The wastage of the cotton stalks (Gossypium hirsutum L.) as low-cost adsorbent for removal of the Basic Green 5 dye from aqueous solutions

Abstract

Abstract Cotton stalks (Gossypium hirsutum L.) waste was investigated as a low-cost and effective adsorbent for the adsorption of Basic Green 5 dye from aqueous solution. The effects of pH solution, initial dye concentration, contact time, sorbent dosage and temperature on the adsorption parameters were investigated. The Langmuir, Freundlich and Dubinin–Radushkevich adsorption models were evaluated using the experimental data. The maximum adsorption capacity was found to be 42.37 mg g−1 from the Langmuir isotherm model at 20 °C. The dimensionless separation factor (RL) values lie between 0.129 and 0.423, indicated favorable adsorption. The adsorption rate data were analyzed according to the Lagergren pseudo-first- and pseudo-second-order kinetic models. It was found that kinetic followed a pseudo-second-order model. The negative values of the ΔG° at 293–323 K and the positive value of the ΔH° (13.585 kJ mol−1) indicate that the sorption process is spontaneous and endothermic in nature. The positive value of ΔS° (0.0467 kJ mol−1 K−1) shows the increasing randomness during adsorption process. The mean adsorption energy from Dubinin–Radushkevich equation was found to be 11.63 kC mol−1, indicating that the adsorption of the Basic Green 5 by cotton stalks occurred through chemical interaction mechanism. The offered mechanism of adsorptive process of the Basic Green 5 dye on a surface of the sorbent, obtained on the basis of cotton stalks, considers forming a complex between dye and sorbent.