The investigation of the photocatalytic efficiency of spherical gold nanocages/TiO2 and silver nanospheres/TiO2 composites

The paper presents the influence of spherical Ag, Au nanoparticles (AgNS) and Au spherical nanocages (AuIND) on the photocatalytic properties (degradation of organic compounds and H2 production) of commercial TiO2 (Evonik Aeroxide P25, Aldrich anatase - AA and Aldrich rutile - AR). The resulted TiO2-based composites were characterized by different techniques, such as XRD (X-ray Diffraction), TEM (Transmission Electron Microscopy), DRS (Diffuse Reflectance Spectroscopy) and X-ray Fluorescence (XRF). For the synthesis of composites in situ (IS) and impregnation (IMP) procedures based on the chemical reduction method were used. The degradation of well-known model pollutants (oxalic acid and phenol) was carried out to find correlation between the applied synthesis procedure and the obtained photocatalytic activities. In all the cases oxalic acid was degraded efficiently by nearly all the composite materials (and showed superior activity compared to the base photocatalysts), while in the case of phenol the noble metal containing nanostructures were less efficient then the corresponding commercial TiO2. Furthermore, it was concluded that in the case of oxalic acid degradation, the nature of the used noble metals did not influence significantly the activity. From the chosen synthesis approaches IS method resulted the most efficient composites. When phenol was degraded, the formation of hydroxylated intermediates was favored instead of the phenol degradation. Under these circumstances, AA and AR based composites were the best when considering simultaneously both the intermediate formation and degradation efficiency values. For photocatalytic H2 production the most efficient photocatalyst was the AuIND_P25_IS, which points out the effectiveness of the IS method.