Biosorption of Acid Orange 7 (AO7) dye by canola waste: equilibrium, kinetic and thermodynamics studies

In order to study the availability of canola residue for biosorption of acid orange 7 (AO7) from aqueous solution, batch experiments were performed for thermodynamic and kinetic studies. Physical characterization of canola samples was determined by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and Brunauer–Emmett–Teller. The equilibrium adsorption data were analyzed using Langmuir and Freundlich isotherms. Langmuir isotherm was well fitted with the experimental adsorption data. Kinetic analysis were performed using pseudo-first order, pseudo-second-order and intra-particle diffusion models. The kinetic analysis indicated that the adsorption kinetic data of AO7 fit better to the pseudo-second-order kinetic model. In addition, the existence of three steps were observed during the adsorption experiment. The first stage represented the transport of AO7 molecules from the surface to pores of the adsorbent external structure. The second stage showed invasion of the molecules into the internal structure of the adsorbent. The adsorption of the molecule on the interior surface of the adsorbent was the last step. The thermodynamic data obtained at different temperatures were used to calculate standard free energy changes (∆G°), standard enthalpy change (ΔH°), and standard entropy change (ΔS°). All ΔG° values are ranged from –4.987 to –0.045 kJ/mol; ΔH° and ΔS° values of canola biomass were 29.62 kJ/mol and 0.107 J/mol K, respectively. Based on the calculation, adsorption of AO7 onto canola biomass was a spontaneous and endothermic process.