Study On The Persistence And Strengthening Of Biochar Support For Nano-zero-valent Iron On Nitrate Removal In Water

In recent decades,groundwater pollution has become a prominent problem due to population growth and increased demand for aquatic products and agricultural products.The artificially disturbed nitrogen cycle leads to an increase in the concentration of inorganic nitrogen in natural water bodies,threatening human health and aquatic ecosystems.Nitrate in water can be converted into many possible products such as ammonia nitrogen,nitrogen and nitrogen oxides through biological or chemical processes.The transformation path is very complicated and the controllability is difficult.It has been a hot and difficult point in the field of international environment research.In this study,pine charcoal biochar was used as a carrier,and a biochar-supported nano-zero-valent iron composite?n ZVI/BC?was prepared by co-precipitation method to study the removal of nitrate pollution in water.Firstly,we used aged n ZVI/BC composites to investigate the corrosion resistance and long-term effectiveness of the materials.On the other hand,this paper also studied the effects of surface modification of biochar supports for zero-valent iron on nitrate reduction from three aspects:carbonization,N-doping,and hydroxylation.In addition,The structures and surface properties of n ZVI/BC composites were characterized by scanning electron microscopy,Fourier-Transform Infrared Spectroscopy,X-ray diffraction and X-ray photoelectron spectroscopy.The main conclusions are as follows:?1?Air aging has barely effect on the n ZVI/BC composite,and there was little change on its surface structure.The NO₃^--N removal rate and N₂selectivity are basically the same as the raw materials,which are about 97%and 61%,respectively.Hydrostatic corrosion significantly changed the surface structure and reactivity of n ZVI/BC composites.With the increase of corrosion time,the removal efficiency of the three aging materials for NO₃^--N was82.82%,77.33%,and 68.96%respectively.After corroding for 72 hours in deionized water,N₂selectivity has dropped from 60.7%to 44.68%.?2?Heat-treatment temperatures of biochar supports during carbonization play a negligible role in nitrate reduction,but high heat-treatment temperature is better for N₂selectivity.By comparison with carbonization,either nitrogen doping or hydroxylation of biochar supports improved the performance of zero-valent iron particles for selective reduction of nitrate to dinitrogen.For hydroxylation,removal rate of nitrate and its selectivity to dinitrogen were up to 93.94%and 81.18%,respectively.For nitrogen doping,the removal rate and the selectivity were also up to 82.63%and 86.02%,respectively.Kinetic analysis indicates that both nitrogen-doped and hydroxylated biochar supports could accelerate nitrate reduction reaction with zero-valent iron.?3?The synergistic effect of n ZVI/BC in the removal of NO₃^--N is related to the higher adsorption capacity of BC,the ideal properties of n ZVI,and the positive interaction between the two substances.First,BC is characterized by a large specific surface area,abundant functional groups,surface charges,and a pore structure that promotes mass transfer of contaminants to its surface.Secondly,the particle size,dispersion and corrosion of n ZVI are well controlled by the BC matrix,which gives the catalyst good catalytic,reduction and oxidation capabilities.Third,BC's functional groups and aromatic structures can transfer electrons and increase conductivity,thereby improving electron utilization efficiency.