Chitosan/Montmorillonite/Graphene Oxide Composites for the Adsorption of Dyes from Single-Component Solutions, Binary...

Industrial waste remains a global issue threatening human health and the balance of the ecosystem. Organic dyes are one of the most significant and widely found pollutants in wastewater. In this study, two novel composites, chitosan/montmorillonite (CS/MT) and CS/MT/graphene oxide (CS/MT/GO), were synthesized for wastewater management by adsorption of reactive black 5 (RB5) and methylene blue (MB) from aqueous solutions, the binary dye system, and real wastewater samples from the textile industry. Moreover, tripolyphosphate sodium (TPP) was used as a cross-linking agent for the bead's formation during the synthetic process. The materials were extensively characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and X-ray diffraction (XRD) techniques. SEM images revealed that the CS/MT/GO composite beads exhibited a larger diameter and a rougher surface than CS/MT, while BET shows that the surface area of CS/MT/GO (44.61 m²/g) is more extended than that of CS/MT (20.01 m²/g). The adsorption experiments showed that CS/MT/GO effectively removed RB5 and MB, providing 222.35 and 203.98 mg/g of adsorption capacities, respectively. Notably, the removal efficiency for RB5 reached 99.1% at pH 2, while, for MB, a maximum removal efficiency of 80.29% was observed at pH 12. Furthermore, the results fit the Freundlich isotherm and pseudo-second-order (PSO) kinetic models well. Moreover, thermodynamic analysis revealed that both dyes' adsorption processes were endothermic and spontaneous. This study aimed to synthesize a reusable GO biomaterial that would be effective in both anionic and cationic dyes. Additionally, reusability was studied, and it was found that CS/MT/GO is more suitable for removing RB5 than MB after 5 regeneration cycles. However, there appears to be a competitive effect between RB5 and MB in binary systems. Finally, the CS/MT and CS/MT/GO composites are suitable for industrial applications, demonstrating excellent adsorption capacity, stability, and reusability for effectively removing pollutants from wastewater.