Controlled Synthesis Of Metal Chalcogenide Micro/Nano-architectures: Optical And Photocatalyst Properties

A well-controlled and the large scale synthesis of chalcogenide based semiconductor materials in the form of micro/nano-architectures have attracted a great attention due to their unique physical and chemical properties. This thesis presents the research work on synthesis of novel architectures of chalcogenides specially sulfides and their composites covering characterization, growth mechanism and versatile natural light driven photocatalyst properties. Advanced and a variety of characterization techniques such as SEM, FESEM, XRD, EDX, XPS, TEM, HRTEM and SAED have been employed for the characterization of novel morphologies obtained for chalcogenides based semiconducting sulfides. Accoding to the photocatalyst applications point of view; heterostructures of chalcogenides based semiconducting materials(BiOCl/Bi2S3) has been fabricated for to enhance the photocatalyst activity and a precise control over novel architectures has been obtained.Initially, well controlled Nanosheets-based hierarchical Microspheres(NSHMS) of pure covellite phase CuS were synthesized using a facile PVP assisted solvothermal process. The reaction conditions were optimized using various amounts of PVP to develop unique hierarchical structured hollow microspheres. CuS hollow structures have a bandgap of ~1.97 eV. These mesoporous structures exhibit excellent photocatalytic activity in degradation of organic dyes(methylene blue) under natural light in comparison to other structures of copper sulphide. These photocatalysts show extraordinary reusability with over 96.5% degradation of organic dye after 6th cycle. A “bottom-up” assembly has been successfully developed to synthesize hollow microspheres with unique and well defined architectures at large scale, which offer a good opportunity to understand the fundamental significance of unusual and complex hierarchical structures for their potential applications.Later on, a variety of well defined, highly symmetric, super complex and hierarchical architectures of covellite copper sulfide have been successfully prepared by a simple solvothermal approach. The effect of various influencing parameters on the formation of CuS hierarchical architectures has been precisely investigated and a possible formation mechanism has been elucidated. The exposure time has been found to be a critical factor in controlling the CuS architecture and highly complex structures were obtained under elongated reaction times. The “as synthesized” architectures exhibited excellent photocatalytic activity in visible region for catalysis of individual dye(methylene blue and rhodamine B) and their mixed solutions in presence of H2O2. The efficient photocatalytic activity can be attributed to careful control over hierarchical CuS structures. Overall, this study is of great importance in “bottom-up” assembly of copper sulfide nanoplates to obtain highly complex structures which offer a good opportunity to understand the fundamental significance of atypical structures.Afterwards, hierarchically structured covellite copper sulfide(CuS) microflowers composed of extremely thin nanosheets have been successfully fabricated via a one-pot sonochemical process, using copper sulphate and thiourea aqueous solution as precursors in the presence of citric acid, without any prefabricated template. Large-scaled architectures are homogeneous, quite separately displaced and assembled by pure hexagonal single crystalline CuS nanosheets, having thickness within 20 nm. The as obtained hierarchical CuS structures possess rather high surface area and the unique double pore size distributions measured from the N2 adsorption isotherms. Moreover, the possible growth mechanism for CuS hierarchical architectures is proposed on the basis of the temporal evolution controlled experiments. Most importantly, these hierarchically structured CuS catalyst showed highly efficient and versatile photo-catalytic activities as well as excellent recyclability in degrading highly concentrated dyes-aqueous solutions methylene blue(MB), rhodamine B(RhB) and their mixed solution(MB+RhB) with the help of hydrogen peroxide(H2O2) under natural light irradiation, suggesting a promising application in wastewater purification.At the end, BiOCl/Bi2S3 heterostructures have been synthesized in an amazingly complex and quite novel architectures form at large scale by a facile and well controlled solvothermal method. A possible growth mechanism has been illustrated in well-organized manners. X-ray diffraction(XRD), transmission electron microscopy(TEM), energydispersive spectroscopy(EDS), and UV–vis spectroscopy were employed to study the structures, morphologies and optical properties of the as-prepared samples. Under visible light, Bi2S3/BiOCl heterostructures displayed much higher photo-catalytic activity than Bi2S3 and BiOCl for the degradation of methyl orange(MO) aqueous dye solution. The increased photo-catalytic activity of BiOCl/Bi2S3 heterostructures could be attributed to the formation of the heterostructure between Bi2S3 and BiOCl, which effectively separate the photo-induced electron–hole pairs and suppress their recombination.