Insights into iron-induced structural changes in N-rich biochar for facilitating efficient organic pollutants removal by peroxymonosulfate activation: Cooperation of enrichment and degradation

Abstract

Naturally nitrogen in waste biomass can be turned into a valuable “treasure”. This work utilized soybean dregs as precursor, successfully fabricated iron-modified N-rich biochar (denoted as Fen-BDBC) catalysts via a green molten salt (KCl/NaCl) method. The physical and chemical changes of biochar substrate after iron modification were explored, combined Fenton-like reactions to establish structure–activity relationship between active sites and organic pollutants degradation. With iron induction, the hybrid structures of biochar could be transformed from sp3 to sp2 more easily, which enhanced its hydrophobicity and promoted interfacial electron-transfer efficiency. Pyridinic N and pyrrolic N structures were protected by the formation of Fe-N, which could participate in the formation of singlet oxygen (1O2) and catalyst-PMS*. Fe0.1-BDBC/peroxymonosulfate (PMS) system achieved 100 % nonradical bisphenol A (BPA) removal by cooperation of surface-confined enrichment and degradation. The contributions of electron-transfer processes (ETP), 1O2, and Fe(IV)=O were 58.3 %, 29.3 %, and 12.4 %, respectively. C=O/O-C=O, pyrrolic N, and Fe-N promoted 1O2 formation, C=C enhanced ETP, while pyridinic N played a dual role. The normalized apparent rate constant (kN, min−1 × 10−3) was calculated to be 31.96, which was superior among biochar-derived catalysts. Fe0.1-BDBC was loaded onto PVDF membrane for continuous and efficient degradation of BPA (nearly 100 % during 36 h operation). This work provided new insights for effective regulation of biochar-based catalysts.