The High Thermal Stable Anatase Titanium Dioxide And The Optimization Of It Photocatalytic Activity

With the rapid industrialization,a large amount of coal,oil and other fossil fuels have been used,which brought on an energy crisis.On the other hand,the cosumption of large amount of fossil energy has generated large amount of industrial waste gas,waste water and dust,and so on,which all damaged the environment seriously.The development of semiconductor photocatalysts,which can be used in the preparation of clean energy(photocatalytic water splitting for preparation hydrogen),photocatalytic wastewater pollution treatment,photocatalytic wastegas treatment and other fields of application,provided a new way of thinking to solve the energy shortage and pollution control.Among these photocatalysts,the titanium dioxide photocatalyst,with its high chemical stability,low toxicity,cheap and so on,has been widely studied in the photocatalysis.However,pure anatase TiO2 still has some shortcomings.For example,the anatase TiO2 has a big band gap of about 3.2 eV,which means that its photo-response range is mainly concentrated in the UV region,so the abundant visible light in solar spectrum or coming from artificial light sources cannot be utilized effectively.The photocatalytic performance of pure anatase TiO2 is very limited under the natural light,which limits its practical applications.Besides this,the anatase TiO2 is a relatively thermally unstable structure at a calcinations temperature higher than about 600?,it will irreversibly transformed into rutile TiO2 which has a poor photocatalytic.This also limits its application and scope.In this paper,the high thermal stability of anatase TiO2 has been studied,and its photocatalytic performance has been optimized.The main content of the article has the following aspects:First,a novel and simple liquid phase method was proposed.The titanium tetrachloride was used as titanium source,which reacted with high concentrations of sodium hydroxide and formed amorphous sodium titanate intermediates.Amorphous hydrated titanium oxide was then obtained through ion exchange method,where acid treatment using HC1,leads to replacement of Na+ ion with H+.After annealing,the pure nano-crystallized anatase TiO2 particles possessed a high thermal stability up to 900?.The formation of amorphous sodium titanate intermediate is very important to inhibit the phase transformation from anatase TiO2 to rutile TiO2 during the reaction process.The concentration of NaOH played a key role in the preparation of amorphous sodium titanate intermediate,which has been confirmed byby the first principle theory.The crystallinity of the samples and the phase composition of the samples have an important effect on the photocatalytic of the samples.The crystallinity of the samples can be improved at high temperature.The optimum heat treatment temperature is obtained by heat treating samples at different temperatures.Second,the sol-gel method at room temperature,combined with a high-temperature hydrothermal method was used to synthesize the mesoporous Si,N co-doped spherical anatase TiO2,which exhibited high thermal stability and high photocatalytic activity.The incorporation of N could expand the the photo-response range of the catalyst to visible light,while the incorporation of Si could stabilize not only the anatase phase at high calcinations temperature,but also the N element at high temperature and during application process thtough the formation of stable Si-N bonds.The influence of the existence of Si-N bond on the stability of N element at high temperature was also comfirmed through simulating and calculated by the first principle density functional theory.Third,a simple high-energy ball mill solid-reaction method was proposed to synthesize the Sidoped TiO2,in which the anatase TiO2 as titanium source and the nano-SiO2 as a silicon source,in order to further simplify the production process and reduce production costs.The final Si,N co-doped TiO2 sample was obtained by heat treating the Si doped TiO2 sample in an ammonia atmosphere,which has a high thermal stability and high photocatalytic activity.The experimental process is simple,template-free and of high reproducibility,which is suitable for the large-scale industrial production.Forth,to expand the photo-response range and optimize the photocatalytic performance,a compound modification method was used to the Si-doped anatase TiO2 sample.We studied the combination of Si-TiO2 with g-C3N4,AgCl or other semiconductors.The photogenerated electron-hole pairs were effectively separated,leading to improved photocatalytic activity and high-stability.