Novel MOF(Zr)-on-MOF(Ce/La) adsorbent for efficient fluoride and phosphate removal

A one-pot method with formic acid regulation was adopted to fabricate a novel MOF(Zr)-on-MOF(Ce/La) adsorbent for fluoride and phosphate removal. Compared to traditional adsorbents, MOF(Zr)-on-MOF(Ce/La) boasted abundant active sites and a wide application range, with adsorption capacities of 173.2 and 92.85 mg g- 1 for fluoride and phosphate, respectively. Comprehensive characterization techniques like SEM-EDS, BET, XRD, FTIR, and TGA were employed to analyze the material's properties. Adsorption experiments investigated multiple effect factors. BET analysis disclosed a specific surface area of 332 m2 g- 1, mainly composed of micropores and mesopores. The adsorbent showed rapid adsorption rates for both ions, with low reliance on adsorption time. The adsorption process was exothermic and spontaneous, favored by higher temperatures. Kinetic and thermodynamic studies favored the pseudo-second-order kinetic and Langmuir models, suggesting monolayer chemical adsorption. Through combined analyses including XPS, XRD, and studies on kinetics and thermodynamics, the fluoride removal mechanism involved electrostatic interaction and ion exchange, while phosphate removal encompassed ion exchange, electrostatic interactions, and complexation. Field wastewater experiments met Chinese standards, and recycling experiments revealed sustained removal efficiencies of 90.20 % for fluoride and 87.27 % for phosphate after two regeneration cycles, highlighting the significant potential of this approach in alleviating fluoride and phosphorus pollution.