Electrocatalytic treatment of phenolic wastewater: A green refinery approach with response surface methodology and toxicity assessment

The persistence of 4-nitrophenol (4-NP) in aquatic environments poses a major environmental challenge due to its toxicity and resistance to conventional treatment. To address this gap, an electro-Fenton process was developed using a nanoferrite catalyst (CoFe₂O₄/natural deep eutectic solvent) for the rapid conversion of this pollutant. The catalyst, with an average size of 12.6 ± 1.77 nm and ferrimagnetic behavior, was characterized in terms of crystallinity, morphology, composition, and magnetism. The process achieved 100 % degradation under optimized conditions: pH 6.0, catalyst dosage 50 mg L−1, current density 70 mA cm−2, 4-NP concentration 2 mg L−1, and a reaction time of 20 min. As the electrochemical progressed, H2O2 concentration increased, particularly under acidic conditions. The active radicals involved in the degradation, HO• and SO4 •-, generated intermediate products that interact to form different compounds. Eleven of these compounds were identified and exhibited low toxicity, showing potential industrial applications. The catalyst enables a new degradation pathway involving radical recombination and secondary reactions, leading to the formation of higher molecular weight products. The technology has also been applied to environmental water samples from rivers that are used to supply water in Brazil, achieving removal efficiencies of between 91.2 % and 99.6 %. This study proposes an innovative solution for wastewater valorization within a circular economy framework. It also contributes to the removal of refractory compounds from the environment, aligning with the Sustainable Development Goals.