Enhanced dye removal using montmorillonite modified with graphene quantum dots in sustainable salep nanocomposite hydrogel

Abstract

AbstractThis research investigated the utilization of graphene quantum dot/montmorillonite (GQD/MMT) as an effective nanofiller in a hydrogel composed of salep biopolymer. The semi-IPN hydrogel was synthesized using salep as the substrate, acrylamide (AAm) as the monomer, ammonium persulfate (APS) as an initiator in free radical polymerization, and N,N'-methylenebisacrylamide (MBA) as a cross-linking agent. The hydrogels were applied to remove safranin (SA), methylene blue (MB), crystal violet (CV), methyl green (MG), congo red (CR), and malachite green (MG) dyes from the water. The diverse properties were analyzed using a scanning electron microscope, fourier infrared spectroscopy, mapping, energy dispersive spectroscopy, weighing analysis, X-ray diffraction, and thermal stability analyses. The optimism of the prepared adsorbent in dye absorption was evaluated by measuring the swelling amount, pH impact, adsorbent dosage, and contact time. The adsorption calculations were described using kinetics and isotherm models. The results indicated that the Langmuir isotherm model (R2 = 99.6) and the pseudo-second-order kinetic model (R2 = 99.9) provided the best fit for the absorption process of MB. The presence of additional amounts of GQD/MMT had a reciprocal effect on the adsorption efficiency due to the accumulation of GQD/MMT in the semi-interpenetrating polymer network (semi-IPN (structure. The findings revealed that the samples exhibited high thermal stability, and the absorption process was primarily chemical. Furthermore, the nanocomposite hydrogels demonstrated distinct mechanisms for absorbing anionic dye (CR) and cationic dye (MB). Under optimal conditions, using 7 wt% GQD/MMT at a concentration of 5 ppm, pH = 7, an adsorbent dosage of 50 mg, at room temperature, and a contact time of 90 min, the maximum removal efficiencies were achieved: MB (96.2%), SA (98.2%), MG (86%), CV (99.8%), MG (95.8%), and CR (63.4%). These results highlight the adsorbent's high absorption capacity, rapid removal rate, and reusability, demonstrating its potential as an eco-friendly and cost-effective solution for removing dyes from water.