Study On Modification And Properties Of Photocatalytic Materials For TiO₂-SiO₂ Photonic Crystals

Although TiO2 is one of the most widely studied photo catalytic materials,the photocatalytic efficiency of single TiO2 suffers from the limitation of its structure and energy band,which restricts its practical application.Therefore,the current research topic on TiO2 is mainly focused on how to improve its photocatalytic degradation performance.Traditional methods such as semiconductor coupling,precious metal loading,doping and other ways can improve the photocatalytic performance of TiO2,but the improvement effect is limited because these methods mainly regulate light absorption and electron excitation transfer processes.In fact,the TiO2 photocatalytic process invol ves various parameters such as light response absorption,electron excitation,transfer and utilization processes,as well as mass transfer and transport of photocatalytic reaction.As a result,to further improve the photocatalytic performance of TiO2 needs to be considered comprehensively from multiple aspects.Studies have shown that increasing the specific surface area of the material and the construction of the porous structure can not only effectively increase the photocatalytic active sites to enhance the photocatalytic reaction process,but also greatly improve the electron utilization rate to avoid charge accumulation.In particular,the introduction of "photonic crystal" structure in photocatalytic materials can realize the light regulation and enhance the light utilization due to the slow photon effect and multiple scattering effect produced by its special periodic structure,thereby improving the photocatalytic performance of the materials.TiO2-SiO2 was prepared by a sol-gel method as the basic research.Starting from the aspects of light absorption,electron transfer and photocatalytic reaction mass transfer,multiple methods such as electronic structure regulation and material structure design were used to regulate and enhance the photocatalytic performance of TiO2-SiO2.Cu2+doped TiO2-SiO2 composite powders were prepared by introducing copper nitrate into the precursor.Porous Cu2+doped TiO2-SiO2 photocatalysts with photonic crystal structure were synthesized by template immersion method.SiO2 photonic crystal-Cu2+doped TiO2-SiO2 composite film was prepared by the vertical deposition method.A series of test methods such as XRD,SEM,FT-IR,UV-vis,PL,XPS,EIS,and MS,etc.were used to analyze the crystal phase,morphology,structure composition,band gap and photoelectric properties of the samples.The photo catalytic degradation performance of the sample was studied under visible light by using Rhodamine B as the target pollutant.Moreover,the enhancement mechanism of the photocatalytic reaction was also explored.The main results are as follows:(1)The TiO2-SiO2 with synergistic effects of adsorption-photocatalysis were prepared by sol-gel method.The morphology of TiO2-SiO2 was changed by controlling the nTi:nSi,water bath temperature and calcination temperature,which affects the photocatalytic degradation efficiency.SiO2 can inhibit the growth of TiO2 particles in the TiO2-SiO2 photocatalyst,reduce the crystallization temperature,refine the grains,avoid agglomeration,improve the dispersion of TiO2,increase surface active sites,and provide the basis for accelerating the photocatalytic degradation reaction.The TiO2-SiO2 sample prepared in a 80?water bath at nTi:nsi=1:3 can be adsorbed 43.70%RhB after a dark reaction for 60 min,and the degradation rate of RhB can reach 98.37%after visible light irradiation for 60 min.(2)Cu2+ doped TiO2-SiO2 with different Cu2+ doping contents were prepared by using copper nitrate as the copper source.Compared with undoped Cu2+,the photocatalytic performance of the samples with moderate Cu2+doping content is significantly improved under visible light irradiation.The micro Cu2+ doping content enhances the crystallization of TiO2-SiO2,promotes the growth of TiO2 particles and reduces the defects.It reduces the band gap of TiO2-SiO2,improves the light absorption capacity,and inhibits the electron-hole pair recombination.With the increment of Cu2+doping content,the photocatalytic performance of the sample increases first and then decreases.The best photocatalytic performance is obtained when the Cu2+doping content is 1%.(3)The porous Cu2+doped TiO2-SiO2 photocatalyst with inverse opal photonic crystal structure was prepared by immersing the sol with two different templates.Photonic crystal structure Cu2+doped TiO2-SiO2 photocatalyst with ordered pore structure can be obtained by controlling the process conditions and using the two templates.Compared with the non-porous Cu2+ doped TiO2-SiO2 sample,the adsorption capacity of the Cu2+doped TiO2-SiO2 with photonic crystal structure is increased by about 30%,the recombination rate of electron-hole pair is reduced,and the surface charge transfer is accelerated.The SiO2 inverse structure@Cu2+doped TiO2-SiO2 catalyst has highly ordered and stable structure.In addition,its crystallization does not be affect by the combustion of organic matter.The catalyst with ordered pore structure effectively increases the specific surface area and accelerates the mass transfer process.At the same time,the light absorption utilization has been enhanced due to the slow photon effect of the photonic crystal.So,it has strong adsorption capacity as well as catalytic degradation performance,which greatly accelerates the degradation efficiency of pollutants.(4)SiO2 photonic crystals with different band gap positions and different thicknesses were prepared on the glass substrate,and then inserted into Cu2+ doped TiO2-SiO2 sol to prepare SiO2 photonic crystals-Cu2+doped TiO2-SiO2 composite film.Photonic crystals can improve the light absorption utilization of Cu2+doped TiO2-SiO2 film through band gap reflection and slow photon effect,to enhance the photocatalytic performance.The photocatalytic performance of the composite film with the photonic band gap position near the absorption edge of Cu2+doped TiO2-SiO2 is the best.With the increase of structure period number of the photonic crystal,the reflected light becomes stronger,while the photocatalytic activity is not improved when the structure period number of photonic crystals reaches a critical value.The photon localization effect of SiO2 photonic crystal exists in a certain range between the photonic crystal and Cu2+doped TiO2-SiO2 film.The farther the distance of Cu2+doped TiO2-SiO2 film from the SiO2 photonic crystal layer,the worse effect that photonic crystal enhances the photocatalytic activity of Cu2+doped TiO2-SiO2 film.