Adsorption of hazardous azocoumarin from aqueous solution using activated carbon made fromrice straw

Batch experiments were conducted to study the adsorption of hazardous azocoumarinonto low cost activated carbon made from rice straw (ACRS) in aqueous solution with respect to concentration of adsorbate, adsorbent dosage, contact time, solution pH and temperature. Surface modification of rice straw using scanning electron microscopy (SEM) was obtained. Surface area and pore volumes of ACRS were determined by nitrogen adsorption/desorption experiments at 77 K. Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were determined. The activation energy of adsorption was also evaluated for the adsorption of azocoumarinonto ACRS. The kinetic data obtained with different initial concentration and temperature were analyzed using a pseudo-first-order and pseudo-second-order equations. The activation energy, change of free energy, enthalpy and entropy of adsorption were also evaluated for the adsorption of azocoumarinonto ACRS. The thermodynamics of the adsorption indicated spontaneous and exothermic nature of the process. The results indicate that ACRS could be employed as low-cost material for the removal of acid dyes from aqueous solution.