Efficient degradation of phenanthrene by biochar-supported nano zero-valent iron activated persulfate: performance...

Biochar-supported nano zero-valent iron (BC@nZVI) is a novel and efficient non-homogeneous activator for persulfate (PS). This study aimed to identify the primary pathways, the degradation mechanism and the performance of phenanthrene (PHE) with PS activated by BC@nZVI (BC@nZVI/PS). BC@nZVI as an activator for PS was prepared by liquid phase reduction method. BC@nZVI was characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffractometer and Fourier transform infrared spectroscopy. The effects of the iron-carbon mass ratio and BC@nZVI dosage were investigated, and a pseudo-first-order kinetic model was used to evaluate the PHE degradation. The results showed that BC supported nZVI and inhibited the agglomeration of nZVI, improving PS's activation efficiency. The optimal iron-carbon mass ratio was determined to be 1:4, accompanied by a dosage of 0.6 g/L of BC@nZVI. During PS activation, nZVI was transformed to Fe²⁺ and Fe³⁺, with the majority being Fe³⁺. The reducibility of nZVI in BC@nZVI enabled the reduction of Fe³⁺ to Fe²⁺ to activate PS. Radical quenching and electron paramagnetic resonance (EPR) revealed that the oxidative radicals in the BC@nZVI/PS system were mainly SO₄^-· and ·OH, where SO₄^-· was the primary free radical under acidic and neutral conditions and ·OH in alkaline conditions. Additionally, BC@nZVI adsorption had a limited role in PHE removal. This study can provide mechanism insights of PHE degradation in water with BC@nZVI activation of the Na₂S₂O₈ system.