Recovery of Metal Ions from Aqueous Solutions by γ-Alumina Creates Value-Added Catalyst Products

Mining and extracting metals from hard rock adversely impact the environment. These impacts could be mitigated by capturing dissolved metals from water (i.e., mine runoff, industrial wastewaters, or even tap water) and converting the metals to products with potential economic benefits (i.e., upcycled into high-value products). We sought to identify a sorbent that can remove dissolved metals from water and in the process of this low-temperature surface adsorption create a catalytic material of potential economic value. We discovered that γ-aluminum oxide (γ-Al₂O₃) can produce a reactive catalyst after removing metal ions (copper (Cu), palladium (Pd), nickel (Ni), and cobalt (Co)) from water, even for dissolved metals at environmentally relevant concentrations. The resulting metal-coated γ-Al₂O₃ behaved, comparable to high-temperature produced catalysts, as a mono- or bimetallic catalyst capable of oxidizing or reducing pollutants (methylene blue, 4-nitrophenol, nitrite, and nitrate). Mono- or bimetallic catalysts synthesized from tap water with metal ions present efficiently oxidized methylene blue (by Cu/γ-Al₂O₃) or reduced nitrate (by Pd-Cu/γ-Al₂O₃) into less harmful species (i.e., ammonium and dinitrogen gas). Results demonstrated the versatile use of γ-Al₂O₃ that removes metal ions from water (i.e., water purification) and produces a valuable γ-Al₂O₃-based byproduct with proven catalytic reactivity (i.e., catalyst production) and commercial markets.