A novel iron-doped mineral/carbon composite electrocatalyst synthesized by reconstituting ash phase of coal gasification fine slag for synergistically improving electrooxidation efficiency

Abstract

Coal gasification fine slag is typical coal-based solid waste, and the crux to its resource utilization is the co-utilization of carbon and ash. A novel iron-doped mineral and carbon composite electrocatalyst (Fe-FSAPH) was synthesized by depolymerizing and reconstituting the ash phase for the collaborative electrocatalytic degradation of m-cresol wastewater. Exogenous iron participated in and promoted mineral reconstitution, increasing Si(-O)1/Si(-O)3 ratio (0.37→1.18) and promoting the formation of active Si-OH groups. The iron-doped minerals dispersedly developed with a sheet-like on carbon matrix, which improved intimate physical proximity and synergistic behavior of carbon/minerals. The obtained Fe-FSAPH, with a specific surface area of 246.52 m2/g, has a large diffusion rate constant KD2 (2.98 mg·min−0.5/g) in the rate-limiting step of m-cresol adsorption. Its electrochemical performances exhibit excellent, including cyclic voltammetry charge of 8.52 mC/cm3, charge-transfer resistance of 0.59 Ω, and Tafel slope of 159 mV/dec. The m-cresol with a concentration of 194.67 mg/L could be electrooxidized within 18 min due to the abundance of •OH and O2•- in the Fe-FSAPH system, which accelerated the radical attack reaction. Moreover, Si-OH groups catalyzed conversion of •OH to O2•- by generating oxygen vacancies and undergoing dehydroxylation, shortening the rapid reaction time of m-cresol removal to 14 min. The introduction of iron enhanced the synergy of carbon and minerals, with •OH generated via the Fenton-like reaction, offering a convenient environment for mineral catalysis. Hence, the study provided new ideas for the comprehensive utilization of carbon and ash and treatment of waste by waste.