Preparation And Photocatalytic Properties Of Bismuth Based Composites

Environmental and energy issues cannot be ignored,and there is an urgent need to find a green technology to solve the above problems.The low energy consumption and pollution-free photocatalysis technology is favored by scientific researchers.This research is mainly based on the Bi-based semiconductor photocatalyst,selecting appropriate modification strategies to prepare photocatalytic materials with superior performance.Based on this,Bi₂WO₆/Bi₂S₃/MoS₂ n-p heterojunction and CuO/TiO₂/Bi₂S₃ composite materials were prepared,and then the physical and chemical properties of the materials were explored and analyzed.The research content can be divided into two parts:（1）Bi₂WO₆ microspheres with diameter of 2.6～3.0μm were prepared by solvothermal method using polyvinylpyrrolidone K30 as structure directing agent,mixed solution of anhydrous ethanol,water and glacial acetic acid as the solvent,Bi（NO₃）₃·5H₂O and Na₂WO₄·2H₂O as metal sources.On this basis,a series of spherical Bi₂WO₆/Bi₂S₃/MoS₂ n-p heterojunction composites were prepared by hydrothermal reaction with the addition of molybdenum source Na₂Mo O₄·2H₂O and sulfur source CH₄N₂S in turn,and applied to photocatalytic reduction of Cr（Ⅵ）under visible light.Bi₂S₃ is formed by the in-situ replacement of WO₆^6?in Bi₂WO₆ by S^2?without additional introduction of Bi element.This process is conducive to maintaining the structural stability of Bi₂WO₆.Scanning electron microscopy（SEM）indicates that the compactness of the sample can be easily adjusted by changing the contents of S and Mo sources in the solution.The results of ultraviolet–visible diffuse reflectance spectra,photoluminescence,transient photocurrent response,and electrochemical impedance spectra indicate that the formation of heterojunctions contributes to enhancing visible-light utilization and promoting photogenerated carrier separation and transfer.The experimental results of photocatalytic reduction of Cr（Ⅵ）under visible light show that the p H value of Cr（Ⅵ）solution has a great influence on the photocatalytic reduction efficiency of the sample,and the photocatalytic reduction efficiency decreases with the increase of p H value of the solution.When the solution p H=2.00,it has the best photocatalytic reduction activity.Among them,BBM-3 achieves the greatest Cr（Ⅵ）reduction rate of 100%within 75 min（λ>420 nm,p H=2）;this rate is considerably better than the Cr（Ⅵ）reduction rate of pure Bi₂WO₆（5%）.The recycling experiment reveals that the Cr（Ⅵ）reduction rate of the BBM-3 can still reach 80%after three cycles,indicating that the photocatalysts have enough stability and reusability.The active substance capture experiment proves that the active substance acting in the photocatalytic reduction process is photogenerated electrons.Based on experimental data and theoretical analysis,the reasonable mechanism of Bi₂WO₆/Bi₂S₃/MoS₂photocatalytic reduction Cr（Ⅵ）is proposed.This work provides new research ideas for the design of ternary heterojunction composites and new strategies for the development of photocatalysts for wastewater treatment.（2）First,Cu₂O cubes were prepared using copper nitrate hydrate（Cu（NO₃）₂?xH₂O）as the copper source.Then using Cu₂O cube as the precursor and tetrabutyl titanate as the titanium source,spherical CuO/TiO₂ composites were prepared.CuO/TiO₂/Bi₂S₃composites were prepared by mixing the Bi₂S₃ quantum dots（Bi₂S₃ QDs）prepared by solvothermal method with CuO/TiO₂ by mechanical stirring.According to the different loadings of Bi₂S₃（5wt%,10wt%,20wt%）,the materials obtained are denoted as CuTiBi-5,CuTiBi-10,CuTiBi-20.X-ray diffraction and X-ray photoelectron spectroscopy confirmed the successful synthesis of CuO/TiO₂/Bi₂S₃ composites.SEM and transmission electron microscopy test results show that the size of Cu₂O cubes is150?300 nm,the average particle size of CuO/TiO₂ nanospheres is 200 nm,and the particle size of Bi₂S₃ QDs is below 10 nm.Compared with the precursor Cu₂O,the particle size of CuO/TiO₂ decreases instead of increasing,because a certain amount of NH₃·H₂O is added in the reaction system during the preparation of CuO/TiO₂,and the reaction of Cu₂O and NH₃·H₂O in the reaction system produces[Cu（NH₃）₄]²⁺.Finally,the samples were applied to photocatalytic hydrogen production.The sample CuTiBi-10had the best photocatalytic hydrogen production rate(16.69μmol h^?1 g^?1),which was2.15 times of the pure CuO.