Removal Of Nitro Compounds With Novel Biochar Materials

As a new type of functional material,biochar has attracted much attention.In recent years,its application in water and soil remediation has gradually increased.However,biochar contains a large number of persistent free radicals（PFRs）,which can can act as redox mediators to promote the degradation and transformation of pollutants,and also produce a large number of reactive oxygen species in the aqueous.However,the degradation effect of PFRS in biochar and biochar composite materials on pollutants has not been studied.In this study,we synthesized a new kind of biochar containing persistent free radicals(BC_PFRs)and its composite nZVI/BC_PFRs,with the investigation of their performance in the removal of typical pollutants.On the one hand,their performance and mechanism were investigated in laboratory prepared p-nitrophenol（PNP）,based on the regulation of a variety of influencing factors,the optimal conditions for removing PNP have been determined.Characterizing the changes of BC_PFRs and nZVI during PNP removal process try to reveal the synergistic effect.Further,PNP degradation pathway was proposed according to the chemical analysis of intermediates with LC-HRMS,and the corresponding redox mechanism were confirmed by quenching experiments,electron paramagnetic resonance and electrochemical tests during the reaction.On the other hand,the performance of BC_PFRs in three systems(e.g.BC_PFRs/Fe²⁺/H₂O₂,BC_PFRs/Fe³⁺/H₂O₂ and only nZVI/BC_PFRs)were investigated on the TNT production wastewater.Meanwhile,the toxicity and components analysis of wastewater before and after treatment were compared by using Photobacterium sp combined with GC-MS and LC-MS.The nZVI/BC_PFRs exhibited an outstanding performance on the removal of PNP.Based on the regulation of a variety of influencing factors,we found the optimal conditions for PNP removal were at 1:1 nZVI/BC_PFRs mass ratio under p H of 3.0.The concentration of PFRs in biochar has a significant effect on the performance of the composites.The PNP degradation is proposed to be a combination of oxidation and reduction pathway,in which the PFRs in biochar mediate the formation of ROS that participate in the oxidation pathway,while both the reducing functional groups in biochar and nZVI participate in the reduction of PNP.BC_PFRs can improve the electron transfer nZVI/BC_PFRs,and the ROSs produced by PFRs mediate the transformation of Fe species.In this section,we found that nZVI/BC_PFRs exhibited the best performance on TOC and TN removal,while the addition of BC_PFRs improved the mineralization ability of Fe²⁺/H₂O₂and the denitrification ability of Fe³⁺/H₂O₂.Meanwhile,the toxicity analysis of the TNT wastewater before and after treatment showed that the effluent from nZVI/BC_PFRs system was less toxic than others.The components analysis of wastewater with GC-MS and LC-MS showed that the types of nitroaromatic compounds were dominantly removed,where nZVI/BC_PFRs system gave the best removal performance.The results suggest BC_PFRs composite is a kind of promising material to tackle the contaminants released in environment,with the prospective application in the contaminated wastewater.