Microwave Synthesis and Photocatalytic Activity of Cadmium Indium Sulfide Nanocomposite

Nanocomposite of CdIn2S4 was synthesized by direct feeding microwave synthesis method, using indium nitrate, cadmium nitrate and thioacetamide as raw material, cetyltrimethyl ammonium bromide(CTAB) as surfactant. The crystal structure, morphology and the optical property of as-prepared sample were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM) and Fluorescence spectra. The results showed that the as-prepared nanocomposite is hexagonal CdIn2S4. The SEM showed that the shape of these nanoparticles is irregular and looks like flake/sphere with some aggregation. The size of most of the aggregate is 100 to 300 nm. The photocatalytic activity of the as-prepared samples was studied by using degradation of methylene bule under visible light. The results show that the photocatalytic activity of CaIn2S4 photocatalyst was very well. When the catalyst was 1.0 g/L, C(H2O2) was 3 mL/L, after 120 min of the irradiation, the degradation rate of CdIn2S4 for methylene blue of 20 mg/L reached 86.06%.


Introduction
The future of modern society will depend on how we solve the urgent environmental and energy issues that we face today. Ever since the decomposition of water on a TiO 2 electrode under UV light irradiation was first reported in 1972 [1], photocatalytic processes based on semiconductors have offered the most promising solutions. They can both be used for water splitting to produce hy- drogen and oxygen and for the degradation of toxic pollutants in wastewater treatment. TiO 2 is by far the most widely used and investigated photocatalyst due to its high efficiency and photostability. In addition, it is non-toxic and commercially available at a low price. However, TiO 2 has a major drawback that has not been overcome till date. As its band gap is rather wide (3.2 eV), TiO 2 needs to be activated through UV irradiation that represents only 4% of the energy of the sunlight arriving on the earth's surface. Therefore, the development of visible-light-driven photocatalysts has become one of the most challenging and urgent topics over the past decades. Recent progress in the field has demonstrated that the development of functionalized ternary and higher stability is an efficient strategy to overcome the intrinsic limitations of MIn 2 S 4 . CdIn 2 S 4 ternary sulfide because of its narrow band gap (2.1 -2.6 ev), there is a strong absorption in the visible region, it posses unique photoelectric properties and catalytic performance [2]- [8]. Ternary metal sulfide CdIn 2 S 4 belongs to the AB 2 X 4 family compound semiconductor compound. The ternary semiconductor due to the narrow band gap and large specific surface area and pore structure, the sufficient contact between the catalyst and the reactant is ensured. It is conducive to the rapid migration and separation of the surface charge of the reactant can effectively inhibit the photogenerated electrons and holes of the composite, improves the photocatalytic efficiency. Binary sulfide is easy to produce light corrosion, the service life is limited, but the ternary sulfide has good stability. At present, several techniques were used to synthesize CdIn 2 S 4 , such as solventhermal (hydrothermal), high temperature decomposition, electrochemical method and so on.
In this study, we report on a direct feeding microwave synthesis method to synthesize CdIn 2 S 4 nanophotocatalyst. The visible-light-driven photocatalytic activity of the CdIn 2 S 4 nanophotocatalyst was evaluated with respect to methylene blue photodegradation.

Synthesis
All chemicals were analytical grade and used without further purification. CdIn 2 S 4 materials were prepared by a direct feeding microwave synthesis method. In a typical procedure, 2.0193 g of Cd(NO 3 were added by stoichiometric ratio, double excess of thioacetamide and 1 g of CTAB were dissolved in 100 ml of deionized water. Then the mixed solution was placed in a microwave refluxing system to react for 20 min with a power microwave radiation of 40% and cool down naturally to the room temperature. Then the precipitate was centrifuged, washed with the deionized water for several times and dried at 60˚C in the vacuum for 4 hours. The final product was collected for the characterization.

Characterization
The crystal structure of photocatalyst was measured by XRD on a Shimadzu XRD-6100 X-ray diffractometer (Cu Kα radiation, λ = 0.15418 nm). The morphology and size of products were determined by SEM. The SEM images were recorded on a Quanta 200 FEG field emission scanning electron microscope.
The optical property was obtained by Cary Eclipse fluorescence spectrometer (USA Varian Company).

Photocatalytic Experiments
The photocatalytic activities of the synthesized powders were evaluated by the degradation 100 ml of 20 mg/l of methylene bule in 0.1 g of CdIn 2 S 4 photocatayst mixture aqueous suspension under visible-light irradiation. First, the mixed solution was placed in the dark, placed 30 minutes to reach the adsorption equilibrium. Then, in the process of photodegradation, every 10 min, the absorbance of the solution was determined by the UV-visible absorption spectrometer. The photocatalysis reaction lasted until the discoloration of the solution was fulfilled or stopped. The formula of the degradation ratio is as follow [9] ( ) Figure 1 shows the XRD pattern of as-prepared sample. showed that the product is the cubic spinel phase of CdIn 2 S 4 (JCPDS File No.

Results and Discussion
27-0060). The diffraction peak is strong and sharp, which indicates that the sample has a high degree of crystallinity.     Reaction of the first 10 minutes, the degradation rate is 50%. Reaction to 40 minutes, the degradation rate is 75%. Reaction to 70 minutes, the degradation rate is 80%. Reaction to 120 minutes, the degradation rate is 86.06%. When the me-

Conclusion
CdIn 2 S 4 nanophotocatalyst have been prepared by the method of direct feeding microwave synthesis, this method is simple. The results showed that the as-prepared catalyst has strong photocatalytic degradation ability. When the catalyst was 1.0 g/L, C(H 2 O 2 ) was 3 mL/L, the degradation rate of CdIn 2 S 4 for methylene blue of 20 mg/L reached 86.06% in 120 min.