Rarasaponin-bentonite-activated biochar from durian shells composite for removal of crystal violet and Cr(VI) from aqueous solution.

This paper presents the preparation of composite material and its application for the adsorption of crystal violet and Cr(VI) from aqueous solution onto acid-activated bentonite (AAB) and rarasaponin-bentonite-activated biochar from durian shells composite (RBAB). The influence of initial pH of the solution and the temperature of adsorption on the adsorbents adsorption performance was also studied. Langmuir and Freundlich models could represent the adsorption equilibria equally well. Thermodynamic parameters such as ∆G°, ∆H°, and ∆S° were evaluated based on the adsorption isotherms. The values of ∆G°, ∆H°, and ∆S° for crystal violet adsorption system demonstrate behavior contrary to the Cr(VI) adsorption system. Where crystal violet adsorption is preferred at high temperatures with qmax, value is 518.64 mg/L; while adsorption Cr(VI) is better at low temperature with qmax, value is 106.30 mg/L. Pseudo-first-order and pseudo-second-order kinetic models could represent the kinetic data well.