Plasma Modified Bismuth-based Photocatalyst And Its Photocatalytic Performance For Carbon Dioxide Reduction

In recent years,global warming caused by excessive emission of carbon dioxide?CO₂?and other greenhouse gases has posed a serious threat to the earth's ecological environment.Using sunlight to drive the catalytic reduction of CO₂ to convert it into fuel or chemical raw materials is one of the ideal methods to alleviate global warming.The key of this method is the selection of high-efficiency photocatalysts.Bismuth-based materials have potential to be used for photocatalytic reduction of CO₂because of their various advantages,such as low cost,non-toxicity,good stability,and suitable band gap.However,bismuth-based photocatalysts have the disadvantages of low utilization rate of visible light and high recombination rate of photogenerated carriers,resulting in low activity.of photocatalytic reduction CO₂.Therefore,it is necessary to improve the performance of photocatalytic reduction CO₂ through surface strategies.In view of the shortcomings of bismuth-based photocatalysts,the thesis uses a convenient and fast plasma method to modify the surface of bismuth-based photocatalysts,aiming to improve the performance of photocatalytic reduction CO₂by improving the photocatalytic light absorption and carrier separation efficiency.The thesis adopts dielectric barrier discharge technology to generate plasma.Firstly,the thesis uses bismuth tungstate?Bi₂WO₆?photocatalyst was used as the target catalyst,and performs plasma modification treatment under argon and hydrogen-argon mixed atmospheres respectively,to determine the optimal plasma modification conditions,and to explore the mechanism of modification to improve the activity of photocatalytic reduction CO₂.Secondly,plasma modification research was conducted on bismuth molybdate?Bi₂MoO₆?photocatalyst to explore the applicability of plasma modification to bismuth-based photocatalysts.The specific research results are as follows:?1?The surface modification treatment of Bi₂WO₆ nanosheets using argon plasma has significantly improved the activity of the photocatalytic reduction CO₂.In the plasma treatment at different times,Bi₂WO₆ after 10 min argon plasma treatment has the best photocatalytic reduction of CO₂ to CO activity,and its CO generation rate reaches 40.6?mol g^-11 h^-1,which is 2.4 times than the untreated Bi₂WO₆,and also has good photocatalytic stability.Exploring the mechanism,it is found that argon plasma helps to introduce more oxygen defects in Bi₂WO₆.Oxygen defects can improve the light absorption of the photocatalyst,and also help the separation of photogenerated electrons and holes,which are beneficial to the performance of photocatalytic reduction CO₂.?2?The hydrogen-argon plasma was used for the rapid treatment of Bi₂WO₆nanosheets,and the optimal modification treatment time is 6 min.Bi₂WO₆ modified by hydrogen-argon plasma has a higher photocatalytic activity to reduce CO₂ to CO than modified Bi₂WO₆ under single argon,and its CO generation rate was further increased to 56.5?mol g^-11 h^-1.Some methane?CH₄?also was produced.The mechanism analysis shows that hydrogen-argon plasma treatment can reduce Bi³⁺in Bi₂WO₆ to bismuth metal.By introducing bismuth metal in situ grow on the surface of Bi₂WO₆,its visible light absorption performance can be enhanced.At the same time,photoluminescence and photocurrent etc also proves that the hydrogen-argon plasma modified Bi₂WO₆ has significantly improved the efficiency of photogenerated electron and hole separation.It also shows that the modification of hydrogen-argon plasma to Bi₂WO₆ introduces bismuth metal,which has a significant role in improving the performance of photocatalytic reduction CO₂.?3?The hydrogen-argon plasma modified Bi₂MoO₆ photocatalyst,compared with the original Bi₂MoO₆,its photocatalytic reduction of CO₂ performance has also been improved.Through experimental research,the optimal time for hydrogen-argon plasma modification treatment of Bi₂MoO₆ was 10 min.Under this condition,the rate of Bi₂MoO₆ photocatalytic reduction of CO₂ to CO increased from 5.46?mol g^-11 h^-1to the highest 16.36?mol g^-11 h^-1.By characterizing the chemical composition and the change of element valence state of the plasma-modified photocatalyst,it was found that BiO_2-x-x containing Bi⁵⁺appeared in the hydrogen-argon plasma modified Bi₂MoO₆,and the presence of BiO_2-x-x can effectively capture photo-generated electrons to prevent the recombination of photogenerated electrons and holes,realizes the efficient separation of Bi₂MoO₆ photogenerated carriers,which ultimately promotes the improvement of the performance of Bi₂MoO₆ photocatalytic reduction of CO₂.At the same time,it also proves that the plasma method has certain universality for improving the performance of bismuth-based photocatalysts to reduce CO₂.