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Dyes removal from wastewater of industries is considered the prime demand of the environment. Three trimellitic anhydride isothiocyanate-cross-linked chitosan hydrogels, previously reported as novel antimicrobial agents, were investigated for the first time in this work as adsorbents for Basic Red 12 (BR 12) cationic dye. These hydrogels behave as polyanionic materials. Their adsorption capacity for the BR 12 dye increased significantly with increasing both the temperature, the solution pH and their cross-linking content. Their adsorption fitted to the pseudo-second-order kinetic model. Their adsorption isotherms conform to the Langmuir model suggesting that the adsorption nature is a monolayer having an optimum sorption capability of 38.27 mg g−1 and removal efficiency of 97.38%. The results proved that the adsorption process is remarkably proceeded by chemisorption phenomenon. The data of adsorption thermodynamics indicate that the adsorption is an endothermic process. The regeneration and reuse of the hydrogels were possible. Thus, incorporation of the functionality of the cross-linker into chitosan within the same structure efficiently enhanced its features. It is a good manner for achieving appropriate series of efficient adsorbents which are considered as favorable nominees in the field of basic dyes removal.

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A chitosan hydrogel cross-linked with the least amount of trimellitic anhydride isothiocyanate (H1) and filled with 0.6 wt% of Single-Walled Carbon Nanotubes (SWCNTs) (H1/SWCNTs) was synthesized. Its structure was proven via Fourier transform infrared (FTIR) spectrum, X-ray diffraction (XRD) pattern, Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) observations. The adsorption capacity for Basic red 12 (BR 12) dye onto H1/SWCNTs at pH 7 and 25°C was 14.80 mg g-1 with a percent removal efficiency of 37.66% which were greater by 1.8 times than that obtained onto the parent hydrogel H1 (8.21 mg g-1and 20.90%, respectively). Its sorption capacity slightly enhanced with decreasing adsorption solution pH. The optimum adsorption capacity of 15.62 mg g-1 and the % removal efficiency of 39.76% were observed at pH 10 and 25°C. The adsorption of BR 12 dye by H1/SWCNTs at different temperatures and different dye solutions pH fitted to kinetic models of the pseudo-second order and the intraparticle diffusion. The adsorption isotherm for BR 12 dye by H1/SWCNTs fitted to the Langmuir isotherm model indicating the monolayer nature of adsorption. BR 12 dye adsorption onto H1/SWCNTs is an exothermic process. Thus, inclusion of SWCNTs into the matrices of functionalized chitosan hydrogel H1 improved its features. It is a suitable way to obtain a favorable composite having a highly performance adsorbing characteristic for cationic dyes removal.