Sequential reduction-oxidation degradation of alkaline nitrophenol wastewater by a novel Al0/O2 system.

Alkaline nitrophenol (NP) wastewater is highly toxic and resistant to direct oxidation. Although reductive treatment can enhance NP degradability, the alkaline environment complicates remediation, especially for zero-valent iron (Fe0) that readily undergoes passivation. To address these challenges, this study developed a sequential reduction-oxidation system employing carbon nanotube-modified micron-sized zero-valent aluminum (CNTs@mAl0) to activate O2 for p-nitrophenol (PNP) degradation under alkaline conditions. In the reduction stage, CNTs@mAl0 achieved complete conversion of PNP to p-aminophenol (PAP). Upon subsequent O2 sparging, the generated PAP underwent further oxidation and mineralization by •OH and 1O2 derived from O2 activation, achieving > 99.9% overall PNP removal and 66.1% TOC removal. Electrochemical analyses and material characterizations (SEM-EDS and XPS) revealed that CNTs not only act as conductive bridges to facilitate electron transfer in mAl0, but also facilitate O2 diffusion and activation through their high specific surface area, hydrophobic porous structure, and π*-electron-rich carbon framework, boosting reactive oxygen species (ROS) generation and enhancing PAP mineralization. Notably, this method effectively removed 98.3% of diazodinitrophenol (DDNP) from real alkaline NP explosive wastewater, while also removing 49.5% TOC, confirming its practical efficacy. Overall, this study offers a promising strategy for the treatment of alkaline wastewater contaminated with refractory nitroaromatic pollutants.