BCOFGs loaded with nano-FexSy for the catalytic degradation of QNC: Contribution and mechanism of OFGs for reductive iron regeneration.

Biochar currently served as the support for dispersed metal nanoparticles and cooperated with pyrite to generate more reactive radicals in organic pollution degradation system. But the mechanism of interaction between biochar and pyrite has not been elucidated. In this paper, biochar with oxygen-containing functional groups (OFGs) served as a stable dispersant to prepare nano-FexSy loaded biochar materials (BCOFGs@nano-FexSy). BCOFGs coordinated with nano-FexSy to overcome its drawbacks, boosting QNC removal efficiency from 28.64% to 100%. The XPS and the linear sweep voltammetry (LSV) results revealed higher Fe(II) content and higher electron transfer rate on used BCOFGs@nano-FexSy, further validating that hydroxyl functional groups on biochar surface provided electrons to Fe(III) to achieve efficient Fe(II)/Fe(III) cycling. Based on comparative experiments and studies on the roles of iron, S(II) species and OFGs, we clearly revealed that OFGs on biochar materials surface coordinated with nano-FexSy to catalyze the degradation of QNC. The degradation efficiency of BCOFGs@nano-FexSy for QNC was still as high as 91.39% after five cycles, providing full demonstrations that OFGs and S(II) as the abundant electron donor coordinated with Fe species for QNC catalytic degradation and further enhanced the catalytic performance and stability of nano-FexSy.