Non-covalent Interaction of Hydroxyl Capped Layered Double Hydroxide Oligomers for Highly Performing Phosphorus Recovery

Abstract

Phosphorus (P) recovery is of great significance to maintaining the virtuous circle of ecosystems. However, the efficiency of present recovery technology based on adsorption is greatly limited that selective adsorption and desorption are trade-off processes especially for metallic hydroxide adsorbents. Herein, we exploit a Ca/Al-LDH oligomer (CALOx) with a hydroxyl end-capping strategy to weaken the strong oriented covalent binding force between the O end of M-O (Metal to Oxygen binding) and phosphate molecules. The resultant adsorbent exhibits a superior saturation of P uptake capacity (297.6 mg g-1) with a high distribution coefficient Kd of 18.15 L g-1 in selectivity, and can increase the P desorption ratio by almost ~7-fold (78.5% vs. 9.81%) in a more neutral aqueous medium (pH 8.0) compared with ordinary Ca/Al-LDH. The adsorbed PO43- or its hydrated form is regulated at the intercalation site of CALOx via non-covalent forces. Due to the exchangeable state of adsorbed P, the subsequent P recovery and the in-situ sorbents regeneration are remarkably facilitated. Our work suggests a new development direction for P recovery and bidirectionally enhances the selective P adsorption and desorption with a balanced course.