In this study, Ni nanoparticle supported by graphene oxide (GO) (Ni-GO) is successfully synthesized through hydrothermal synthesis and calcination, and Cr(VI) is extracted from aqueous solution. The morphology and structure of Ni- GO composites are characterized by scanning electron microscopy (SEM), trans mission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). High-resolution transmission electron microscopy (HRTEM) and XRD confirms the high dispersion of Ni nanoparticle after support by GO. Loading Ni on GO can obviously enhance the stability of Ni-GO composites. It can be calculated from TGA that the mass percentage of Ni is about 60.67%. The effects of initial pH and reaction time on Cr(VI) removal ability of Ni-GO are investigated. The results indicate that the removal efficiency of Cr(VI) is greater than that of bared GO. Ni-GO shows fast removal capacity for Cr(VI) (<25 min) with high removal efficiency. Dynamic experiments show that the removal process conforms to the quasi-second order model of adsorption, which indicates that the rate control step of the removal process is chemical adsorption. The removal capacity increases with the increase of temperature, indicating that the reaction of Cr(VI) on Ni-GO composites is endothermic and spontaneous. Combined with tests and characterization, the mechanism of Cr(VI) removal by rapidly adsorption on the surface of Ni-GO and reduction by Ni nanoparticle is investigated. The above results show that Ni-GO can be used as a potential remediation agent for Cr(VI)-contaminated groundwater.

Abstract
1. Introduction
2. Materials and Methods
    2.1 Materials
    2.2 Preparation of Ni-GO
    2.3 Sample characterization
    2.4 Batch experiments
3. Results and Discussion
    3.1 Characterization results
    3.2 Removal of Cr(VI) by Ni-GO
    3.3 XPS analysis
4. Conclusions
References

• Wan-Xia Wang(Key Laboratory of and Functional Molecule Design and Interface Process, Anhui Jianzhu University)
• Dong-Lin Zhao(Key Laboratory of and Functional Molecule Design and Interface Process, Anhui Jianzhu University) Corresponding author
• Chang-Nian Wu(Key Laboratory of and Functional Molecule Design and Interface Process, Anhui Jianzhu University)
• Yan Chen(Key Laboratory of and Functional Molecule Design and Interface Process, Anhui Jianzhu University)
• Won-Chun Oh(Department of Advanced Materials Science & Engineering, Hanseo University) Corresponding author