Interactive effect of garlic straw on the sorption and desorption of Direct Red 80 from aqueous solution

The present research describes the sorption potential of low cost and easily available garlic straw for the removal of an azo textile dye, Direct Red 80 (DR 80), which is frequently used in the textile industry, from aqueous phase. The adsorbent was first subjected to several structural and chemical characterizations by FTIR, 13C NMR, TGA, XRD and SEM. The influence of variables including pH, concentration of the dye and amount of adsorbent, particle size, contact time and temperature on the dye removal has been investigated. Three kinetic models were used to describe the sorption process. Three isotherm models were applied to evaluate the sorption equilibrium, and its thermodynamic parameters were calculated. More than 85% removal efficiency was obtained within 100 min at adsorbent dose of 0.2 g per 10 mL for initial dye concentration of 100 mg mL−1. The maximum capacity of the garlic straw for sorption of DR 80 was 107.53 mg g−1 at pH 4 and 323 K. The sorption kinetic data were found to be in accordance with pseudo-second order kinetics. The sorption process and equilibrium of DR 80 were well fitted by Langmuir model. Calculation of various thermodynamic parameters such as free energy change, ΔG° enthalpy change, ΔH°; and entropy change, ΔS° indicate feasibility and endothermic nature of DR80 sorption. Desorption experiments were conducted for regenerating garlic straw which exhibited higher desorption capacity after sorption DR 80 using NaOH at pH 11. Overall, the relatively low cost and high capabilities of raw garlic straw make him a potentially attractive sorbent for the removal of DR 80 from the aqueous solution.