Fabrication of a porous hexagonal rod-like La-containing Mg-MOF for the removal of phosphate and polynomial regression fitting and DFT analysis

A porous hexagonal rod-like La-containing Mg-MOF was rationally designed and fabricated via a controlled hydrothermal route to achieve efficient phosphate removal from aqueous media. The introduction of La 3+ and Mg 2+ generated a La-containing Mg-MOF with enhanced surface reactivity and abundant adsorption sites. Structural and surface characterization using FTIR, SEM-EDS, BET, and XPS suggested the successful formation of the La-containing Mg-MOF, its mesoporous architecture, and effective integration of both metal sites. Adsorption experiments demonstrated high phosphate uptake, strong selectivity, and stable performance over a broad pH range and in the presence of competing anions. Kinetic analysis indicated that the adsorption process followed pseudo second-order behavior, suggesting surface site-controlled adsorption. Thermodynamic evaluation revealed that phosphate adsorption was spontaneous, endothermic, and entropy-driven. Isotherm modeling showed excellent agreement with the Langmuir model, yielding adsorption capacity of 448.59 mg g −1 . Mechanistic insights derived from density functional theory calculation, FTIR and XPS analyses revealed that phosphate removal occurred through a synergistic combination of outer sphere electrostatic interactions and inner-sphere complexation involving ligand exchange and coordination with La-containing active sites. Furthermore, polynomial regression fitting models were applied to investigate the quantitative relationships between phosphate adsorption capacity and experimental parameters such as pH, initial concentration, contact time, adsorbent dosage, and solution volume, achieving R 2 values above 0.98. These results demonstrate La-containing Mg-MOF are highly promising candidates as next-generation adsorbents for efficient phosphate removal in water treatment systems.