Bifunctional Mn2+/La3+ redox-acid sites in layered double hydroxide for self-regenerative and ultradeep phosphate capture/recovery

The sustainable management of phosphorus, a vital yet scarce resource, is severely challenged by its excessive discharge into water bodies, which causes eutrophication. Achieving ultralow phosphate concentrations while enabling efficient recovery demands advanced materials that transcend the capacity and functionality limits of conventional adsorbents. Herein, we report a rationally designed MnLa-layered double hydroxide (LDH) with synergistic redox-acid bifunctional sites for self-regenerative phosphate capture and recovery. This material achieves an exceptional adsorption capacity of 108.87 mg P/g and reduces phosphate to trace levels below 0.012 mg/L, surpassing stringent eutrophication thresholds. Crucially, the MnLa-LDH exhibits self-enhanced functionality: the La 3+ acid sites provide strong Lewis acidity for specific inner-sphere complexation, while the adjacent Mn 2+ /Mn 3+ redox couples act as a molecular engine to dynamically regenerate surface hydroxyl groups, sustaining high activity over multiple cycles. Systematic characterization confirms that phosphate uptake triggers a dynamic structural self-optimization, remarkably increasing the specific surface area by 112.6 %. The material demonstrates broad pH adaptability, high selectivity, and outstanding reusability (87.5 % capacity retention after 10 cycles) with 92.3 % phosphate recovery. This work provides a novel design paradigm for smart environmental functional materials based on synergistic site engineering, paving the way for sustainable water treatment and closed-loop resource circulation.