SiO2 mediated templating synthesis of γ-Fe2O3/MnO2 as peroxymonosulfate activator for enhanced phenol degradation dominated by singlet oxygen

Abstract

Cost-effective and low-toxicity of MnO2 is regarded as a promising alternative to Co-based catalyst for peroxymonosulfate (PMS) activation to degrade recalcitrant organic pollutants. However, the sluggish Mn(IV)/Mn(III) redox cycling and limited specific surface area greatly hampered its wide application. To solve this challenge, a mesoporous γ-Fe2O3@MnO2 magnetic catalyst with SiO2 assistance (s-γ-Fe2O3@MnO2) was synthesized. Physicochemical characterization confirmed part MnO2 was coated on γ-Fe2O3 surface while the other existed independently. Furthermore, BET surface area of s-γ-Fe2O3@MnO2 was more than two times that of the counterpart without SiO2 assistance (ws-γ-Fe2O3@MnO2). s-γ-Fe2O3@MnO2 exhibited enhanced PMS activation capacity with 97.6% phenol removal efficiency within 80 min, superior to other samples. Various influencing parameters on phenol oxidation were optimized. Reactive oxygen species (ROS) scavenging experiment and electron paramagnetic resonance (EPR) validated co-existence of hydroxyl radicals (·OH) and sulfate radicals (SO4·−) as well as singlet oxygen (1O2) during PMS activation. However, phenol degradation was a non-radical oxidation process dominated by 1O2. A rational reaction mechanism was proposed. Fe(II) promoted Mn(IV)/Mn(III) redox cycling and the enlarged surface area derived from SiO2 mediated templating synthesis were responsible for the enhanced phenol degradation. This strategy can give a guidance for synthesis of highly efficient catalyst for sewage remediation.