Direct (one-step) synthesis of TiO2 and Pt /TiO2 nanoparticles for photocatalytic mineralisation of sucrose

TiO(sub 2) and Pt/TiO(sub 2) nanoparticles were made by a one-step flame spray pyrolysis (FSP) process that resulted in mostly anatase (69-85 wt%) powders with controlled specific surface area and crystallite size. These particles resulted in shorter half-lives for sucrose photomineralisation, up to 50% lower than Degussa P25. Co-precipitation of Pt on TiO(sub 2) during FSP increased the rutile content and slightly increased the specific surface area. Close control over Pt deposit size during this process was possible by varying the Pt concentration in the feed precursor. The dispersion of the Pt was high, 45-77% (at 4.0-0.1 atom% Pt) and corresponded to metal deposit size of 2.5-1.4 nm, respectively. An optimum photocatalytic activity was observed at 0.5 atom% Pt loading. At low Pt loading (0.1 atom% Pt), the activity was lower than that of FSP-made TiO2 since the high photocurrent density of the Pt deposits increased the electron-hole recombination. The deposit size was also too small to establish sufficient electrical contact for efficient interfacial charge transfer between the photocatalysts and sucrose. Additional studies on the photocatalytic mineralisation of sucrose under oxygen enriched conditions reaffirmed the postulation that both FSP-made TiO(sub 2) and improved Pt/TiO(sub 2) photocatalysts favoured a reductive pathway which was different and faster than the pathway followed when using Degussa P25 TiO(sub 2). The intricate relationship between photocatalyst characteristics and its performance is highlighted.