Carbon inverse opal decorated with Fe@Fe₂O₃ core-shell nanoparticles: A novel cathode in heterogeneous electro-Fenton process for tetracycline degradation

Designing high-performance cathode materials with engineered surfaces is essential for progressing heterogeneous electro-Fenton (HTEF) processes used in wastewater treatment. This research focuses on the surface engineering of a robust cathode by incorporating core-shell Fe@Fe₂O₃ nanoparticles (FFO) within a three-dimensional carbon inverse opal (CIO) structure. The resulting CIO/FFO composite is specifically engineered to develop a highly active and stable electrocatalytic surface. The macroporous CIO design offers a significant specific surface area for the dispersion of nanoparticles and promotes mass transport, while the FFO nanoparticles act as active sites for the oxygen reduction reaction that produces H₂O₂. Additionally, the distinctive core-shell arrangement enhances an efficient Fe³⁺/Fe²⁺ redox cycle directly on the surface of the cathode, facilitating the continuous production of hydroxyl radicals (^•OH). Thorough surface and structural evaluations, utilizing SEM, TEM, XRD, and XPS, validated the effective and uniform incorporation of FFO nanoparticles onto the CIO scaffold and identified the chemical states of the surface elements. Electrochemical impedance spectroscopy and cyclic voltammetry indicated that the CIO/FFO cathode exhibits enhanced charge transfer kinetics and a greater electrochemically active surface area in comparison to a bare graphite electrode. In the HTEF process, the CIO/FFO cathode accomplished an impressive 86% degradation of tetracycline (TC) within 60 min and demonstrated considerably higher mineralization efficiency. The effects of operational parameters on surface reactivity were systematically optimized. Importantly, the cathode showed remarkable surface stability, with negligible iron leaching (100 µg l ⁻¹) over several cycles, and demonstrated a high level of resistance to interference from anions and natural organic materials. The process of degradation was clarified by conducting radical quenching experiments and analyzing surface-mediated by-products using GC–MS. This research offers a foundational insight into the relationship between structure, properties, and performance at the CIO/FFO interface, positioning it as a potentially effective and environmentally friendly surface-engineered cathode for the efficient removal of antibiotics from water.