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Novel template-free, large scale synthesis of nanostructured CdxZn1-xS with tuneable band structure for H2 production and organic dye degradation using solar light Sunil N Garaje, Sanjay K Apte, Sonali D Naik, Jalindar D Ambekar, Ravindra S. Sonawane, Milind V. Kulkarni, Ajayan Vinu, and Bharat Bhanudas Kale Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/es3045955 • Publication Date (Web): 14 May 2013 Downloaded from http://pubs.acs.org on May 24, 2013

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Environmental Science & Technology

Novel template-free synthesis of nanostructured CdxZn1-xS with tuneable band structure for H2 production and organic dye degradation using solar light Sunil N. Garaje ¥, Sanjay K. Apte ¥, Sonali D. Naik ¥, Jalindar D. Ambekar ¥, Ravindra S. Sonawane ¥, Milind V. Kulkarni ¥, Ajayan Vinu §* and Bharat B. Kale ¥* ¥

Centre for Materials for Electronic Technology (C-MET), Govt. of India, Panchawati, off Pashan road, Pune: 411008, INDIA.

§

Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Corner College and Cooper Roads (Bld 75) Brisbane, Queensland 4072, Australia

KEYWORDS: Metal Sulfide, Solid State Reaction, Nanomaterials, Nanocomposite and Photocatalysis ABSTRACT We have demonstrated a template-free large scale synthesis of nanostructured CdxZn1-xS by a simple and a low-temperature solid state method. Cadmium oxide, zinc oxide and thiourea in various concentration ratios are homogenized at moderate temperature to obtain nanostructured

ACS Paragon Plus Environment


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CdxZn1-xS. We have also demonstrated that phase purity of the sample can be controlled with a simple adjustment of the amount of Zn content and nanocrystalline CdxZn1-xS (X=0.5 & 0.9) of hexagonal phase with 6-8 nm size and 4-5 nm sized Cd0.1Zn0.9S of cubic phase can be easily obtained using this simple approach. UV-Vis and PL spectrum indicate that the optical properties of as synthesized nanostructures can also be modulated by tuning their compositions. Considering the band gap of the nanostructured CdxZn1-xS well within the visible region, the photocatalytic activity for H2 generation using H2S and methylene blue dye degradation is performed under visible-light irradiation. The maximum H2 evolution of 8320 µmol h−1g-1 is obtained using nanostructured Cd0.1Zn0.9S, which is four times higher than that of bulk CdS (2020 µmol h−1g-1) and the reported nanostructured CdS (5890 µmol h−1g-1). As synthesized Cd0.9Zn0.1S shows two fold enhancement in degradation of methylene blue as compared to the bulk CdS. It is noteworthy that the synthesis method adapted provides an easy, inexpensive and pollution free way to synthesize very tiny nanoparticles of CdxZn1-xS with a tunnable band structure on a large scale, which is quite difficult to obtain by other methods. More significantly, environmental benign enhanced H2 production from hazardous H2S using CdxZn1-xS is demonstrated for the first time. INTRODUCTION Nanostructured semiconductors are important for the fabrication of next-generation nanoscale optoelectronic devices.1–3 In particular, semiconducting metal sulfide nano particulates possess novel optical and electrical properties and are considered as building blocks for photovoltaic devices including dye sensitized cells and hybrid nanocrystal-polymer composite solar cells and optoelectronics applications. The much efforts have been expended on their integration into optical switches,4 field emitters, 5 sensors 6, 7 and lasers.8


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Photocatalytic H2 production from H2S is of great interest from both theoretical and practical viewpoints due to its possible application for converting sunlight energy into chemical energy, which is an important green chemistry issue. 9–16 Highly corrosive and toxic hydrogen sulfide (H2S) has been continually vented out to environment in fairly huge amount (15-20%) by the oil refineries and is global threat to environment. The acidic H2S is an environmental pollutant because of its toxic and corrosive nature. Hence, the decomposition of H2S to green products has attracted immense attention because of the environmental problems which harmfully effect human life. H2 is an attractive sustainable clean energy source because of both the energy crisis caused by the depletion of fossil fuel reserves and the environmental pollution caused by continuous burning of fossil energy resources containing very large amount of sulfur compound.17-19 Conventional TiO2 photocatalysts possess excellent activity and stability, but require near-ultraviolet (UV) irradiation (about 4% of the solar spectrum) for effective photocatalysis, which severely limits their practical applications.

20–23

It is highly desirable to

develop a photocatalyst that can use visible light effectively under sunlight. Chalcogenides are regarded as good candidates for visible-light photocatalysts. Among them, CdS is the most often applied for photocatalytic H2 production due to its high activity under visible light and sufficiently negative flat-band potential.24,

25

However, there are still some shortcomings

prohibiting its wide usage such as its photocorrosion and the need to employ noble metals as cocatalysts. 26–28 Considerable efforts are still being made to improve the photocatalytic properties of CdS catalysts. Different strategies are reported in literature to modify the photocatalytic properties of CdS like control of particle size, addition of co-catalysts and combination with different elements to form mixed photocatalysts. Among these, the combination of semiconductors of different band gap forming composite materials is an interesting way for the



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photoactivity control because the potentials of the conduction and valence bands of composite materials shift successively with composition. The optoelectronic and structural properties of ZnS make this material interesting as semiconductor for combining with CdS. ZnS has a wide band gap of 3.2 eV that may improve the photoabsorption ability of CdS and ZnS may form a continuous series of composite materials with CdS (CdxZn1-xS) where metal atoms are mutually substituted in the same crystal lattice.

29–31

Although much research has been done to study the

structural and optical properties of CdxZn1-xS composite materials as colloidal nanocrystals for optoelectronic applications32-37 but very limited information is available for its application as a photocatalyst for H2O splitting.38-40 However, there is no literature available on H2S splitting by using nanostructured CdxZn1-xS as a photocatalyst. In these studies, it has been shown that both optical properties and photocatalytic activity depend strongly on Zn composition in CdxZn1-xS. The synthesis of such composites (nanoscale) has been reported for academic interest and methods used are not giving constituent results at large scale. Maria Antoniadou et al

38(b)

have

reported CdS-ZnS and CdS-ZnS/TiO2 using co-precipitation method. However, the method is well known and produces pollutants like sodium nitrate. Further, the photoelectrocatalaysis studies of these composites have been performed. Synthesis of such nanostructured CdxZn1-xS composite of size 4-8nm at large scale is a challenge and has not been attempted so far. In view of this, we have investigated large scale synthesis method for such nanostructured composite. In the present work, we have demonstrated the large scale synthesis of nanostructured tertiary CdxZn1-xS by a simple, template-free, low-temperature method using solid-solid phase condition for the first time. This method allows us to fabricate the CdxZn1-xS in large scale which will pave the way for commercialization. The obtained materials have been extensively characterized by several sophisticated techniques in order to obtain its structural, morphological and optical


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properties. We have also investigated the visible light driven photocatalytic activity for the production of H2 using H2S and methylene blue dye degradation by using as synthesized CdxZn1-xS.

EXPERIMENTAL

Analytical grade Cadmium oxide, Zinc oxide and thiourea were purchased from the local chemical manufacturer (Qualigens Chemicals) and were used as received. Synthesis: The CdxZn1-xS were prepared by solid-solid phase reaction. All analytical grade reagents, cadmium oxide, zinc oxide and thiourea of purity 99.9% were used without further purification. The cadmium oxide, zinc oxide and thiourea (two moles) were mixed with appropriate amounts and ground by using pestle and mortar. The mixture was placed in the alumina crucible and kept in electrical oven at 140° C for 16 hours. The product was thoroughly washed with distilled water to remove by-product and excess thiourea followed by washing with anhydrous ethanol. The final product was dried at 70° C for 4 hours in laboratory oven. The details of the quantity of precursors used and product obtained per batch is mentioned in supporting information S I. The details of the optimization of reaction parameters are also given in supporting information S II. Characterization: Synthesized samples were characterized by X-ray diffractometer (Model-D8, Advance, Bruker AXS). The samples were also characterized with transmission electron microscopy (TEM, model Philips, EM-CM-12) to determine the particle size and morphology. XPS was carried out by using an ESCA-3000 instrument (VG Scientific Ltd., England). The Brunauer–Emmett–Teller technique (BET) was applied to investigate the surface area by using



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SMART SORB 91, Smart Instruments Co. India. The optical properties were recorded from UVVisible-Near

infrared

(UV-Vis-NIR)

spectrophotometer

(SHIMADZU

UV-3600).

Photoluminescence spectrum was recorded by photoluminescence spectrometer Perkin-ElmerLS-55. Photocatalytic activity measurement for H2 evolution: The photocatalyst was introduced as a suspension into cylindrical quartz reactor. A Xe-lamp light source ((LOT ORIEL GRUPPE, EUROPA, LSH302) of 450 W with cut off filter (> 420 nm) was used. At a constant temperature of 25 ± 1oC, vigorously stirred suspension was purged with argon for 1h and then hydrogen sulfide (H2S) was bubbled through the solution for about 1hr. Each experiment was carried out using 0.5 g of catalyst in 750 ml of KOH solution (0.5 M) with H2S flow 2.5 ml min-1. The excess H2S was trapped in NaOH solution. The amount of evolved H2 was measured using graduated gas burette and analyzed using Gas Chromatograph (Model Shimadzu GC-14B, MS-5 Å column, TCD, Ar carrier). Photocatalytic activity measurement for methylene blue degradation: The photocatalytic activity of degradation of methylene blue (MB) in an aqueous solution, carried out in direct sunlight. For each run, 50 mg of photocatalyst sample was dispersed in 50 ml of a 20 ppm aqueous solution of MB. Prior to the irradiation, the suspension was magnetically stirred in the dark for 120 min to establish an adsorption–desorption equilibrium between the photocatalyst and MB. The mixture was then kept in direct sunlight. At certain time intervals, aliquots of about 1ml were withdrawn from the suspension and filtered. The measurement of MB concentration in the filtrate was carried out using UV-Vis–NIR spectroscopy (Perkin Elmer λ-950 spectrometer). The area of the absorption bands integrated in the range 500–750nm was used to monitor the


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progress of reaction. The absorption data obtained was then used to calculate the percent degradation. 3. RESULT AND DISCUSSION Structural study of CdxZn1-xS: CdxZn1-xS with different Cd molar ratios of (a) X=0.1, (b) X=0.5 and (c) X= 0.9 were obtained from the precursor CdO, ZnO and two moles of thiourea. Initially, 1 and 1.5 mole of thiourea has been used for reaction which showed partial formation of CdxZn1-xS. However, when two moles of thiourea were used for the reaction, the complete formation of CdxZn1-xS was observed. In view of this, all reactions were performed using two moles of thiourea for complete formation of CdxZn1-xS. The product was characterized using XRD. Figure 1 show the X-ray diffraction pattern of (a) standard XRD pattern of CdS (JCPDS No. 80-0006), (b-d) nanostructured CdxZn1-xS, and (e) standard XRD pattern of ZnS (JCPDS No. 05-0566). From the XRD pattern, it is concluded that the diffraction peaks of as synthesized CdxZn1-xS were shifted to a higher angle side from hexagonal CdS to cubic ZnS with the increase in Zn content. The successive shift in the diffraction peaks indicate that as synthesized samples are not a merely mixture of CdS and ZnS but shows the existence of single phase CdxZn1-xS by inserting Zn ion into CdS lattice.

41-43

. The XRD pattern of CdO, ZnO and as synthesized

CdxZn1-xS is given in supporting information (S III). It clearly shows the absence of reactants in the as synthesized sample CdxZn1-xS. We have also shown the XRD pattern of CdS, ZnS, mix powder of CdS0.5ZnS0.5 and CdxZn1-xS in supporting information (S IV), which also confirms the formation of single phase CdxZn1-xS. The nanostructured CdxZn1-xS (X=0.5, 0.9) existing in the hexagonal phase and Cd0.1Zn0.9S shows the cubic phase. Similar phenomenon has also been reported earlier.

44, 45

It is considered that Zn2+ ion gets incorporated in the CdS lattice or



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entered to its interstitial sites because the radii of Zn2+ ion (0.74 Ao) is smaller than that of Cd2+ (0.97Ao). The average crystallite size of the as synthesized samples were calculated using Scherrer formula and observed to be 3.00, 2.00 and 2.2 nm for CdxZn1-xS (X=0.1, 0.5, 0.9), respectively. X-ray Photoelectron Spectroscopy Study: Figure 2 shows the representative XPS spectra of as synthesized Cd0.1Zn0.9S: (a) survey spectrum, (b) high resolution Cd 3d spectrum, (c) Zn 2p3 peaks and (d) S 2p3 spectrum. The survey XPS spectrum (figure 2 a) of the product shows the presence of Cd, Zn and S along with the O and C. The presence of very small amount of C and O in the spectrum is due to the carbon tape used for measurement and the adsorbed gaseous molecules such as CO2 and H2O, respectively. High resolution XPS spectra of Cd 3d, Zn 2p33/2, Zn2p31/2 and S 2p3 are shown in figure 2 (b-d), respectively. The Cd 3d, Zn 2p, and S 2p3 peaks at binding energies 405.26 (Cd 3d 5), 412.02 (Cd 3d 5), 1045.37 (Zn 2p1/2), 1022.40 (Zn 2p3/2) & 162.15 (S 2p3) were attributed to the Cd0.1Zn0.9S molecular environment. The peaks are in good agreement with data reported in the literature for CdxZn1-xS. 46 Transmission Electron Microscopy: The size and the morphologies of as synthesized nanostructured CdxZn1-xS have been investigated using HRTEM analysis. Figure 3 shows HRTEM images of nanostructured CdxZn1-xS, (a, b) x = 0.1, (c, d) x = 0.5 and (e, f) x = 0.9, respectively. Insets of figure show ED pattern of respective samples. HRTEM images of as synthesized nanostructured CdxZn1-xS shows the spherical particle morphology with average particle size in the range of 4-8 nm. There is no appreciable effect on morphologies of as synthesized CdxZn1-xS except particle size. We obtained 6-8 nm size for


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CdxZn1-xS (x=0.5, 0.9) and 4-5 nm size for Cd0.1Zn0.9S. Electron diffraction (ED) patterns show good crystallinity of as synthesized nanostructured CdxZn1-xS. The surface area of CdxZn1-xS was also measured using the Brunauer–Emmett–Teller technique (BET). The surface area of the precursor i. e. zinc oxide and cadmium oxide was observed to be 2.74 and 1.89 m2 g-1, respectively. The surface areas of CdxZn1-xS (x= 0.1, 0.5, 0.9) was observed to be 323, 278 and 215 m2 g-1 respectively. Surprisingly, the highest surface area was observed for Cd0.1Zn0.9S. It was also observed that there is a decrease in surface area with an increase in the ratio of cadmium in CdxZn1-xS. The particle size increases with increase in cadmium in the composition which ultimately decreases the surface area. Formation mechanism: In the present solid state reaction, the desired molar ratios of oxides are reacting with two mole of thiourea according to the following reaction. 2(NH2)2 CS

2H2S + 2NH2CN

xCdO + 1-x ZnO + 2H2S

(1)

CdxZn1-xS + H2O

(2)

---------------------------------------------------------------------------------------------------------xCdO + 1-x ZnO + 2(NH2)2 CS

CdxZn1-xS + 2NH2CN + H2S + H2O

(3)

2NH2CN +H2S

NH2CSNH2 + NH2CN

(4)

NH2CN + H2O

NH2CONH2

(5)

The reaction (1) is generally reversible in excess thiourea and hence the reaction is proceeding through intermediate reaction (4). The NH2CN obtained in the reaction (4) is again reacting with water and forms urea (5). The scheme 1 represents the overall formation mechanism of nanostructured CdxZn1-xS. The solid solution of oxides (CdO + ZnO) is surrounded by thiourea. At the desired temperature i. e. 140 0C, the reaction (1) takes place. The H2S formed is proceeding through the solid solution and slowly reacting with oxides. Due to excess



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environment of H2S within the solid, intermediate gas solid reaction takes place and form the CdxZn1-xS as per the scheme 1. As per overall reaction, we obtained unreacted thiourea and urea (4, 5). This has been confirmed by standard chemical analysis method i. e. iodometric titration. After rigorous washing of the product, the filtrate obtained was tested for thiourea using iodometric titration. We found a presence of nearly 50% thiourea in the filtrate which may be due to unutilized excess thiourea. UV-Vis-DRS Spectroscopy study: The UV-Vis-DRS Spectrum of nanostructured CdxZn1-xS (figure 4) shows the sharp absorption edges for all samples, and the absorption onset is gradually blue-shifted from CdS to ZnS with the presence of Zn molar ratio. UV-Vis spectrum of as synthesized samples (x=0.9, 0.5, 0.1), it is concluded that the spectra of as synthesized samples shifts noticeably towards lower wavelengths as the concentration of Zn increases, implying that this sample is not a simple mixture of CdS and ZnS, but single phase CdxZn1-xS . The UV-Vis-DRS spectra of mix powder of CdS and ZnS of different concentration (supporting Information S V) also confirms the formation of single phase CdxZn1-xS.

The

bandgap of as synthesized CdxZn1-xS increases as the concentration of Zn increases (2.48 to 2.85 eV). The details of the bandgap of CdxZn1-xS samples are given in Table 1. From the optical properties, it can be concluded that band gap can be tuned with the composition. Photoluminescence study: Figure 5 shows the photoluminescence spectra of as synthesized CdxZn1-xS, excited at 380 nm. The photoluminescence spectrum of CdxZn1-xS shows emissions at 475, 500 nm and 520 nm. These emission peaks correspond to the yellow and green light emission in the scale of visible light spectrum. The photoluminescence spectrum of Cd0.1Zn0.9S shows strong emissions at 475, 500 nm and weak emission at 520 nm. The emission observed at 475 nm is attributed to the well known zinc


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sulfide related luminescence of zinc vacancies. The emission peaks at 500 nm is due to the recombination of electrons from the energy level of sulfur vacancies with the holes from the energy level of zinc vacancies.

47

The weak emission peak at 520 nm is attributed to the

cadmium sulfide related luminescence.

48

The photoluminescence study shows that there is

increase in intensity of emission peaks at 520 nm and decrease in intensity of emission peaks at 475 nm with increasing the concentration of Cd (x) in CdxZn1-xS, which is quite understood. Photocatalytic activity measurement: As synthesized samples of CdxZn1-xS (x= 0.1, 0.5 and 0.9) have band gap in the range of 2.85-2.48 eV at room temperature. Hence, due to its good spectral response to visible light the photocatalytic activitie of CdxZn1-xS have been investigated. We have investigated photocatalytic H2 evolution from H2S splitting under visible-light irradiation. We have also studied the methylene blue (MB) dye degradation under normal sun light. Photocatalytic H2 Evolution from H2S Splitting: The photocatalytic H2 evolution reaction was performed using as-synthesized nanostructured CdxZn1-xS under ambient conditions. Series of experiments were performed to compare the H2 evolution rate by CdxZn1-xS with nano CdS and bulk CdS. The H2 evolution data is summarized in Table 2. From figure 6, it can be clearly observed that all of the CdxZn1-xS samples (x=0.1, 0.5 and 0.9) shows much better activity of H2 production than bulk and nano CdS. The linearity of the graph clearly shows the stable H2 evolution rate of CdxZn1-xS. Table 2 shows the rate of H2 evolution of the as synthesized nanostructured CdxZn1-xS and bulk CdS. It is noteworthy that, the catalyst Cd0.1Zn0.9S shows the highest activity of H2 production

i. e. 8320 µmol h−1 g-1 under visible

light irradiation, which is much higher than that of bulk CdS, reported nanostructured CdS [48] as well as other photocatalyst reported so far.

49-52

The activity was decreased with the increasing



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concentration of Cadmium (x). There is a decrease in photocatalytic activity with decreasing band gap. Most probably the optimum band gap (2.85eV) and the position of conduction band and valence band are more important for the good photocatalytic activity. Generally, more negative potential of the conduction band of the CdxZn1-xS will allow for more efficient H2 generation. In view of this, higher activity obtained for Cd0.1Zn0.9S is quite understood. Firstly, the highest activity of H2 evolution under visible light irradiation probably attributed to the Cd0.1Zn0.9S that possesses an optimum band gap and a moderate position of conduction band with an appropriate amount of doped Zn into the lattice of CdS provides suitable impurity energy levels which make the excited electrons from the valence band of CdS to easily inject into the conduction band. Additionally, the lower particle size obtained for Cd0.1Zn0.9S is also responsible for enhancement of H2 evolution due to increase in surface to volume ratio. The highest surface area obtained for Cd0.1Zn0.9S is self explanatory to validate higher activity. The all above photocatalyst shows the very good stability after the photocatalytic reaction. The supporting information (S VI) shows the XRD pattern of all photocatalyst after the photocatalytic reaction. Photocatalytic degradation of methylene blue (MB): It is well known that the dye industry has a problem of disposal of methylene blue (MB) due to its high solubility in water. Traces of this dye are harmful to human beings. It causes skin diseases and intestinal problems. In view of this, MB degradation under sunlight was performed using nanostructured CdxZn1-xS. Figure 7 shows the photocatalytic degradation of MB: (a-b) UV-Vis absorption spectra of degraded MB solution (20 ppm) using as-synthesized CdxZn1-xS, (c) photocatalytic degradation in percent mode of as-synthesized CdxZn1-xS and bulk CdS. The Cd0.9Zn0.1S shows the maximum degradation of MB (94.15%) as compared to the Cd0.1Zn0.9S (78.07) and bulk CdS (49.7) as well.


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As synthesized Cd0.9Zn0.1S shows two fold enhancements in degradation of MB as compared to the bulk CdS. Surprisingly, photodegradation activity decreases with the increasing the concentration of Zn in the nanostructured

CdxZn1-xS. If we compare with photo-reduction of H2S to produce H2,

exactly the reverse trend has been observed. Here, again the photoluminescence study is supporting the photodegradation of MB. Generally the organic waste degradation is due to the oxidation occurring due to light. It is quite well known that holes are responsible for the oxidation and electrons for reduction. We believe that the electrons from the energy levels of sulfur vacancies produced by this excessive thiourea increase the hole–electron recombination process. Photoluminescence study clearly shows the strong emission at 500 nm in case of Cd0.9Zn0.1S due to due to the recombination of electrons from the energy level of sulfur vacancies with the holes from the energy level of zinc vacancies. It clearly shows that the weak transport of electrons at the surface which ultimately increases the degradation of MB via oxidation process which accelerated by holes. Hence, the higher photodegradation obtained using Cd0.9Zn0.1S as compared to Cd0.1Zn0.9S is quite understood. It is noteworthy that the desired band gap can be obtained using fixing the composition to obtain highest photocatalytic activity. We have demonstrated the large scale synthesis of nanostructured tertiary CdxZn1-xS by a simple, template-free, low-temperature using solid state reaction. The uniform distribution of CdxZn1-xS with spherical morphology has been obtained. XRD analysis showed that the as synthesized nanostructured CdxZn1-xS (X=0.5, 0.9) existing in the hexagonal phase and the Cd0.1Zn0.9S shows the cubic phase with a crystallite size of 3.02, 2.17 and 2.06 nm for x=0.1, 0.5 and 0.9, respectively. Whereas HRTEM analysis revealed the particle size of the as-synthesized



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CdxZn1-xS is in the range of 3–8 nm. The as synthesized CdxZn1-xS show bandgap in the range of 2.85-2.48 eV, which is higher than the CdS and lower than the ZnS. The bandgap of as synthesized CdxZn1-xS increases as the concentration of Zn increases. The as synthesized CdxZn1xS

showed an excellent photocatalytic activity for H2 evolution by H2S splitting and methylene

blue dye degradation. As-synthesized CdxZn1-xS showed excellent rates of H2 evolution compared to bulk CdS and nanostructured CdS, as well. The maximum H2 evolution of 8320 µmol h−1g-1 is obtained using CdxZn1-xS (x=0.1), which is more than four times higher than that of bulk CdS (2020 µmol h−1g-1) and reported nanostructured CdS (5890 µmol h−1g-1), as well. This is mainly due to the moderate band gap of Cd0.1Zn0.9S as compared to the other CdxZn1-xS (x=0.5, 0.9). As synthesized Cd0.9Zn0.1S shows two fold enhancement in degradation of MB as compared to the bulk CdS. Significantly, these CdxZn1-xS can be synthesized at a larger scale easily with tuning of band structure. The proposed simple methodology is believed to be a significant breakthrough in the field of nanotechnology, and the method can be further generalized as a rational preparation scheme for the large-scale synthesis of various other nanostructured metal nanocomposites.


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FIGURES: Figure 1. X-ray diffraction patterns of (a) Standard CdS (JCPDS No. 80-0006), (b-d) as synthesized CdxZn1-xS and (e) Standard ZnS (JCPDS No. 05-0566)



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Figure 2. Representative XPS spectra of as synthesized CdxZn1-xS (x=0.1): (a) survey spectrum, high resolution (b) Cd 3d, (c) Zn 2p3 and (d) S 2p3 spectrum


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Figure 3. HRTEM images of as-synthesized CdxZn1-xS: (a, b) x = 0.1, (c, d) x = 0.5 and (e, f) x = 0.9 with ED patterns as an inset



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Figure 4. UV-Vis Diffuse reflectance spectra of as synthesized CdxZn1-xS

Figure 5. Photoluminescence spectra of as synthesized CdxZn1-xS


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Figure 6. Photocatalytic activities for H2 production by as-synthesized CdxZn1-xS, nanostructured and bulk CdS



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Figure 7. Photocatalytic degradation of MB: (a-b) UV-Vis absorption spectra of degraded MB solution (20 ppm) using as-synthesized CdxZn1-xS, and (c) photocatalytic degradation in percent mode of as-synthesized CdxZn1-xS and bulk CdS

SCHEMES:

Scheme 1. Schematic representation of the formation mechanism of nanostructured CdxZn1-xS


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TABLES Table 1. Details of bandgap of as synthesized nanostructured CdxZn1-xS Sr. No .

Samples

Absorption peaks (nm)

Bandgap (eV)

1.

Cd0.1Zn0.9S

435

2.85

2.

Cd0.5Zn0.5S

480

2.58

Cd0.9Zn0.1S

502

2.48

3.

Table 2. Photocatalytic activities for H2 evolution from H2S Sr. No.

Samples

Rate of H2 evolution (µmol h−1 g-1)

1.

Cd0.1Zn0.9S

8320

2.

Cd0.5Zn0.5S

7400

3.

Cd0.9Zn0.1S

6300

4.

Nanostructured CdS

5890

5.

Bulk CdS

2020



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ASSOCIATED CONTENT Supporting Information: The details of the quantity of precursors used and obtained product (CdxZn1-xS) per batch, the details of the optimization of reaction parameters, XRD pattern of CdO, ZnO, and as synthesized CdxZn1-xS, XRD pattern of CdS, ZnS, mix powder of CdS0.5ZnS0.5 and as synthesized CdxZn1-xS, UV-Vis-DRS spectra of CdS, ZnS and mix powder of CdS and ZnS with different concentration, XRD pattern of as synthesized CdxZn1-xS after the phocatalytic reaction. This material is available free of charge via the Internet at http://pubs.acs.org

AUTHOR INFORMATION AUTHOR EMAIL ADDRESS: [email protected] / [email protected] CORRESPONDING AUTHOR FOOTNOTE: Tel. No. : (020) 25899273, 25898141, 25898390 Mob. No. : 9423014560 Fax No. : (020) 2589 8180/085 E-mail : [email protected] / [email protected] ACKNOWLEDGEMENTS: The authors would like to thank Dr. D. P. Amalnerkar, Executive Director, C-MET for encouragement and Nanocrystalline Materials Group C-MET for support. BBK would like to thank Department of Electronics and Information and Technology (DeitY), Govt. of India, for financial support. We also acknowledge Dr. K. R. Patil, National Chemical Laboratory (NCL), Pune for XPS characterization.


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52. Bhirud, A. P.; Sathaye, S. D.; Waichal, R. P.; Nikam, L. K.; Kale, B. B. An eco-friendly, highly stable and

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for

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TOC Art


Template-Free Synthesis of Nanostructured Cd - American

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