Study On Modification Of Organic Ligands To Improve The Performance Of Metal Electrocatalysis In Eliminating Water Pollutants

In recent years,with the rapid development of economy,the environmental water pollution has become increasingly serious,and the factors that cause water pollution are diverse.Among them,chlorinated organic pollutants（COPs）and nitrates are the more typical pollution factors.COPs are highly toxic,easy to accumulate and difficult to biodegrade.Nitrate has certain toxicity（long-term drinking of nitrate-containing water is prone to symptoms of anemia）,and it is the main cause of eutrophication of water bodies,This poses a greater threat to human survival and ecological security.At present,the treatment technologies for COPs and nitrates mainly include physical,chemical,and biological methods.Among them,electrocatalytic reduction technology is gradually being a focus of the research of water pollution treatment at home and abroad due to its green,high-efficiency,mild reaction conditions,strong selectivity,and no secondary pollution.Metal Pd and Cu are ideal catalysts for electrocatalytic reduction of COPs and nitrate due to their superior properties and higher catalytic activity.However,the noble metal palladium（Pd）has problems such as high cost,low current efficiency and poor electrode stability in the process of electrocatalytic reduction.The electrocatalytic reduction of metal Cu in nitrates has unsatisfactory electrocatalytic activity,low ammonia yield and low selectivity,low current efficiency and easy oxidation and deactivation during the reaction process,which limit the practical application of metal Pd and Cu in environmental remediation.Therefore,how to improve the catalytic efficiency of Pd-based and Cu-based nanomaterials in electrocatalytic reduction technology has become a more critical issue.In response to the above key scientific issues,this paper uses surface ligand modification strategies to modify metal Pd-based and Cu-based catalysts to obtain higher electrocatalytic activity and better Faraday efficiency and selectivity.The specific results are as follows:（1）In the Pd-based electrocatalytic hydrogenation reduction dechlorination（EHDC）system,in order to reduce the amount of Pd-based catalyst and improve its intrinsic activity.In this paper,a new strategy is proposed,which is to coordinate the modification of tetraethylammonium chloride（TEAC）molecular ligands to carbon-supported Pd NPs,and then prepare a Pd/amine working electrode under the action of a reduction potential.Experimental and theoretical analysis shows that TEAC adsorbed on Pd NPs can be converted into molecular amines（mainly TEA）under the reduction potential,and then form a strong N-Pd bond.The prepared Pd/amine catalyst and the palladium catalyst prepared by the traditional method are applied to the EHDC reaction.The Pd/amine catalyst showed higher catalytic activity and durability,and their mass and intrinsic activities are 2.32 min^-1g _Pd^-1and 0.16min^-1cm _Pd^-2,respectively,and it produces fewer toxic by-products.Further mechanism studies have shown that the amine ligand introduces three effects:H⁺pump effect,electronic effect and steric effect.Among them,the H⁺pump effect increases the local H⁺concentration to increase the amount of H*produced,and the electronic effect and steric effect alleviate the strong adsorption of phenol,and the released Pd active sites are beneficial to the adsorption of 2,4-DCP.Under the synergy of these effects enhances the EHDC performance of Pd.We believe that this work provides a new idea for adjusting the catalytic performance of metal nanocatalysts by modifying electrodes after synthesis,and also provides a new strategy for using the ligand environment to solve urgent environmental crises such as COPs.（2）In the electrocatalytic reduction of nitrate system,in order to increase the stability of the catalyst,improve the inherent activity of the copper-based catalyst,and increase the selectivity of the electrocatalytic reduction of nitrate to ammonia products.In this paper,a simple immersion method is used to modify the surface of Cu（OH）₂ nanowires（grown in situ on foamed copper,Cu-Cu（OH）₂）with1,4-naphthalenedicarboxylic acid（1,4-NDC）Molecular ligand synthesis of Cu-Cu（OH）₂-NDC catalyst.The experimental characterization results found that1,4-NDC does not change its crystal structure but has a greater impact on the morphology of Cu（OH）₂ nanowires during the electroreduction activation process,making it converted into dense Cu（OH）₂ nanowires Particles.Three electrodes of pure foamed copper（Cu）,Cu-Cu（OH）₂ and Cu-Cu（OH）₂-NDC were tested for electrocatalytic reduction of nitrate.The results showed that Cu-Cu（OH）₂-NDC electrode shows higher nitrate reduction efficiency（100%）,ammonia selectivity（92.4%）and Faraday current efficiency（58.9%）,which are better than Cu-Cu（OH）₂and pure foamed copper（Cu）electrode.Through the stability test of Cu-Cu（OH）₂ and Cu-Cu（OH）₂-NDC electrode,we found that with the increase of the number of reactions,the nitrate reduction performance of Cu-Cu（OH）₂ electrode gradually decreases（ammonia selective reduced from 79.6%to 41.8%,Faraday efficiency from52.5%to 29.6%）,while the catalytic performance of the Cu-Cu（OH）₂-NDC electrode remains stable（the ammonia selectivity and current efficiency are maintained at 90%）and about 60%).The above results indicate that the organic ligand modified copper-based catalyst can significantly improve the electrocatalytic nitrate reduction performance.From the perspective of environmental protection and energy saving,this work provides a new strategy to remove nitrate pollution,and make it recycled into useful ammonia chemical commodities,and reduce the demand for energy-intensive and unsustainable Haber-Bosch ammonia production.The research work in this paper provides a new strategy for the in-depth study of the mechanism of electrocatalytic reduction of COPs and nitrates and the improvement of electrocatalytic reduction performance,and is of great significance to the application of electrocatalytic reduction technology in actual environmental remediation.