Towards Circular Water Treatment: Adsorption Mechanism and Analytical Characterization of Metformin Retention on Amberlite XAD7HP Resin

This study evaluates the adsorption, structural characterization, and regeneration performance of acrylic resin Amberlite XAD7HP (X7) for the removal of metformin (MET), an emerging pharmaceutical contaminant. MET concentrations after adsorption were quantified using the linear UV–Vis method at 232 nm (R2 = 0.9998). Adsorption kinetics followed the pseudo-second-order model (R2 =0.9881), and equilibrium data fitted the Langmuir isotherm, confirming monolayer adsorption. Desorption experiments showed that acidic media were ineffective (<10%), whereas the mixed (1:1) MeOH–1M HCl system achieved 89.3% MET recovery, enabling efficient resin desorption. FTIR confirmed MET retention through attenuation of N–H stretching bands at 3360–3290 cm−1, the shift of the C=N vibration from 1628 cm−1 to 1605 cm−1, and the appearance of a new band at 1542 cm−1, indicating hydrogen bonding and dipole–dipole interactions with the resin. SEM micrographs revealed a clear transition from the X7, rough morphology to a smoother, partially occluded surface after adsorption, consistent with pore filling by MET. EDX analysis further confirmed MET uptake through the appearance of a distinct N signal and increased O content, serving as elemental markers of drug adsorption. TG/DSC demonstrated enhanced thermal stability and modified decomposition profiles for the resin loaded with MET, while XRD patterns confirmed the amorphous nature of X7 and the absence of crystalline MET deposits, indicating molecular-level dispersion. The integrated analytical, structural, kinetic, and desorption results highlight the potential of desorbed acrylic resin as a sustainable material for mitigating pharmaceutical pollution in aquatic environments.