Preparation Of Bismuth Oxyhalide And Its Photocatalytic Performance Of Nitrogen Fixation

The current method of industrial ammonia synthesis consumes about 2%of the world energy while meeting the chemicals and foods needed by our society,and the huge amounts of carbon dioxide released during the reaction aggravates global warming.Photocatalytic nitrogen fixation based on visible light semiconductors is a green and promising alternative method.Creating efficient photocatalytic materials is the key to realizing photocatalytic nitrogen fixation.Bismuth oxyhalide（Bi O_mX_n）with layered structure and internal electric field shows good photocatalytic activity and stability for many reactions.In this paper,bismuth-rich Bi₁₂O₁₇Br₂and Bi₁₂O₁₇Br_xI_2-xcatalysts were prepared by liquid phase method,and their performance of photocatalytic nitrogen fixation were evaluated with visible light irradiation.The main research results are as follows:（1）A serials of Bi₁₂O₁₇Br₂were prepared by one-step hydrolysis under mild conditions,and their crystal phase,interaction with N₂,optical and electrochemical features were systematically characterized and analyzed.The results show that the photocatalytic performance of Bi₁₂O₁₇Br₂for N₂fixation could be greatly improved by increasing the hydrolysis time.Under full-spectrum and visible light（λ>420 nm）irradiation,without any additives,only N₂and water,the rates of NH₄⁺production are 735μmol?L^-1?g^-1?h^-1and 144μmol?L^-1?g^-1?h^-1,respectively.Electrochemical measurements results state that Bi₁₂O₁₇Br₂prepared with long-time hydrolysis has low electrochemical impedance,which could be beneficial to the efficient separation of photogenerated carriers.As a result,long-time hydrolysis make Bi₁₂O₁₇Br₂a promising catalyst for photocatalytic fixation of nitrogen under visible light.（2）Bi₁₂O₁₇Br_xI_2-xsolid solution was successfully synthesized by an efficient hydrolysis method.SEM observation shows that it has a sheet-like structure with a scale of 50-300 nm and a thickness about 15nm.The introducing I constructs a brand new energy band structure,which can reduce the band gap and improve the light absorption.Nitrogen temperature-programmed desorption（N₂-TPD）experimental results demonstrate that the introduction of I obviously strengthen the interaction between N₂and the catalysts,thus effectively improve the activation ability of nitrogen.Electrochemical impedance and photocurrent responses measurements indicate that the photogenerated carrier separation efficiency of the Bi₁₂O₁₇Br₁I₁solid solution is significantly promoted.Compared with pure Bi₁₂O₁₇Br₂and Bi₁₂O₁₇I₂,under full-spectrum and visible light（λ>420 nm）irradiation,Bi₁₂O₁₇Br₁I₁with the 1:1 molar ratio of Br to I has the best photocatalytic nitrogen fixation activity,and the rate of NH₄⁺production is406μmol?L^-1?g^-1?h^-1and 178μmol?L^-1?g^-1?h^-1,respectively.Reuseing experiments show such catalyst has good stability and could be used for recycling.