One-step synthesis of biochar supported nZVI composites for highly efficient activating persulfate to oxidatively degrade atrazine

Abstract Biochar supported nZVI composites (nZVI@BC) have received extensive attention due to their important application potential in the field of environmental pollution remediation. However, one-pot synthesis of nZVI@BC faces challenges. In this study, a type of nZVI@BC was successfully prepared by a simple one-pot method via oxygen-limited high-temperature co-pyrolysis of the mixture of soybean straw powder and Fe2O3. The XRD results showed that in the absence of biomass, Fe2O3 is transformed into Fe3O4 instead of Fe0. Interestingly, in the presence of biomass, a large amount of Fe0 and a small amount of Fe3C are formed. Moreover, the as-designed composites could effectively activate Na2S2O8 (PS) promoting the oxidative degradation of atrazine. A series of reaction kinetics in different systems were carried out to explore the effect of synthesis conditions, and reaction parameters on the degradation process of atrazine. And we have obtained a representative catalyst, which was produced by pyrolysis of a mixture of soybean straw and Fe2O3 (mass ratio=7:1) at 800 °C. In the representative catalyst-PS system, the atrazine removal rate was up to 93.8%, and the apparent activation energy (E) was calculated as 83.34 kJ/mol that is lower than that reported previously in heat-activated PS oxidation system of atrazine, demonstrating that nZVI@BC as a catalyst can effectively reduce the reaction activation energy to promote the degradation of atrazine. SO4-, ·OH, PFRs and 1O2 are jointly contribute to the degradation efficiency of atrazine. The oxidation mechanism of atrazine mainly includes 1) alkyl-oxidation, 2) de-alkylation, 3) dehydrogenation, 4) dechlorination hydroxylation, and 5) olefination.