Preparation And Photocatalytic Properties Of Urchin-like TiO₂/ZnO Composite Microspheres

Titanium dioxide（TiO₂）has been studied extensively in the field of photocatalysis because of its excellent photoelectric properties and stability.However,TiO₂ can only use the ultraviolet light in photocatalytic reaction due to its wide band gap（3.2 e V）,and TiO₂ has a high recombination rate of photo-generated electron-hole pairs.As a result,TiO₂ photocatalyst has the problems of low utilization efficiency of sunlight and low photocatalytic efficiency.In view of the above problems,based on ZnO nanomaterials and Au nanoparticles,the photocatalytic performance of TiO₂ was improved by constructing heterostructure and local surface plasmon resonance（LSPR）of noble metals in this study.The research contents are as follows:1.Firstly,urchin-like TiO₂/ZnO composite microspheres were prepared by a simple two-step hydrothermal method,in which potassium titanium oxalate was used as titanium source,and zinc nitrate hexahydrate was used as zinc source.The prepared composite microspheres had large specific surface area（131 m²/g）and suitable pore structure（average pore size was 11.75 nm,pore volume was 0.42 cm³/g）.Moreover,the close contact between TiO₂ and ZnO leads to the formation of type II heterojunction,which is conducive to the separation of photogenerated electron-hole pairs and promotes the photocatalytic performance.Secondly,the photocatalytic degradation of tetracycline hydrochloride（TCH）by the composite microspheres was studied,and the loading amount of ZnO was optimized.Under UV irradiation（300 W Xenon lamp）,the composite microspheres（TZ60）with the mass ratio of ZnO to TiO₂ of 8 wt%had excellent photocatalytic performance（the amount of catalyst was 0.5 g/L）.After 4 h illumination,the removal rate of TCH with initial concentration of 100 mg/L was 99.3%,and the reaction rate constant was 0.01588 min^-1.The excellent photocatalytic performance of the composite microspheres lies in the strong adsorption capacity of TCH（51 mg/g）;h⁺and·O₂^-are the main active substances,which lead to the demethylation,C-C double bond breaking and C-O double bond formation in TCH.TCH was first degraded into intermediate products,and then further degraded into small molecule organic compounds or mineralized into inorganic compounds,such as CO₂and H₂O,with a mineralization rate of 41.4%.2.A series of Au-TiO₂/ZnO composites with different Au loading were prepared by in-situ growth of Au nanoparticles（10-25 nm）on the surface of urchin like composite microspheres TZ60 by the sodium citrate reduction method.Under the effect of LSPR,the absorption spectrum of Au-TiO₂/ZnO composites is extended to the visible region,and Au nanoparticles are in close contact with semiconductor materials to form Schottky junction,which can extend the lifetime of photogenerated electron-hole pairs and improve the visible-light photocatalytic activity of the composites.Methyl orange（MO）and TCH were used as the target degradation products to evaluate the visible light photocatalytic performance of the materials.The results showed that the composite（ATZ2）with 1 wt%Au had the most significant photodegradation effect.Compared with TZ60,the removal rates of MO and TCH by ATZ2 increased by 2.73 and 0.64times,respectively,and the reaction rate increased by 3.50 and 2.57 times.