Valorization of cardboard waste adsorbents for efficient malachite green removal – equilibrium, kinetics, and thermodynamics

Abstract

ABSTRACT This work was aimed at evaluating the adsorptive properties of cardboard waste-based adsorbents for malachite green removal. The adsorbents were produced through hydrothermal carbonization and/or phosphoric acid activation and characterized for specific area, surface morphology, and functional groups. Batch adsorption was performed at varying concentrations, contact times, and temperatures. Results show that the activated carbon derived from cardboard waste with surface area of 196 m2/g exhibits a 134 mg/g (31.6%) adsorption capacity of malachite green. On the other hand, the cardboard hydrochar displays a peak capacity at 400 mg/g (94%) due to dye precipitation before the magnitude subsides to 47 mg/g (5.7%) at higher concentration of 820 mg/L. The equilibrium data of activated carbons could be well described by the Langmuir model, while the kinetics fitted well with the pseudo-second order model. The adsorption of malachite green is endothermic and spontaneous at high solution temperature.