Graphene Oxide–Chitosan Composite Material for Treatment of a Model Dye Effluent

Graphene oxide (GO) was cross-linked with chitosan to yield a composite (GO-LCTS) with variable morphology, enhanced surface area, and notably high methylene blue (MB) adsorption capacity. The materials were structurally characterized using thermogravimetric analysis and spectroscopic methods (X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and <sup>13</sup>C solid-state NMR) to support that cross-linking occurs between the amine groups of chitosan and the −COOH groups of GO. Equilibrium swelling studies provide support for the enhanced structural stability of GO-cross-linked materials over the synthetic precursors. Scanning electron microscopy studies reveal the enhanced surface area and variable morphology of the cross-linked GO materials, along with equilibrium and kinetic uptake results with MB dye in aqueous media, revealing greater uptake of GO-LCTS composites over pristine GO. The monolayer uptake capacity (<i>Q</i><sub>m</sub>; mg g<sup>–1</sup>) with MB reveals twofold variation for <i>Q</i><sub>m</sub>, where GO-LCTS (402.6 mg g<sup>–1</sup>) > GO (286.9 mg g<sup>–1</sup>). The kinetic uptake profiles of MB follow a pseudo-second-order trend, where the GO composite shows more rapid uptake over GO. This study reveals that the sorption properties of GO are markedly improved upon formation of a GO–chitosan composite. The facile cross-linking strategy of GO reveals that its physicochemical properties are tunable and versatile for a wider field of application for contaminant removal, especially over multiple adsorption–desorption cycles when compared against pristine GO in its highly dispersed nanoparticle form.