Fig. 1 shows the XRD patterns of the as-synthesized samples. All the diffraction peaks in Fig. 1a and e can be indexed to the tetragonal BiOI phase (JCPDS card no. 10-0445) with lattice constants of a=b=3.994 Å, c=9.149 Å and the tetragonal BiOBr phase (JCPDS card no. 09-0393) with lattice constants of a= b=3.926 Å, c=8.103 Å, respectively. No characteristic peaks of other crystalline impurities were observed. With increasing amounts of BiOBr in the BiOBr/BiOI composites (Fig. 1b–d), the