Non-covalent interaction of hydroxyl-capped layered double hydroxide oligomers for high-performance P recovery

Abstract

Phosphorus (P) recovery is of great significance for maintaining the virtuous circle of ecosystems. However, the efficiency of the current recovery technology based on adsorption is greatly limited because 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. CALOx exhibits a superior P uptake capacity at saturation (297.6 mg g⁻¹) with a high distribution coefficient K_d of 18.15 L g⁻¹, demonstrating excellent selectivity. Compared with ordinary Ca/Al-LDH, it can increase the P desorption ratio by almost 7-fold (78.5% vs. 9.81%) in a more neutral aqueous medium (pH 8.0). The adsorbed PO₄³⁻ or its hydrated form is regulated at the intercalation site of CALOx via non-covalent forces. The exchangeable state of adsorbed P remarkably facilitates the subsequent P recovery and the in situ sorbent regeneration. Our work suggests a new direction for the development of P recovery and bidirectionally enhances the selective P adsorption and desorption in a balanced manner.