Removal of methylene blue and acid orange 7 from aqueous solutions by activated carbon coated with zinc oxide (ZnO) nanoparticles: equilibrium, kinetic, and thermodynamic study

Abstract

Various industries like textile, plastic, pulp, and paper produce dye containing wastewaters that have harmful effects on the environment as well as human health. The aim of this study was to investigate the effect of granular activated carbon (AC) coated by zinc oxide nanoparticles (ZnO-np) in the removal of dyes, methylene blue (MB) and acid orange 7 (AO7), from aqueous solutions. The morphology of the AC and AC–ZnO was determined by SEM and the FTIR spectra confirmed the strong interaction between AC and ZnO. The effect of various parameters, such as nanoparticles loading onto the AC, pH, contact time, dye concentration, ion strength, temperature, and adsorbent regeneration, was studied on the adsorption. The results showed that the surface structure of the raw AC was porous and had irregular shapes, but the surface of the modified AC (AC–ZnO) due to the homogenous coating of the ZnO-np onto the AC was approximately uniform and regular. The sorption capacity and optimum contact time for the removal of MB (32.22 mg/g) and AO7 (32.13 mg/g) by AC–ZnO were obtained as 32.22 mg/g during 120 min and 32.13 mg/g over 150 min, respectively. The optimum pH for the sorption of MB occurred at pH 11 and for AO7 was obtained at pH 3. The results also showed that Langmuir isotherm and pseudo-second-order kinetic models fitted the experimental data better than other isotherm and kinetic models. It is obviously clear that AC–ZnO, in comparison with raw AC, was more efficient sorbent for the removal of MB and AO7 and it can be proposed for the removal of these dyes from aqueous solutions.