Adsorption characteristics of 1,2,4-trichlorobenzene, 2,4,6-trichlorophenol, 2-naphthol and naphthalene on graphene and graphene oxide

Adsorption of 1,2,4-trichlorobenzene (TCB), 2,4,6-trichlorophenol (TCP), 2-naphthol and naphthalene (NAPH) on graphene (G) and graphene oxide (GO) was investigated using a batch equilibration method and micro-Fourier transform infrared spectroscopy. All adsorption isotherms of four aromatics on G and GO were nonlinear, indicating that except for hydrophobic interaction, some specific interactions were involved in adsorption. For G, four aromatics had similar adsorption capacity at pH 5.0 in despite of their different chemical properties. A series of pH-dependent experimental results showed that 2-naphthol had higher adsorption capacity on G at alkaline pH than that at acidic pH. Theoretical calculation ascribed this to higher π-electron density of anionic 2-naphthol than that of neutral 2-naphthol, which facilitated the π–π interaction formation with G. For GO, the adsorption affinity of four aromatics increased in the order: NAPH < TCB < TCP < 2-naphthol. FTIR results revealed that TCB, TCP and 2-naphthol were adsorbed on G mainly via π–π interaction. In contrast, high adsorption of TCP and 2-naphthol on GO was attributed to the formation of H-bonding between hydroxyl groups of TCP and 2-naphthol and O-containing functional groups on GO.