Activation of persulfate by nanoscale zero-valent iron loaded porous graphitized biochar for the removal of 17β-estradiol: Synthesis, performance and mechanism

In this work, the porosity, graphitization and iron doping of biochar were realized simultaneously by the pyrolysis of biomass and potassium ferrate (K2FeO4), then the iron-doped graphitized biochar was reduced to synthesize nanoscale zero-valent iron loaded porous graphitized biochar (nZVI/PGBC). 17 beta-estradiol (E2) is an environmental endocrine disruptor that can cause great harm to the environment in small doses. Experiments illustrated that nZVI/PGBC (100 mg/L) could completely remove E2 (3 mg/L) within 45 min by activating sodium persulfate (PS, 400 mg/L). The E2 removal efficiency of nZVI/PGBC was obviously superior to that of pristine biochar (BC), iron-doped graphitized biochar (Fe/GBC), nanoscale zero-valent iron (nZVI) and porous graphitized biochar (PGBC). The removal efficiency could be affected by reaction conditions, including reaction temperature, acidity, dosage of catalyst and oxidant and water matrix. Quenching experiments and electron spin resonance (ESR) demonstrated that SO4-center dot and HO center dot were both responsible for E2 degradation. This study indicated that Fe-0 and Fe2+ were the main catalytic active substances, while the catalytic ability of PGBC was not obvious. The reaction mechanism was proposed, that is, PS was activated by electrons provided by the redox reaction between Fe2+ and Fe3+, and PGBC acted as the carrier of nZVI, the adsorbent of E2 and the mediator of electron-transfer. This study demonstrates that nZVI/PGBC can be used as an effective activator for PS to remove organic pollutants in water. (C) 2020 Elsevier Inc. All rights reserved.

Automated summary

In this study, biochar was pyrolyzed with potassium ferrate to achieve porosity, graphitization, and iron doping simultaneously, resulting in the synthesis of nanoscale zero-valent iron loaded porous graphitized biochar. The nZVI/PGBC showed superior efficiency in removing 17 beta-estradiol compared to other materials, and the removal efficiency was affected by reaction conditions. The reaction mechanism involved the activation of persulfate by Fe2+ and Fe3+ redox reactions, with PGBC acting as a carrier for nZVI and a mediator for electron transfer in E2 degradation.