Mechanistic Insight into the Heterogeneous Electro-Fenton/Sulfite Process for Ultraefficient Degradation of Pollutants over a Wide pH Range

Electro-Fenton (EF) has received widespread attention in terms of water decontamination in advanced oxidation processes but still has the bottlenecks of a narrow pH (∼3) application range and a slow rate of reduction of the iron ion to sustain high treatment efficiency. Herein, an iron–carbon catalyst was synthesized to develop a heterogeneous EF/sulfite (hetero-EF/sulfite) process, which expanded the pH application range to 7 and increased the rate constant of carbamazepine (CBZ) degradation 10.74 times compared with that of the hetero-EF process. The catalyst was systematically characterized; important process factors such as the applied current, initial pH, and CBZ, catalyst, and sulfite dosage were investigated, and a possible degradation mechanism and a possible pathway were proposed. The quenching experiments and electron paramagnetic resonance test revealed the existence of active species such as •OH, SO4•–, O2•–, 1O2, and their mutual transformation, in which •OH and O2•– were dominant. This work also verified the suitability of the hetero-EF/sulfite for different pollutants, and its universal enhancement for different heterogeneous and homogeneous catalysts. This modified EF process expands the pH application range and enables the co-generation and transformation of free radicals, which has broad prospects for application in the effective degradation of organic pollutants for water purification.