Ball milling-assisted preparation of N-doped biochar loaded with ferrous sulfide as persulfate activator for phenol degradation: Multiple active sites-triggered radical/non-radical mechanism

Designing Fe-carbon catalyst with multiple active sites for persulfate (PS) activation to water purification is challenging. Herein, nitrogen-doped biochar (NBC) loaded with ferrous sulfide (FeS) was synthesized via two-step ball milling. In FeS@NBCBM/PS system, both electron transfer process and reactive oxygen species (ROSs) including SO4⋅−, O⋅H, O2•− and 1O2 contributed to phenol degradation. Surface-bound S(II) not only interacted with PS for generating SO4•−, but also accelerated Fe(III)/Fe(II) circulation by reducing Fe(III). NBC was favorable for phenol adsorption and exposure of oxygen-containing groups, graphitic and pyridinic N active sites, which mediated electron transfer or ROSs formation. Owing to multiple active sites, this system fast achieved almost complete phenol degradation with excellent adaptability to wide pH range of 3–9, high anti-interference capacity to coexisting substances, and was efficient to various water matrices. Furthermore, phenol degradation pathways were elucidated by DFT calculations with intermediate products showing lower toxicity, demonstrating great potentials of proposed system.