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.
Highlights
Wastewater containing dyes is very difficult to be treated, since the dyes are recalcitrant organic molecules, resistant to aerobic degradation, and stable to light, heat and oxidizing agents (Kyzas et al 2012)
The results show that the adsorption process is spontaneous and endothermic nature
The value of the maximum experimental sorption capacity calculated from the Langmuir equations is equal to 42.37 mg g−1, which is close to value of equilibrium sorption capacity experimentally obtained from sorption isotherm (33.2 mg g−1, Fig. 2), whereas the calculated value KF (6.127 mg g−1), corresponding to the sorption capacity of a sorbent, differs from the experimental value of sorption capacity
Summary
Wastewater containing dyes is very difficult to be treated, since the dyes are recalcitrant organic molecules, resistant to aerobic degradation, and stable to light, heat and oxidizing agents (Kyzas et al 2012). Results indicated that according to the Langmuir isotherm, the maximum sorption capacities are 37.59 and 34.48 mg g−1 for Basic Blue 3 and Reactive Orange, respectively. Thermodynamic calculations demonstrated that the adsorption process of Basic Green 5 onto glucose biochar occurred spontaneously (− ΔG°) was endothermic nature (ΔH° = + 80.34 kJ mol−1) and resulted in increased system randomness (ΔS° = + 0.386 kJ mol−1). Batch studies were performed to address various experimental parameters like, contact time, temperature and adsorbent dosage for the removal of dye. The research results on the removal of the Basic Green 5 from water solutions by cotton stalk, which is an agrowaste material, were given in the presented work. The effects of the sorbent dosage, initial dye concentration, contact time and temperature were studied, and equilibrium isotherm data were analyzed by the Langmuir, Freundlich and Dubinin–Radushkevich isotherm models. The sorption properties of the cotton stalks waste toward Basic Green 5 are executed for the first time, and it defines the novelty of this work
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