Photodegradation of organics by Pt/TiO2 and Ag/ZnO nanoparticles

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TiO2 and Pt/TiO2 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 TiO2 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 TiO2 and improved Pt/TiO2 photocatalysts favoured a reductive pathway which was different and faster than the pathway followed when using Degussa P25 TiO2. The intricate relationship between photocatalyst characteristics and its performance is highlighted.

High surface area Ag-ZnO catalysts have been made by flame spray pyrolysis and characterized by x-ray diffraction, nitrogen adsorption, UV-vis spectroscopy and electron microscopy (SEM and TEM) combined with energy dispersive x-ray spectroscopy (EDXS) for elemental mapping. Silver metal clusters deposited directly on ZnO nanocrystals were obtained from this process. The Ag loading (1 to 5 at.%) controlled the Ag cluster size from 5 to 25 nm but did not influence the ZnO crystal size. Photodegradation of 10 ppm methylene blue (MB) solution was used to evaluate the performance of these FSP-made Ag-ZnO and was compared to wet-made Ag-ZnO and reference titania photocatalysts. The rate of photodegradation was optimal for Ag loading around 3 at.%. The best photocatalytic performance was exhibited by flame-made Ag-ZnO produced at the longest high-temperature residence times having high crystallinity as determined by XRD and UV-vis.

Recent relevant publications:

  1. W.Y. Teoh, L. Madler, D. Beydoun, S.E. Pratsinis, R. Amal, "Direct (one-step) Synthesis of TiO2 and Pt/TiO2 Nanoparticles for Photocatalytic Mineralization of Sucrose", Chem. Eng. Sci., 60, 5852-61 (2005).
  2. M.J. Height, S.E. Pratsinis, O. Mekasuwandumrong, P. Praserthdam, Appl. Catal. B Environ., (2006).
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