Abstract
Adsorbent material was prepared using distillers’ grains (DG), which is a waste product of distilleries. The DG was pre-treated with NaOH and esterification-modified with CS2, which is a commonly used anionic modifier. The structure and morphology of the adsorbent was characterized by FTIR, XRD, EDS, SEM, BET, and zeta potential. The related mechanism of adsorption of malachite green (MG) onto modified distiller’s grains (MDG) was studied by adsorption experiments and molecular simulation techniques. The experimental results showed that CS2 successfully modified the DG fiber, and simultaneously yielded the MDG with a uniform pore distribution. MDG had a considerable adsorption capacity of 367.39 mg/g and a maximum removal rate of 96.51%. After eight adsorption–desorption cycle experiments, the adsorption removal rate of MDG to MG dye remained at 82.6%. The adsorption process could be fitted well by a pseudo-second-order kinetic model (the correlation coefficient R2 > 0.998) and Freundlich isotherm adsorption equation (the correlation coefficient R2 > 0.972). Moreover, the adsorption of MG dye by MDG is a spontaneous, endothermic, and increased entropy process. The results of molecular simulation showed that the mechanism of MG molecules onto MDG was mainly chemical adsorption. The adsorption performance of MG onto MDG was better and more stable than DG. Molecular simulation also provided a theoretical guidance of MDG adsorption–desorption for the research on recycling of DG resources.
Highlights
Distillers’ grains (DG) are residues obtained from the solid-state distillation and brewing processes of fermented grains, usually generated due to incomplete fermentation
FTIR and XRD results evidenced that the groups in modified distiller’s grains (MDG) have changed, but that modification treatment did not change the structure of cellulose
The increase in initial concentration of malachite green (MG) in the wastewater resulted in an increase in adsorption capacity and a decrease in removal rate
Summary
Distillers’ grains (DG) are residues obtained from the solid-state distillation and brewing processes of fermented grains, usually generated due to incomplete fermentation. Malachite green (MG), known as alkaline green, is a triphenylmethane-type dye [3] DG fibers can form modified distiller’s grains (MDG) via chemical modification and react with the cationic groups of MG, which can further enhance the adsorption performance of distillers’ grains. In the existing studies, the adsorption efficiency and adsorption capacity of MDG are not very high, and is only used once, without multiple cycles of adsorption If it can be reused many times, its resource utilization rate will be greatly improved. The present work can provide a reference for the high value-added comprehensive utilization of DG as a waste product of distilleries. This work provides a method for the disposal of wastewater containing triphenylmethane-type dyes using the concept of “disposing waste with waste”
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