Fabrication And Characterization Of CdS-base Semiconductor Photocatalytical Materials

In recent years, much attention has been focused on semiconductorphotocatalysis, because this technique can make full use of the renewable solarenergy to solve the environmental problems and energy crises. CdS, avisible-light-driven photocatalyst, has excellent photocatalytic performance,which was researched widely. Noble metal/semiconductor heterostructures canachieve the enhanced photocatalytic effect by promoting the separation ofphotogenerated electron and hole. Ag was widely studied owing to the lowcost. Cu2O is a kind of low efficient, non-toxic and easy preparation ofphotocatalyst. It has matched band structure with that of Cu2O. Cu2O/CdScomposite can separate effectively of photogenerated electrons and holes.Therefore, effective heterostructural materials of Ag/CdS and Cu2O/CdS werefabricated by hydrothermal method. Finally, the causes of enhancedphotocatalytic efficiency were discussed based on characterized themorphology, crystal structure and optical properties. Some new and interesting results are as following：1. Different morphologies of CdS, through changing the concentration ofthiourea, were synthesized via hydrothermal method. The influences oftemperature, reaction time and different solvent on the morphologies of CdSwere studied. The results showed that the morphologies of CdS have gonefrom dendrites to the mixture of dendrites and spheres to spheres withgradually changing the molar ratio of Cd/S from1:2to1:5to1:10. Theresearch also found that CdS nanowires were formed when en-en as solvent. Inaddition, the formation mechanisms of CdS nanoproducts are further discussedin this study.2. Ag/CdS heterostructural materials were successfully synthesized byultrasound-assisted polyols and hydrothermal method. Structures andmorphologies of the obtained Ag/CdS composites were characterized by XRD,SEM, and TEM; the experimental results indicate that the composites arecomposed of Ag nanowires serving as the core and CdS particles as the shelland a possible formation mechanism of Ag/CdS heterostructural compositeswas proposed. Comparing studies on the degradation of methylene blue wereemployed by using pure CdS, pure Ag, and Ag/CdS composites, respectively.The results show that the Ag/CdS composites possess higher photocatalyticdegradation efficiency. The enhanced photocatalytic effect for Ag/CdScomposites is mainly attributed to the photogenerated electron transfer fromCdS to Ag nanowire, while photogenerated holes still remain in CdS’s valence band. Consequently, the effective separation of photogenerated electrons andholes improve the photocatalytic efficiency of Ag/CdS composites greatly.3. CdS/Cu2O heterostructural materials were successfully synthesized bya solvent-thermal process followed by a chemical bath deposition process.Structures and morphologies of the obtained CdS/Cu2O composites werecharacterized by XRD, SEM, and TEM; the experimental results indicate thatthe surface of CdS nanowires (NWs) is decorated with spherical Cu2O whosediameter ranges from100to200nm. Through crystal shape-evolution, thegrowth mechanism of these hierarchical nanostructures was rationallyproposed. Briefly, in the chemical bath deposition process, Cu(OH)2colloidsgenerate firstly, and then the colloids transform into nanobelts after addingascorbic acid (AA). With the reaction time further increasing, nanobeltsaggregate together to form the hierarchical nanospheres on the surface of CdSNWs. The photoactivity of CdS/Cu2O composite for methyl orange (MO)photodegradation was investigated in detail. The obtained high photocatalyticefficiency can be attributed to the heterojunction structure, which results in theefficient separation of photo-generated electrons and holes.