Impact of synthesis conditions on Pb(II) removal efficiency from aqueous solution by green tea extract reduced graphene oxide

Abstract

Graphene has a great potential in environmental remediation due to its unique physical and chemical properties. However, the relationships between synthetic conditions and contaminant removal are still unclear. In this study, a biogenic method was used for the reduction of graphene oxide (GO) using green tea extract and the reduced graphene oxide (RGO) produced was subsequently used to remove Pb(II) from aqueous solution. Hence, the impact of bioreduction synthetic conditions of RGO on Pb(II) removal efficiency was examined. The new findings included (1) that reduction of GO by green tea (GT) extract at a ratio of 2:1 (GO:GT), 80 °C and pH 8, led to a RGO material capable of removing 97.2% of a 10 mg·L−1 Pb(II) solution under the adsorption conditions of pH 4.5 and a RGO dose of 0.4 g·L−1 at 30 °C; (2) characterization results showed good dispersion of RGO, and removal of oxygen functional groups from GO, increased Pb(II) adsorption. Pb(II) removal efficiency was largely dependent on reduction conditions during synthesis of RGO; where efficient removal of oxygen-containing groups during reduction favored Pb(II) removal. Furthermore, during biogenic synthesis RGO was also capped by biomolecules such as polyphenols which decreased aggregation leading to enhanced Pb(II) removal efficiency.