Study On The Preparation And Performance Of Defect-State Photocatalysts For Visible Light Response

Semiconductor photocatalysis technology can convert the low-density solar energy to high-density chemical energy,exerting great potential applications for settling energy crisis,environmental pollution,and used for a wide range of applications such as water splitting,CO₂ reduction,wastewater treatment and air purification.Compounding efficient semiconductor photocatalysis is the key to realize the practical application and commercial development of photocatalysis.The common semiconductor photocatalysts,such as titanium dioxide（TiO₂）,bismuth oxychloride（BiOCl）and so on,have good photocatalytic activity.However,it only takes up about 4%of solar energy as ultraviolet light,narrowing the band gap,which leads to low utilization of solar energy.As a result,it limits the practical application and hinders the commercial development.The introduction of self-defects in semiconductors can modulate the energy band structure of semiconductors and broaden the light absorption.It can also be used as an active site for photocatalytic reactions,which has received extensive attention.The self-defect is formed by the disorderly loss of the semiconducor’s own elements,such as oxygen vacancies in the oxide semiconductor.If the loss of defects can be further controlled,an ordered defect will form or a phase transition will occur to form a new phase.For this reason,we propose to improve the photoresponse range by introducing self-defects and further doping at its defect sites to modify the photocatalytic activity.In this thesis,self-defects were introduced into TiO₂ and BiOCl semiconductor photocatalysts by thermal reduction method.Bi₁₂C_l7Cl₂,a new phase formed by ordered defects in BiOCl,was further synthesized.The structure and photocatalytic properties were characterized and analyzed respectively.On this basis,we did Ag doping in the defect-state semiconductor,and studied the effect of Ag introduction on the photocatalytic performance in the defect state.The details are as follows:（1）TiO₂ with different{001}and{101}crystal faces was treated by ethylene glycol thermal reduction method,and TiO₂ with self-defects was synthesized.The TiO₂ with exposing{001}tended to be blue and the TiO₂ with exposing{101}tends to be yellow,which effectively extended the long-wavelength response of visible light.It was found that the TiO₂ with exposing{101}exhibited the highest photocurrent response and photocatalytic hydrogen production activity under visible light conditions,and the hydrogen production efficiency reached 174 mmol g^-1 h^-1.The photo deposition of Ag instead reduced the photocatalytic efficiency of TiO₂.（2）Black BiOCl was obtained through the thermal reduction of ethylene glycol.Further studies revealed that not only the presence of oxygen defects,but also a large number of surface Bi defects.The visible light catalytic performance of the BiOCl was significantly improved,and the photocurrent was doubled compared to the original white BiOCl.The degradation efficiency of dye was increased from the original 1.73×10^-3 min^-1 to 18×10^-3min^-1.Further,Ag was loaded on the defected BiOCl by solvothermal method.It was found that Ag tended to form particles,and the plasma effect enhanced the visible light absorption performance.However,the photocatalytic activity was reduced due to the reduction of the defect active sites.（3）The Bi₁₂O₁₇Cl₂ with few or even single layers in BiOCl was synthesized by hydrolysis.Ag nanoparticles could not be observed after the photo deposition of Ag.However,the presence of Ag was detected by both Raman Spectroscopic Analysis and X-Ray Photoelectron Spectroscopy.When the doping amount was 5 wt%,photocatalytic activity hotocatalytic activity was the highest.And the degradation efficiency of methylene blue increased from 20%to 90%after 180 min.