Adsorption of phenanthrene and 1-naphthol to graphene oxide and L-ascorbic-acid-reduced graphene oxide: effects of pH and surfactants

In this study, reduced graphene oxide (RGO) was synthesized by (L)-ascorbic acid reduction, which was a relatively mild and environmental friendly reduction method, and the adsorption of organic contaminants was compared to graphene oxide (GO) to probe the potential adsorption mechanisms. The morphology properties of GO and RGO were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared transmission (FTIR), Raman spectrometer, transmission electron microscope (TEM), and scanning electron microscopy (SEM). The adsorption affinities of GO and RGO for phenanthrene and 1-naphthol were studied in batch experiments. The effects of pH and surfactants were also assessed. The results demonstrated that RGO reduced by (L)-ascorbic acid show significantly greater adsorption affinity for both phenanthrene and 1-naphthol than GO, and even greater than most of RGOs that reduced by the strong reductive reagents. This was mainly attributed to the hydrophobic interaction, pi-pi interaction, and H-bonding between graphene sheets and organic contaminants. Both GO and RGO showed stronger adsorption to phenanthrene than to 1-naphthol. The adsorption of 1-naphthol increased with decreasing pH and reached a maximum around pH = 7.34. The surfactants, sodium dodecyl benzene sulfaonate (SDBS) and cetyltrimethyl ammonium bromide (CTAB), had negligible influence on adsorption to GO. Note that CTAB significantly inhibited the adsorption of phenanthrene/1-naphthol on RGO, which could be attributed to the pore blockage effect. In addition, RGO could be regenerated and reused with high recyclability over five cycles. The present study suggests that RGO obtained via (L)-ascorbic acid reduction can be deemed as a promising material for organic contaminated wastewater treatment.