Mechanism insight into sulfidated nano zero-valent iron/biochar activated persulfate for highly efficient degradation of p-chloroaniline

Nano zero-valent iron (nZVI) and its composites utilized as persulfate (PS) activators has attracted extensive attention for the complete oxidative degradation of organic contaminants. However, the intrinsic agglomeration and the passivation layer on nZVI surface seriously impeded the electronic transmission performance, which significantly decreased the utilization efficiency of nZVI. Herein, sulfidated nano zero-valent iron/biochar (S-nZVI/BC) was prepared by the co-sulfuration method via liquid phase reduction approach to promote PS activation for p-chloroaniline (PCA) degradation. The PCA removal efficiency reached 96.43% after 10 min of reaction, and the reaction rate constant (k) and the reaction stoichiometric efficiency (RSE) were 0.337 min^-1 and 3.50% in the S-nZVI/BC₅₀₀ activated PS system, which were 10.3 fold and 9.5 fold with respect to nZVI/BC, respectively. The reactive oxygen species (ROS_S) of SO₄^•-, •OH and O₂^•- were generated and accounted for PCA degradation. The intermediates of p-chloronitrobenzene, chlorobutane, butanol and butyric acid were identified and the oxidative degradation pathways of PCA were proposed. The excellent performance of S-nZVI/BC for PS activation was attributed to the improved electron transfer capacity, enhanced conversion of Fe(III) to Fe(II), lower decomposition energy barrier of PS and less dissociation of Fe atom by S doping. This study provides an insight mechanism into S-nZVI/BC activated PS for highly efficient degradation of PCA in water.