Influence of the surface structure of the TiO2 support on the properties of the Au/TiO2 photocatalyst for water treatment under visible light

Plasmonic composites combining titanium dioxide (TiO2) with highly dispersed noble metal nanoparticles have attracted great interest as they exhibit improved photocatalytic performance compared to the bare TiO2. In this article, TiO2–Au composite nanorods were synthesised by wet impregnation in combination with calcination. The obtained plasmonic composites were characterized by TEM, SEM, XRD, N2 sorption, UV-Vis diffuse reflectance spectroscopy (UV-Vis DR) and reversed double-beam photoacoustic spectroscopy (RDB-PAS) analysis. The RDB-PAS analysis revealed that the TiO2 nanorods (TNR) contain amorphous areas on the surface that influence the size of the grown gold nanoparticles. The amount of amorphous phase on the TiO2 surface of the analysed TNR samples increases from 16.4%, 17% and 20.2% for TNR-A, TNR-B and TNR-C, respectively, and is closely related to the point of charge(pHPZC), which increases from the 3.9 ± 0.06, 4.7 ± 0.07 and 5.7 ± 0.04 for TNR-A, TNR-B and TNR-C, respectively. Au nanoparticle size distribution analysis obtained on the TNR surface shows that smaller Au nanoparticles are formed with pHPZC increase of the TNR support, i.e. 14.8 nm, 12.5 nm and 11.6 nm for TNR-A, TNR-B and TNR-C, respectively. This confirms that the differences in the surface charge of the TiO2 support influence the extent of hydrolysis of the Au precursor and its subsequent nucleation. Finally, the formation of OH• radicals was monitored using fluorescence probe method with coumarin as the probe molecule. The results revealed that the TiO2/Au composites are capable of generating OH• radicals under visible light illumination, with cat-C, containing the smallest Au particle sizes, being the most active among the materials tested.