Efficacy Of Carbon-Based Zero Valent Iron To Activate Persulfate To Degrade Benzopyrene In Soil

With the continuous development of social industrialization,a large amount of benzo[a]pyrene（BaP）produced by human activities has entered the soil through a variety of ways,making the soil organic pollution increasingly serious.BaP is characterized by high chemical stability and difficulty in degradation.It can accumulate in environmental media and migrate over long distances,and then enter human organs and tissues through respiratory system,digestive system and skin contact,posing serious threats to human health.Thus,it is extremely urgent to explore effective disposal methods of BaP in soil.Persulfate advanced oxidation technology in the degradation of organic pollutants have shown great advantages.Therefore,in this study,biochar loaded by zero-valent iron（nZVI）composite(nZVI@BC₈₀₀)with a unique structure of graphene nanoshell-encapsulated nZVI was synthesized by a one-step carbothermal reduction method using ptassium ferrate and corn stover biomass after mixing and grinding,and it was used for studies on degradation of BaP in soil.On this basis,the effect and mechanism of BaP removal by nZVI@BC₈₀₀activated persulfate（PS）oxidation were investigated.Moreover,the effects of nZVI@BC₈₀₀/PS system on soil microbial community structure during the remediation of BaP-contaminated soil were explored.The main findings were summarized as follows:（1）The surface functional groups and morphology characteristics of nZVI@BC₈₀₀were analyzed by SEM,TEM and XRD and other characterization techniques.SEM results showed that nZVI@BC₈₀₀had a porous structure,and the loading treatment could make nZVI particles uniformly disperse on the surface of BC.TEM,XRD and Raman results showed that nZVI@BC₈₀₀has a core-shell structure with nZVI particles as the core and multi-layer graphite carbon as the shell,which could effectively prevent the rapid passivation and agglomeration of nZVI.In addition,the surface area and pore size analysis showed that the specific surface area and pore volume of nZVI@BC₈₀₀were 287.08 m²/g and 0.176 cm³/g,respectively,which were mainly composed of mesopores.（2）Batch experiments were conducted to explore the degradation effect of nZVI@BC₈₀₀/PS system on BaP-contaminated soil.The results showed that the amount of nZVI@BC₈₀₀,PS concentration,soil-water ratio,soil p H value,soil inorganic anions and organic matter all affected the removal effect of BaP by nZVI@BC₈₀₀/PS system.When nZVI@BC₈₀₀dosage was 1%of soil mass（1 wt%）,PS concentration was 0.5 g/L and soil-water ratio was 1:4,the removal rate of BaP in soil reached 73.95%within 60 min.（3）The degradation mechanism of BaP in soil by nZVI@BC₈₀₀/PS system was investigated.The reactive oxygen species during the oxidative degradation of BaP in nZVI@BC₈₀₀/PS system were identified by radical quenching experiments and electron spin resonance techniques.The results showed that sulfate radical(SO₄^?-),hydroxyl radical（^?OH）and singlet oxygen（¹O₂）were all involved in the oxidative degradation of BaP and¹O₂ was the main active species in the system.In addition,the electrochemical analysis result showed that nZVI@BC₈₀₀material had good electron transfer ability.The results of XPS analysis showed that C=O on nZVI@BC₈₀₀surface activated PS to attack BaP.nZVI reduced Fe³⁺to Fe²⁺and promoted the Fe²⁺/Fe³⁺cycle on the catalyst surface.And the XPS results confirmed the SEM and TEM results.According to GC-MS results,the possible degradation paths of BaP in nZVI@BC₈₀₀/PS system was speculated.BaP was eventually mineralized into CO₂and H₂O after oxidation by ring-opening,decarboxylation and carbon chain cracking.（4）The changes in the microbial community structure during the remediation of BaP-contaminated soil by the nZVI@BC₈₀₀/PS system were explored.The results showed that the nZVI@BC₈₀₀/PS system could effectively reduce the biological toxicity of BaP,thereby increasing the relative abundance and effect.The addition of nZVI@BC₈₀₀promoted the growth of PAHs-degrading bacteria such as Bacillus and Massilia,which were resistant to stress,so that they could continuously remediate contaminated soil and further improved functional bacteria in PAHs-contaminated pollution.