Zero-valent iron loaded on N-doped biochar fabricated by one-step pyrolysis of K2FeO4 and coffee grounds as a persulfate activator for Bisphenol A degradation

Abstract

Nanoscale zero-valent iron loaded on N-doped biochar (nZVI/NBC) is a novel catalyst for activating peroxydisulfate (PDS) toward efficient degradation of endocrine disruptors in water. In this study, spent coffee grounds were modified by K2FeO4 and then transformed into nZVI/NBC by one-step pyrolysis. The nZVI/NBC modified with 0.3 mol/L K2FeO4 displayed an excellent PDS activating performance, and the specific surface area and average pore width of this nZVI/NBC were 277.19 m2/g and 2.47 nm, respectively. Bisphenol A (BPA) as a typical endocrine disruptor can be efficiently degraded by nZVI/NBC/persulfate advanced oxidation process. The optimum dosage of nZVI/NBC was 0.1 g/L, and the optimum PDS concentration was 20 mM. pH (3−9) had little effect on BPA degradation. In addition, the presence of Cl− had a facilitating effect on BPA degradation, while CO32− and HPO42− had strong inhibitory effects. nZVI/NBC had long-term stability in that the activation rate remained stable after five cycles and 90 days of storage in air and natural light. This study also investigated the activation mechanism of PDS by nZVI/NBC and concluded that radical (•OH, SO4•−, and O2•−) and non-radical (1O2) processes were simultaneously presented under the synergistic catalysis of ZVI and N. The formation of metastable PDS intermediates on the surface of biochar substantially enhanced the adsorption of PDS/BPA and the electron transfer process. Finally, the degradation pathways of BPA were speculated based on nine identified intermediates. Overall, this study described a rapid and green method for nZVI/NBC fabrication, which simultaneously achieved the recycling of spent coffee grounds and the degradation of endocrine disruptors in water.