Mineralize complex organic contaminants using only oxygen on dense copper atoms embedded in the walls of carbon nanotubes

Abstract

In this study, a novel catalytic air oxidation (CAO) process is proposed based on a facilely synthesized nanocomposite catalyst. The catalyst was prepared using Cu single atoms (CuSA) embedded on multiwalled carbon nanotubes (CNTs), denoted as CNTs@CuSA, with mass ratio of CuSA up to 10.02 %. Humic acid (HA) and other typical refractory contaminents were used to investigate the ability of CNTs@CuSA in CAO. The catalysts were pre-excited to cross the energy barrier at 120 °C for 10 min, and then used to catalyze the oxidation of HA at 90 °C in 50 min. The CNTs@CuSA with CuSA mass ratio 8.39 % showed a superior catalytic activity, and 99 % of HA in solution was degraded with 98 % of organic carbon mineralization. Aberration-corrected transmission electron microscopy, electron paramagnetic resonance spectroscopy, and density functional theory calculations were applied to detect the mechanism. The results showed that the Cu-N coordination sites on CNT walls and the confinement effect of CNTs activated O2 to produce ·OH radicals, with a high activation efficiency. Moreover, this catalyst remained active after multiple cycles. This result provides a new catalyst to support low-temperature catalytic air oxidation for organic wastewater treatment.