Preparation of Flower-Like Bi/CuS Photocatalyst by Photo-Reduction Method

Congo Red（CR），as one of azo dyes，is widely used in production because of its easy solubility in water，low cost and good dyeing effect. Traditional methods to degrade Congo red include microwave treatment，electrochemical catalysis，adsorption，and etc. However，photocatalytic technology，which uses solar energy to degrade organic pollutants and reduce carbon dioxide，presents the advantages of simplicity and no secondary pollution. It has raised the wide research of dye wastewater treatment in recent years. Among them，CuS，as a p-type semiconductor material，has the characteristics of low cost and high stability compared with other photocatalysts. Flower-shaped CuS can improve the photocatalytic efficiency by more efficient utilization of solar energy. However，CuS needs to be modified for some defects，such as easy electron-hole combination. Metal modification is one of the important ways to improve the photocatalytic activity. The existing form and content of doped metal have an important influence on the recombination of photo-generated electrons and holes，and then affect its photocatalytic activity. As a dopant，Bi has attracted much attention because of its high electron transfer efficiency，low cost and easy availability. In this study，the flower-shaped CuS material was synthesized by solvothermal method with copper chloride，thiourea and N，N-dimethylformamide as raw materials. Bi/CuS composite was prepared by photo-reduction method，and metal Bi was loaded on the surface of CuS catalyst. X-ray diffraction（XRD），scanning electron microscope （SEM），transmission electron microscope（TEM）and Zeta potential diagram were used to characterize the catalyst. The results showed that the crystallinity and purity of CuS were high，and metal Bi was successfully loaded on the surface of CuS catalyst. The prepared CuS had flower-ball/hedgehog-like morphology and good dispersibility. The spherical structure of Bi/CuS was maintained. In the optimized Bi/CuS（45）example，it could be seen that Bi elements were uniformly distributed in the composite from elemental analysis. The surface of CuS was negatively charged，and its potential could be changed from negative to positive by doping Bi metal. At the same time，Bi/CuS showed positive electricity，and pollutant CR showed strong negative electricity，resulting in the effectively adsorption of pollutants and increased reactive sites to realize the effective degradation of pollutants. In addition，the modified Bi/CuS showed positive electricity，and the Zeta potential of Bi/CuS also enhanced with the increase of illumination time，which changed the charge distribution on the catalyst surface. The comparison of UV-vis diffuse reflectance spectroscopy，photoluminescence spectra and band gap between CuS and Bi/CuS（45）showed that pure CuS had a strong broad spectrum absorption peak. It facilitated the electrons on the surface of copper sulfide excited from valence band to conduction band. Meanwhile，the light absorption intensity of Bi/CuS（45）within 300~800 nm was stronger than that of pure CuS. Therefore，the introduction of Bi could promote the light absorption performance of CuS. In addition，metal Bi doping induced the decreased PL intensity，since the photo-generated electrons transferred from CuS surface to metal Bi，and realized the electron quenching. Therefore，doping Bi could effectively inhibit the recombination of electron-hole pairs，prolonged the life of photo-generated carriers，and then promoted the improvement of photocatalytic activity. The decrease of the band gap width after metal Bi loading was beneficial to the separation of photo-generated carriers and the improvement of the catalytic activity. During the degradation of CR，CuS，Bi/CuS（30），Bi/CuS（45），Bi/CuS（60）and Bi/CuS（75）catalysts presented the higher activity than that without catalyst. Comparing to the low degradation efficiency of CR on CuS of only 17.8%，the degradation efficiencies were 82.5%，89.5%，86.6% and 45.4% on Bi/CuS（30），Bi/CuS（45），Bi/CuS（60）and Bi/CuS（75），respectively. Especially，Bi/CuS（45）presented the highest activity with more than four times than CuS. Therefore，doping Bi on CuS could greatly improve the photocatalytic degradation of CR solution. Bi/CuS photocatalyst effectively improved the adsorption capacity and light harvesting，and inhibited the recombination of photo-generated carriers. As a result，the photocatalytic performance was greatly improved and it showed the application prospect for the removal of organic pollutants. © 2023 Editorial Office of Chinese Journal of Rare Metals. All rights reserved.