Preparation and characterization of activated carbons from winemaking wastes and their adsorption of methylene blue

Abstract

This work reports the preparation of activated carbons via the hydrothermal treatment at 523 K/30 bar of two common winemaking wastes: bagasse and cluster stalks. The hydrothermal carbons produced by the above treatment were turned into activated carbons via their exposure to KOH and carbonization at 1073 K. These were then subjected to Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy examination, and the determination of their Brunauer–Emmett–Teller surface area. The ability of the activated carbons to adsorb methylene blue in aqueous solution was then examined, determining the influence of time, methylene blue concentration, and temperature. Equilibrium conditions were reached for reaction times between 180 and 240 min at pH 7. The adsorption isotherms were found to better fit the Langmuir than the Freundlich model, and the adsorption kinetics fitted a pseudo-second-order model. The maximum adsorption at 303 K was 714–847 mg g−1. Thermodynamic studies revealed the adsorption of methylene blue to be spontaneous and exothermic. These results show that high-quality activated carbons can be produced from winemaking waste.