A Novel Ce/Fe Bimetallic Metal-Organic Framework with an Ortho-Dodecahedral Multilevel Structure for Enhanced Adsorption Application

Abstract

The synthesis of a novel Ce/Fe bimetallic metal-organic frameworks (Ce/FcDA/FA-MOFs) through an innovative hydrothermal method, utilizing Ce as the central metal, and 1,1'-ferrocene dicarboxylic acid (FcDA) and formic acid (FA) as ligands are reported. Optimization of hydrothermal time, feed ratio, and the addition of FA resulted in Ce/FcDA/FA-MOFs with ideal ortho-dodecahedral hierarchical configurations. Comprehensive characterization through 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 phosphate adsorption's spontaneous, efficient, and heat-absorbing 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, the adsorption mechanism of Ce/FcDA/FA-MOFs on phosphate was investigated through FT-IR, XRD, and XPS analyses of the adsorbed samples, revealing 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 developing environmentally sustainable materials with potential applications in water treatment.

Keywords: Ce/Fe bimetallic MOFs, Ortho-dodecahedral multilevel structure, Phosphate, Adsorption, Reaction mechanisms