Preparation Of Modified NZVI And Removal Of Chlorophenolic Pollutants

Chlorophenols（CPs）are a widely used class of highly toxic aromatic compounds that can cause water and soil contamination when entering the environment during production and use.Nanoscale zero-valent iron（nZVI）has received much attention due to its abundant source,non-toxicity and ease of preparation.nZVI has high removal efficiency for heavy metals and chlorine-containing organic pollutants.However,nZVI is prone to oxidation,agglomeration and deactivation.Modification of nZVI with porous material loading,metal doping and vulcanisation can effectively prevent agglomeration and deactivation of nZVI during use and improve the catalytic life of nZVI.Modified nZVI for the removal of chlorinated organic matter is a current research hotspot.In this study,different preparation methods were used to obtain sulphated nZVI（S-nZVI）for the degradation of 2,4,6-trichlorophenol（TCP）in water and soil,respectively.Biomass carbon loaded ultrafine zero-valent iron and zero-valent iron/iron phosphide composites were prepared using coffee grounds and activated sludge as raw materials for the efficient removal of pentachlorophenol（PCP）from soil.The main studies were as follows.（1）The S-nZVI materials were synthesised by ball milling,vacuum chemical vapour deposition（vacuum CVD）and liquid phase reduction methods.The materials prepared by ball milling（nZVI/FeS₂）and vacuum CVD（FeS_x@Fe）have good crystallinity and strong reducibility,while the zero-valent iron sulphide（S-nZVI（aq））prepared by liquid-phase reduction has low crystallinity and is highly susceptible to oxidation.nZVI/FeS₂has better degradation and mineralisation of trichlorophenols in water than FeS_x@Fe,S-nZVI（aq）and nZVI.S-nZVI（aq）and nZVI.The newly prepared S-nZVI（aq）was less efficient in the removal of contaminants due to its poor crystallinity and susceptibility to corrosion.After ageing,several materials produced well-crystalline and stable Fe₃O₄ and FeOOH cladding layers on the surface,which had similar degradation and mineralisation capabilities for TCP.In addition,the nZVI/FeS₂ prepared by ball milling had a better ability to remove TCP from soil than FeS_x@Fe,S-nZVI（aq）and nZVI.（2）Biomass charcoal-loaded nano-zero-valent iron composites（BC/nZVI）were prepared using coffee grounds and ferrous acetate as raw materials and used for the removal of PCP from soils by a carbothermal method.PCP was completely removed from soils within 72 h at a BC/nZVI addition of 10%,and no degradation products were detected,indicating complete mineralisation of PCP to inorganic substances.Masking experiments showed that electron reduction and oxidation of singlet oxygen（¹O₂）generated by BC/nZVI activation of dissolved oxygen were the main active agents in PCP degradation,with hydroxyl radicals（·OH）and superoxide anion radicals(O₂^·-)also contributing to PCP degradation.The active sites of PCP in BC/nZVI and the reactive processes between BC/nZVI and soil were investigated by flotation or sieving combined with magnetic separation,and"visualised"by SEM,EDX-mapping,XPS and XRD.BC/nZVI is simple to prepare,environmentally friendly and recyclable,and has good application prospects in the field of soil remediation.（3）A highly activated sludge biomass carbon/iron phosphide/nano zero-valent iron catalyst（SC-Fe₃P/nZVI）was prepared by the carbothermal method using activated sludge as the carbon source and FeCl₃·6H₂O as the iron source and used for the removal of PCP from soil.When SC-Fe₃P/nZVI and water were added at 2.5%and 100%,respectively,PCP was completely removed within 0.5 h.This removal efficiency was not affected by soil pH and masking agent.Free radical quenching experiments and electron spin resonance techniques showed that several active substances in the reaction system,including electrons,·OH,¹O₂ and O₂^·-,contributed to the efficient removal of PCP.biomass carbon,iron phosphide and zero-valent iron in the SC-Fe₃P/nZVI material were all active components for PCP degradation.