SnO2 nanocomposites and its structural and optical properties

Figure 3(a) shows the formation of the uniformly distributed mixed morphology such as spherical with ellipsoidal shaped nanoparticles in the SDS assisted CeO 2 /SnO 2 nanocomposite..[r]

Morphological controlled synthesis of CeO2/SnO2 nanocomposites and its structural

and optical properties

S Usharani, V Rajendran

DOI: 10.1016/j.jsamd.2017.08.001

Reference: JSAMD 115

To appear in: Journal of Science: Advanced Materials and Devices

Received Date: 28 June 2017

Revised Date: 30 July 2017

Accepted Date: 2 August 2017

Please cite this article as: S Usharani, V Rajendran, Morphological controlled synthesis of CeO2/SnO2

nanocomposites and its structural and optical properties, Journal of Science: Advanced Materials and

Devices (2017), doi: 10.1016/j.jsamd.2017.08.001.

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Morphological controlled synthesis of CeO 2 /SnO 2 nanocomposites and its structural and

optical properties

S Usharani* and V Rajendran Department of Physics, Presidency College, Chennai-05, Tamilnadu, India

Corresponding author Email address: sushamoorthy15@gmail.com Abstract

CeO2/SnO2 nanocomposites with different dimensional nanostructures were synthesized

by the wet chemical method, using various surfactants such as SDS, CTAB and Triton X-100 The prepared CeO2/SnO2 samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Transmission electron microscopy (TEM), UV-Diffuse Reflectance Spectroscopy (UV-DRS) and Photoluminescence (PL) spectroscopy The XRD patterns reveal the presence of a mixed phase of SnO2 and CeO2; The TEM analysis showed the mixed morphology of uniformly dispersed spherical with ellipsoidal shape observed at SDS assisted CeO2/SnO2 nanocomposites; whereas spherical with hexagonal shape nanostructure was observed at Triton X-100 assisted CeO2/SnO2 nanocomposites The one dimensional (1D) nanorod like structure observed for the CTAB assisted CeO2/SnO2 nanocomposites shows CTAB acting as a face-specific capping agent to form rod-shaped micelles The room temperature photoluminescence emission studies of CeO2/SnO2 nanocomposites showed strong peaks in the

UV region, and several peaks in the visible region, which are likely to have originated from the oxygen vacancies and are potential material for optoelectronic device applications The UV results show the absorption edges shifted to a high energy region and the blue shifts that had occurred in all the samples

Keywords: CeO2/SnO2; Surfactants; Mixed morphology; Nanorods; Optical properties

1 Introduction.

Nanomaterials with various morphologies are a pillar of today’s nanoscience and bioscience, considerably used as biomarkers, therapeutics, catalysts and structural reinforcements [1] Recent research groups synthesised zero dimensional (0D), one dimensional (1D), two dimensional (2D) and three dimensional (3D) nanostructured materials and reported their potential for varied applications, such as electrocatalysts, gas sensing and photocatalysts [2-6] The ability to enhance the properties by controlling the particle size and morphology may lead to potentially useful technological applications [2] In recent years great efforts have been made in

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developing an easy process to prepare size and shape controlled nanomaterials Various research groups reported, using various solvents, surfactants and pH, which strongly influenced the shape and size of the nanomaterials [7-10], in particular, using various surfactants which may play an important role in synthesizing size and morphology controlled nanomaterials [11]

The shape and size dependent optical and electronic properties of semiconducting nanomaterials, such as CdS/SnO2, TiO2, ZnO, CeO2, CeO2/ZrO2, CuO/CeO2, CeO2/TiO2, SnO2

have various applications such as gas sensors, detectors for infrared light and lasers, solar cells, optical materials, luminescence devices, and optoelectronic devices [12-17] SnO2 and CeO2

nanomaterials reveal that they are promising materials for optoelectronic devices such as solar cells, conductive layers, and transistors due to its excellent electrical and optical properties [17-20] Significantly, the mixed metal oxide nanocomposites of SnO2/CeO2 have received much attention, because of their excellent physicochemical properties and their potential applications [21-24] Our work shows the synthesis of CeO2/SnO2 nanocomposites by the wet chemical method using anionic-Sodium Dodecyl Sulphate (SDS), cationic-cetyl trimethyl ammonium bromide (CTAB) and nonionic-Triton X-100 surfactants, and investigates the influence of the surfactants on their crystalline nature, size, morphology and optical properties The synthesis of CeO2/SnO2 nanocomposites with different morphologies has been reported in earlier literature [25,26]; however, to the best of our knowledge, there is no report in literature regarding the morphological controlled synthesis of CeO2/SnO2 nanocomposites with different surfactants such as SDS, CTAB and Triton X-100 In this paper, we investigate the synthesis of CeO2/SnO2

nanocomposites with nanorod, hexagonal and spherical with ellipsoidal morphology, and their structural and optical properties

2 Experimental

2.1 Materials

Analytical grade Cerrous chloride (CeCl3), tin (II) chloride dihydrate (SnCl2.2H2O), ammonium hydroxide (NH4OH), SDS, CTAB and Triton X-100 were purchased from Aldrich and used without any further purification Double distilled water was used as a solvent to prepare the CeO2/SnO2 nanocomposites

2.2 Preparation of CeO2/SnO2 nanocomposites

In a typical synthesis, 0.1 M of cerrous chloride (CeCl3) was mixed with 100 ml of water and stirred for 15 min Similarly, 0.1 M of tin (II) chloride dehydrate (SnCl2.2H2O) was mixed

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with 100 ml of water and stirred for 15 min These two aqueous solutions were mixed together with constant stirring for 30 min at room temperature and then 1 g of anionic surfactant SDS was added and the stirring was continued for 1 h After 1 h the aqueous ammonium hydroxide (NH4OH) solution was added dropwise to attain the pH value of 6.5 under vigorous stirring The stirring was continued overnight at room temperature and the resulting milky white colloidal gel product was obtained The prepared sample was initially dried at 100oC for 12 hrs, and later the dried sample was transferred into the alumina crucible and calcined in a muffle furnace at 600oC for 8 hrs The same procedure was repeated to prepare the CeO2/SnO2 nanocomposites of cationic and non-ionic surfactants, such as CTAB and Triton X-100

2.3 Characterization details

The structure of the prepared sample was analyzed using X-ray diffraction (XRD) analysis The XRD pattern of the nanopowders was recorded using a powder X-ray diffractometer (Schimadzu model: XRD 6000), using CuKα (λ=1.5417 Å) radiation The operating conditions were 40 kV and 30 mA in the scanning range 20-70˚ at the rate of 2 deg/min The crystallite size of the nanocomposites was calculated using Debye Scherrer’s

formula D = 0.89λ/βcosθ, where λ represents the wavelength of the X-ray, θ indicates Bragg’s angle, and β is the FWHM of the characteristic peaks Fourier transform infrared (FTIR) spectra

were taken using an FTIR model Bruker IFS 66 V spectrometer, using the KBr-pellet technique The EDX studies were carried out by the Philips model CM 20 High- resolution images and selected area electron diffraction patterns were observed with a JEOL JEM-2200FS transmission electron microscope (TEM) operating at 200 kV using a copper grid For TEM imaging, a small amount of the sample was dispersed in acetone and sonicated for 1 min, after which the solution was drop-casted onto carbon coated copper-grids Diffuse reflectance UV-vis spectra were recorded in Nujol mode on a CARY 5E UV–vis–NIR spectrophotometer The photoluminescence emission spectra were carried out on a Fluoromax-4 spectrofluorometer with

a Xe lamp as the excitation light source

3 Results and discussion

The XRD patterns of the CeO2/SnO2 nanocomposite prepared with different surfactants are shown in Fig 1(a-c) The diffractogram indicates the formation of the cubic fluorite structure

of CeO2 (JCPDS card No 43-1002) at 2θ values 28.5, 33.0, 47.4, 56.4, 59.1 and 69.5, that correspond to (111), (200), (220), (311), (222) and (400) crystal planes, respectively [19]

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Similarly, the diffraction peaks indicate that the formation of cassiterite type tetragonal structure

of SnO2 (JCPDS card No.41-1445) at 2θ values 26.6, 33.7, 37.7, 51.7, 54.7, 61.9, 64.6 and 66.1 correspond to (110), (101), (200), (211), (220), (310), (112), and (300) crystal planes, respectively [27] The XRD results show that the prepared CeO2/SnO2 nanocomposites exhibit a good crystalline nature [9,26,28], due to the influence of the anionic (SDS), cationic (CTAB) and nonionic (Triton X) surfactants and no other peaks were found, which indicates that the formation of nanocomposites is of high purity The crystallite sizes of the CeO2/SnO2

nanocomposite are calculated by using the Debye-Scherrer equation (Equation 1) from full width

at half maximum (FWHM) values of the CeO2 and SnO2 planes

D = 0.89λ/βcosθ (1)

where λ represents the wavelength of the X-ray, θ indicates Bragg’s angle, and β is the

FWHM of the characteristic peaks It was found to be 34.1, 32.0 and 30.8 nm for the CeO2/SnO2

nanocomposites for the surfactants of SDS, CTAB and Triton X respectively The XRD results show that the peak intensity of the Triton X assisted CeO2/SnO2 nanocomposite shown in Fig 1(c), was notably lower than that of the other two surfactants such as SDS and CTAB assisted CeO2/SnO2 nanocomposites (Fig 1.(a,b)), which may be due to the smaller particle size

The FTIR spectra of the prepared CeO2/SnO2 nanocomposites with three different surfactants are shown in Fig 2(a-c) In the spectra, the peaks observed at 3422 and 1637 cm-1 are ascribed to the presence of the –OH and H2O functional groups The overlapped absorption band

in the region 549-691 cm-1 is due to the Sn-O-Sn and Ce-O stretching vibrations and is in close agreement with the reported values [29,30] The absorption band centered at 2918 cm-1 is

assigned to the C-H stretching vibrations from the SDS, CTAB and Triton X [11]

Fig 3(a-c) is the TEM image of the CeO2/SnO2 nanopowder for three different surfactants such as SDS, CTAB and Triton X Figure 3(a) shows the formation of the uniformly distributed mixed morphology such as spherical with ellipsoidal shaped nanoparticles in the SDS assisted CeO2/SnO2 nanocomposite Baljinder Singh et al reported that a less polar anionic surfactant (due to a long hydrophobic chain) may adsorb on the ZnO surface, thus leading to the formation of small nanorods [31] Samaele et al reported that SDS assisted nanomaterials produce a mixed morphology such as nanorods with sphere like particles [32] During the nanostructure formation, the anionic surfactant SDS acts as a transporter of the particle, and leads to control the growth direction that is adsorbed on to the intermediate colloidal species

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surface In the presence of SDS, the products are capped by the surface modifier and the restriction of the particle growth in a definite direction leads to the formation of a spherical with ellipsoidal structure, as well as to prevent the agglomeration and produce the dispersible morphology [32] As shown in Figure 3(b), the CTAB assisted sample shows the rod like structure The CTAB plays an important role in the formation of nanorods [33] Leonardo Scarabelli et al reported the synthesis of a gold nanorod, using CTAB as a surfactant CTAB act

as a face- specific capping agent to form rod-shaped micelles, which are expected to induce anisotropic growth on spherical seeds In the presence of CTAB, the chloride ions (Cl-) from the precursor will be eventually replaced by bromide ions (Br-) from the surfactant, leading to a complex formation that will influence their redox potential, which is cathodically shifted In this, the redox potential will influence the growth kinetics to form the nanorods [34] In Fig 3(c), the Triton X assisted CeO2/SnO2 nanocomposite shows the spherical with hexagonal morphology The surfactant plays an important role in controlling the morphology of the sample In the crystallization process, the surfactant Triton X-100 which might be attributed to the steric repulsions among surface molecules leads to hindering the growth and form agglomerated spherical with hexagonal shape nanomaterials [31,32] The high resolution and low resolution images of SDS, CTAB and Triton X assisisted CeO2/SnO2 nanocomposites are shown in the supplementary material (S1) The selected area electron diffraction (SAED) patterns of the samples are shown in an inset of Fig 3(a-c), which reveals that all the samples were polycrystalline in nature Fig 3(d-f) shows the EDX spectra of the CeO2/SnO2 nanocomposites for the three different surfactants, such as SDS, CTAB and Triton X-100 It confirms that Sn, Ce and O are the only elements present in the CeO2/SnO2 nanocomposite which demonstrated the purity of the prepared catalyst with different surfactants

The UV absorption spectra of the prepared samples with three different surfactants are shown in Fig 4(a-c) The absorption edges are observed at 458, 424 and 371 nm for the SDS, CTAB and Triton X-100 assisted CeO2/SnO2 nanocomposite As observed from the spectra, the absorption edges are shifted to a high energy region and the blue shifts occurred in all the samples Considering the blue shift of the absorption positions of the bulk SnO2, the absorption onset of the present samples is assigned to the direct transition of the electrons in the SnO2 nano crystals [35] The absorption spectra showed strong absorption below 400 nm It is noted that the absorption of ceria in the UV region originates from the charge transfer transition between the

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O2- (2p) and Ce4+ (4f) orbit in CeO2 [36] Further, the optical band gap energy of all the prepared

samples was calculated using the following equation

(αhυ) = C (hυ–Eg)n (2)

Here α is the absorption coefficient, hυ is the photon energy, C is the constant, and n = 1/2 for a

directly allowed transition The optical absorption coefficient α was calculated according to the

equation α = (2.303x103 Aρ)/lc, where A is the absorbance of the sample CeO2/SnO2, ρ is the

real density of, l is the path length, and c is the concentration of the CeO2/SnO2 suspensions For

the indirect transitions, the plots of (αhυ)2 versus photon energy for the different surfactants

assisted CeO2/SnO2 nanocomposites, are shown in Fig 5(a-c) The band gap energies of the

samples prepared with different surfactants obtained by the (αhυ)2 versus (hυ) curve are 2.7,

2.92 and 3.3 eV respectively The band gap energy suggests that the CeO2/SnO2 nanocomposite

is a potential material for opto-electronic devices [9] The crystallite size (D), morphology and

band gap values of CeO2/SnO2 nanocomposite with different surfactants-SDS, CTAB and Triton

X are shown in Table.1

Fig 6(a-c) shows the room temperature PL emission spectra of the CeO2/SnO2

nanocomposites for different surfactants The strong UV emission peak at 324 nm is ascribed to

the nearest band edge emission of the excitons [37] In addition to this, strong blue green

emission peaks at 463 and 477 nm were observed Similarly, the weak emission peaks appearing

in the spectra at 415, 434, 447, 486 and 519 nm are due to the transition in the defect states In

the cubic structure of CeO2, the oxygen ions are not closely packed for which ceria produce

many oxygen vacancies When an oxygen atom was lost from CeO2, an electron pair was trapped

in the oxygen vacancy cavity, which gives F centres In ceria, the oxygen defect states were

present just below the Ce 4f level Thus the emission peak that appeared in CeO2 can be assigned

to the oxygen related defects [36] The emission peaks that appeared at 463, 477, 415, 434, 447,

486 nm are observed due to F centres in CeO2 CeO2 has some percentage of Ce3+ which is

present in the grain boundary The presence of Ce3+ in the CeO2 material acts as a hole trap and

the oxygen vacancy as an electron trap These two undergo radiative recombination resulting in

the 519 nm emission peak [36] The PL intensity was observed to be high in SDS assisted

CeO2/SnO2 nanocomposites compared to CTAB and Triton X assisted CeO2/SnO2

nanocomposites The high intensity PL emission peaks were due to the uniformly distributed

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spherical with ellipsoidal mixed morphology of CeO2/SnO2 nanocomposites The strong photoluminescence of the CeO2/SnO2 nanocomposites in the UV region suggests that they may find uses as luminescent labels and light-emitting molecular substances in nanoscale photoluminescent or nano-optoelectronic devices, photonic applications and as optical memory materials in optical memory systems in the future [38]

4 Conclusion

CeO2/SnO2 nanocomposites were successfully synthesized by the wet chemical method with various surfactants such as SDS, CTAB and Triton X-100 The XRD patterns reveal the presence of a mixed phase of SnO2 and CeO2; and possess good crystalline nature in all the surfactants assisted CeO2/SnO2 nanocomposites Furthermore, the Triton X assisted CeO2/SnO2

nanocomposites possess low intensity peaks which reveal the lower particle size The FTIR results confirmed the formation of the Ce–O and Sn–O bond The EDX studies revealed the chemical compositions of the CeO2/SnO2 sample The TEM studies revealed the decrease in particle agglomeration and the various morphologies with respect to the addition of different surfactants In particular, the CTAB assisted CeO2/SnO2 nanocomposites show the 1D nanorod like structure The UV and photoluminescence property of the CeO2/SnO2 nanocomposites shows that it could be used for optoelectronic device applications The size and morphological controlled nanocomposite materials make them promising candidates for future optoelectronic

devices, spintronic devices, gas sensing and visible light photocatalytic performance

Acknowledgement

Authors are grateful to the Department of Science and Technology (DST), India for financial support to carry this work

References

[1] H Heinz, C Pramanik, O Heinz, Y Ding, R.K Mishra, D Marchon, R.J Flatt,

I.E-Lopis, J Llop, S Moya, R.F Ziolo, Nanoparticle decoration with surfactants: Molecular interactions, assembly, and applications, Surf Sci Rep 72 (2017) 1-58

[2] B Ahmed, S Kumar, S Kumar, A.K Ojha, Shape induced (spherical, sheets and rods)

optical and magnetic properties of CdS nanostructures with enhanced photocatalytic activity for photodegradation of methylene blue dye under ultra-violet irradiation, J Alloys Compd 679 (2016) 324-334

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[3] X Jiaqiang, W Ding, Q Lipeng, Y Weijun, P Qingyi, SnO2 nanorods and hollow

spheres: Controlled synthesis and gas sensing Properties, Sens Actuators, B 137 (2009) 490-495

[4] X Jin, J Lim, N-S Lee, S-J Hwang, A powerful role of exfoliated metal oxide 2D

nanosheets as additives for improving electrocatalyst functionality of grapheme, Electrochim Acta 235 (2017) 720-729

[5] A A Firooz, A R Mahjoub, A A Khodadadi, Highly sensitive CO and ethanol

nanoflower-like SnO2 sensor among various morphologies obtained by using single and mixed ionic surfactant templates, Sens Actuators, B 141 (2009) 89-96

[6] W Dong, B Song, G Zhao, G Han, Effects of pH on morphosynthesis and

photocatalytic activity of calcium titanium oxides via a facile aqueous strategy, Mater Res Bull 48 (2013) 4633-4640

[7] J Gajendiran, V.Rajendran, Synthesis and characterization of coupled semiconductor

metal oxide (ZnO/CuO) nanocomposite, Mater Lett 116 (2014) 311-313

[8] N Talebian, H.S.H Zavvare, Enhanced bactericidal action of SnO2 nanostructures

having different morphologies under visible light: Influence of surfactant, J Photochem Photobiol., B 130 (2014) 132-139

[9] S Usharani, V Rajendran, Optical, magnetic properties and visible light photocatalytic

activity of CeO2/SnO2 nanocomposites, Eng Sci Technol., an Int J 19 (2016)

2088-2093

[10] K.M Hyie, N.A Resali, W.N.R Abdullah, W.T Chong, Synthesis and Characterization

of Nanocrystalline Pure Cobalt Coating: Effect of pH, Procedia Engineering 41 (2012) 1627-1633

[11] S Gnanam, V Rajendran, Facile hydrothermal synthesis of alpha manganese sesquioxide

(α-Mn2O3) nanodumb-bells: Structural, magnetic, optical and photocatalytic properties, J Alloys Compd 550 (2013) 463-470

[12] Ch Venkata Reddy, R.V.S.S.N Ravikumar, G Srinivas, J Shim, M Cho, Structural,

optical, and improved photocatalytic properties of CdS/SnO2 hybrid photocatalyst nanostructure, Mater Sci Eng B 221 (2017) 63-72

M AN

[13] D T Jayaram, S Runa, M L Kemp, C K Payne, Nanoparticle-induced oxidation of

corona proteins initiates an oxidative stress response in cells, Nanoscale, 9 (2017)

7595-7601

[14] V L Prasanna, R Vijayaraghavan, Insight Into the Mechanism of Antibacterial Activity

of ZnO-Surface Defects mediated Reactive Oxygen Species even in Dark, Langmuir, 31 (2015) 9155-9162

[15] Q Yuan, H-H Duan, L-L Li, L-D Sun, Y-W Zhang, C-H Yan, Controlled synthesis

and assembly of ceria-based nanomaterials, J Colloid Interface Sci 335 (2009) 151-167 [16] Y Zhang, J Xu, P Xu, Y Zhu, X Chen, W Yu, Decoration of ZnO nanowires with Pt

nanoparticles and their improved gas sensing and photocatalytic performance, Nanotechnology 21 (2010) 285501 (7pp)

[17] S Bagherian, A K Zak, X-ray peak broadening and optical properties analysis of SnO2

nanosheets prepared by sol-gel method, Mater Sci Semicond Process 56 (2016) 52-58 [18] V K Tomer, S Duhan, A facile nano casting synthesis of mesoporous Ag-doped SnO2

nanostructures with enhanced humidity sensing performance, Sens Actuators, B 223 (2016) 750-760

[19] V Ramasamy, G Vijayalakshmi, Effect of Zn doping on structural, optical and thermal

properties of CeO2 nanoparticles, Superlattices and Microstruct 85 (2015) 510-521 [20] J Malleshappa, H Nagabhushana, B.D Prasad, S.C Sharma, Y.S Vidya, K.S

Anantharaju, Structural, photoluminescence and thermoluminescence properties of CeO2

nanoparticles, Optik 127 (2016) 855-861

[21] H.R Pouretedal, Z Tofangsazi, M.H Keshavarz, Photocatalytic activity of mixture of

ZrO2/SnO2, ZrO2/CeO2 and SnO2/CeO2 Nanoparticles, J Alloys Compd 513 (2012)

359-364

[22] E L Foletto, S Battiston, G C Collazzo, M M Bassaco, M A Mazutti, Degradation of

Leather Dye Using CeO2-SnO2 Nanocomposite as Photocatalyst Under Sunlight, Water Air Soil Pollut 223 (2012) 5773-5779

[23] W Qin, L Xu, J Song, R Xing, H Song, Highly enhanced gas sensing properties of

porous SnO2-CeO2 composite nanofibers prepared by electrospinning, Sens Actuators, B

185 (2013) 231-237