig. 3(a)). The typical TEM image shows that the shapef the copper selenide nanoparticles is spherical, with the average

Please cite this article in press as: S. Sonia, et al., Influence of growth and phreflux condensation method, Appl. Surf. Sci. (2013), http://dx.doi.org/10.10

article size of 20–40 nm which is coincidence with the averagerain size calculated from the XRD pattern. The TEM image of theample shows nearly spherical morphology and good monodisper-ity. The selected area electron diffraction (SAED) pattern of the

90 ◦C and time of 12 h (d) EDX analysis of CuSe nanoparticle synthesized at rection

sample (Fig. 3(b)) shows the discontinuous diffraction rings, sug-gesting that the crystalline domains of the nanocrystalline powdershave certain preferred orientations instead of the random orienta-tions. This diffraction pattern exhibits a typical lattice spacing ofabout 3.160, 2.625, 1.791 and 1.603 A, corresponding to the planes(102), (006), (108) and (116) respectively, which are confirmedwith the XRD results.

3.3. Optical analysis

The optical absorption peaks of the CuSe nanoparticles preparedwith different reaction parameters are shown in Fig. 4(a–c). In thepresent case, the absorption is maximum at 350 nm for the materialprepared with a reaction time of 12 h and a reaction temperatureof 50 ◦C. This peak is related to the plasmon band of the nano-sized copper selenide particles (Fig. 4(a)). Fig. 4 (b) indicates that asthe temperature of copper selenide increases to 70 ◦C, the absorp-tion band becomes stronger and sharper. Further it moves to ashorter wavelength of 345 nm. This indicates that the size of thenanoparticles is decreasing when the temperature is increased. Asthe temperature of the copper selenide is increased to 90 ◦C, theabsorption band is shifted towards shorter wavelength of 344 nm(Fig. 4(c)) and also the peak become very stronger and sharper com-pared to the peak obtained in the reaction temperatures 50 ◦C and

otocatalytic properties of copper selenide (CuSe) nanoparticles using16/j.apsusc.2013.07.022

70 ◦C. In every case, the absorption peak shifts towards lower wave-length as the temperature of the copper selenide is increased. Thepeak also gets stronger. This is probably because of reduction inthe particle size and hence increases in the surface to volume ratio.

ARTICLE IN PRESSG Model

APSUSC-25996; No. of Pages 6

4 S. Sonia et al. / Applied Surface Science xxx (2013) xxx– xxx

F 0 ◦C (ct

Avoamteispattaftt(a

˛

wbaFcte

ig. 3. TEM image of CuSe refluxed at different reaction temperature (a) 50 ◦C (b) 7emperature of 90 ◦C and time of 12 h.

lso it may be due to the confinement of electron and hole in aery small volume [32]. In Fig. 4(a–c) no sharp absorption edge isbserved at large wavelengths. The set of sharp absorption peakst shorter wavelengths is due to exciton absorption and confine-ent of electron and hole. The sharp absorption edge implies that

he particles are spherical in shape [33–35]. The stronger excitonffect is an important character of the quantum confinement effectn nano-semiconductors, since the carriers are confined in a verymall region that makes the electron and holes move only in aotential well. At the same time, it can enhance the coupling inter-ction, due to which the excitons are bounded more strongly. Hencehe probability of binding is increased, which lead to apparent exci-on absorption peak and hence the blue shift. Usually, the opticalbsorption at the absorption edge corresponds to the transmissionrom valence band to conduction band, while the absorption inhe visible region corresponds to some localized energy states inhe band gap. The optical band gap was calculated by plotting ˛h�vs) h� plot. For forbidden electronic transition in materials, thebsorption coefficient is given by

h� = k(h� − Eg)p (2)

here p = 1/2 for direct forbidden gap and p = 3 for indirect for-idden gap [18,22,36]. (˛h�)1/2 versus h� plots for CuSe preparedt different temperatures and reaction timings are shown in

Please cite this article in press as: S. Sonia, et al., Influence of growth and phreflux condensation method, Appl. Surf. Sci. (2013), http://dx.doi.org/10.10

ig. 5(a–c). Good linear relationship between (˛h�)1/2 and h� indi-ates that the nature of transition in CuSe nanoparticles is directransition. The band gap Eg calculated by extrapolating the lin-ar part of the curve to zero absorption is ranging from 2.34 to

) 90 ◦C and time of 12 h (d) SAED pattern of CuSe nanoparticles refluxed at reaction

3.05 eV which is blue shifted from the bulk CuSe (2.2 eV) [18,20]and this blue shift is due to quantum confinement effect. FromFig. 5(a–c) it is clear that as the particle size decreases the bandgap gets increased. Nanosize effect and the structural defectsmight lead to the blue shift of the copper selenide nanoparticles[32].

3.4. Photocatalytic activity

Fig. 6(a–b) shows the photo-degradation activity of the preparedCuSe nanoparticles was examined against two organic dyes, viz.,Methylene blue (MB) and Rhodamine-B (RhB) for the optimizedsample prepared at reaction temperature (90 ◦C) and time (12 h).Photocatalysis refers to the oxidation and reduction reactions onsemiconductor surfaces, mediated by the valance band holes andconduction band electrons, which are generated by the absorptionof ultraviolet or visible light radiation. In a typical experiment, 3 mgof CuSe was dissolved in 1 mole aqueous solutions of RhB and MB.In order to make homogeneous dispersion, the solutions are soni-cated for 20 min. The resultant solution was kept in a dark conditionto obtain equilibrium between the catalyst and organic (RhB andMB) molecules. Then the solution was illuminated by a UV lightsource (�max = 365 nm) to induce photochemical reaction. Strongabsorption peaks at 554 and 665 nm are observed for RhB and MB

otocatalytic properties of copper selenide (CuSe) nanoparticles using16/j.apsusc.2013.07.022

respectively.As seen in the figures, a substantial decrease in the absorbance

of dyes (RhB and MB) was observed after conducting the reactionunder UV light irradiation. The solution turned colourless within

ARTICLE IN PRESSG Model

APSUSC-25996; No. of Pages 6

S. Sonia et al. / Applied Surface Science xxx (2013) xxx– xxx 5

4 hrs

8 hrs

12hrs

(c)343.81 nm

Ab

so

rban

ce (

a.u

) (b)345.23 nm

350 400 450 500 550Wavelength(nm)

(a)349.93 nm

Ft

9c

�

tF(tiwTcut

−

ta

−

wrtapf0rf

1.0 1.5 2.0 2.5 3.0 3.5

hν (eV )

2.7

5eV2.5

8eV

2.3

4eV

(c)

(αh

ν)1/2

2.8

3eV2.

70eV

2.5

2eV

(b)

3.0

5eV2.7

3eV

2.5

6eV

(a) 12hrs8hrs4hrs

Fig. 5. Plot of (˛h�)1/2 vs h� of CuSe nanoparticles refluxed at different reactiontemperatures (a) 50 ◦C (b) 70 ◦C and (c) 90 ◦C.

0

1

2

3

400 600 800

0

1

2

3

MB

MB+CuSe

15 min MB +CuSe

30 min MB +CuSe

45 min MB +CuSe

60 min MB +CuSe

75 min MB +CuSe

90 min MB +CuSe

(b)

Ab

so

rba

nc

e (

a.u

)

Wavelength (nm)

RhB

RhB +CuSe

15min RhB +CuSe

30 min RhB +CuSe

45 min RhB +CuSe

60 min RhB +CuSe

75 min RhB +CuSe

90 min RhB +CuSe

(a)

ig. 4. Optical absorption spectra of CuSe nanoparticles refluxed at different reac-ion temperatures (a) 50 ◦C (b) 70 ◦C and (c) 90 ◦C.

0 min of irradiation. The efficiency of degradation (� %) was cal-ulated using

(%) = (1 − A/A0) × 100, (3)

Where, A0 is the absorption maximum at t = 0, A be the absorp-ion maximum after degradation for a particular illumination time.ig. 7(a) shows the changes of RhB and MB concentration ratioA/A0) as a function of illumination time. Fig. 7(b) shows thathe degradation percentage increases as the UV irradiation timencreases. The degradation efficiency for the CuSe nanoparticles

ith the RhB and MB are calculated as 87 and 76% respectively.he highest degradation was achieved for RhB than MB. The photo-atalytic degradation of the organic dyes by the CuSe nanoparticlesnder UV light obeyed pseudo-first order kinetics with respect tohe absorption intensity of dyes:

dA/dt = kappA (4)

Integration of the equation (with A = Aabs at t = 0, with Aabs beinghe initial concentration in the bulk solution after dark adsorptionnd t the reaction time) lead to

ln(A/A0) = kapp t (5)

here A and A0 are the absorption intensities at time t = t and t = 0espectively, kapp and t are the apparent reaction rate constant andime respectively. Accordingly, a plot of –ln(A/A0) versus t will yield

slope of kapp and results are shown in Fig. 8. The linearity of thelot suggested that the photodegradation reaction approximately

−1

Please cite this article in press as: S. Sonia, et al., Influence of growth and photocatalytic properties of copper selenide (CuSe) nanoparticles usingreflux condensation method, Appl. Surf. Sci. (2013), http://dx.doi.org/10.1016/j.apsusc.2013.07.022

ollowed pseudo-first order kinetics with kapp of 0.0155 min and.0174 min−1 for degradation of MB and RhB respectively. Theesult suggests that the CuSe nanoparticles are effective catalystsor RhB and MB degradation.

Fig. 6. Photo-degradation of CuSe nanoparticles of two organic dyes (a) RhB and (b)MB.

ARTICLE ING Model

APSUSC-25996; No. of Pages 6

6 S. Sonia et al. / Applied Surface S

0 20 40 60 80 100

0.0

0.2

0.4

0.6

0.8

1.0

Irradiation time (min)

(a)

0

20

40

60

80

100

η(%

)A

/A0

RhBMB

(b)

Fig. 7. (a) Changes of RhB and MB concentration ratio C/C0 as a function of illumina-tion time (b) Degradation efficiency of two organic dyes by the CuSe nanoparticlesunder UV irradiation.

0 40 80

0.0

0.7

1.4

2.1

-ln

(A

/A0

)

Irradiation time (min)

MB

RhB

kapp =0.0155 min-1

kapp =0.0174 min-1 (a)

(b)

FC

4

pi

[

[

[

[

[

[[

[

[

[

[[

[

[

[

[

[

[

[[

[

[[[33] A. Moores, F. Goettmann, New Journal of Chemistry 30 (2006) 1121.

ig. 8. First order kinetics plot for the photodegradation of (a) MB and (b) RhB byuSe nanoparticles under UV light irradiation.

. Conclusion

Please cite this article in press as: S. Sonia, et al., Influence of growth and phreflux condensation method, Appl. Surf. Sci. (2013), http://dx.doi.org/10.10

In summary, highly crystalline CuSe nanoparticles have beenrepared using cost effective reflux condensation method by vary-

ng the reaction time and temperature. The XRD analysis confirms

[[

[

PRESScience xxx (2013) xxx– xxx

the phase purities with (102) peak orientation of CuSe with crys-tallite size varying from 22 nm to 9 nm with change in reactioncondition. The optical studies confirm the strong blue shift is dueto the quantum confinement effect. The prepared CuSe had excel-lent photocatalytic properties and the photocatalytic degradationefficiency of the nanoparticles on two organic dyes Methylene blue(MB) and Rhodamine-B (RhB) in aqueous solution under UV regionis found to be around 76 and 87% respectively.

References

[1] N. Murase, R. Jagannathan, Y. Kanematsu, M. Watanabe, A. Kurita, K. Hirata,T. Yazawa, T. Kushida, The Journal of Physical Chemistry B 103 (1999)754.

[2] K. Honda, A. Fujishima, Nature 238 (1972) 37–38.[3] T. Kawai, T. Sakata, Nature 286 (1980) 474–476.[4] T. Mishra, J. Hait, Noor Aman, R.K. Jana, S. Chakravarty, Journal of Colloid and

Interface Science 316 (2007) 80–84.[5] D. Wang, Z. Zou, J. Ye, Chemical Physics Letters 384 (2004) 139–143.[6] A.L. Linsebigler, G. Lu, J.T. Yates, Chemical Review 95 (1995) 735–758.[7] S. Cho, J.W. Jang, J. Kim, J.S. Lee, W. Choi, K.H. Lee, Langmuir 27 (2011)

10243–10250.[8] L. Zhang, H. Yang, J. Yu, F. Shao, L. Li, F. Zhang, H. Zhao, The Journal of Physical

Chemistry B 113 (2009) 5434–5443.[9] J. Yu, J. Zhang, S. Liu, The Journal of Physical Chemistry B 114 (2010)

13642–13649.10] Y. Li, S. Luo, L. Yang, C. Liu, Y. Chen, D.S. Meng, Electrochimica Acta 83 (2012)

394–401.11] T.D.T. Ung, Q.L. Nguyen, Advances in Natural Sciences: Nanoscience and Nano-

technology 2 (2011) 045003.12] G.B. Sakra, I.S. Yahia, M. Fadel, S.S. Fouad, N. Romcevi, Journal of Alloys and

Compounds 507 (2010) 557–562.13] P.S. Kumar, J. Sundaramurthy, D. Mangalaraj, D. Nataraj, D. Rajarath-

nam, M.P. Srinivasan, Journal of Colloid and Interface Science 363 (2011)51–58.

14] P.S. Kumar, A. Dhayal Raj, D. Mangalaraj, D. Nataraj, Applied Surface Science255 (2008) 2382–2387.

15] K.R. Murali, R. John Xavier, Chalcogenide Letters 6 (2009) 683–687.16] R.H. Bari, V. Ganesan, S. Potadar, L.A. Patil, Bulletin of Material Science 32 (2009)

37–42.17] A.B.M.O. AL-Mamun, A.H. Islam, Bhuiyan, Journal of Materials Science: Materi-

als in Electronics 16 (2005) 263–268.18] Y. Hu, M. Afzaal, M.A. Malik, P. O’Brien, Journal of Crystal Growth 297 (2006)

61–65.19] M.Z. Xue, Y.N. Zhou, B. Zhang, L. Yu, H. Zhang, Z.W. Fu, Journal of The Electro-

chemical Society 153 (2006) A2262–A2268.20] Y.J. Yang, S. Hu, Journal of Solid State Electrochemistry 13 (2009) 477–483.21] R. Seoudi, A.A. Shabaka, M.M. Elokr, A. Sobhi, Materials Letters 61 (2007)

3451–3455.22] P. Kumar, K. Singh, O.N. Srivastava, Journal of Crystal Growth 312 (2010)

2804–2813.23] P.S. Kumar, S.A. Syed Nizar, J. Sundaramurthy, P. Ragupathy, V. Thavasi,

S.G. Mhaisalkar, S. Ramakrishna, Journal of Materials Chemistry 21 (2011)9784–9790.

24] D. Li, Z. Zheng, Y. Lei, S. Ge, Y. Zhang, Y. Zhang, K.W. Wong, F. Yanga, W.M. Lauc,CrystEngComm 12 (2010) 1856–1861.

25] G. Xiao, J. Ning, Z. Liu, Y. Sui, Y. Wang, Q. Dong, W. Tian, B. Liu, G. Zou, B. Zou,CrystEngComm 14 (2012) 2139.

26] M.S. Bakshi, P. Thakur, P. Khullar, G. Kaur, T.S. Banipal, Crystal Growth andDesign 10 (2010) 4.

27] G. Xiao, Y. Zeng, Y. Jiang, J. Ning, W. Zheng, B. Liu, X. Chen, G. Zou, B. Zou, Small9 (2013) 793–799.

28] D. Chen, Recent Patents on Nanotechnology 2 (2008) 183–189.29] D. Zhao, Z. He, W.H. Chan, M.M.F. Choi, The Journal of Physical Chemistry 113

(2009) 1293–1300.30] P.K. Basu, Theory of Optical Processes in Semiconductors Bulk and Microstruc-

ture, Clarendon Press, Oxford, 1997.31] W.W. Yu, Y.A. Wang, X. Peng, Chemistry of Materials 15 (2003) 4300–4308.32] M.N. Kalasad, M.K. Rabinal, B.G. Mulimani, Langmuir 25 (2009) 12729–12735.

otocatalytic properties of copper selenide (CuSe) nanoparticles using16/j.apsusc.2013.07.022

34] S. Link, M.A. El-Sayed, The Journal of Physical Chemistry 3 (2000) 409.35] C.S. Prajapati, P.P. sahay, Journal of Applied Surface Science 258 (2011)

2823–2826.36] B. Pejova, I. Grozdanov, Journal of Solid State Chemistry 158 (2001) 49–54.