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 (Fe 0 ) 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@mAl 0 ) to activate O 2 for p -nitrophenol (PNP) degradation under alkaline conditions. In the reduction stage, CNTs@mAl 0 achieved complete conversion of PNP to p -aminophenol (PAP). Upon subsequent O 2 sparging, the generated PAP underwent further oxidation and mineralization by •OH and 1 O 2 derived from O 2 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 mAl 0 , but also facilitate O 2 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.