A composite photocatalyst of zinc oxide (ZnO) nanoparticles decorated with different content of reduced graphene oxide (rGO) was prepared via a simple and facile one-step method in this paper. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectra, and UV–Vis diffuse reflection spectroscopy (UV–Vis DRS) were used to characterize the crystal structure, morphology and optical properties of the rGO–ZnO composite photocatalyst. The photocatalytic properties of the composites were investigated using methyl orange (MO), a typical orange compound, as a test pollutant. The results showed that rGO–ZnO composites displayed significantly enhanced photocatalytic activity in MO degradation than pure ZnO, and the pseudo-first-order kinetic constant on the optimal rGO–ZnO composite was 14 times as great as that on pure ZnO. The enhanced photocatalytic ability of the rGO-ZnO composites was mainly benefited from the high specific surface area and high conductivity of rGO, which facilitated efficient charge separation in the rGO-ZnO nanocomposite.

    Abstract
    1 Introduction
    2 Experiment
        2.1 Materials
        2.2 Preparation of graphene oxide sheets (GO)
        2.3 Preparation of ZnO
        2.4 Preparation of rGO–ZnO composite
        2.5 Material characterization
        2.6 Measurements of photocatalytic activity
    3 Results and discussion
        3.1 Crystal structures
        3.2 Morphology characterizations
        3.3 Raman spectra analysis
        3.4 UV–Vis DRS analysis
        3.5 Photocatalytic activity
        3.6 Photocatalytic mechanism
    4 Conclusions
    Acknowledgements 
    References

• Yingdi Ma(College of Materials Science and Engineering, Hunan University, Hunan Province Key Laboratory for Spray Deposition Technology and Application, Hunan University)
• Yanli Liu(College of Materials Science and Engineering, Hunan University, Hunan Province Key Laboratory for Spray Deposition Technology and Application, Hunan University)