Correlation of the Photocatalytic Activities of Cu, Ce and/or Pt-Modified Titania Particles with their Bulk and Surface Structures Studied by Reversed Double-Beam Photoacoustic Spectroscopy

Abstract

Modified titania photocatalyst powder samples were prepared using the sol-gel method for copper (Cu) and cerium (Ce) doping and impregnation for platinum (Pt) loading. Their bulk crystalline structures were investigated using X-ray diffractometry (XRD) with the Rietveld analysis. The surface/bulk structure, surface properties, and morphologies were observed using reversed double-beam photoacoustic spectroscopy (RDB-PAS), nitrogen adsorption, and scanning electron microscopy, respectively. The results from the XRD revealed that all samples were mainly anatase (ca. 80% or higher) with small amounts of rutile and non-crystalline components. The specific surface areas of all samples were in the range of 115–155 m2 g−1. Ce and Cu species were mainly distributed, while Pt was potentially loaded as a partially oxidized form on the titania surface. The results from the RDB-PAS indicated the changing of the energy-resolved distribution of electron traps (ERDT) from the original titania surface upon doping of the metals (Cu, Ce, and Pt), which altered their catalytic activities. The metals photocatalytic activities with UV irradiation were measured in two representative reactions; (a) CO2 evolution from acetic acid under the aerobic condition and (b) H2 evolution from deaerated aqueous methanol. In reaction (a), the Cu and/or Ce modification gave almost the same or slightly lower activity compared to the non-modified titania samples, while platinum loading yielded ca. 5–6 times higher activity. For reaction (b), the photocatalytic tests were divided into two sets; without (b1) and with (b2) Pt deposition during the reaction. Similar enhancements of activity from the Pt loading sample (and by Cu modification) were observed in reaction (b1) without in-situ platinum deposition, while the unmodified and Ce-doped samples were almost inactive. For the activities of reaction (b2) with in-situ platinum deposition, the unmodified samples showed the highest activity while the Cu-modified samples showed significantly lower activity.