Research On Modification Of Titanium Dioxide And Carbon Nitride For Application In Photocatalysis And Optoelectronic Device

Semiconductor materials have attracted a lot of attention from researchers in solar energy conversion,especially in photocatalysis as well as photoelectrochemical cells.Improving the visible light absorption capacity and carrier separation efficiency of semiconductor materials is the main way to obtain efficient photocatalytic and photovoltaic conversion efficiency.TiO₂and carbon nitride（g-C₃N₄）are semiconductor material with good photocatalytic activity and has received a lot of attention.However,TiO₂has a large band gap（Eg≈3.2 e V）and can only absorb UV light in the solar spectrum which only accounts for 4%of the solar spectrum,resulting in its low utilization of solar light.g-C3N4 has visible light absorption capability,but suffers from severe carrier complexation,low photocatalytic and photoelectric conversion efficiency.In view of the problems faced by both,this paper improves the visible light absorption ability and carrier separation ability by doping and sensitization of TiO₂,and changes the specific surface area and light absorption ability of g-C₃N₄by doping and evaporation of S,thus improving the photocatalytic and photoelectric conversion efficiency.The specific research contents are as follows:Firstly,Although TiO₂is a broadband gap semiconductor（Eg=3.2 e V）,it shows photodegradation activity under visible light irradiation after dye sensitization.Compared with the esterification reaction of hydroxyl（-OH）and dye carboxyl（-COOH）on the surface of TiO₂,the electrostatic interaction between TiO₂and dye makes the semiconductor show better photosensitivity.In this paper,Bi/Al co-doped anatase titanium dioxide[Ti_1-xBi_2x/3Al_2x/3O₂（0≤x≤0.3）]was designed to enhance the electrostatic interaction.The role of Al ion is to enhance the solubility of Bi3⁺in titanium dioxide nanocrystals.A new impurity band gap is generated after doping with high concentration of Bi element,which not only promotes the absorption of visible light in semiconductors,but also improves the utilization of photogenerated carriers.Through transmission electron microscopy（TEM）,optical absorption（UV-vis）,photodegradation activity and density functional theory（DFT）calculations,it is found that the Bi dopant is the electron capture site.It first accumulates electrons through the photocatalytic degradation reaction,making it show that it has negative charge,enhancing the electrostatic adsorption between the catalyst and the positively charged dye molecules,and finally realizing the efficient photosensitive degradation of rhodamine B.In addition,sensitized titanium dioxide has excellent photodegradation cycling.Secondly,Graphitized carbon nitride（g-C₃N₄）is a new organic,non-metallic polymeric semiconductor material（E g≈2.7e V）with good visible light activity and an absorption edge reaching near 460 nm.It has received a lot of attention due to its simple synthesis process,low cost,high activity and good chemical stability.However,its application which in photocatalytic and photoelectrochemical cells is limited by its small specific surface area,limited light absorption,and severe photogenerated carrier complexation.In this paper,by calcining sulfur mixed with g-C₃N₄,in which firstly sulfur is doped into g-C₃N₄,and with the extension of high temperature time,sulfur is evaporated and porous g-C₃N₄is formed,which makes the active sites that can participate in redox increase and the light absorption ability is enhanced.Under simulated sunlight irradiation,its photocatalytic degradation rate of organic pollutant rhodamine B（Rh B）,photocatalytic total hydrolysis rate and photocurrent density were 3.14 times,2.32 times and 1.7 times higher than those of pristine g-C₃N₄,respectively.