Development And Application Of Bismuth-based Metal Electrocatalytic Materials For Nitrate Reduction In Wastewater

With the rapid development of industry and agriculture in our country,the concentration of nitrogen-containing pollutants in wastewater is continuously increasing,and the total nitrogen content in domestic sewage is as high as 50 mg L^-1 in some areas.The high concentration of nitrate-nitrogen not only destroyed the ecological balance in water,but also threatened people’s health.How to achieve efficient,fast and safe removal of nitrate in wastewater has become an urgent problem.At present,most of the electrochemical reduction of nitrate is mainly to reduce it to nitrogen,which has problems such as low efficiency,poor selectivity of reduction products,easy to cause secondary pollution of water bodies,and waste of resources.Based on this,Bi-based metals with abundant resources,low price,low toxicity and environmental friendliness are used as electrodes to selectively reduce nitrate to ammonia,and systematic researches have been carried out in the aspects of catalyst design and synthesis,nitrate reduction mechanism,practical wastewater application.First,two methods were developed to inhibit the hydrogen evolution reaction activity of the catalyst,which improved the utilization of catalyst active sites and promoted the removal of nitrate.From the perspective of stress engineering,BiOI amorphous precursors were processed by different in-situ topological methods,and the internal oxygen content was adjusted to obtain different stressed Bi nanosheets.Based on the inhibition of the hydrogen evolution activity of the materials by tensile stress,its adsorption capacity for nitrate was enhanced,and the Faradaic efficiency of nitrate reduction to ammonia was improved.From the perspective of surface engineering,a stable hydrophobic film of ZIF-8 was constructed on the surface of the sample to inhibit its hydrogen evolution activity.At the same time,the establishment of the ZIF-8 film also effectively prevented the leaching of Bi elements,improved the stability of the catalyst,reduced the overall resistance of the sample,and improved the electron transport efficiency.Second,two effective methods to enhance the material’s electrical conductivity and enhance its catalytic activity were developed.The conductive polymer PEDOT was electrodeposited on the surface of Bi nanosheets.The results showed that the nitrate removal efficiency of the electrode material modified by PEDOT was improved by12.3%.In view of the problem of poor conductivity of Bi₂O₃ obtained by oxidation during the use of Bi nanosheets,a seed-mediated hydrothermal preparation method for in-situ growth of Bi₂O₃ on carbon cloth was further designed.Compared with the carbon cloth drop-coated Bi₂O₃ sample,the in-situ growth reduced the overall resistance of the material,improved the specific surface area,and increased the nitrate removal efficiency by 10.9%.Finally,considering the limited improvement of nitrate removal only by reducing the overall resistance,a one-step hydrothermal method was developed to prepare Cu₂O particles modified oxygen vacancy-rich BiO_2-x nanosheets by introducing transition metal Cu and vacancies.The introduction of oxygen vacancies increased the removal efficiency of nitrate by about 17.6%,the introduction of Cu₂O effectively increased the active sites and reduced the resistance of the catalysts,and the removal efficiency of nitrate increases by 26.7%.