Green removal of phenolic azo dye from aqueous solutions using rice straw fly ash

The present adsorption of phenolic azo dye onto rice straw fly ash (rsfa) from aqueous solutions was investigated,in which the influence of solution ph,contact time,concentration of adsorbate,adsorbent dosage and temperature were investigated. more than 85 % removal efficiency was obtained within 50 min. at an adsorbent dose of 0.05 g for initial dye concentration of 30-100mg/l at ph 2. the experimental equilibrium data were analyzed using two common adsorption models: langmuir and freundlich. the results revealed that freundlich isotherm fits the experimental results well.kinetic analysis was conducted using pseudo-first-order and pseudo-second-order models. the activation energy of adsorption was also evaluated and found to be +17.68 kj.mol-1 indicating that the adsorption is physisorption. all δg° values were negative; the δh° and δs° values of rsfa were -19.78 kj.mol-1 and 0.039 j.mol-1.k-1,respectively,indicating that the adsorption was feasible,spontaneous and exothermic process in nature.