Overlooked self-catalytic mechanism in phenolic moiety-mediated Fenton-like system: Formation of Fe(III) hydroperoxide complex and co-treatment of refractory pollutants

Applications of Fenton-like reactions (Fe(III)/H2O2) without catalyst have low efficiency in remediating pollutants. Herein, pollutants containing phenolic moiety (P, e.g., paracetamol (PCM)) were demonstrated to make Fe(III)/H2O2 system highly effective in degrading a wide range of contaminants. Kinetics analysis shows the self-catalytic degradation of PCM with optimum performance at pH 4.0, and Fe(III)/Fe(II) conversion was accelerated without the assistance of cocatalyst. Based on state-of-art spectroscopy measurements and theoretical calculations, the overlooked self-catalytic mechanism was revealed. In the presence of phenolic moiety, a yellow-colored high-spin P-Fe(III)-OOH complex can be formed in Fe(III)/H2O2 system, which subsequently converts to Fe(II). Afterwards, the oxidation of P gives hydroquinone that also facilitates the cycling of Fe(III)/Fe(II). The accumulated Fe(II) reacts with H2O2 to generate hydroxyl radicals, the major species responsible to oxidize pollutants, thereby achieving efficient decontaminant performance. Results provide new insights into the self-catalytic Fenton-like process for remediating a mixture of pollutants.