Carboxylic Acid-Terminated Carbon Nanoflakes for Selective Adsorption of Water-Soluble Cationic Dyes

Carbon-based nanomaterials have always been in high demand because of their efficient adsorption capabilities. Herein, we synthesized water-dispersible carboxylic acid-terminated carbon nanoflakes (CNFs) by simple acid treatment in aqueous solution of glucose. The as-synthesized CNFs have been used for the adsorption of multiple water-soluble cationic dyes and even from a mixture of spiked industrial wastewater. Here, we have used six water-soluble model dyes methylene blue (MB), crystal violet (CV), rhodamine B (RhB), congo red (CR), methyl orange (MO), and metanil yellow (MY) for adsorption studies. CNFs show significant adsorption capacity toward cationic dyes (MB, CV, and RhB) compared to anionic dyes (CR, MO, and MY). Selectivity in adsorption of cationic dyes on negatively charged CNFs adsorbents has occurred via electrostatic interaction. The adsorption capacities of CNFs toward three cationic dyes (MB, CV, and RhB) are ∼148, ∼132, and ∼118 mg g –1, respectively. More importantly, it is observed that CNFs have performed as better adsorbents than the well-known commercially available activated charcoal for the tested dyes. The adsorption process has been studied by varying different regulating parameters such as pH of the solution, initial dye concentration, temperature, and the concentration of CNFs and analyzed in terms of kinetic and isotherm models. Moreover, the adsorbed dyes could be desorbed completely from nanoflake surfaces and are efficient for multicyclic use.