Solvothermal Synthesis of One Dimensional Copper Doped Cadmium Sulphide Nanorods and Their Photocatalytic Performance

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LECopyright © 2013 by American Scientific Publishers

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Printed in the United States of America

Journal of Nanoengineering and NanomanufacturingVol. 3, pp. 1–7, 2013

(www.aspbs.com/jnan)

Solvothermal Synthesis of One DimensionalCopper Doped Cadmium Sulphide Nanorodsand Their Photocatalytic PerformanceSudhir S. Arbuj, Sagar R. Bhalerao, Sunit B. Rane,Uttam P. Mulik∗, and Dinesh P. Amalnerkar

Centre for Materials for Electronics Technology, Off Pashan Road, Panchwati, Pune 411008, India

ABSTRACT

In this study, one dimensional Cu doped CdS with higher aspect ratio was synthesized by solvothermal tech-nique. The Cu doping concentration was varied from 0.1 to 5 mol% (CuxCd1−xS where x= 0.001, 0.005, 0.01and 0.05). The prepared compositions were characterized using various spectroscopic techniques such as,UV-visible and photoluminescence, X-ray diffraction, Field emission scanning electron and Transmission elec-tron microscopy. X-ray diffractogram shows formation of crystalline CdS with hexagonal wurtzite structure. TheDRS exhibits absorption edge between 520 to 530 nm revealing the band gap of 2.38 to 2.34 eV. Photolumines-cence spectrum yielded two distinct peaks at ∼515 and 602 nm. The broad emission band around ∼515 nmcorresponds to the band edge excitation. FE-SEM micrographs demonstrate the formation of nanorods with30–50 nm diameter and 0.5 to 10 �m length. The aspect ratio of CuxCd1−xS nanorods increased with increasein copper doping up to 1 mol%. TEM confirms the formation of crystalline nano rods of Cu doped CdS materi-als. The photocatalytic activity of the prepared Cu doped CdS was investigated for methylene blue degradation.Among the prepared compositions, Cu0.01Cd0.99S exhibits higher rate of degradation, rate constant observed is1.42×10−2 min−1.

KEYWORDS: Solvothermal Synthesis, 1D Nano Structures, Photocatalysis, Dye Degradation.

1. INTRODUCTION

The semiconducting metal chalcogenide nanorods andnanowires have been investigated in great details due totheir unusual optical and electrical properties and poten-tial applications in nanodevices.1–3 Among the II–VI semi-conductors, CdS is one of the most studied chalcogenidehaving direct band gap of 2.4 eV.4�5 Particularly, the onedimensional nanostructures exhibit interesting physico-chemical properties and have potential applications in lightemitting diodes, solar cells, photocatalysis, optoelectronicdevices etc.6–9 These properties of metal chalcogenides canbe further improved using transition metal doping. It isevident from the literature, use of transition elements asa dopant increases the luminescent properties of chalco-genide materials.10–13 Recently large number of methodshave been tried to synthesize 1D metal sulphides suchas thermal evaporation, physical vapor deposition, elec-trochemical deposition and solvothermal technique.14–17

∗Author to whom correspondence should be addressed.Email: [email protected]: xx Xxxx XxxxAccepted: xx Xxxx Xxxx

Among these methods solvothermal route is simple, con-venient, less energy consuming and does not require anyharsh reaction conditions.18 Many researchers reported thesolvothermal synthesis of 1D CdS, using ethylenediamine(EDA) as a solvent.19–21 The EDA is well known struc-ture directing agent but still it is important to understandthe formation mechanism of 1D nanostructure with con-trolled aspect ratio. Lee et al. reported the synthesis ofone dimensional CdS nanowires and studied the formationmechanism.22 Synthesis of CdS nano wires using mixedsolvents of EDA and dodecanethiol were reported by Xuet al.23 However these synthesized nanowires and rodswere still unsatisfactory in there aspect ratios. Up till nowfor the improvement of aspect ratios, many efforts weredirected towards optimizing the reaction conditions likeuse of different solvent ratios, reaction temperatures andtime. In this study, we have demonstrated the synthesisof one dimensional copper doped CdS nanostructures bysolvothermal technique and studied their physico-chemicalproperties particularly for the influence of Cu dopingtowards the aspect ratio of CuxCd1−xS nanorods/wires. Theamount of Cu doping affecting the aspect ratio of nanorodsand their photocatalytic activity was evaluated for methy-lene blue degradation.

J. Nanoeng. Nanomanuf. 2013, Vol. 3, No. 2 2157-9326/2013/3/001/007 doi:10.1166/jnan.2013.1123 1

Solvothermal Synthesis of One Dimensional Copper Doped Cadmium Sulphide Nanorods and Their Photocatalytic Performance Arbuj et al.

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LE2. EXPERIMENTAL DETAILS

2.1. Chemicals

In the present study, the analytical grade cadmiumnitrate (Cd(NO3�2 4H2O), copper chloride (CuCl2 2H2O),thiourea, and ethylenediamine (EDA) were used withoutany further purification.

2.2. Synthesis of One Dimensional Cu Doped CdS

The CuxCd1−xS (where x= 0, 0.001, 0.005, 0.01 and 0.05)nanorods were synthesized using solvothermal technique.For this purpose 10−x mmol Cd(NO3�2 4H2O, ‘x’ mmolof CuCl2 2H2O and 20 mmol of thiourea were dissolvedseparately in 25, 10 and 25 mL of ethylenediamine respec-tively and mixed together with constant stirring. The resul-tant mixture was stirred for 10 min, transferred into teflonlined stainless steel autoclave and was further heated at200 �C for 8 hrs. The resultant mass was centrifuged,washed with distilled water and ethanol several times.It was subsequently, dried at 80 �C for 4 hrs in an oven andused for the further physico-chemical analysis and photo-catalytic study.

2.3. Characterization

The crystal structure phases were identified using pow-der XRD (Bruker AXS model D-8, 10 to 70� range,scan rate = 1� min−1� equipped with a monochroma-tor and Ni-filtered Cu K� radiation. Diffuse reflectanceUV-Visible absorbance spectra were recorded using Shi-madzu UV-Vis-NIR spectrophotometer (Model UV-3600)over a wavelength range 300 to 800 nm. The absorbancewas measured against the BaSO4 as a reference. Thephotoluminescence analysis was performed on Shimadzuspectrofluorophotometer (RF-5301PC). The morphologicalcharacterization of the samples was accomplished usingHITACHI S-4800. Microstructure analysis was carried outusing transmission electron microscopy performed usingTechnai 20 G2 (FEI, Netherlands) microscope operating at200 kV.

2.4. Photocatalytic Activity Study

For the evaluation of photocatalytic activity, 50 mg of pow-dered CuxCd1−xS was suspended in a 100 ml of aqueousMB solution (10 ppm MB, pH = 7) in a 250 ml conicalflask and stirred for 1 h in dark at room temperature. Thenthe mixture was continuously stirred under 400 W mer-cury vapour lamp irradiation in closed box. The mercuryvapor lamp was kept vertically in the quartz tube, providedwith the water circulation arrangement in order to minimizethe heating effect due to IR radiation. At regular intervalsof time, aliquots of aqueous solution were taken from theflask, centrifuged and the UV-visible absorption spectrum

of the clear solution was recorded using a double beamspectrophotometer. The decrease in the absorbance value at664 nm wavelength, corresponding to the typical peak forthe absorption spectra of MB, was utilized to determine theextent of degradation of MB and the photocatalytic activityof the sample with respect to irradiation time.

3. RESULTS AND DISCUSSION

3.1. X-Ray Diffraction Analysis

The resultant material was analyzed by powder X-raydiffractometry to identify the crystalline phases. TheXRD patterns corresponding to all the compositions ofCuxCd1−xS reveal the formation hexagonal phase (Fig. 1).The diffraction peaks at 2� = 24�8, 26.5, 28.1, 36.6, 43.6,47.8 and 51.8 can be indexed to (100), (002), (101), (102),(110), (103) and (112) crystal planes of hexagonal CdS(PDF card 41-1049 JCPDS) respectively. The intensityof (002) plane goes on decreasing with increase in cop-per doping concentration upto 1 mol% doping and againincreases for 5 mol%. The decrease of (002) peak intensityindicates the preferred orientation along c-axis of formednanorods. From the XRD analysis it is revealed that cop-per might be doped in the CdS structure and no extraneouspeaks attributed to CuS, Cu2S or CuO are visible in XRDpattern. For lower copper doping, the peaks due to CuS,Cu2S and CuO are not be visible as it is below the XRDdetection limit but for 5% Cu doping if such phases formedwould be easily identified. The XRD pattern of CuxCd1−xSmaterial does not contain any peak corresponds to CuS,Cu2S and Cu2O confirms the Cu doping in CdS lattice.The shift in the 2� values in the XRD peaks with Cudoping was not observed however, amount of Cu dopingappears to hold strong influence on preferred orientationof hexagonal CdS.

(112

)

(103

)

(110

)

(102

)(101

)

(002

)(1

00)

CdS

Cu0.001Cd0.999S

Cu0.005Cd0.995S

Cu0.01Cd0.99S

10 20 30 40 50 60 70 80

Cu0.05Cd0.95S

2θ (deg.)

Inte

nsity

(a.

u.)

Fig. 1. XRD pattern of CuxCd1−xS (where x = 0, 0.001, 0.005, 0.01and 0.05) nanorods.

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Arbuj et al. Solvothermal Synthesis of One Dimensional Copper Doped Cadmium Sulphide Nanorods and Their Photocatalytic Performance

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400 500 600 700 800

Abs

orba

nce

(a.u

.)

Wavelength (nm)

485 nmCdS

Cu0.001Cd0.999S

Cu0.005Cd0.995S

Cu0.01Cd0.99S

Cu0.05Cd0.95S

Fig. 2. UV-visible absorbance spectra of CuxCd1−xS (where x = 0,0.001, 0.005, 0.01 and 0.05) nanorods.

3.2. UV-Visible and Photoluminescence Spectra

The UV-Visible absorbance spectra of Cu doped CdS areshown in Figure 2. The Cu doped CdS having 0.001 moledoping shows absorbance at 502 nm, while other pre-pared composition have absorbance peak at 485 nm.23�24

This appreciable blue shift suggests quantum size effect.To study the band gap and optical properties of preparedone dimensional material, the CuxCd1−xS samples wereanalyzed by diffuse reflectance spectra (shown in Fig. 3)and photoluminescence spectra (shown in Fig. 4). TheDRS shows the absorption edge in the range of 520 to530 nm for all compositions which correspond to a bandgap of 2.38 to 2.34 eV respectively. The absorbance edgeof Cu0�001Cd0�999S is 527 nm showing red shift as compare

400 500 600 700 800

0.0

0.5

1.0

1.5

Abs

orba

nce

Wavelength (nm)

Cu0.001Cd0.999S

Cu0.005Cd0.995S

Cu0.01Cd0.99S

Cu0.05Cd0.95S

Fig. 3. Diffuse reflectance UV-visible absorbance spectra of CuxCd1−xS(where x = 0�001, 0.005, 0.01 and 0.05) nanorods.

500

500

Wavelength (nm)

Inte

nsity

(a.u

.)

Inte

nsity

(a.u

.)

Wavelength (nm)

CdSCu0.001Cd0.999SCu0.005Cd0.995SCu0.01Cd0.99SCu0.05Cd0.95S

550

700650600550

Fig. 4. Photoluminescence spectra of CuxCd1−xS (where x = 0, 0.001,0.005, 0.01 and 0.05) nanorods at 400 nm excitation wavelength.

to other prepared compositions. The DRS results corrobo-rate with UV-Visible absorbance spectra of prepared com-position taken in liquid mode. The change in the band gapand absorbance profile is due to the change in the dimen-sions of the nanorods and dimensions of the nanorodsdepend on the amount of copper doping. The PL spec-trum of CdS exhibits broad green emission band at 525 nmcorresponding to the band edge emission. The Cu dopedCdS ranging from 0 to 1 mol% (0.0 to 0.01 mol) dis-plays blue shift in the green emission band, the peaks areobserved at 525, 521, 506 and 507 respectively.19�22 The5 mol% (Cu0�05Cd0�95S) Cu doping shows emission peak at515 nm. Along with band edge emission, the CuxCd1−xSnano material shows more intense band at 602 nm. Thepeak at 602 nm corresponds to the Cu doping.

3.3. FE-SEM and TEM Analysis

The morphology and dimensions of CuxCd1−xS sampleswere examined by FESEM analysis. The high and lowresolution FESEM images are reproduced in Figure 5.The Cu0�001Cd0�999S shows formation rod like morphologywith uniform size and smooth surface, the thickness andlength of the rods are around 35 and 500 nm respec-tively (Figs. 5(a), (a’)). The Cu having 0.005 mole dop-ing concentrations, results increase in the length of therods from 0.5 to 2 �m having diameter in the range of30 nm (Figs. 5(b), (b’)). Further increase in Cu doping(0.01 mole) in CdS crystal leads the formation of evenlydistributed 5 to 10 micron sized nanorods having diameterin the range of 45 to 50 nm. FESEM analysis clearly showsthe formation of rod like morphology and the aspect ratiochanges with increase in Cu doping concentration upto0.01 mole. The Cu0�05Cd0�95S exhibits rod like morphologywith uneven sized rods. XRD result supports the FESEM

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Solvothermal Synthesis of One Dimensional Copper Doped Cadmium Sulphide Nanorods and Their Photocatalytic Performance Arbuj et al.

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LE(a)

(b)

(c)

(d) (d’)

(a’)

(b’)

(c’)

Fig. 5. FESEM images of CuxCd1−xS where x = (a), (a’) 0.001, (b), (b’) 0.005, (c), (c’) 0.01 and (d), (d’) 0.05.

analysis, the intensity of (002) peak goes on decreas-ing indicates the preferred orientation along c-axis up to0.01 mole copper doping and again for 0.5 mole copperdoping the intensity of 002 peak increases. This clearly

indicates the influence of copper doping on the length ofCuxCd1−xS nanorods.

The microstructure of CuxCd1−xS (x = 0�001 and 0.5)was investigated by TEM (Fig. 6). TEM of Cu0�001Cd0�999S

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Arbuj et al. Solvothermal Synthesis of One Dimensional Copper Doped Cadmium Sulphide Nanorods and Their Photocatalytic Performance

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LE(a)

(b)

(a’)

(b’)

(002)(102)

(100)

(002)(100)

0.336 nm

0.336 nm

Fig. 6. TEM images of (a), (a’) Cu0�001Cd0�999S and (b), (b’) Cu0�5Cd0�95S.

images indicate that the rods are uniform in thickness butthe length varies from 100 to 400 nm. The SAED patternshown in the inset of Figure 6(a’) confirms the forma-tion of highly crystalline hexagonal cupper doped CdSnanorods. The measured inter planar spacing 0.335 nmcorresponds to the (002) plane of wurtzite CdS. This (002)is the growth direction of CdS nanorods confirmed bySAED pattern. TEM analysis of Cu0�05Cd0�95S indicatesthe formation of nanorods with variations in the lengthof the rods. The SAED pattern and inter planar spac-ing clearly indicates the wurtzite CdS structure indicatingc-axis orientation.

3.4. Photocatalytic Activity Study

The photocatalytic activity of CuxCd1−xS samples wasevaluated by degradation of aqueous MB solution under400 W Hg lamp illumination. The decrease in theabsorbance of MB with irradiation time is plotted inFigure 7. The CuxCd1−xS (where x = 0, 0.001, 0.005,0.01 and 0.05) showed respectively 68, 62, 83, 85 and

54% MB degradation in 2 hrs of irradiation time. Amongall the prepared compositions, Cu0�01Cd0�99S shows high-est photocatalytic activity towards MB degradation. Thepure CdS reveals only 62% MB degradation, it clearlyindicates that Cu doping with 0.005 and 0.01 molenhances photocatalytic activity while other compositionslower the photocatalytic activity. For higher Cu doping(0.05 mol), photocatalytic activity dropped suddenly pre-sumably because doping of Cu creates certain defects andthat defects may act as an electron–hole recombinationcentre. It is well documented that upto certain extent ofmetal doping in metal chalcogenides there is an increasein photocatalytic activity, which in turn, depends on prepa-ration method. The reaction kinetics of MB degradationis studied and plot of lnC0/Ct versus time of irradiationis shown in Figure 8. The plot shows pseudo first orderreaction rate. The rate constant values of CuxCd1−xS forphotocatalytic MB degradation are shown in Table I. Therate constant for MB degradation using Cu0�01Cd0�99S cat-alyst is 1�42×10−2 min−1 which is almost 1.5 times thatof CdS (0�91×10−2 min−1�.

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Solvothermal Synthesis of One Dimensional Copper Doped Cadmium Sulphide Nanorods and Their Photocatalytic Performance Arbuj et al.

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400 500 600 700 800

0.0

0.5

1.0

1.5

2.0MB15 min30 min60 min90 min120 min

Abs

orba

nce

(a.u

.)

Wavelength (nm)

Cu0.001Cd0.999S

400 500 600 700 800

0.0

0.5

1.0

1.5

2.0 0 min15 min30 min60 min90 min120 min

Abs

orba

nce

Wavelength (nm)

Cu0.005Cd0.995S

400 500 600 700 800

0.0

0.5

1.0

1.5

2.0 0 min15 min30 min60 min90 min120 min

Abs

orba

nce

Wavelength (nm)

Cu0.01Cd0.99S

400 500 600 700 800

0.0

0.5

1.0

1.5

2.0 0 min15 min30 min60 min90 min120 min

Abs

orba

nce

Wavelength (nm)

Cu0.05

Cd0.95S

400 500 600 700 800

0.0

0.5

1.0

1.5

2.0 MB 15 min 30 min 60 min 90 min 120 min

Abs

orba

nce

Wavelength in nm

CdS

Fig. 7. UV-visible absorbance spectra of MB dye under 400 W mercury vapor lamp irradiation.

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0 20 40 60 80 100 120

0.0

0.5

1.0

1.5

2.0

ln C

0/C

t

Time of Irradiation (min)

CdSCu0.001Cd0.999S

Cu0.005Cd0.995S

Cu0.01Cd0.99S

Cu0.05Cd0.95S

Fig. 8. Chemical kinetics study of photocatalytic MB degradation usingCuxCd1−xS (where x = 0, 0.001, 0.005, 0.01 and 0.05) nanorods.

Table I. The crystallite size and rate constant values of Cu doped CdSnanorods.

%MB aRate constant bPLSr. no. Material degradation (min)−1 band nm

1 CdS 68 0.91×10−2 5252 Cu0�001Cd0�999S 62 0.79×10−2 5213 Cu0�005Cd0�995S 83 1.29×10−2 5064 Cu0�01Cd0�99S 85 1.42×10−2 5075 Cu0�05Cd0�95S 54 0.65×10−2 515

Notes: aCalculated from the slope of plot lnC0/Ct versus time of irradiation.bGreen emission band peak in Figure 3.

4. CONCLUSIONS

The solvothermal technique was applied for synthesis ofone dimensional Cu doped CdS nano rods. XRD confirmsthe formation of crystalline hexagonal wurtzite structure,the intensity of (002) peak indicates the extent preferredorientation. Band gap of all compositions is estimated tobe 2.34 to 2.38 eV whereas, PL shows blue shift in theband edge emission band. The FESEM and TEM confirmthe formation of crystalline one dimensional rod like mor-phology of CuxCd1−xS samples. The length of the rodsincreases with increase in Cu doping concentration from0.5 to 10 �m. The Cu0�01Cd0�99S showed the highest photo-catalytic activity for MB degradation as compared to other

compositions. The Cu doped CdS indicated increased pho-tocatalytic activity than the pristine CdS.

Acknowledgments: The authors are thankful to theDepartment of Electronics and Information Technology,Government of India, New Delhi for financial support.Authors acknowledge Dr. B. B. Kale for FE-SEM analysisand Mr. Rajendra Damkale for useful discussions.

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