Effective removal of phenol from wastewater using a hybrid process of graphene oxide adsorption and UV-irradiation

The focus of this work is the removal of phenol from water by graphene oxide (GO) nanoparticles, prepared by two different methods, through a hybrid adsorption–UV-irradiation process. The GO1 and GO2 were prepared using (H2SO4 and H3PO4) and (H2SO4, H3PO4, and HNO3), respectively. The effect of different parameters namely, pH, initial phenol concentration, and temperature on the adsorption process was investigated. Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize the prepared graphene oxides (GO1 and GO2). Various adsorption isotherm models were investigated including Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich adsorption isotherm models. The results showed that UV-irradiation had a positive effect on the adsorption process as the adsorption capacity increased. Additionally, maximum removal percentage was obtained at pH 2 for GO1 for both experimental sets. Similarly, GO2 without exposure to UV-irradiation showed the highest adsorption capacity at pH 2, while with the effect of UV-irradiation, the optimum pH was 6. Furthermore, increasing the initial concentration of phenol led to the increase in adsorption until it reached an equilibrium where the adsorption decreased and remained constant. Furthermore, the maximum adsorption capacity increased with the effect of UV exposure from 70.43% to 90.82% for GO1 and from 86.75% to 95.95% for GO2. Moreover, increasing the temperature caused the adsorption capacity to decrease and the thermodynamic results showed that the adsorption processes were feasible and spontaneous for GO1 (with and without UV exposure), and GO2 (only with UV exposure).