XRD analysis is conducted to reveal the crystalline of all
photocatalysts, as illustrated in Fig. 2. The loading of Pt obviously
does not change the XRD pattern of the support, namely
SrTiO3:Rh [27] and CuGaAlO4 [26]. This is due to the fact that Pt
loading is very small and highly dispersed on the supported surface.
For commercial WO3, the resulted XRD pattern is similar to
that of orthorhombic WO3 (JCPDS file 20-1324) [26]. TEM observations
are consistent with the results of XRD. From the observations,
several well-dispersed Pt nanoparticles with size of near 1–3 nm
are located on the surface of both Pt/SrTiO3:Rh and Pt/CuAlGaO4
photocatalysts (Fig. 3). Moreover, Pt loading does not change the
shape and morphology of these supported photocatalysts. X-ray
photoelectron spectroscopy (XPS) was also conducted in order to
investigate in more detail the loading of Pt. Fig. 4 reveals two possible
peaks at 73.6–74.1 and 77–77.4 eV, which are attributed to
4f7/2 and 4f5/2 of Pt oxide, respectively