Application Of In-situ Modified And Ion-induced Growth Tungsten-based Materials In Photocatalytic CO₂ Reduction

With the change of global climate and the development of human society,the utilization of carbon dioxide as a resource is an important goal to improve the living environment of human beings and promote the development of human society.As a new technology that uses solar energy as the source power to realize energy conversion,photocatalytic technology has broad development prospects in realizing the goal of recycling carbon dioxide.The key point of photocatalytic technology is to develop photocatalyst with high activity,high selectivity and high stability.Tungsten trioxide,as a material with photo-corrosion resistance and stability under polar conditions,has attracted much attention in the field of photocatalysis.In this paper,in-situ modification and modification of hydrothermal synthesis process are mainly used to improve its performance in photocatalytic CO₂reduction.The main research contents are as follows:（1）In situ modification of commercial WO₃（WO₃-C）produces metal vacancies and interstitial metals,which synergistically improves its performance in CO₂photocatalytic reduction reaction.Firstly,WO₃was subjected to hierarchical acid treatment using aqua regia to obtain WO₃-A samples after acid treatment and WO₃-W samples after repeated washing after acid treatment.In the photocatalytic CO₂reduction,the two samples showed better photocatalytic activity than untreated WO₃-C.The photocatalytic CO₂reduction activity of WO₃-A samples treated with aqua regia is better than that of WO₃samples treated with HCl or HNO₃.The good activity and stability of WO₃-A photocatalyst were confirmed through recycling experiments.Aqua regia treatment can change the existence of impurity metals contained in WO₃,which would affect the photocatalytic CO₂reduction performance of WO₃-A.Characterizations including XRD,XRF,EPR,XPS,Raman,HRTEM verified that the enhanced photocatalytic CO₂reduction activity of WO₃-A samples is attributed to the synergistic effect of metal vacancies and interstitial impurities obtained by acid treatment.DFT theoretical calculations further verified that the electronic band structures of WO₃with the presence of metal vacancies and interstitial metals are conducive to photocatalytic CO₂reduction,manifested in the reduction of band gaps and the generation of defect energy levels,enhancing light absorption performance and photoreduction reactivity.In addition,calcination and partial vulcanization of tungsten trioxide at different temperatures can further improve its photocatalytic CO₂reduction performance.（2）The modification of tungsten trioxide is achieved by adjusting the hydrothermal synthesis process.The introduction of chromium ions promotes the formation of tungsten trioxide in the higher p H environment.The obtained Cr doped tungsten trioxide has more uniform particle sizes and the higher photocatalytic CO₂reduction reactivity.Tungsten trioxide was synthesized by hydrothermal method using sodium tungstate as a tungsten source,and a series of different tungsten trioxide samples were obtained by changing the p H value of the precursor solution.The effects of the presence or absence of chromium salts were compared on the composition,morphology,photoresponsivity and photocatalytic performance of the obtained products.The introduction of Cr³⁺into the precursor solution at different p H conditions improves the photocatalytic CO₂reduction performance of the obtained material.Moreover,at p H=4.5,into the sample Na Cr W-4.5 synthesized with the introduction of Cr³⁺has the best photocatalytic activity.The introduction of Cr³⁺can stabilize the crystal structure of tungsten oxide and reduce the formation of bulk oxygen vacancies.A stable crystal structure helps to enhance the transport of electrons.By changing the amount of Cr³⁺to adjust the ratio of Cr³⁺to W,adjusting the hydrothermal synthesis time,and introducing different metal ions,the photocatalytic CO₂reduction performance of tungsten trioxide materials can be optimized and improved.