Electro-Fenton degradation of emerging contaminants using Cu-Co bimetallic-modified nickel foam cathodes: The role of metal surface structure and singlet oxygen

Antibiotic contamination in water presents a substantial threat to both the ecosystem and public health, whereas the electro-Fenton (EF) process is acknowledged as an effective method for removing refractory organics from wastewater. Based on this, we propose a multiphase EF process that utilizes coral-like Cu-Co bimetallic hydroxide (CuCoOOH) and oxide (CuCo₂O₄) modified nickel foam (NF) electrodes as cathodic materials, thereby facilitating simultaneous oxygen diffusion and the in-situ generation and activation of H₂O₂. It has been demonstrated that the EF process with CuCo₂O₄-modified cathodes effectively degraded tetracycline (TC) under low energy consumption conditions ([Na₂SO₄]₀ = 10.0 mM, [Current density]₀ = 5.0 mA/cm²), achieving a removal efficiency of 96.7 %. However, the removal efficiency of the CuCoOOH-modified cathode EF process for TC (10 mg/L) was only 78.2 %. Furthermore, the CuCo₂O₄/NF/EF system demonstrates superior environmental tolerance and electrode repeatability. Electron paramagnetic resonance and quenching experiments demonstrated that ·OH, ·O₂^–, and ¹O₂ participated in the oxidation process in both EF processes, with ¹O₂ identified as the primary contributor to the oxidation of TC. In-situ Raman spectroscopy and density functional theory reveal the relationship between the Cu-Co bimetallic configuration and the in-situ generation trends and formation free energy of H₂O₂. Differences in the degradation intermediates, pathways, and toxicity evolution of TC in two EF processes were identified using LC-MS. It is ultimately emphasized that the CuCo₂O₄-modified NF cathode EF process is more cost-effective and detoxifying, while the cathode exhibits dual Fenton-like activity, ensuring sustained and efficient wastewater treatment.