Enhanced atrazine degradation in the Fe(III)/peroxymonosulfate system via accelerating Fe(II) regeneration by benzoquinone

Fe(II)-involved advanced oxidation processes could effectively degrade refractory contaminants, but the slow transformation of Fe(III) to Fe(II) limits their wide application. Herein we reported that p-benzoquinone (BQ) could accelerate Fe(III)/Fe(II) cycle and promote atrazine (ATZ) degradation in the Fe(III)/peroxymonosulfate (Fe(III)/PMS) system through reconstructing active Fe(II)/PMS system. Under the identical experimental conditions, ATZ degradation efficiency in the BQ/Fe(III)/PMS system (99.8%) was superior to that in the Fe(III)/PMS system (23.2%), suggesting the indispensable role of BQ in Fe(II) regeneration and PMS activation. Reactive species sulfate radical (SO4•−), hydroxyl radical (•OH) and ferryl ion (Fe(IV)) were involved in the BQ/Fe(III)/PMS system based on alcohol quenching experiments, ESR tests and the selective transformation from methyl phenyl sulfoxide (PMSO) to methyl phenyl sulfone (PMSO2). ATZ degradation mechanism was proposed based on LC-MS detection, among which dealkylation and dechlorination-hydroxylation were the dominant transformation pathways. The BQ/Fe(III)/PMS system showed satisfactory catalytic performance at pH 2.5–7.0 and low Fe(III) concentration, which expanded the pH range and avoided the addition of a large amount of Fe. More importantly, the increase of PMS concentration not only enhanced the oxidative degradation of ATZ and its two main chlorinated byproducts (atrazine-desethyl (DEA) and atrazine-desisopropyl (DIA)), but also facilitated the removal of toxic BQ. Cl− inhibited the degradation of ATZ and caused the accumulation of DEA and DIA, and the higher Cl−, the more obvious this effect. This study provided a new approach to improve the Fe(III)/PMS system by boosting Fe(III)/Fe(II) cycle with quinons.