Refractory organic wastewater treatment via thermal activation of molecular oxygen on a confined Al₂O₃@Cu catalyst

Catalytic air oxidation of refractory organic wastewater often faces limitations such as low efficiency and high energy consumption. Herein, by encapsulating size-tuned copper nanoparticles (NPs) within porous Al₂O₃ and finely optimizing the associated Cu(I)/Cu(II) ratio, we realized a catalytic mechanism that synergistically leveraged spatial confinement and a low-temperature thermal induction effect (LTIE). Porous-Al₂O₃-enabled spatial confinement improved surface crystallinity and effectively suppressed copper NPs aggregation. Compared to the high energy required by gas-phase O-O bond homolysis (∼5.16 eV), O-O activation on the Al₂O₃@Cu catalyst required dramatically less energy (∼0.1 eV) owing to efficient charge transfer. Under low-temperature conditions, the LTIE promoted hot-electrons generation and transfer, thereby enabling the cascade production of reactive oxygen species (including ·OH, ·O₂⁻, and ¹O₂), resulting in exceptional performance in the catalytic air oxidation of refractory organic pollutants. In batch experiments, the LTIE caused an 86% reduction in ultraviolet absorbance at 254 nm for actual biogas slurry at 90°C within 5 h. Further, a continuous bench-scale system demonstrated an average chemical-oxygen-demand removal rate of 92%, compliant with wastewater treatment standards. This study presents an efficient strategy integrating spatial confinement, electron transfer, and thermal activation to achieve complete mineralization of refractory organic pollutants in wastewater.