Synthesis And Photocatalytic Properties Research Of TiO₂/ZnO Micro/Nano-materials And Core-shell Structure

Since 21^st century,the rapid development of industry has produced lots of organic waste,which is toxic or not directly bio-degradable.Without effective treatment,these contaminants will not only result in serious environmental problems,but also threaten human health and survival.Recently,based on the unique physical and chemical properties of semiconductor material,semiconductor-based photocatalysts have become one of the most effective materials for the treatment of organic pollutants.Although a great deal of research and exploration have been focused on semiconductor-based photocatalysts,few photocatalysts can meet the requirements for practical applications.At present,powdery semiconductor photocatalytic materials still have the low catalytic efficiency,a narrow light-response range and a difficulty in recovery and recycle,which limits their practical application.In this paper,TiO₂ and ZnO powdery semiconductors with wide band gap were the main object of research,and how to improve their photocatalytic activity and practicability in the degradation of organic pollutants were the focus of research.The specific research work is listed as follows:?1?By solvothermal and hydrogen reduction techniques,four kinds of TiO₂nanocrystal with different morphologies were prepared,including elongated rhombic,dog-bone,oval and core-shell structured oval.XRD,SEM,TEM,PL and so on analysis instruments were used to characterize the crystallinity,morphology and optical properties of TiO₂ samples.Moreover,the roles of oleic acid,oil amine as surface covering agents and hydrogenation in the growth of TiO₂ crystal grain were investigated,then the corresponding growth mechanism was proposed.The result of photocatalytic test under simulated solar irradiation showed that the oval-shaped TiO₂ sample with core-shell structure was superior to other TiO₂ samples in catalytic activity.And this TiO₂ sample exhibited well recyclability during multiple photocatalytic tests.The special core-shell structure,larger specific surface area and narrow band gap?2.67 eV?did attribute to the excellent properties of this TiO₂ sample.?2?Be aimed at the bottleneck of TiO₂ photocatalyst in practical application that is not easy to be separated and recovered,we synthetized magnetic separable Fe₃O₄/SiO₂/mTiO₂ core-shell microspheres,in which Fe₃O₄ core as magnetic carrier,intermediate SiO₂ layer as electronic barrier and TiO₂ as photocatalytic active layer.By changing dosage of tetrabutyl titanate,three Fe₃O₄/SiO₂/mTiO₂ samples with different thickness and microstructure of TiO₂ layer were prepared,and the growth mechanism was explained in detail.Photocatalytic test results showed the Fe₃O₄/SiO₂/mTiO₂sample that was prepared with 0.6 ml TBOT?FST-0.6?exhibited superior photocatalytic activity than other Fe₃O₄/SiO₂/mTiO₂ samples,and FST-0.6 powdery sample was recovered effectively with the help of an appropriate magnetic field.Moreover,duo to the unique microstructure and larger specific surface area,the recovered FST-0.6 sample maintained the activity without significant decline during multiple photocatalytic tests.Accordingly,a rational photocatalytic mechanism was proposed.?3?To further improve the photocatalytic activity of Fe₃O₄/SiO₂/mTiO₂ core-shell microspheres,Au particles with a diameter of about 20 nm were deposited on the surface of mesoporous TiO₂ photocatalytic active layer by in-situ reduction method,and a novel Fe₃O₄/SiO₂/mTiO₂-Au photocatalyst with a four-layer core-shell structure was synthetized.The role of SiO₂ inter-layer and Au particles in the photocatalyst was studied.The activities of various samples in photocatalytic test followed the order:Fe₃O₄/SiO₂/mTiO₂–Au>Fe₃O₄/SiO₂/mTiO₂>Fe₃O₄/mTiO₂>P25.Furthermore,Fe₃O₄/SiO₂/mTiO₂–Au sample was easily recycled by using a magnet while had no significant decrease in photocatalytic efficiency during circular photocatalytic test.These excellent properties of Fe₃O₄/SiO₂/mTiO₂–Au sample were mainly ascribed to two factors:firstly,SiO₂ interlayer can avoid Fe₃O₄ core with a narrow gap band?0.1eV?from becoming the recombination center of photo-generated electron-hole pairs,and can also protect the magnetic Fe₃O₄ carrier from chemical corrosion.Secondly,the loading of Au can effectively improve the separation efficiency of photo-induced electron-hole pairs.?4?To improve the photocatalytic performance and simplify the recover technology ZnO material,four kinds of magnetic chestnut-like Fe₃O₄/SiO₂/ZnO/Au?FSZA?core-shell microspheres with different amount of Au were prepared by step-by-step chemical methods.The test results of TEM,SEM and so on showed that all microspheres possessed good dispersity,uniform core-shell structure and high magnetization.Additionally,the effect of Au loading amount on photocatalytic performance was stutied by the degradation of RhB.The FSZA sample with better activity and the optimal Au loading amount were founded.Based on the above results of research,we found that loading a proper amount of Au particles not only increased the specific surface area of FSZA core-shell microspheres,but also improved separation efficiency of the photo-generated carriers.Thus,Au particles can greatly improving the photocatalytic performance of FSZA microspheres.Notably,this Fe₃O₄/SiO₂/ZnO/Au sample was easily recovered by using a magnet,which was reused at least five times without any appreciable reduction in photocatalytic efficiency.?5?Based on the study of magnetic ZnO-based composite photocatalyst,considering that ZnO can only respond to UV light and its low quantum efficiency,a series of three-dimensional multi shell Fe₃O₄/SiO₂/ZnO/ZnSe?FSZ-ZnSe?photocatalysts with a type II heterojunction were fabricated by regulating the deposition of ZnSe particles.The photocatalytic performances of all samples under UV and visible light irradiation were investigated by the decolorization of RhB,and the optimal ZnSe depositing amount was founded.No matter which light source was used,FSZ-ZnSe sample with optimal amount of ZnSe exhibited enhanced photocatalytic activity in comparison with Fe₃O₄/SiO₂/ZnO sample.This was attribued to the sensitization of a proper amount of ZnSe particles that not only facilitated the separation of photo-induced carriers but also extended the light absorption of ZnO-based composite photocatalyst.Moreover,compared to visible light radiation,the same FSZ-ZnSe sample under UV light showed remarkably enhanced photocatalytic activity.base on the.A special Z-scheme type transfer of electrons for FSZ-ZnSe sample under UV light was confirmed using radical trapping experiments and hydroxyl radical formation determination study.Meanwhile,FSZ-ZnSe sample exhibited excellent magnetic response and high stability during the recycling photocatalytic experiments.