Graphene as an Efficient and Reusable Adsorbent Compared to Activated Carbons for the Removal of Phenol from Aqueous Solutions

The adsorption capacity of graphene for removing phenol from aqueous solutions was evaluated and compared to those obtained for three different commercial activated carbons. In this study, graphene, W-35 activated carbon, RB2H2 activated carbon, and Nuchar granular activated carbon were investigated. Various techniques such as X-ray diffraction, BET surface analysis, and scanning electron microscopy were used to characterize the adsorbents. The adsorption of phenol onto graphene was investigated under different experimental conditions including temperature, solution pH, adsorbent dosage, and initial concentration of phenol. For comparison, adsorption experiments of phenol onto the activated carbons were also conducted. The adsorption of phenol onto graphene and activated carbons could be described by the pseudo-second-order kinetic model and the Langmuir equilibrium isotherm. The maximum adsorption capacities predicted by the Langmuir isotherm for graphene, W-35, RB2H2, and Nuchar granular activated carbons were found to be 233, 200, 91, and 167 mg/g, respectively. The thermodynamic study demonstrated that the adsorption of phenol onto graphene and activated carbons is a spontaneous and exothermic process. Regeneration of graphene was found to be possible using sodium hydroxide or methanol as eluents over five adsorption-desorption cycles.