Improved utilization of active sites for phosphorus adsorption in FeOOH/anion exchanger nanocomposites via a glycol-solvothermal synthesis strategy

Metal oxide/hydroxide-based nanocomposite adsorbents with porous supporting matrices have been recognized as efficient adsorbents for phosphorus recovery. Aiming at satisfying increasingly restrictive environmental requirements involving improving metal site utilization and lowering metal leakage risk, a glycol-solvothermal confined-space synthesis strategy was proposed for the fabrication of FeOOH/anion exchanger nanocomposites (Fe/900s) with enhanced metal site utilization and reduced metal leakage risk. Compared to composites prepared using alkaline precipitation methods, Fe/900s performed comparably, with a high adsorption capacity of 19.05 mg-P/g with an initial concentration of 10 mg-P/L, a high adsorption selectivity of 8.2 mg-P/g in the presence of 500 mg-SO 4 2− /L, and high long-term resilience (with a capacity loss of ~14% after five cycles), along with substantially lower Fe loading amount (4.11 wt.%) and Fe leakage percentage. Mechanistic investigation demonstrated that contribution of the specific FeOOH sites to phosphate adsorption increased substantially (up to 50.97% under the optimal conditions), in which Fe(III)-OH was the dominant efficient species. The side effects of an excessively long reaction time, which included quaternary ammonium decomposition, FeOOH aggregation, and Fe(III) reduction, were discussed as guidance for optimizing the synthesis strategy. The glycol-solvothermal strategy provides a facile solution to environmental problems through nanocrystal growth engineering in a confined space.