Evaluation of reduced graphene oxide from cotton waste as an efficient phenol adsorbent in aqueous media

Abstract

The elimination of organic substances, as well as phenol, in conventional and biological process, has been considered a challenge for the petroleum industry due to the significant oxygen demand in the receiving bodies of water and its toxicity to aquatic life. In this work, reduced graphene oxide (rGO), obtained from cellulosic biomass (CB-rGO), as cotton waste, was employed as a phenol adsorbent in an aqueous solution simulating refinery effluent. The CB-rGO was characterized using HRTEM, RAMAN, XRD, FTIR, BET and Zeta analysis. The behavior of variables such as pH, contact time, temperature, CB-rGO mass and adsorbate concentration on the characteristics of the adsorption process were continuously investigated. These parameters of the adsorption process were evaluated across a range of adsorbent concentrations from 100–300 mg.L^− 1, pH in the range of 2–11, contact time of 20–60 min and temperature of 20–60°C. The adsorption isotherm data were better described by the Freundlich equation compared to the Langmuir and Sips models, despite the negligible difference in R² values. Additionally, the kinetics study of confirmed pseudo-second order as the most appropriate model. Mechanism diffusion was analyzed using the Boyd model and confirmed to be the rate-limiting step in the adsorption process. The endothermic nature of this CB-rGO adsorption process with phenol was confirmed by verifying the thermodynamic data. This successful removal of phenol from synthetic effluent highlights the promising potential of this emerging adsorbent compared to other materials identified to remove this contaminant.