Studies on synthesis and characterization of activated carbon prepared from cocoa theobroma cacao shell and its adsorption modeling of dissolved organic pollutants

Abstract

Adsorption is one of the most commonly used methods in water treatment processes. It is attractive due to it easy operation and the availability of a wide variety of commercial adsorbents. Adsorbents prepared from waste materials for the treatment of dyeing effluents have high significance in environmental sustainability. The objective of the present study is to characterize quality and evaluate the efficiency of using an agricultural byproduct, cocoa (Theobroma cacao) shell activated carbon as an adsorbent for the removal of acid (AR18, AB92), basic (RhB, MG) ,direct (CR, DB GL) and reactive (RO16, RB2) dyes. The BET surface area and pore size distribution of CSAC were determined by adsorption-desorption nitrogen isotherms at the temperature of 196°C using surface area analyzer. The equilibrium adsorption isotherms have been examined by applying Langmuir, Freundlich, Temkin, Harkins-Jura and Halsey isotherm models.. To test the recoverability of the adsorbed dye molecules, desorption experiments were done with neutral pH water, sulphuric acid (1M), sodium hydroxide (1M) and 50 % acetic acid (v/v) as the desorbing agents. Desorption of all dyes studied except DB GL in acetic acid (organic medium) indicated the adsorption of dyes on CSAC was through by activated chemisorption mechanism. Desorption of DB GL by alkaline medium confirmed the physisorption mechanism. The magnitude of activation energy (Ea) was evaluated for confirming the type of adsorption. Various thermodynamic parameters, such as Gibbs free energy change (and#916;G0), enthalpy change (and#916;H0) and entropy change (and#916;S0), were calculated, which indicated that the present system was spontaneous and endothermic process. A single stage batch adsorber design of the adsorption of all dyes onto CSAC has been studied based on the Langmuir isotherm equation. The results indicated that CSAC could be employed as an alternative to commercial adsorbents in wastewater treatment for the removal of colour and dyes. newline newline newline