WS2-cocatalyzed peroxymonosulfate activation via an enhanced Fe(III)/Fe(II) cycle toward efficient organic pollutant degradation

Abstract

Sulfate radicals based AOPs (SR-AOPs) in practical application are suppressed by slow Fe(III)-to-Fe(II) conversion cycle, seeking an efficient strategy to enhance PMS activation for the desirable efficacy of organic pollutant (OP) degradation is thus of great interest. Herein we report a transition metal sulfide-enhanced PMS activation to fast and completely oxidize BPA with an improved Fe(III)/Fe(II) cycle via the co-catalytic effect of metal sulfides. Among these metal sulfide co-catalyzed PMS systems considered, the WS2/Fe(II)/PMS system showed the highest efficiency for BPA degradation. In this AOP, 99.4% of BPA could be degraded within 20 min, and WS2 exhibited an exceptional reusability, which could be extendable to degrade other refractory organic pollutants and treat actual leachate. Quenching tests and ESR analysis indicated that sulfate radical (·SO4−) and hydroxyl radical (·OH) mainly contributed to the desirable degradation of BPA. The generated singlet oxygen (1O2) by WS2-induced PMS activation would react with Fe(II) to form ·O2−, which also led to BPA degradation. Combining density functional theory (DFT) calculations with intermediate products detection, elaborate degradation pathways of BPA included hydroxylation and ring-opening reaction. Protonation of WS2c-surfaces induced sulfur vacancies, resulting in highly exposed W(IV) sites where Fe(III)-to-Fe(II) cycle was enhanced. WS2 exhibited excellent stability and reusability even after five cycles. This cocatalytic effect of WS2 can inspire other advanced Fe(II)-based PMS AOPs through surface vacancy engineering of transition metal sulfides.