Preparation Of Cadmium Sulfide-based Composite Photocatalysts And Study On Their Performance And Mechanism To Degrade Pollutants In Water

In recent years,tetracycline organic compounds and lignin organic compounds have caused serious water pollution,and lignin compounds are the only renewable aromatic resources in the world.Developing green,convenient,efficient and sustainable technologies to degrade tetracycline and convert lignin is a top priority of current research.Photocatalysis technology based on semiconductor materials and irradiated by unlimited sunlight has been extensively researched and proven to be a green technology to solve water pollution problems and to realize the value of pollutants themselves.Cadmium sulfide（Cd S）is widely used as a photocatalyst,but its severe photogenerated electron-hole pair complexation and high photocorrosion affect its practical application.Therefore,this project focuses on elemental doping,surface modification and heterojunction construction of Cd S to break this limitation and optimize the morphology,structural composition and reaction conditions to obtain high-performance,highly stable and selective nanocomposite photocatalytic systems for the degradation of tetracycline and conversion of lignin.In addition,the intermediate products of tetracycline degradation and the process of lignin bond breaking were investigated,and the pathway and mechanism of photocatalytic reaction were clarified,which provided the theoretical basis for the subsequent construction of highly active photocatalytic systems for degrading organic pollutants in water bodies.The specific research contents and innovation points of this project are as follows:（1）Cd Zn S nanoparticles,In₂O₃ nanocubes and Cd Zn S/In₂O₃ heterojunction photocatalysts were synthesized by hydrothermal and water bath methods for the photocatalytic degradation of tetracycline in water.The Cd Zn S solid solution has a tunable energy band structure and more negative conduction band positions than Cd S;the modulation of the morphology can provide more catalytic active sites;the construction of heterojunctions can improve the visible light absorption and carrier recombination.Meanwhile,a series of experimental and characterization results confirm the significantly enhanced catalytic activity of Cd Zn S/In₂O₃ composites compared with monomeric Cd Zn S and In₂O₃.The degradation efficiency of the best-performing composites for tetracycline can be as high as 1.3 and 32.4times that of Cd Zn S and In₂O₃ monomers,respectively,and have good stability of photocycling utilization,with only 2%decrease in degradation efficiency after four cycles.In addition,the active species of the catalytic system was identified by capture experiments,and combined with the determination of the intermediate products to clearly elaborated the pathway and mechanism of tetracycline degradation by the Cd Zn S/In₂O₃ catalytic system.（2）Cd S-SH/Ti O₂ heterojunction nanocomposites were prepared by introducing Ti O₂nanosheets in the synthesis of Cd S-SH nanoparticles through a water bath method for the photocatalytic degradation of the lignin model compound 2-phenoxy-1-phenylethanol.The experimental data showed that the Cd S-SH/Ti O₂ composites had superior catalytic degradation performance than Cd S,Cd S-SH and Ti O₂.Under the optimal reaction conditions as well as photocatalytic performance,Cd S-SH/Ti O₂ degraded 2-phenoxy-1-phenylethanol up to 99%,and the yields of value-added products phenol and acetophenone were up to 85%and87%,respectively.The enhanced catalytic activity firstly resulted from the introduction of sulfhydryl（-SH）ligands on the surface of Cd S,which enabled the catalyst to come into close contact with 2-phenoxy-1-phenylethanol;secondly,the successful construction of the heterojunction resulted in the broadening of the visible light absorption range and the obvious separation of photogenerated electron-hole pairs,and the introduction of Ti O₂ enhanced the selectivity of the catalyst for the degradation of 2-phenoxy-1-phenylethanol.In addition,the key roles of electrons,holes and Cα-radical in the catalytic system were confirmed in combination with the capture experiments,and the reaction pathway of photocatalytic degradation of lignin model compounds was proposed.