Kinetic and Thermodynamic Study of the Adsorption of Malachite Green Dye Using Graphene Nanoplatelets

Water contamination by dyes is a pressing issue that must be addressed to ensure quality of life for humans, animals, and the environment. Adsorption, due to its versatility and low cost, is a promising method for removing dyes from contaminated water. Carbon-based materials have proven to be excellent dye adsorbents. In this study, commercial-grade graphene nanoplatelets (GNPs) without any surface modifications were used to adsorb malachite green dye from model solutions. Using a mass loading of 2 g⋅L −1 and an initial dye concentration of 600 ppm, nearly 90% removal was achieved within two hours, without adjusting the pH of the dye solution. The kinetic data fitted well with the pseudo-second-order model, while the adsorption isotherms followed the Langmuir model, indicating a maximum adsorption capacity ( q max ) of 1000 mg⋅g −1 . Thermodynamic analysis indicated that the adsorption process was spontaneous, endothermic, and irreversible. Overall, the findings suggested that the process is viable and corresponds to a chemisorption mechanism. The chemical structures of malachite green and GNPs favour adsorption via 𝜋–𝜋 interactions, eliminating the need for surface modification of GNPs. This not only enhances the adsorption process but also avoids the generation of byproducts and residues, aligning with the principles of green chemistry.