Metal-Free Carbon Cocatalysis in Fenton Chemistry

To address the challenges of low hydrogen peroxide utilization efficiency and excessive iron sludge accumulation in conventional Fenton processes, metal-free carbon cocatalysts harness their cost-effectiveness, ecofriendliness, and modifiable surface to propel green and enhanced Fenton chemistry. Their cocatalytic efficacy stems from structural features (pore architecture, hybridization state, and dimension) and surface properties (defect, heteroatom, functional group, graphitic structure, and site distribution), resulting in carbon cocatalysts playing multifaceted roles in assisting Fenton systems. This overview provides mechanistic insights into carbon cocatalyzed Fenton reactions, focusing on electron sources for iron reduction, and categorizes mechanisms into three approaches (electron donors, carbon-Fe(III) complexes, and electron mediators). Research studies have evolved from early-stage carbon cocatalysts for direct Fe(III) reduction to advanced systems utilizing coadsorbed pollutants or hydrogen peroxide as electron donors. Critical Fe(III)/Fe(II) cycles for sustainable Fenton oxidation are elucidated through electrochemical analysis, density functional theory calculations, and kinetics modeling. Multiple future strategies of carbon cocatalyzed Fenton processes for practical applications were proposed, including pretreating high-concentration refractory organic wastewater, post-treating persistent organic pollutants, and integrating enrichment techniques for trace pollutant removal with minimal chemical input. This review aims to deepen understanding and highlight application prospects of metal-free carbon cocatalyzed Fenton techniques for sustainable water remediation.