Preparation And Photocatalytic Activity Of Narrow Band CuS,In₂S₃,CuInS₂ Semiconductor Nanomaterials

In the past few decades,organic pollution has become one of the most serious environmental pollution problems.Photocatalytic technology has been widely used in elimination and degradation of toxic chemicals and other fields.However,semiconductor materials with wide band gap（such as TiO₂,ZnO,etc.）can absorb only part of ultraviolet light of the total solar energy,while most visible light can not be used.Therefore,development of the narrow band gap semiconductor materials has attracted wide attention from scientists.In recent years,many kinds of chalcogenide semiconductor materials with narrow band gap also have attracted great interest.Here,CuS,In₂S₃ and CuInS₂ semiconductor nanomaterials were prepared successfully in this thesis,and the optical properties and photocatalytic properties of containing Cu,In,Cu/In chalcogenide semiconductor were investigated systematically.The main contents are as follows:Firstly,covellite CuS nanoparticles were synthesized though a simple hot injection approach using cupric oxide and elemental sulfur as the precursors in an oleic acid/liquid paraffin system.The influences of different molar ratios of Cu²⁺ : S^2- on the structure,composition and morphology were investigated.In addition,the thermal stability of CuS with the molar ratio of 1 : 1 was studied.Finally,the optical properties were investigated systematically,covellite CuS with band gap of 1.5 eV presents a broad absorption in the visible-light and near-infrared region.The PL emissions peaks can be divided two parts: one part in green region,correlating with the near band edge electronic transition;another part in blue region,which might be due to the defects presented in the CuS crystalline structure.Secondly,tetragonal β-In₂S₃ with different morphologies was synthesized by a simple hydrothermal method using Na₂S,H₂NCSNH₂,Na₂S₂O₃ and InCl₃ as the precursors,respectively.The experimental results indicated that the type of sulfur sources affect the crystallinity and morphology of the products.The as-prepared In₂S₃ reveal dramatically broad absorption bands in the visible-light and ultraviolet-light region,and a emission peak at 470 nm and several emission peaks behind 500 nm.Moreover,the photocatalytic degradation rates of Rhodamine B with different In₂S₃ in the visible light were higher than in the ultraviolet light generally,both can be up to 96%.And,the as-prepared In₂S₃ using Na₂S as precursor at 180 oC for 18 h showed a higher absorption activity for Rhodamine B solution about 99.47% in one hour,which indicates the as-prepared In₂S₃ is porous and has double function of absorption and photocatalysis.Thirdly,p-type and n-type Cu InS₂ semiconductor nanocrystals were fabricated through a simple hot injection approach in aerobic and anaerobic environment.The results showed that the as-prepared CuInS₂ is composed of nanosheets and nanorods stacked structure;both of the p-type and n-type CuInS₂ nanocrystals present a broad absorption in the visible-light and ultraviolet-light region and the band gap of the two products are 1.39 eV,but the PL are different obviously,which indicated O₂ plays an important role in the preparation process.Meanwhile,we investigated the photocatalytic activity to different dyes with p-type and n-type CuInS₂ nanocrystals as catalysts.In addition to Methylene Blue,the photocatalytic activity of p-type CuInS₂ nanocrystals to Rhodamine B,Methyl Orange and Congo Red is higher than n-type CuInS₂ nanocrystals,indicating that the positively charged holes have the strong ability of catalytic oxidation.Finally,the formation mechanism was be proposed,we believed the chalcopyrite Cu₂S was pre-synthesized in the oleic acid/paraffin system,and the final chalcopyrite CuInS₂ nanocrystals was sysnthesized through Cu⁺ replaced by In³⁺ in the chalcopyrite Cu₂S.