Mechanistic insights into Pb(II) removal from aqueous solution by green reduced graphene oxide

As one of the important contaminants in wastewater, Pb(II) becomes a severe public health problem because of its non-biodegradable and persistent nature. In this study, reduced graphene oxide (RGO) prepared using green tea extract was successfully used to remove Pb(II) from aqueous solutions. A 96.6% of Pb(II) was removed at 10 mg/L Pb(II) and 0.4 g/L RGO with pH 4.5 at 30 °C, and the adsorption of Pb(II) by RGO followed pseudo-second-order kinetics. To confirm the removal mechanism, various methods (Transmission Electron Microscopy, Raman spectroscopy and X-ray diffraction) were used to characterize RGO before and after Pb(II) adsorption. The results showed that the surface of RGO after Pb(II) adsorption became rougher, and the interlayer spacing increased from 0.36 nm to 0.40 nm, indicating that Pb(II) was adsorbed on the surface and between the layers of RGO. Finally, the adsorption mechanism of Pb(II) by RGO was proposed, Pb(II) was adsorbed on the surface of RGO via the electrons on the π-bond on RGO and the interaction of Pb(II) with oxygen-containing functional groups, which were supported by the Fourier Transform Infrared and X-ray photoelectron spectroscopy results.