Preparation Of TiO₂-based Composites And Investigation On Its Photocatalytic Properties

With the environmental degradation and energy shortages becoming increasingly serious,the conflict between mankind and nature is growing.It is urgent to search new energy sources and solutions to deal with those problems.Besides,Solar-powered photocatalysis with mild reaction conditions and environmental friendliness can be used to degrade different types of pollutants such as unsaturated organics,dyes,pesticides,heavy metals（Cr,Hg,Pb）and antibiotics,and the degradation products are non-toxic and non-hazardous products such as water,CO₂and inorganic substances.This technology is therefore considered to be a potential and promising wastewater treatment technology.Nevertheless,the photocatalytic activities of photocatalytic materials is the core problem to be solved in photocatalysis technology.In recent years,many researchers have obtained many results in improving the photocatalytic performance and stability of photocatalysts.Besides,TiO₂,one of the typical photocatalysts,can be modified by doping,compounding and controlling its morphology to improve its visible light absorption range and photocatalytic efficiency.However,the use of TiO₂-based catalysts still suffers from complex preparation processes,high preparation costs and difficult powder recovery.In this paper,TiO₂-based materials are investigated as follows:1.Ag/TiO₂composite photocatalysts with Ag loading ratios of 0.5%,1%,3%and 5%were prepared by the solvothermal method without calcination,tetrabutyl titanate as raw material,and glycine as morphology control agent.Among them,Ag/TiO₂with 1%Ag loading（Ag/TiO₂-1）showed the better photocatalytic performance,achieving 98%and 95%degradation of Rhodamine B（RhB）and tetracycline（TC）at 25 min under simulate solar light.The relevant characterisation results showed that the photocatalyst Ag/TiO₂-1 consisted of 22 nm diameter nano-rod TiO₂and 5.5 nm diameter Ag nanoparticles with a band gap width of 2.95 e V and a higher specific surface area of 158.3 m²/g.Under the surface plasmon resonance effect of Ag NPs,the band gap width of TiO₂became narrower,the visible light absorption range became larger and the photogenerated electron-hole separation efficiency was increased,and it had a higher specific surface area,which could provide more active sites.After the 6th cycle experiment,Ag/TiO₂-1 still maintained96%and 95%of TC and RhB degradation,showing excellent stability,and the active substance capture experiment indicated that the active substances were h⁺and·₂^-,and the photocatalytic mechanism of Ag/TiO₂-1 was tentatively proposed.2.Firstly,SiO₂microspheres with average particle sizes of 160 nm,250 nm and400 nm were obtained by sol-gel method using tetrabutyl silicate as the raw material,and secondly,TiO₂was loaded onto the surface of SiO₂microspheres of the three particle sizes by solvothermal method to obtain TiO₂/SiO₂binary composite powder in the form of rod TiO₂,respectively.The photocatalytic results showed that the visible light photocatalytic performance of the 160 nm diameter TiO₂/SiO₂microspheres was better,with the degradation rates of RhB and TC reaching 90%and80%,respectively,at 120 min under visible light.Finally,a novel ternary BiOBr/TiO₂/SiO₂composite powder was constructed by loading BiOBr onto the surface layer of TiO₂/SiO₂binary composite powder using in situ liquid deposition technique.The system can degrade 99%of RhB and 87%of TC at 80 min under simulated visible light.The system is characterised by the use of SiO₂as a template and the step-by-step assembly of flake BiOBr and rod TiO₂onto the surface of biocompatible SiO₂microspheres to form a multi-component BiOBr/TiO₂/SiO₂ternary composite powder,which has excellent visible light catalytic properties.3.Cellulose acetate（CA）membranes as catalyst carriers have the advantages of high porosity and good hydrophilicity,which are not only beneficial for catalyst degradation but also for recycling.In this section,we used a simple coating method to composite BiOBr/TiO₂/SiO₂with cellulose acetate to prepare a serial of composite films of the same thickness（1000μm）and different BiOBr/TiO₂/SiO₂loading ratios（1%,2%and 5%）as well as the same ratio（5%）and different thicknesses（200μm,300μm,400μm,600μm,1000μm）.The photocatalytic experiments confirmed that the higher the BiOBr/TiO₂/SiO₂loading ratio,the better the performance.5%of the BiOBr/TiO₂/SiO₂/CA with 0.01g membranes in this system had the better photocatalytic performance,degrading 68%of RhB at 60min under simulated sunlight illumination（0.1g）.Under sunlight,the membranes with 0.05 g degraded 99.16%of RhB after 48 h,with a better self-cleaning effect.In addition,the thinner the membrane,the better its photocatalytic performance and self-cleaning effect.Compared to the membrane with a thickness of 1000μm,the membrane with 0.05g with a thickness of 400μm degrades 70.71%RhB in 60min under simulated sunlight and 99.11%RhB after 24h under sunlight,respectively.In this thesis,three composite powders,Ag/TiO₂,TiO₂/SiO₂and BiOBr/TiO₂/SiO₂,and a BiOBr/TiO₂/SiO₂/CA composite film were prepared with the aim of preparing TiO₂-based composite catalysts with low cost,good biocompatibility and high visible light photocatalytic efficiency and recyclability.All the above materials exhibited certain visible light photocatalytic properties.Among them,the BiOBr/TiO₂/SiO₂composite powder formed using BiOBr/TiO₂/SiO₂/CA composite film with cellulose acetate（CA）is more conducive to its recovery after photocatalytic degradation and has practical applications,not only in the field of photocatalysis but also in molecular and ionic filtration with potential application prospects.