Removal of PdCl ₂ From Aqueous Solutions Onto Functionalized Magnetite: Experimental and Computational Approach

This study reports the synthesis, characterization, and adsorption performance of magnetite (Fe3O 4 ) functionalized with sodium 3‐sulfobenzoate (MSF) for the removal of PdCl 2 from aqueous solutions, supported by experimental and computational approaches. The adsorbent was prepared by surface functionalization and characterized using TEM, SEM, EDS, XRD, and FTIR, confirming a spinel Fe 3 O 4 structure, sulfonate incorporation, and an average particle size of 18.3 nm. Batch adsorption experiments revealed that Pd removal efficiency increases with an increase in adsorbent dosage, reaching an optimum adsorption capacity of 1.8 mg·L −1 . The adsorption process is influenced by temperature, with the optimum adsorption capacity observed at 30°C. The adsorption capacity is dependent on initial Pd concentration, with equilibrium achieved at 15–20 μM. Thermodynamic modeling showed that the adsorption fitted both Langmuir ( R 2 = 0.985) and Freundlich ( R 2 = 0.983) isotherms, indicating monolayer adsorption on heterogeneous adsorption sites. The Langmuir constant ( K l = 3.54 × 10 5 L·mol −1 ) and monolayer capacity (1.29 × 10 −6 mol·g −1 ) suggest strong site‐specific interactions, while the Dubinin–Radushkevich model yielded a mean adsorption energy of 11.13 kJ·mol −1 , confirming chemisorption. Kinetic studies demonstrated that the process follows a pseudo–second‐order model ( R 2 = 0.99), indicating chemical interaction rather than physical adsorption. FTIR analysis of spent adsorbents showed reduced OH band intensity, suggesting Pd coordination at hydroxyl sites, while XRD confirmed structural integrity after adsorption. SEM and EDS mapping revealed heterogeneous Pd distribution on the surface. Density functional theory (DFT) simulations using CASTEP supported these findings, showing strong orbital hybridization between Pd 4d and O 2p orbitals, Pd–O bond lengths of 2.08 Å, and an adsorption energy of −7.89 kJ·mol −1 , indicative of exothermic ligand coordination. This confirms that PdCl 2 adsorption on MSF occurs through chemisorption by complexation at sulfonate and hydroxyl sites.