All-In-One solution for simultaneous phosphonate degradation and orthophosphate recovery by NiFe-Layer double Hydroxide/PDS

Phosphate recovery presents an effective solution to address the conflicting problems of phosphorus pollution and scarcity. However, recovering organic phosphates, such as 1-hydroxyethane 1,1-diphosphonic acid (HEDP), is comparatively complex, which involves multiple processes. Herein, we developed an innovative all-in-one solution to simplify these processes by combining NiFe-layered double hydroxides (NiFe-LDH) and peroxydisulfate (PDS). This combination achieved approximately 90 % conversion of HEDP to orthophosphate, with 100 % of the resulting orthophosphate recovered in 120 min. The exceptional performance in simultaneous HEDP degradation and recovery can be attributed to dual roles of Ni and Fe in NiFe-LDH/PDS. The polyvalent Ni functions as an electron shutter (Ni 2+ ⇋ Ni 3+ ⇋ Ni 2+ ) in the redox cycles between PDS and HEDP, accounting for effective HEDP degradation. The high complexation stability between Fe(Ⅲ) and orthophosphate (log K  = 9.92) allows Fe(Ⅲ) to serve as binding sites for orthophosphate recovery. Moreover, NiFe-LDH/PDS effectively treats HEDP across wide pH ranges (3–––10), which can be ascribed to pH buffers originating from protonation/deprotonation in NiFe-LDH layers. The recovered phosphorus with NiFe-LDH exhibited a slow-release property under soil water solution without notable Ni release, which highlighted its potential usage as a slow-release fertilizer. These features—catalytic and binding sites, and high compatibility—allow NiFe-LDH to achieve concurrent degradation and recovery of organic phosphate in a single solution.