Electrosorptive phosphate recovery using La(OH)₃-Mg-Al LDH composite with induced oxygen vacancies and tuned...

A La(OH)₃-decorated Mg-Al layered double hydroxide composite was incorporated with carbon black and PTFE binder and coated onto activated carbon fibre (ACF) to fabricate a composite electrode (denoted as MAL) for enhanced electrosorptive phosphate capture via electronic structure modulation and oxygen-vacancy engineering. The optimized MAL_0.5 (La/Mg-Al LDH = 1:4) exhibited a 1.7-fold higher phosphate uptake and a 1.2-fold larger surface area than pristine La(OH)₃. Under an applied bias of 4.0 V, MAL_0.5 achieved a maximum electrosorption capacity of 86.38 mg/g, with 4.83- and 4.4-fold enhancements in adsorption capacity and kinetics, respectively, compared with open-circuit operation. Kinetic and equilibrium analyses revealed pseudo-second-order and Langmuir behaviours, confirming a chemisorption-dominant process. Coexisting-anion experiments showed that the inhibitory effect of competing anions on phosphate electrosorption followed the order Cl^- > NO₃^- > HCO₃^- > SO₄^2- > CO₃^2-, suggesting that specific surface interactions played an important role in the overall electrosorption process. Spectroscopic characterizations further verified the formation of abundant oxygen vacancies and strong La-LDH interfacial coupling, while DFT calculations demonstrated that electronic redistribution around La sites significantly enhanced the intrinsic phosphate adsorption affinity and strengthened La-P coordination. The electrode also maintained stable performance in real wastewater and enabled efficient phosphate recovery through electro-desorption. This work provided a mechanistically validated strategy for constructing La-based electrosorptive materials with accelerated charge transfer, enhanced active-site accessibility, and strong environmental adaptability, highlighting their potential for practical phosphate remediation in complex aqueous systems.