Adsorption and thermodynamic studies of hazardous azocoumarin dye from an aqueous solution onto low cost rice straw based carbons

Abstract A new hazardous azocoumarin dye has been synthesized and characterized using different spectroscopic techniques. The adsorption of hazardous azocoumarin dye onto low cost rice straw based carbons (RSC) was investigated in an aqueous solution in a batch system with respect to initial dye concentration, contact time, solution pH and temperature. Surface modification of rice straw using scanning electron microscopy (SEM) was obtained. The surface area and pore volume of RSC were determined by nitrogen adsorption/desorption experiments at 77 K and found to be 67.4 m 2  g − 1 and 0.134 cm 3  g − 1 , respectively. Experimental data indicated that the adsorption capacity of RSC for azocoumarin dye was higher in acidic rather than in basic solutions. 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 and found to be + 15.56 kJ mol − 1 indicating that the adsorption is physisorption. The pseudo-first-order and pseudo-second-order kinetic models were used to describe the kinetic data. The dynamic data fitted the pseudo-second-order kinetic model well. The thermodynamics of the adsorption indicated spontaneous and exothermic nature of the process. The results indicate that RSC could be employed as low-cost material for the removal of acid dyes from an aqueous solution.