Interfacial phosphate ions dehydration for advanced phosphate removal and recovery

Phosphate removal and recovery by adsorption is vital in addressing the phosphorus-induced water eutrophication and mitigating the depletion of phosphorus resources. However, the formation of hydrated phosphate clusters serves to impede the mass transfer of phosphate from water to the adsorbent. Herein, we demonstrated that interfacial phosphate ions dehydration, by regulating the interfacial hydrogen bonding between water molecules and the surface polar groups of malonamide-modified La(OH)₃ (MA-La(OH)₃), can deliver superior phosphate removal and recovery. The malonamide carbonyl and amino groups weakened the phosphate ions hydration layer via hydrogen bonding interactions with hydrated H₂O (C=O···H and NH···O), thereby enhancing the phosphate ions charge density to promote their migration and coordination with La sites. Impressively, MA-La(OH)₃ exhibited an excellent phosphate removal rate of 99.0% with a high adsorption capacity of 175.4 mg P g^-1, far surpassing La(OH)₃ (79.0% and 112.4 mg P g^-1). The adsorbed phosphate was concentrated to 429.5 mg L^-1 into the residual alkaline solution from MA-La(OH)₃ synthesis and further converted to struvite, reducing the total removal cost by 17.5%. This study offers a proof-of-concept strategy for advanced phosphate removal and recovery, and highlights the importance of interfacial phosphate ions dehydration in enhancing mass transfer and surface adsorption.