Yolk-shell Fe₂O₃@mesoporous hollow carbon sphere hybrid sub-micro reactors for effective degradation of organic contaminants

Carbon–metal oxide composites are important class of catalytic materials in persulfate (PS)/peroxymonosulfate (PMS) activation. But, their poor catalytic stability during oxidation limits its practical use. Herein, we demonstrate the yolk-shell architecture strategy for the fabrication of highly stable Fe₂O₃ mesoporous carbon hollow spheres (Fe₂O₃@MCHS) catalyst. The prepared material exhibits high PS activation ability for effective degradation of phenolics. The surface properties of hybrid Fe₂O₃@MCHS system were examined using FE-SEM, TEM, BET and VSM techniques. Physical characterization data confirmed that Fe₂O₃@MCHS sub-micro reactors possess a magnetic property, high specific surface area (SSA; >1200 m² g⁻¹), orderly arranged mesopores, and excellent degree of particle dispersion. Owing to the fact, the Fe₂O₃@MCHS catalyst exhibited highest reactivity for the degradation of 2,4-dichlorophenol and bisphenol-A by PS even with very low catalyst dosage (10 mg L⁻¹). ESR and scavenging experiments exclude the role of reactive radicals and other reactive oxygen species (ROS) (¹O₂) during pollutant degradation. Open circuit potential (OCP) measurements further reveal that low pollutant degradation efficiencies in the presence of ¹O₂ scavengers (L-histidine and NaN₃) were caused due to strong interaction between scavenging molecules and catalytic surfaces rather than ROS quenching. Electrochemical investigation also supports that degradation occurs through mediating electron transfer from pollutant to Fe₂O₃@MCHS. This study provides new understanding in PS activation and also in developing stable PS activating hybrid catalytic systems for pollutant degradation.