Mesoporous nanocomposite polydopamine-coated graphene oxide/maghemite for high-efficient adsorption of diclofenac sodium in batch mode: synthesis, characterization, RSM modeling and optimization

Abstract

To address significant health issues and ecological damage associated with drug pollutions in wastewater, a novel mesoporous nanocomposite, polydopamine-coated graphene oxide/maghemite (PDA-GO/ɣ-Fe₂O₃), was synthesized and utilized for removing diclofenac sodium (DCF) from aqueous solution in batch mode. This study proposed an efficient method for synthesizing PDA-GO/ɣ-Fe₂O₃ nanocomposites, emphasizing the eco-friendly attributes of the modified GO (PDA-GO) and maghemite nanoparticles (ɣ-Fe₂O₃). The adsorbent structure was characterized using XRD, BET analysis, FTIR, FE-SEM, and EDX. BET measurements showed that the adsorbent’s mean pore diameter was approximately 7.5 nm, confirming its mesoporous structure. The EDX spectrum displayed peaks corresponding to oxygen, carbon, iron, and nitrogen in the composition of the PDA-GO/ɣ-Fe₂O₃ nanocomposite. FTIR analysis showed the presence of various functional groups, including hydroxyl, carboxylate, and carbonyl groups, on the surface of the PDA-GO/ɣ-Fe₂O₃ composite. The R² values obtained from the quadratic models using RSM-CCD for the composite adsorbent were 0.988 and 0.998 for removal efficiency and adsorption capacity, respectively. The optimal operating parameters to reach the maximum adsorption capacity of 151.9 mg/g and removal efficiency of 93.12% were determined at an initial DCF concentration of 32.5 mg/L, a temperature of 25 °C, a contact time of 40 min, and a pH of 3, using the CCD-RSM methodology. The kinetics of adsorption were well described by the Fickian diffusion model. By performing four repeated cycles of DCF adsorption/desorption using NaOH solution as an eluent at pH 8, reductions in removal efficiency of 2 and 10% were observed during first three cycles and fourth cycle, respectively.