Controlled Synthesis Of CuS/ZnS Composite And Its Photocatalytic Property Study

How to solve the energy shortage and environmental pollution are enormouschallenges facing the world today. Photochemical water splitting into hydrogen is apotentially effective solution to solve the energy shortage, because it only needs light,photocatalyst and water. As a wide band gap semiconductor, ZnS exhibits highactivity for photocatalytic H2production even without cocatalysts, resulting from therapid generation of electron-hole pairs upon photoexcitation and highly negativereduction potentials of excited electrons. However, ZnS only responses to ultravioletlight irradiation. Therefore, it is necessary to make it responsive to visible light. Inthis dissertation, CuS/ZnS composites with different morphologies were obtained bycation-exchange reaction between ZnS or ZnS(ethylenediamine)0.5precursor andCu(NO3)2solution. The obtained composites were characterized by XRD, SEM,HR(TEM), EDS, UV-vis diffuse reflectance analysis and so on. CuS/ZnS compositephotocatalysts possessed excellent photocatalytic activity and stability for hydrogenevolution from an aqueous solution containing0.35M Na2S and0.25M Na2SO3under visible light irradiation even without noble metal cocatalyst. As an importantacidic oxide material, W18O49is of special interest due to its unique defect structureand distinct physical and chemical properties, such as field emission, strongabsorption of near-infrared light. It is also used as a novel adsorption material. Themain work is summarized as follows:1. CuS/ZnS composite spheres with diameter of200-400nm were successfullyprepared by a simple cation-exchange reaction between ZnS spheres and Cu(NO3)2solution. CuS nanoparticles with a few nanometers in diameter were observed on thesurface of ZnS spheres. The synthesized CuS/ZnS composite spheres showedphotocatalytic properties effective for hydrogen evolution from an aqueous Na2S andNa2SO3solution under visible light irradiation without any cocatalysts. The highestrate of H2evolution reached695.7μmol h-1g-1, which exceeded7times that of themechanical mixture of CuS and ZnS. The enhancement in the photocatalytic activityof CuS/ZnS composite spheres was supposed to be due to the direct interfacial charge transfer of the CuS/ZnS heterojunction.2. ZnS(ethylenediamine)0.5hexagonal plates were first synthesized by asolvothermal reaction in a mixed solvent consisting of ethanol and ethylenediaminewith the same volume ratio. CuS/ZnS composite hexagonal plates were prepared bythe cation-exchange reaction between the as-prepared ZnS(ethylenediamine)0.5andCu(NO3)2solution. The photocatalytic activity test indicated that the obtainedcomposite possessed a high photocatalytic performance, which reached1233.5μmol h-1g-1.3. Hierarchical CuS/ZnS nanosheet-assembly flowers were synthesized by acation-exchange reaction between the as-prepared ZnS(ethylenediamine)0.5templateand Cu(NO3)2solution. The prepared CuS/ZnS nanosheet-assembly flowers exhibitedhigh visible-light photocatalytic H2-generation activity with the highest rate of1206.2μmol h-1g-1. The enhanced photocatalytic H2-generation activity was achieved owingto the hierarchical organization of nanosheets and the direct interfacial charge transfer.4. W18O49nanourchins were synthesized via a solvothermal reaction of WCl6intriethylene glycol. They possessed high specific surface area of103.4m2g-1andexhibited excellent adsorption capacity for the removal of methylene blue (MB) andrhodamine B (RhB). The equilibrium adsorption capacity toward MB and RhBreached150.3and81.78mg g1, respectively. Oxygen vacancies in W18O49playedimportant role in the adsorption of organic pollutants. The adsorption kinetics of MBand RhB were both well described by the pseudo-second-order model. The adsorptionwas found to be controlled by both surface adsorption and intraparticle diffusion.