Biodegradable and Reusable Multivalent Metal Ion-Anchored Hydrotalcite-Based Biopolymer Composites for Efficient Phosphate Removal From Water

Abstract

Excess phosphate in aquatic systems causes eutrophication, resulting in severe deterioration of water quality. To address this challenge, the present study aimed to synthesize hydrotalcites incorporated with Ca, Ce, and La metal ions ((Ca-La)HT and (Ca-Ce)HT) and to develop their biopolymeric-based hybrid composites using alginate, gelatin, and pectin. The resulting materials included Alg/(Ca-Ce)HT, Gel/(Ca-Ce)HT, Pec/(Ca-Ce)HT, Alg/(Ca-La)HT, Gel/(Ca-La)HT, and Pec/(Ca-La)HT, which were evaluated for phosphate removal from water. Among them, Gel/(Ca-Ce)HT and Gel/(Ca-La)HT exhibited the highest adsorption capacities of 42 and 45 mg g⁻¹, respectively, and were therefore selected for detailed adsorption studies. The composites were characterized using FTIR, XRD, EDAX, and SEM analyses. Batch adsorption experiments were performed to investigate the effects of contact time, adsorbent dosage, solution pH, pH_zpc, and competing co-ions. Isotherm analysis indicated that phosphate adsorption followed a multilayer adsorption mechanism. Thermodynamic studies confirmed that the adsorption process was spontaneous, while kinetic analysis showed that the adsorption behavior was best described by the intraparticle diffusion and pseudo-second-order model. The adsorption performance of the gelatin-based composites was further validated using real water samples. Additionally, the composites showed good stability and effective phosphate removal over repeated adsorption–desorption cycles, highlighting their potential as efficient, reusable adsorbents for phosphate remediation.