Preparation And Photocatalytic Properties Of CdS Ternary Composites

Dye wastewater（usually containing aromatic groups such as rhodamine B,methyl orange,methyl blue and so on）has high chemical stability and complex biological toxicity.And it contains a large number of organic and inorganic pollutants,once discharged into the water without treatment,will lead to microbial reproduction,consumption of a large amount of dissolved oxygen.At present,the commonly used treatment methods of dye wastewater include physical method,biological method,advanced oxidation method and photocatalytic method.Among them,semiconductor photocatalysts have attracted wide attention because of their high efficiency in converting solar energy and great potential in decomposing organic pollutants.Cadmium sulfide has a suitable band gap width（2.4 e V）and band edge position,which has a broad application prospect in the field of visible light driven photocatalysis such as pollutant degradation,hydrogen evolution and organic synthesis.But cadmium sulfide also has many disadvantages,such as unstable chemical properties and easy to photocorrosion.In this thesis,the advantages of CdS are used to construct the ternary semiconductor heterojunction photocatalytic material to improve the carrier separation rate and thus improve the photocatalytic activity.The details are as follows:1.Preparation and Photocatalytic degradation of CdS/g-C₃N₄/Vermiculite.CdS/g-C₃N₄/Vermiculite rhodamine B and methylene blue.The results show that CdS/g-C₃N₄/Vermiculite composite has good photocatalytic degradation activity for rhodamine B and methylene blue,and the degradation rate can reach98%within 60 min.XRD,BET,UV and PL showed that the catalytic efficiency of CdS/g-C₃N₄/Vermiculite was significantly improved due to its large specific surface area and good electron transfer efficiency between g-C₃N₄and CdS.In addition,the degradation rate of the catalyst can still reach 96%after repeated4 times,indicating that the composite catalyst has good stability.Particle trapping experiments and ESR studies showed that·O₂^-was the main active substance,and a possible photocatalytic degradation pathway was proposed.2.Preparation and photocatalytic degradation of CdS/g-C₃N₄/BiOIO₃.CdS/g-C₃N₄/BiOIO₃ternary composites were prepared by calcination and hydrothermal methods.Compared with CdS,g-C₃N₄and BiOIO₃monomers,the photocatalytic degradation efficiency and stability of CdS/g-C₃N₄/BiOIO₃have been greatly improved.Under visible light,the degradation rate of CdS/g-C₃N₄/BiOIO₃can reach about97%,which is 2.85 times that of CdS monomer.Moreover,after four cycles of tests,the degradation rate remains almost unchanged,indicating good stability of CdS/g-C₃N₄/BiOIO₃.The construction of CdS/g-C₃N₄/BiOIO₃ternary heterojunction can not only improve the photocatalytic activity,but also the synergistic effect of g-C₃N₄and BiOIO₃can effectively inhibit the recombination of electrons and holes,accelerate the transfer of photogenerated electrons,and explain the catalytic mechanism of CdS/g-C₃N₄/BiOIO₃.3.Preparation and photocatalytic degradation of CdS/Bi₂S₃/BiOIO₃.CdS/Bi₂S₃/BiOIO₃was successfully synthesized by hydrothermal method with BiOIO₃as substrate.Through performance tests,it was found that the photocatalytic activity of CdS/Bi₂S₃/BiOIO₃could reach about 98%in 30 min,which was significantly improved compared with monomer catalyst.After five cycles,the activity of the catalyst did not decrease obviously,indicating that the catalyst has excellent stability.A preliminary study on the photocatalytic mechanism showed that the synthesis of CdS/Bi₂S₃/BiOIO₃successfully broadened the light absorption range and reduced the electron-hole recombination rate.Meanwhile,possible charge transfer routes based on CdS/Bi₂S₃/BiOIO₃system are proposed.