Synthetic Process And Reduction Ability Of Nanoscale Zero-valent Iron?nZVI? Assembled On Magnetic Fe₃O₄/graphene

Due to its tiny size,large surface area and high surface reactivity,Zero-valent iron?nZVI?materials have been widely used in the reduction and degradation of pollutants such as organic halides,heavy metals and nitroaromatic compounds.However,nZVI is easily agglomerated and easily oxidized because of small particle size,large specific surface area and magnetic properties on the surface.It is In this study,graphene and Fe₃O₄ were combined to magnetic graphene?MG?was synthesized by combining graphene and Fe₃O₄,nZVI was loaded on MG to improve nZVI material.In this study,nano-zero-valent iron-magnetic graphene composites?nZVI@MG?were successfully prepared and characterized.The hexanitrohexaazaisowurtzitane?CL-20?was selected as the target pollutant,The removal performance of CL-20 in solution by nZVI@MG was further investigated.The effects of different reaction conditions on the degradation efficiency of CL-20 were discussed.The process of contaminant removal was fitted to kinetic model;The intermediate products of CL-20degradation were analyzed,and two possible degradation pathways emerged.The results showed that:?1?The nZVI@MG composite material can be successfully synthesized by hydrothermal method-sodium borohydride reduction method.The addition of MG carrier successfully dispersed nZVI,improved the agglomeration of nZVI,increased the stability of nZVI material and maintained its reactivity.?2?The removal of CL-20 by the nZVI@MG composite material is attributed to the synergistic effect of carrier adsorption and nZVI reduction.nZVI@MG can achieve complete degradation of CL-20 in 120 min,while The removal rates in 120 min of commercial iron powder?Fe⁰?,nZVI,nZVI@rGO were only 27.9%,53.2%,and57.7%,respectly.?3?the degradation effect on pollutants can be affected by controlling the mass ratio of nZVI,Fe₃O₄ and rGO in the nZVI@MG composite.The increase of Fe₃O₄ can make the nZVI and material be closer and tighter,providing more sites for adsorption and reduction reactions,significantly improviing the degradation efficiency.?4?The degradation of CL-20 by the material is affected by the reaction environment.The lower the pH,the higher the salt content,and the more favorable the reaction.However,the improvement of pH and salt content is very limited,showing the superiority of nZVI@MG composite in the reduction reaction.?5?The pseudo-first-order kinetics and pseudo-second-order kinetics models were fitted to the CL-20 degradation reaction of nZVI@MG.The data show that the pseudo-second-kinetic model can describe the adsorption and reaction better.In the process,the correlation coefficient R² value reached 0.9945,indicating that the chemical adsorption process was carried out in the reaction,the eduction reaction promotes the adsorption process.?6?Three intermediate products of the reaction of CL-20 with zero-valent iron materials have been analyzed by LC-MS and GC-MS.Thus two reduction pathways of CL-20 were emerged,one is to open the top C-C bond to carry out denitration reaction,and the other is the N-NO2 nitroreduction reaction on the cage structure.