Aplicação do nanomaterial óxido de grafeno como adsorvente para remoção de metais pesados em soluções aquosas

Abstract

Heavy metals are toxic to human health and to other living beings, for its bioaccumulation capacity and transport within the food chain. The removal of heavy metals from polluting sources is of fundamental importance in order to guarantee the environmental quality of aquatic systems. Several treatment methods have been applied to remove these types of pollutants from liquid effluents. Adsorption is considered an efficient, selective and economical separation method for removing heavy metals in effluents. The adsorbent is the key point of the adsorptive process, since its physicochemical properties will be responsible for capturing contaminants in the medium. Graphene oxide (GO) has been a promising material in adsorption studies for heavy metal removal. In this work, GO was characterized by FTIR and Raman spectroscopy, SEM and point of zero charge (PCZ). GO characterization has shown characteristic of graphene-based materials, indicating that graphite oxidation and exfoliation occurred successfully. The adsorption study of Cd (II) and Pb (II) by GO were carried out in batch systems. The effect of adsorbent mass, contact time and initial metal concentration were evaluated. Langmuir, Freundlich and Sips models were applied to the equilibrium data. Adsorption kinetics of Cd (II) and Pb (II) were evaluated by Pseudo-First Order, Pseudo-Second Order and Weber-Morris intraparticular diffusion models. The Freundlich model described well Pb (II) adsorption by OG (R² = 0.96), while Cd (II) has shown a linear isotherm. Pseudo-First and Pseudo-Second Order models presented a good fit to the kinetic data (R² > 0.992). GO was successfully used in 5 adsorption cycles, after desorption carried out with NaOH solutions, maintaining high efficiency (>90%). The nanoadsorbent showed high potential for removing Cd (II) and Pb (II) in aqueous media. However, due to its high hydrophilicity, the functionalization or production of easily separated composites is recommended.