Preparation Of Titanium Dioxide-based Photocatalytic Materials And Their Visible Light Degradation Properties

Green chemistry contributes to the sustainable development of human beings.Among them,photocatalysis,as an important part of the research field of green chemistry,shows great potential in solving energy shortages and treating environmental pollution.In recent years,hydrogen production from photolysis of water for providing new energy sources and photodegradation of organic matter for curbing environmental pollution have become two core components of research on photocatalytic materials.However,most of the photocatalytic materials have not yet been industrialized,still in the laboratory or theoretical stage,and the efficient use of sunlight has not been realized because of its low photocatalytic efficiency.Titanium dioxide,as the only photocatalytic material for industrial mass production,which only responds to ultraviolet light less than 5%of sunlight,has hampered expansion of its research scope.In order to solve this problem,a series of titanium dioxide-based photocatalytic materials with visible light response were synthesized by combining TiO₂ with SiO₂,graphene oxide,g-C₃N₄,Ag₃PO₄ and other materials.The microstructure and properties of the materials were characterized by using XRD、SEM、TEM、Raman、BET、TGA、UV-vis and so on.And the photodegradation of organic dyes（methyl orange,rhodamine B）under the visible light irradiation and its mechanism were discussed in this paper.Firstly,with the advantages of mesoporous SiO₂ with high specific surface area,well-ordered pore channel and continuous adjustable pore size,TiO₂/Si O₂ binary composites were prepared by sol-gel method and hydrothermal method.The research results showed that compared with pure TiO₂,the TiO₂/SiO₂ binary composites have significantly improved the degradation efficiency of methyl orange solution under ultraviolet or visible light.When the Ti/Si molar ratio was 1:20,the degradation rate of the methyl orange solution on TiO₂/SiO₂ composite material increased from 24%to 99%under 20 min UV irradiation,and increased from 2%to 40%under 55 min visible light irradiation.Therefore,TiO₂ supported on mesoporous SiO₂ with high specific surface area can achieve good dispersion of TiO₂,and expand its“red shift”in the photoresponsive region,thereby improving the photocatalytic effect of the material.Secondly,by using the excellent conductivity of graphene,a series of TiO₂/RGO composites were prepared by hydrothermal method based on two different titanium sources,and the influence of the RGO loading,hydrothermal temperature and hydrothermal time on microstructure and photocatalytic effect of TiO₂/RGO composites in the visible region were investigated in this section.The research results showed that the prepared TiO₂/RGO composite,TBOT as the titanium source,had better photocatalytic activity than pure TiO₂,which not only reflected the increase of the photoresponse in the ultraviolet region,but also realized the absorption of light in the visible region.The main reason may be that combining with RGO reduces the agglomeration of pure TiO₂,increased the specific surface area of the samples,and most importantly,the good conductivity of RGO accelerated the transfer of photo-generated electrons,inhibited the recombination of photogenerated electron-holes pairs,and thus enhanced the efficiency of photocatalytic degradation of methyl orange solution.Moreover,using Ti（SO₄）₂ as a titanium source,TiO₂/RGO composite,prepared by hydrothermal method at 200°C for 24h also showed the excellent photocatalytic effect with a degradation rate of 99.9%in visible light for 3min,demonstrating the increase of hydrothermal temperature and hydrothermal time promoted the photocatalytic effect of the sample.Finally,by using the visible light response characteristics of Ag₃PO₄ and g-C₃N₄,the g-C₃N₄/TiO₂ binary composite system was firstly prepared by calcining method,and then Ag₃PO₄/g-C₃N₄/TiO₂ ternary composite was prepared by depositing Ag₃PO₄ on the surface of g-C₃N₄/TiO₂ by precipitation method.In order to investigate the optimum composition ratio,visible light degradation effect and photocatalytic reaction mechanism of Ag₃PO₄/g-C₃N₄/TiO₂ ternary composites,morphology and photocatalytic effect of pure TiO₂,Ag₃PO₄,and g-C₃N₄,and the binary g-C₃N₄/TiO₂,Ag₃PO₄/g-C₃N₄,Ag₃PO₄/TiO₂ were studied in advance.The experimental results showed that compared with the mono-and binary materials,the efficiency of degradation of 4 mg/L rhodamine B solution on the prepared Ag₃PO₄/g-C₃N₄/TiO₂ ternary composite with the m_melamine:m_TiO2iO2 ratio of 1:1 and the m_Ag3PO4:m_g-C3N4/TiO2-C3N4/TiO2 ratio of 50:1 after 10 min visible light irradiation reaches to 99.5%,and the visible light degradation effect was optimized.Therefore,the matched band gaps of the components were favorable to prolong the recombination of the photogenerated electron-hole pairs in this ternary system and extend the absorption of light to the visible region,thereby improving the photocatalytic performance of the materials.