Crystal phase transformation-driven upcycling of secondary aluminum dross to γ-Al2O3 nanorods for peroxymonosulfate activation and ciprofloxacin degradation

Typically, the high-temperature calcination of secondary aluminum dross (SAD) following pyrometallurgical or hydrometallurgical treatments yields α -Al 2 O 3 as the primary product. However, the inherent lack of catalytic activity in this material restricts its application as a high-value-added catalyst. Herein, we propose a targeted "waste-to-catalyst" upcycling strategy that achieves the phase transformation of SAD into γ -Al 2 O 3 nanorods for peroxymonosulfate (PMS) activation and ciprofloxacin (CIP) degradation. Aluminum was first extracted via a Na 2 CO 3 -assisted roasting-leaching process, achieving an aluminum recovery efficiency of 85.1% and a final purity exceeding 98.5%, providing a high-quality precursor. The recovered material was subsequently engineered into a specific nanorod morphology through a geometry-controlled hydrothermal treatment followed by low-temperature calcination. The optimized catalyst (B-400) exhibited superior catalytic performance, removing over 98.5% of CIP within 1.5 h. Notably, the reaction rate constant increased to 2.53 h –1 , which is significantly higher than the 1.34 h –1 observed for unmodified alumina. Mechanistic investigations and theoretical calculations revealed that the enhanced activity originates from the combined effect of the unique nanorod structure and low crystallinity, which collectively preserve abundant coordinatively unsaturated Al 3+ sites and oxygen vacancies. These active sites facilitate PMS activation to generate singlet oxygen ( 1 O 2 ) as the dominant reactive species responsible for pollutant degradation. This work establishes a practical pathway not only for mitigating the environmental risk posed by SAD but also for its directional conversion into high-performance, functional catalytic materials, thereby contributing to a circular economy.