Preparation And Photocatalytic Reduction Of CO₂ Performance Of Ag/Bi₂MoO₆/BiOBr Composite Film

Excessive burning of fossil fuels will to the emission of a large amount of CO₂ into the air,causing the greenhouse effect,resulting in energy shortage and environmental pollution problems increasingly serious.Therefore,it is very necessary to reduce the content of CO₂in the air,reduce the impact of the greenhouse effect,realize the resource utilization of carbon,and develop renewable and clean hydrocarbon energy to relieve the over-dependence on traditional fossil fuels.Using solar photocatalytic reduction of CO₂ as hydrocarbon fuel is a relatively simple method.The hydrocarbon generated by reduction can be used as renewable energy to alleviate the problem of energy shortage in our country to a certain extent.This method has attracted the attention of researchers as early as 1978,which can not only reduce the content of CO₂,but also realize the recycling of carbon resources,and achieve the best of both worlds.When it comes to photocatalytic technology,the core problem is to construct an efficient photocatalytic system.In recent years,many attentions have been paid to the photocatalytic reaction of bismuth based materials.Bi₂Mo O₆ is one of the bismuth based material,which has a unique layered structure and appropriate band gap width with good light response ability,so it has become one of the researchers of photocatalyts.However,the single Bi₂Mo O₆semiconductor catalytic is usually modified by some means due to its high recombination rate of photogenerated carriers.On the other hand,so far most of the photocatalyst exists in the form of powder.Although the powdered catalysts may have good catalytic performance in the photocatalytic process,but the powder catalyst have many shortcomings,such as solid-liquid separation difficult,easy agglomeration,it is easy to cause secondary pollution,difficult to recycle and reuse,etc.,which will potentially increase the cost of catalyst and affect the scope of catalyst use.Based on the above mentioned problems,we used bismuth plate as the substrate to prepare bismuth based film in situ,and the constructed heterojunction and precious metal modification to prepare bismuth based composite film.Bismuth based complex prepared by the above method can not only realize the immobilization of powder catalyst to overcome the shortcomings of powder catalyst,but also improve the performance of the photocatalyst for catalytic reduction of CO₂.The specific research contents are as follows:（1）Bi₂Mo O₆ film was prepared in situ by electrochemical method and ion exchange method with Bi plate as anode and Ti plate as cathode,and the photocatalytic performance of Bi₂Mo O₆ thin film for reduction of CO₂ was studied.The effect of reaction time on the Bi₂Mo O₆film formation was investigated.（2）In order to improve the photocatalytic reduction performance of a single Bi2Mo O6film,we prepared Bi₂Mo O₆/Bi OBr composite film based on bismuth plate through electrochemical method combined with ion exchange method,and studied the photocatalytic reduction CO₂ performance of Bi₂Mo O₆/Bi OBr composite film.In addition,the influence of the p H of electrolyte solution on the preparation of composite film was explored in the preparation process.The Bi₂Mo O₆/Bi OBr composite film was prepared under the selected optimal process conditions and a series of characterization were carried out.Combined with the characterization data,a possible mechanism of photocatalytic reduction of CO₂ was proposed.The Bi₂Mo O₆/Bi OBr composite film shows a good performance of photocatalytic reduction of CO₂ to CO under 300 W X-lamp irradiation,which can reach 117.21μmol·g^-1,which was 1.5times that of the single Bi2Mo O6 film.Moreover,Bi2Mo O6/Bi OBr composite films show good stability after three cycles.Various analysis results show that the Bi₂Mo O₆/Bi OBr composite film has a high photocatalytic activity due to the band gap between Bi2Mo O6 and Bi OBr can be well matched and form a Z-scheme heterjunction,which effectively promotes the separation of photogenerated electron hole pairs and improves the utilization of electrons.Furthermore,the photocatalytic performance of Bi2Mo O6/Bi OBr composite films was improved.（3）In order to further improve the performance of Bi₂Mo O₆/Bi OBr composite film for the photocatalytic reduction of CO₂ to CO,we used photodeposition method to deposit precious metal Ag on the prepared Bi₂Mo O₆/Bi OBr film to obtain Ag/Bi₂Mo O₆/Bi OBr film.In order to explore the effect of Ag deposition amount on the performance of photocatalytic reduction of CO₂ in Bi₂Mo O₆/Bi OBr composite film,we deposited silver with different mass fractions on Bi₂Mo O₆/Bi OBr composite film and then used it to study the performance of photocatalytic reduction of CO₂ into CO.Through the experiments,it was found that with the increase of silver deposition,the performance of Ag/Bi₂Mo O₆/Bi OBr composite film for the photocatalytic reduction of CO₂ to CO increase first and then decreases.When the siliver deposition was 1.5%,the performance of Ag/Bi₂Mo O₆/Bi OBr film for the photocatalytic reduction of CO₂ to CO is the best.The yield of CO is 134.5μmol·g^-1.According to UV-Vis,it can be know that precious silver has surface plasmon resonance（SPR）essect,which causes the red shift of the light absorption band edge of Ag/Bi₂Mo O₆/Bi OBrfilm and improves the light absorption.In addition,precious metal Ag can be used as the intermediate bridge between Bi₂Mo O₆ and Bi OBr for charge transmission,and the generated Schottky barrier can hinder the recombination of photogenerated electron hole pairs.Therefore,compared with single Bi₂Mo O₆/Bi OBr film,Bi₂Mo O₆/Bi OBr film after deposition of noble Ag has the best performance in photocatalytic reduction of CO₂.