P-doped biochar regulates nZVI nanocracks formation for superefficient persulfate activation

In this study, a novel P-doped biochar loaded with nano zero-valent iron (nZVI) composite (nZVI@P-BC), with abundant nanocracks from inside to outside in nZVI particles, was designed for ultra-efficient persulfate (PS) activation and gamma-hexachlorocyclohexane (gamma-HCH) degradation. Results showed that P-doping treatment significantly enhanced specific surface area, hydrophobicity and adsorption capacity of biochar. Systematic characterizations revealed that the additional electrostatic stress and continuously generated multiple new nucleation sites of P-doped biochar were the main mechanism for the formation of nanocracked structure. nZVI@P-BC with KH2PO4 as P precursor showed superefficient PS activation and gamma-HCH degradation, by which 92.6 % of 10 mg/L gamma-HCH was removed within 10 min using 1.25 g/L catalyst and 4 mM PS, being 10.5-fold greater than that of without P-doping. Electron spin resonance and radical quenching test showed that center dot OH and 1O2 were the dominant active species, and further revealed that the unique nanocracked nZVI, high adsorption capacity and abundant P sites in nZVI@P-BC enhanced their generation and mediated extra direct surface electron transfer. nZVI@P-BC also exhibited high tolerance to different anions, humic acid and wide pH conditions. This work provides a new strategy and mechanism insight for the rational design of nZVI and diversified application of biochar.

Automated summary

In this study, a novel P-doped biochar loaded with nano zero-valent iron (nZVI) composite (nZVI@P-BC) was developed for efficient persulfate activation and gamma-hexachlorocyclohexane degradation. The P-doped biochar enhanced the specific surface area, hydrophobicity, and adsorption capacity. The nanocracked structure in nZVI@P-BC, induced by the electrostatic stress and new nucleation sites of P-doped biochar, facilitated the PS activation and degradation.