Preparation Of Copper Sulfide Heterogeneous Junction And Its Optical Property Regulation

In recent years,copper-based chalcogenide Cu_2-xE?E=S,Se,Te?nanocrystals?NCs?have gained excellent catalytic performance,light absorption properties,high electrical conductivity and high specific capacity,making them suitable for solar cells,photocatalysis.and sensors.Among Cu_2-xE NCs,CuS NCs have received lots of attention in recent years due to their unique near-infrared localized surface plasmon resonance?LSPR?properties.In this thesis,CuS-based heterojunctions with controlled LSPR properties were prepared by chemical conversion method at room temperature,including CuS@Au₂S core-shell by ion exchange,CuS@Au core-shell and Au-CuS dimer heterojunction by redox reaction,and their formation mechanisms were studied.The main research contents and results are as follows:?1?CuS Ncs were prepared in an oil phase via a heating method.The experimental results showed that the prepared product is CuS?JCPDS No.00-006-0464?with good monodispersity.The morphology of as-synthesized CuS is nanosheet and the diameter is about 18.6 nm.In addition,CuS has a strong LSPR absorption peak at 1239 nm.?2?With the pre-prepared CuS NCs as the base material,CuS@Au core-shell structures were synthesized with CuS as a core and Au as a shell by reacting CuS NCs with Au³⁺at room temperature in the absence of OM and AA,or in the presence of AA alone.Studies have shown that the LSPR performance of CuS@Au core-shell structures can be tuned by changing the molar ratios of precursor Au:Cu.The reaction mechanism is as follows:Au³⁺reacts with Cu⁺in CuS via redox reaction,and Cu⁺is oxidized to Cu²⁺and enters the solution,while Au³⁺is reduced to Au elemental to form Au shell in situ.In addition,AA can provide electrons when present,which could alleviate the direct destruction of CuS crystal structure by Au³⁺,making the preparation of the CuS@Au core-shell become more controllable.?3?With the pre-prepared CuS NCs as the base material,CuS@Au₂S core-shell structures were synthesized with CuS as a core and Au₂S as a shell by reacting Cu⁺in CuS NCs with Au³⁺via ion exchange at room temperature in the presence of OM alone.Studies have shown that the Au₂S shell thickness can be controlled by changing the reaction time and the Au:Cu molar ratios,leading to tuning the LSPR performance of CuS@Au₂S core-shell structures.The reaction mechanism can be speculated as follows:?i?The Au³⁺diffuses into CuS and exchanges with Cu⁺in the CuS NCs.The Cu⁺expelled from the CuS NCs can reduce the Au³⁺left in the solution to Au⁺which in turn can then diffuses into the CuS NCs and exchange with the host Cu⁺.In this case,the Cu⁺released from the starting covellite NCs is oxidized to Cu²⁺by the Au³⁺in the solvent.?ii?The Au³⁺is reduced to Au⁺by OM,then the Au⁺exchanges with the host Cu⁺of the CuS NCs.?iii?The Au³⁺is reduced to Au⁰ by OM,then the as-formed Au⁰ is captured by the CuS NCs.As the Au⁰ and CuS inter-diffuse,the Au⁰ is oxidized by S-S covalent bond in CuS to Au⁺.The formed Au⁺then locally exchanges with the host Cu⁺of CuS.?4?With the pre-prepared CuS NCs as the base material,Au-CuS dimer heterojunction were synthesized at room temperature in the presence of both OM and AA.Studies have shown that the LSPR performance of the Au-CuS dimer heterojunction can be tuned by changing the reaction time and the Au:Cu molar ratios.The reaction mechanism is as follows:Due to the protective effect of surface ligand OM on CuS NCs,the direct reaction of Au³⁺with CuS NCs is avoided.AA acts as a reducing agent,and Au³⁺is reduced to Au elemental on the surface of CuS NCs and Au particle is formed in situ,and finally Au-CuS dimer heterojunction is formed.