depicts the X-ray diffraction (XRD) patterns of all photo-catalysts and their references. In details, Fig. 1a reveals patterns ofthe prepared GaN:ZnO sample and its precursors of -Ga2O3andZnO. Clearly, the position of the d (1 0 0) diffraction peak of GaN:ZnOshifted slightly to higher angles (2-theta), in comparison with thatof ZnO. Moreover, no peaks can be assigned to either Ga2O3or ZnO,indicating that complete nitridation of the precursors was achievedby nitriding a mixture of -Ga2O3and ZnO at 1125 K for 15 h. Thisphenomenon is consistent with that observed in previous stud-ies [19,20]. There is no noticeable change in their XRD patternsbefore and after loading the Ni/NiO as co-catalysts, (Fig. 1b), sug-gesting that Ni/NiO co-catalysts did not change the structure ofbulk. However, the presence of Ni/NiO co-catalyst slightly reducesthe GaN:ZnO crystallites. All the peaks of GaN:ZnO have inten-sity higher than that of GaN:ZnO–Ni/NiO. Additionally, we alsoobserved no change in the XRD pattern of GaN:ZnO–Ni/NiO after8 h of reaction, indicating that this photocatalyst was essentiallystable in the reaction. Fig. 1c shows that the XRD pattern of WO3which is similar to that of orthorhombic WO3(JCPDS file 20-1324)[13]. Obviously, the peaks of Pt are not detected, showing that Ptloading is very small and highly dispersed on the WO3surface.