Revealing the Overlooked Catalytic Ability of γ-Al2O3: Efficient Activation of Peroxymonosulfate for Enhanced Water Treatment

Activated alumina (gamma-Al2O3) is one of the few nanomaterials manufactured at a ton-scale and successfully implemented in large-scale water treatment. Yet its role in advanced oxidation processes (AOPs) has primarily been limited to functioning as an inert carrier due to its inherently nonredox nature. This study, for the first time, presents the highly efficient capability of gamma-Al2O3 to activate peroxymonosulfate (PMS) for selectively eliminating electron-rich organic pollutants in the presence of Cl-. Through experimental and theoretical analysis, we revealed that gamma-Al2O3, characterized by uniquely strong Lewis acid sites, enabled robust inner-sphere complexation between PMS and Al(III) sites, triggering the oxidation of Cl- to free chlorine through a distinctive, low-energy-barrier Eley-Rideal pathway. Such a unique pathway resulted in a 42.7-fold increase in free chlorine generation, culminating in a remarkable 145.9-fold enhancement in the degradation of carbamazepine (CBZ) compared with the case without gamma-Al2O3. Furthermore, this catalyst exhibited high oxidant utilization efficiency, stable performance in real-world environmental matrices, and sustained long-term activation for over 1206 bed volumes (BV) with a CBZ removal rate exceeding 90% in fixed-bed experiments. These favorable features render gamma-Al2O3 an extremely promising nanomaterial for sustainable water treatment initiatives.