Synthesis and sorption performance of imidazole-based hydrogels for selective palladium recovery in green...

A novel poly(ethylene glycol)/acrylic acid/imidazole (PEG/AAc/IMZ) hydrogel was synthesized via free-radical polymerization and evaluated as an adsorbent for the recovery of Pd(II) ions from aqueous solutions. The synthesized hydrogel was characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX), confirming the successful incorporation of the functional groups responsible for metal-ion binding. Batch adsorption experiments were conducted to investigate the effects of contact time, solution pH, initial Pd(II) concentration, phase ratio (V/m), and temperature on the adsorption performance. The adsorption efficiency was strongly influenced by the solution pH, with optimum Pd(II) uptake achieved at pH 4. Under the optimized conditions (contact time = 60 min, V/m = 0.1 L/g, initial Pd(II) concentration = 100 mg/L, and temperature = 25 °C), the PEG/AAc/IMZ hydrogel exhibited an adsorption efficiency of 85%. Equilibrium data were best described by the Langmuir isotherm model (R² = 0.989), yielding a maximum adsorption capacity of 24.26 mg/g, which is in good agreement with the experimental value (25.15 mg/g). Kinetic studies revealed that Pd(II) adsorption followed the pseudo-second-order model, indicating that the adsorption rate is governed by the availability of active adsorption sites. Thermodynamic investigations demonstrated that the adsorption process was spontaneous and exothermic in nature. Furthermore, selectivity experiments performed in the presence of competing metal ions (Pt, Ni, and Zn) confirmed the preferential uptake of Pd(II), following the order: Pd > Ni > Pt > Zn. The developed PEG/AAc/IMZ hydrogel therefore represents a promising adsorbent for the selective recovery of Pd(II) from multicomponent aqueous systems.