Study On Regulation And Mechanism Of Electrocatalytic Reduction Of Nitrate By Cu-based Active Sites

In recent years,the situation of nitrate pollution in water has become increasingly serious and has become a global environmental problem.Excess nitrates entering the body can increase the risk of gastrointestinal cancer or methemoglobin disease.Electrocatalytic reduction treatment of nitrate has been widely concerned because of its simple operation conditions,mild reaction conditions,dependence on green renewable energy,high efficiency and control.The products of electrocatalytic reduction of nitrate are usually harmless nitrogen or ammonia of certain economic value.Select appropriate catalyst to regulate the products of electrocatalytic reduction of nitrate,and then recover the target product of nitrate reduction--ammonia by certain methods,which is the main process of nitrate electrocatalytic reduction of ammonia process.Copper based catalyst has been widely studied because of its low cost,wide source,certain inhibition of hydrogen evolution and main product of ammonia nitrogen.However,there will be some accumulation of nitrous oxide byproduct in the reaction process,and large materials will reduce the utilization rate of active sites.Based on this,we have carried out some research.In this thesis,efficient and stable nano-scale Ti O₂-Cu catalyst was synthesized by wet chemical reduction method.According to the X-ray photoelectron spectroscopy（XPS）analysis and the DFT calculation results,the strong interaction between the introduced support Ti O₂and Cu nanoparticles promotes electron transfer,and contributes to the formation of more electron-deficient Cu^δ+species.Combined with the finite element method（FEM）,we found that the introduction of Ti O₂could enhance the local electric field on the surface,promote the adsorption and deionization of water,and improve the electrocatalytic performance of the catalyst.The in-situ electrochemistry tests were performed on the catalysts using in situ Differential electrochemistry mass spectrometry（in situ DEMs）.The product paths were determined by combining with DFT calculations.The influence of different initial pollutant concentration,different working voltage and different ions on catalyst performance was explored.The nitrate removal rate of catalyst could reach 100%,and the selectivity of ammonia nitrogen could reach 91.2%.By further reducing the size of copper,the precursor material of Ce-MOF was synthesized by hot solvent method,and the single atom copper-doped cerous oxide catalyst was prepared by calcination after loading copper phthalocyanine.The monoatomic form of the catalyst was characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）and high resolution transmission electron microscopy（TEM/HRTEM）.The coordination of monoatomic copper was further verified by synchrotron radiation analysis.The+2 valence state of Cu was obtained by X-ray photoelectron spectroscopy（XPS）.Cu doping can increase the content of oxygen vacancy on the catalyst,enhance the adsorption of nitrate and intermediate products,and improve the electrocatalytic activity of the catalyst.The electrochemical active area of the catalyst is 0.27 m².In situ experiments with ¹⁵N isotope labeling proved that the ammonia produced was completely derived from the added NO₃^-pollutant,and revealed the reaction path of NO₃^--N conversion to NH₃-N.In order to recover ammonia nitrogen,the product of electrocatalytic reduction of nitrate nitrogen,water samples are treated by gas diffusion membrane acid adsorption,which can fully recover ammonia nitrogen in water and generate ammonium sulfate with certain economic value,with a wide range of recoverable concentration.Recycling products while removing targeted pollutants is in line with the concept of circular economy and contributes to sustainable development.In this work,we designed and synthesized two different Cu-based active site catalysts,studied the mechanism of catalyst reduction process,explored the reaction path,and provided ideas for the catalytic system with Cu as the active site.At the same time,we converted the target pollutant nitrate nitrogen into ammonia nitrogen with economic value and realized recovery,proving the feasibility of catalytic conversion from nitrate nitrogen to ammonia nitrogen.Or make a contribution to the restoration of water environmental pollution.