γ-Al₂O₃ selectively adsorbs transition group metals from contaminated waters to produce bi-metallic catalysts for...

Metals present in industrial or mining wastewater are hazardous to human health and the environment, and their remediation is costly. In this study, we used γ-Al₂O₃ to capture transition metals (e.g., Pd, Cu, Ni, and Co) from wastewater and used the spent adsorbent as catalysts for nitrate reduction. Based on a pH-dependent surface-mediated redox reaction mechanism, Pd and Cu ions are selectively adsorbed onto γ-Al₂O₃ at ambient temperature without involving the use of chemical reductants, thus transforming these pollutants into active catalytic sites. We particularly focused on Pd/Cu bimetallic catalysts, finding that the Pd and Cu ion concentrations in contaminated water impacted both nitrate reduction efficiency and nitrogen selectivity. The best nitrate reduction occurred with 0.74 wt% Pd and 0.66 wt% Cu on γ-Al₂O₃, achieving high nitrate reactivity and ∼81 % selectivity for N₂ formation over 10 cycles. Ni and Co, which have smaller redox potential differences than Pd and Cu, showed limited interference with Pd and Cu adsorption, allowing γ-Al₂O₃ to form Pd-Cu bimetallic catalysts selectively in batch and column tests. Overall, metal-based catalysts can be fabricated under ambient conditions while remediating metal-contaminated wastewater, thereby producing functional products (e.g., hydrogenation catalysts), which is consistent with circular economy principles.