Design And Preparation Of TiO₂ Based Composites And Study On Their Photocatalytic Degradation Of Tetracycline

In the past few decades,tetracycline（TC）has been widely used in a variety of industriessuch as medical and health,livestock and poultry breeding and aquaculture industries to prevent infection and fight infectious diseases.Due to the certain stability of TC antibiotics,they cannot be completely absorbed and metabolized after use,which leads to the discharge of antibiotic molecules into various water bodies in the form of metabolites,causing adverse effects on the ecosystem.To address this problem,a variety of strategies have been used for the removal of TC class antibiotics.Due to the high chemical stability of antibiotics,it is difficult to remove and degrade them by common physical and chemical methods and biological treatment methods.Compared with traditional treatment technology,photocatalytic degradation of antibiotics is a green,economic and efficient method,which has great application potential and has been widely concerned.Titanium dioxide（TiO₂）has been the most studied semiconductor in the field of photocatalysis since 1972,when it was discovered that it could use solar energy to break down water.Among them,a large number of studies hope to improve the photocatalytic activity of TiO₂ by adjusting the size,crystal face and morphology of TiO₂.However,due to the limited light absorption capacity of TiO₂ in the ultraviolet region and the rapid recombination of electron hole pairs,its application in the field of photocatalysis is severely limited.In order to utilize sunlight more efficiently,it is necessary to design and prepare photocatalyst systems with both enhanced photocatalytic activity and visible light excitation activity.In this paper,the traditional titanium source is easy to spontaneous hydrolysis and condensation reaction,and it is difficult to accurately control the reaction process and final product structure.Two kinds of photocatalysts,In₂S₃/TiO₂ and TiO₂/CdS,were successfully synthesized by hydrothermal method by preforming soluble solid state Titanium-oxo-clusters as titanium sources.The experimental results show that the two composites can effectively degrade tetracycline（TC）in water under visible light.Compared with the single component,the photocatalytic degradation of tetracycline by the composite material has been significantly improved.The structure characterization and performance analysis of different samples were carried out by using multiple analysis and testing techniques.The mechanism and degradation route of photocatalytic degradation of TC by composite materials were studied and described.The main findings are as follows:1.The In₂S₃/TiO₂ composites were successfully synthesized by one-step hydrothermal method and used to degrade tetracycline（TC）in water effectively under visible light.Preformed soluble solid state Titanium-oxo-clusters were used as titanium sources can effectively avoid the spontaneous hydrolysis and condensation reactions of traditional titanium sources.Compared with the direct addition of TiO₂,the nucleation of TiO₂ can be controlled in hydrothermal process dependent on the solubility of Titanium-oxo-clusters in water,leading to formation of homogeneous heterostructure of TiO₂ and In₂S₃.The as-prepared In₂S₃/TiO₂composite achieved the better performance of photodegradation TC than that of pure TiO₂ and In₂S₃.Meanwhile,the mole ratio of In and Ti was 0.34:1 among In₂S₃/TiO₂ composite displayed the best photocatalytic activity,which the efficiency for degrade TC（40 mg/L）reached 78.1%within 60 min higher than 54.6%of In₂S₃/TiO₂ composite prepared by commercial TiO₂ powders.Furthermore,the capture experiments showed that the holes and superoxide radical were the main active substances in photocatalytic reactions,which elucidated the photocatalytic mechanism of In₂S₃/TiO₂ heterostructure.The exploration in this work can boost new insight for the development of TiO₂ based catalysts and provide a new raw material and a facile synthetic method for the large-scale production of TiO₂ based composite materials.2.The TiO₂/CdS composites with different TiO₂ contents were synthesized by simple in-situ hydrothermal method.The fine TiO₂ nanoparticles assembled by the decomposition and assembly of the Titanium-oxo-clusters precursor were uniformly dispersed on the surface of the CdS nanorods.The prepared samples were characterized and analyzed by a number of testing techniques.The results showed that TiO₂/CdS composites have higher photocatalytic activity than single component CdS and TiO₂ under visible light.The Ti/Cd molar ratio of 1:2 showed the best photocatalytic performance,and the degradation efficiency of TC（40 mg/L）reached77.3%within 12 minutes.The close interfacial contact and synergistic effect between TiO₂ and CdS can not only protect CdS nanorods from photocorrosion,but also effectively transfer the photoexcited electrons of CdS to TiO₂ nanoparticles,thus improving the efficiency of photogenerated charge separation of CdS.