Removal of p-nitrophenols by BC@nZVI activated persulfate: A study of key factors and mechanisms

Abstract

Straw biochar loaded zero-valent iron nanoparticles were prepared by co-precipitation method using agricultural waste straw biochar as a carrier for the removal of p-nitrophenol (PNP) by activated sodium persulfate (PS). The physicochemical properties of BC@nZVI were characterized using SEM, EDS, FTIR, BET, and RAMAN. The effects of PS concentration, catalyst concentration, initial pH, coexisting anions, and different activation systems on the degradation of PNP were investigated. The results showed that the best activation effect was exhibited at pH= 7, BC@nZVI dosage of 2 g/L, and PS concentration of 1 mM, and the removal of 40 mg/L PNP reached 91.7 % in 10 min. The high concentration of PS (4 mM) triggered free radical competition to inhibit the degradation, and the removal rate was only 74.5 % at 1 mM. In addition, bicarbonate ions (0–20 M) had a significant inhibitory effect on this system. Electron spin resonance (ESR) demonstrated that SO4⋅− and·OH were the major radicals, and SO4⋅− was preferentially generated. The intermediate products were identified by LC-MS, XRD and XPS characterization, which showed that adsorption and redox were the main degradation mechanisms, with p-benzoquinone was the oxidized product and substances such as 4-heptanone and propionic acid were the reduced products. This study proves that BC@nZVI activated PS is an efficient and excellent means of removing PNP and a good way to reuse agricultural waste.