Preparation Of TiO₂-based Nanocomposites And Metal Doped Materials And Their Photocatalytic Performance

In the aspect of environmental purification,photocatalytic degradation of organic pollutants has an irreplaceable effect.Therefore,the selection and research of photocatalyst has attracted much attention.TiO₂,as the most widely used photocatalyst,has not only the advantages of easy preparation,low cost,non-toxicity,and high efficiency,but also the great significance of development and utilization for photocatalyst.In view of several steps during the photocatalytic process,optimization of each step is crucial to enhance the photocatalytic efficiency.In this dissertation,according to the shortcomings of TiO₂,such as response only to ultraviolet light due to the large band gap width?3.2 e V?,easy recombination of photoelectron and hole,and uneasy separation of TiO₂ powder,ion doping and composite modification were applied to TiO₂ so as to improve the photocatalytic efficiency and expand the light absorption range,with the hope of realizing degradation of organic pollutants under visible light.The transition metal and rare earth metal have rich d-orbital electrons,which provides favorable conditions for the transfer of photo-generated electrons.According to the large band gap of TiO₂,Ag,La,Nb,and Fe doping into the matrix of TiO₂ by liquid precipitation or sol-gel method.The formed Ti-O-M structures can increase the surface defects and active surface area of the doped materials.The charge imbalance in such structures will induce the partial transformation of Ti⁴⁺into Ti³⁺,and thus the band gap of the TiO₂/M materials are narrowed,reduce the band gap of TiO₂,which can enhance visible light response.The optimum conditions such as doping ratio,calcination temperature,and calcination time were determined by orthogonal design.The composites fabricated under the optimum experimental conditions showed excellent catalytic effect in the process of degrading MO.For example,La-TiO₂ film prepared by the suitable parameters?with0.01mol%La?displays twice higher activity than the pristine TiO₂ in MO degradation,and the Fe-TiO₂ composites synthesized by the optimal condition?with1.0mol%Fe?exhibit the best visible light catalytic performance,i.e.the degradation efficiency of MO can reach 56.62%in 3 hours.PPy and PT conductive polymers and GO and RGO not only have excellent conductivity,high specific surface area,but also provide a certain visible light response.The photocatalitic response range of TiO₂ can be prolonged by the combination of TiO₂ and PT,PPy,GO,and RGO with high electrical conductivity.Solid UV-Vis diffuse reflectance spectra show obvious absorption in 400-700 nm,and the absorption edges are red-shifted.The band gap of TiO₂/PPy-120 and TiO₂/RGO is 2.87 and 2.48 e V,respectively.Binary nanocomposites have wider response in the visible region,and the photogenerated charge can be successfully derived and transported to the catalyst surface to increase the ability of the active particles to bind to the reactants.This kind of binary composites exhibit excellent photocatalytic activities in the process of degrading MO.In addition,TiO₂/Co Fe₂O₄composites have ferromagnetic properties and response in the visible light range.After efficient degradation of MO,TiO₂/Co Fe₂O₄ composites can be easily separated and reused.The experimental results show that with a molar ratio of TiO₂to Co Fe₂O₄ at about 1:0.01 and a calcination tempreture at 450 ^oC.The TiO₂/Co Fe₂O₄ composites have a saturation magnetization of 2.5 emu/g,and degradation rate of MO can reach 37.3%.As the binary composites can't make full use of the characteristics and advantages of each component,the synthesis of ternary composites has great significance because the advantages of the three components can be fully used.The TiO₂/Fe/RGO,TiO₂/RGO/PPy,TiO₂/Fe/PPy,and TiO₂/Co Fe₂O₄/RGO ternary composites were synthesized by hydrothermal method and coprecipitation method.The advantages of the ternary composites are that the recombination frequency of photogenerated electron and holes is reduced while the light absorption range is extended,and more electron and holes are involved in the degradation reaction,which effectively improves the efficiency of photocatalytic degradation of MO.TiO₂/Fe/RGO ternary composites have the advantage of low band gap width.When the ratio of Fe-TiO₂ and GO is 1:0.1,the photocatalytic activities of the composites is the best.After 3 h,the degradation rate of MO by TiO₂/Fe/RGO-0.1 is 91.33%,1.65 times higher than that of Fe-TiO₂ nanoparticles.TiO₂/RGO/PPy ternary composites have the ability of rapid photoelectric separation of photogenerated electrons and holes.The introduction of PPy can not only extend the response range in the visible region,but also inhibit the recombination of photogenerated electrons and holes.Using APS as oxidant,the degradation of MO by the as-prepared TiO₂/RGO/PPy-0.07 nanocomposites can reach 98.43%in 2 h.TiO₂/Co Fe₂O₄/RGO has the advantages of excellent photocatalytic performance and magnetic separation,with a saturation magnetization of 5.0 emu/g and MO degradation rate of 75.6%in 2h,2.03 times higher than that of the TiO₂/Co Fe₂O₄ composites.