Adsorption of hexavalent chromium from aqueous solutions by graphene modified with cetyltrimethylammonium bromide.

In this study, cetyltrimethylammonium bromide was chosen to modify graphene, which was prepared using a modified Hummers' method. The characteristics of graphene and modified graphene were characterized by X-ray diffraction, Fourier transform infrared spectrum, X-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy. The effect factors including pH, contact time, temperature, and dosage on the adsorption properties of Cr(VI) onto graphene and modified graphene were investigated. Batch experiments were conducted to evaluate the adsorbance of Cr(VI) from aqueous solution using graphene and modified graphene as the adsorbent under different conditions. The results revealed that the optimal pH for the adsorption was about 2, and the best suitable temperature was at 293 K. The adsorption processes were rapid within the first 5 min and reached equilibrium in about 40 min. The adsorption kinetics fitted well with pseudo-second-order model. The adsorption capacity of Cr(VI) on modified graphene inferred from the Langmuir model was 21.57 mg/g at 293 K. The thermodynamic parameters indicated that the adsorption of Cr(VI) onto modified graphene was an exothermic and spontaneous process.