Chitosan composites for thionine dye adsorption

Chitosan (Cs) composites with carbon nanotube (Cs/CNT) and with activated carbon (Cs/AC) were prepared, characterised and applied for adsorption of thionine dye. Optimum adsorption conditions were adsorbent dose 0.1 g, dye concentration 30 mg/L, solution pH 5 and adsorption time 120 min. The overall results confirm the adsorption ability of Cs/CNT > Cs/AC > Cs where the adsorption ability of pure Cs reached 59.3%, 73.7% with Cs/AC and reached its maximum value of 98.5% with Cs/AC adsorbent material. Adsorption isotherm was studied by three isothermal models, and the results indicate the adsorption of thionine dye using the three adsorbents fit Freundlich > Langmuir > Dubinin–Radushkevich (D–R) model. The correlation coefficient (R2) obtained from Langmuir model did not fit the experimental data of thionine dye where (R2) obtained from Freundlich model indicate a multilayer adsorption with physicosorption type. The results of D–R isotherm model indicate that the physisorption nature of thionine dye was less than 8 kJ mol−1 indicating the physisorption nature of adsorption using Cs, Cs/AC and Cs/CNT.