Nanoscale zero-valent iron/biochar composite as an activator for Fenton-like removal of sulfamethazine

In this work, biochar-supported nanoscale zero-valent iron (nZVI/BC) was synthesized and used as an activator for Fenton-like removal of sulfamethazine (SMT). The possible removal mechanisms in the reaction system were proposed. nZVI was mainly responsible for H2O2 decomposing to generate OH for the degradation of SMT, while BC played multiple roles, i.e., preventing nZVI aggregation, adsorbing SMT, activating H2O2, and alleviating nZVI passivation. The effects of various factors (i.e., the mass ratio of nZVI to BC, solution pH, H2O2 concentration and nZVI/BC dosage) on SMT removal were evaluated. The highest removal efficiency (74.04%) of SMT (10 mg/L) was achieved at the optimal conditions (the mass ratio of nZVI and BC = 1:5, pH = 3, H2O2 = 20 mM and nZVI/BC = 1.2 g/L). Additionally, the feasibility of recycling of nZVI/BC composites was examined. It was found that the removal efficiency of SMT decreased significantly from 74.04% to 53.28% and 38.02%, respectively, in the second and third run of experiments. X-ray diffraction analysis of the recycled composites demonstrated the gradual loss of Fe0 content after each run of experiment, which resulted in the decrease of catalytic activity of nZVI/BC composites and thus the drop of SMT removal.