A novel Ce/Fe bimetallic metal-organic framework with ortho-dodecahedral multilevel structure for enhanced phosphate adsorption

The synthesis of novel Ce/Fe bimetallic metal–organic frameworks (Ce/FcDA/FA-MOFs) via an innovative hydrothermal method is reported. This method utilizes Ce as the central metal and 1,1′-ferrocene dicarboxylic acid (FcDA) and formic acid (FA) as ligands. Optimization of hydrothermal time, feed ratio, and the addition of FA yielded Ce/FcDA/FA-MOFs with ideal ortho-dodecahedral hierarchical configurations. Comprehensive characterization via FT-IR, XRD, SEM, EDS, XPS, and N₂ adsorption/desorption analyses elucidated the influence of FA on morphology and chemical structure. Phosphate adsorption tests on Ce/FcDA/FA-MOFs revealed sustained strong selectivity and adsorption capacity, even in the presence of coexisting anions and variations in pH. Kinetic, thermodynamic, and isothermal simulations indicated spontaneous, efficient, and heat-absorbing phosphate adsorption properties on Ce/FcDA/FA-MOFs. Fitting parameters from the Langmuir adsorption model demonstrated a maximum adsorption capacity of up to 530.25 mg g⁻¹, attributed to physical/chemical adsorption during the reaction. Furthermore, investigation into the adsorption mechanism of Ce/FcDA/FA-MOFs on phosphate through FT-IR, XRD, and XPS analyses of the adsorbed samples revealed a complex process involving the electrostatic mutual attraction of outer-sphere entities and ligand exchange in the inner-sphere. This study advances our understanding of Ce/FcDA/FA-MOFs as effective adsorbents for phosphate and contributes to the development of environmentally sustainable materials with potential applications in water treatment.