Dual-mode catalytic degradation of diclofenac by copper oxide-modified TiO2/MnOx composites: insights from dark and UV-A activation†

Diclofenac sodium (DCF), a widely used nonsteroidal anti-inflammatory drug, is a persistent pharmaceutical contaminant that resists removal by conventional wastewater treatment. In this study, CuO-modified TiO₂/MnO_x composites were developed as multifunctional catalysts for DCF degradation under both dark and UV-A conditions. The materials exhibited dual-mode reactivity through distinct mechanisms: (i) non-radical oxidative degradation under dark conditions, and (ii) radical-mediated photocatalysis under UV-A irradiation. Under illumination, the formation of an interfacial p–n–p heterojunction between CuO, MnO_x, and TiO₂ generated internal electric fields that directed charge carrier migration—electrons flowing from the conduction band of TiO₂ toward CuO and MnO_x domains, and holes in the reverse direction. This spatial charge separation suppressed recombination and sustained redox cycling between Cu²⁺/Cu⁺ and Mn⁴⁺/Mn³⁺, promoting continuous ROS generation. In the absence of light, DCF degradation proceeded via non-radical oxidative pathways involving surface-bound reactive oxygen species and redox-active metal centers. Surface-sensitive XPS and hydroxyl quantification (TOTH) revealed elevated Mn³⁺/Mn⁴⁺ ratios, enriched surface-associated lattice oxygen, and high –OH group densities for the most active catalysts. These features collectively facilitated pollutant adsorption, oxygen activation, and sustained interfacial electron transfer. LC-MS/MS analysis confirmed a consistent degradation pathway across both regimes, involving hydroxylation, decarboxylation, and dechlorination of DCF. The Cu/5Ti5Mn-HT and Cu/8Ti2Mn-HT catalysts achieved exceptional dark-phase degradation efficiencies (∼99.8% and ∼99.4%, respectively), while Cu/TiO₂ exhibited the highest UV-A photocatalytic performance (∼42%). These findings demonstrate the synergistic advantage of redox-active metal oxides and interfacial design, establishing CuO–MnO_x–TiO₂ composites as promising candidates for advanced pharmaceutical pollutant remediation.