Preparation Of Wood-based Self-supported Carbon Electrode And Its Application In Nitrate Wastewater Treatment

With the continuous development of global industrialization and the continuous increase of population,serious water pollution and fresh water shortage have been brought about.Nitrogen emissions from industrial production and excessive use of nitrogen fertilizer in agriculture bring a large amount of nitrate ions in water,which is a great threat to human health and ecological environment safety.Electrochemical-based nitrate wastewater treatment technology requires no additional chemical input and consumes only electricity to continuously remove nitrate from wastewater,thus attracting the attention of researchers.At present,the electrodes used in electro-chemical nitrate wastewater treatment are usually consisted of active substances,adhesives,collectors and others,causing the defects of large dead volume,poor utilization of active substances,limited life,difficult large-scale preparation.Therefore,the development of high-performance,large-scale preparation of self-supporting electrode materials is the key to the practical application of electrochemical nitrate wastewater treatment technology.Based on the above problems,this paper carries on the following two aspects of research:（1）Using natural beech wood chips as raw material and sodium thiosulfate as pore-forming agent,sulfur-doped ultra-micro wood carbon electrode（SUMW）was prepared from top to bottom,which was used for selective capacitive deionization to remove nitrate from solution.Natural beech wood’s 3D multistage structure has good mechanical stability,which is helpful for the transmission of solution and the diffusion of ion.We impregnated beech wood chips with sodium thistosulfate solution and carbonized/activated them.A large number of sulfur-doped ultra-micropores were introduced to prepare S-doped ultra-microporous wood carbon electrode（SUMW）while maintaining the original wood structure.The results show that SUMW samples exhibit different E_pzc（Potential of zero charge）values in different solutions,which can be used as a direct basis to determine the appropriate applied voltage to achieve selective capative deionization.When the electrode potential is higher than E_PZC-NO₃^-and lower than E_PZC-SO₄^2-,good nitrate/sulfate separation effect can be achieved,and high ion selectivity and adsorption capacity can be achieved at the same time.When the applied voltage is 0.8V,the nitrate adsorption capacity up to 373 umol g^-1 and selectivity coefficient up to 25(₃-_∕42-=25)can be obtained simultaneously.The ion-selective capacitive deionization based on E_pzc can promote the practical application of CDI（capative deionization）technology in wastewater treatment,such as desalination of brine,recovery of specific elements,etc.（2）Molten salt Biomass carbon aerogel supported Fe₃O₄（Fe₃O₄-MSCA）was prepared in one-step by using biomass waste as raw material,which was used as self-supported electrode for electrocatalytic nitrate reduction.We use zinc chloride/potassium chloride molten salt as high temperature solvent to enable the cross-linking and pyrolysis process to occur continuously,so as to realize one-step preparation of biomass carbon aerogel.Fe₃O₄-MSCA showing good nitrate electrocatalytic reduction ability.In a solution containing 100 PPM NO₃^--N,at a voltage of-1.3 V,the nitrate removal rate was up to 81%within 24h,and the nitrogen selectivity of the reduction product was up to 76%.The one-step synthesis of carbon aerogel from molten salt has a simple process and low cost,which provides a feasible route for large-scale preparation of biomass carbon aerogel and a new idea for electrocatalytic treatment of nitrate wastewater.