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We have previously demonstrated that TiO2 nanoparticles can be functionalized by photodeposition with silver or gold particles in the 1–2 nm range presumed to be desirable for catalysis applications. However, the preparation of these samples directly on microscope grids, while conducive to particle size determinations, did not produce sufficient materials for reaction studies. We report here scale-up techniques designed to produce greater quantities of material for testing, while maintaining characteristics that contribute to uniformity in the deposition process. For the scale-up process, an irradiation source with highly uniform intensity is necessary to generate Ag/TiO2 samples with consistent Ag loading. In addition, control of the precursor concentration is also required to produce Ag/TiO2 samples with high Ag loading and narrow Ag size distribution. The optimum conditions for the scale-up process found in this study involved Ag photodeposition from a 5 × 10−3 M AgNO3 solution using a high pressure Hg lamp at 366 nm for 60 s. Under these reaction conditions, the size of Ag particles determined by TEM and HAADF-STEM imaging was within 1–2 nm and the Ag loading was ~3.2 wt%. Achievement of this level of uniformity required control of the uniformity of illumination, as well as of the solution concentration and irradiation conditions. Higher solution concentrations and higher power led to the growth of larger (ca. 10 nm) silver particles. In contrast, the loading and size distribution of the Ag particles photodeposited were remarkably insensitive to the source and morphology of the TiO2 nanoparticles utilized. No Ag peak was resolved in the XRD patterns for Ag/TiO2 samples obtained from the optimized scale-up process, corroborating the size range determination of the Ag nanoparticles. XPS showed that the Ag particles in all cases were metallic Ag.

Photodeposition of Ag nanoparticles on commercial TiO2 particles and nanoparticles was performed in order to provide direct visualization of the spatial distribution of photoactive sites on sub-micrometer-scale and nanoscale TiO2 particle surfaces and to create materials for potential catalytic applications. HRTEM (high-resolution transmission electron microscopy) and HAADF-STEM (high-angle annular dark-field scanning transmission electron microscopy) were used to characterize these materials. The size and spatial distributions of the Ag nanoparticles on the commercial TiO2 were not uniform; the concentration of Ag was higher on grain boundaries and at the edges of these submicrometer particles. In the case of TiO2 nanoparticles, the size distribution of the Ag nanoparticles deposited was relatively uniform and independent of irradiation time and photon energy. The amount of Ag deposited on TiO2 nanoparticles was at least 6 times higher than that on the commercial samples for comparable irradiation conditions. Compared to the case of Ag photodeposition, the difference in the amount of Au photodeposited on TiO2 particles and nanoparticles was even greater, especially at low precursor concentrations. Photodeposition on TiO2 nanoparticles is suggested as a potential method for the preparation of Au/TiO2 catalysts, as loadings in excess of 10 wt % of uniform 1 nm metal particles were achieved in this work.