g-C3N4-BiOBr Composites: Synthesis and High Photocatalytic Performance under Visible-Light Irradiation

A novel p-n heterojunction composite photocatalyst of graphitic carbon nitride-BiOBr (g-C3N4-BiOBr) fabricated by deposition of BiOBr nanoflakes on g-C3N4 surface were presented. The structures and properties of as-synthesized samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), UV-Vis diffuse reflection spectroscopy (DRS) and photoluminescence (PL). The photocatalytic activity was evaluated by degradation of methyl orange (MO) aqueous solution under visible-light irradiation. The study results show that the composite photocatalysts were consisted of two components of g-C3N4 and BiOBr, and the BiOBr nanoflakes can be rapidly deposited on g-C3N4 sheet surface. In comparison with pure BiOBr and g-C3N4, the g-C3N4-BiOBr composite photocatalysts shows more absorption intensity within the visible light range and the sorption edge shifts to lower energy direction. The optimum photocatalytic activity of the 2:8 g-C3N4-BiOBr composite sample was 1.8 and 1.2 times as high as those of individual g-C3N4 and BiOBr after 100 minutes irradiation with visible light. After reusing 4 cycles, the photodecomposition rate of MO still remains 84%, which proves the enhancement of photocatalytic activity and stability of the composite photocatalyst. The PL emission intensity of the composite photocatalyst decreased remarkably due to the suppression of photogenerated charges recombination. The enhancement in both photocatalytic performance and stability was induced by a synergistic effect, including the improved charge separation efficiency of the photoinduced electron-hole pair at the interface of g-C3N4 and BiOBr, the inhibition of photoinduced charge recombination and the extension of the absorption bands comparing with the sole component. A series of radical trapping experiments demonstrate that the holes should be the main active species in MO photodegradation and a possible photocatalytic mechanism is proposed.