Nanocomposite Chitosan@graphene Oxide-Based Aerogel Beads for Anionic and Cationic Dye Removal: Synthesis, Characterizations, and Complexed Interfacial Interactions in Batch and Column Studies

One of the greatest global threats to the environment and human health is the persistent pollution of water. Adsorption is a recognized remediation method that effectively and efficiently removes pollutants from water. In this work, nanocomposite aerogel beads of chitosan-graphene oxide (CS/GO) and chitosan-reduced graphene oxide (CS/rGO) were synthesized by a simple three-step procedure and evaluated as an adsorbent material for water purification. In particular, two model pollutant molecules, namely, indigo carmine (IC, anionic dye) and methylene blue (MB, cationic dye), were used to study the adsorption behavior of the developed materials by kinetics and isothermal analyses in batch configuration. Adsorption kinetics follows the Elovich model well, while adsorption isotherms are better described by the Freundlich model. CS/GO aerogel beads had greater MB affinity, while CS/rGO exhibited better IC adsorption removal, with maximum adsorption capacities of 254 and 109 mg g–1, respectively, according to Langmuir fitting. In view of this result, the adsorption behavior of mixed CS/GO and CS/rGO beads at 1:3, 1:1, and 3:1 weight ratios was also investigated with the aim of achieving broad-spectrum removal capacity, that is, the ability to remove both anionic and cationic species at the same time. In addition, a custom-made fixed-bed configuration at a 15 mL scale was exploited to evaluate the adsorption capacity of CS/GO and CS/rGO beads over MB and IC, respectively, under flow conditions. Finally, the applicability of mixed CS/GO–CS/rGO beads for the removal of water contaminated with mixed dyes was also demonstrated.