Design and development of photocatalysts of high activity and highly efficient photocatalytic reaction systems based on the understanding of photocatalytic reaction mechanisms

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1. Action spectrum analyses: It was revealed that this is one of the best methods for the evaluation of photocatalysts and photocatalytic reaction by showing that methylene blue, a frequently employed photocatalytic reaction substrate, is decomposed through photosensitizing mechanism as well as photocatalytic reaction. Moreover, pseudo action spectra taken by using optical cut-off filters show different shape compared from true action spectra.2. Preparation of highly active titania photocatalyst through novel gas phase reaction: High temperature as-phase synthesis of metal oxide particles is favorable since crystallization of particles is promoted without aggregation to give larger particles. In this study, new type of titania preparation method enabling rapid heating-rapid cooling of titanium(IV) chloride was developed. The resulting anatase small crystallites were of decahedral shape exposing two kinds of lattice facet, 101 and 001 and showed high photocatalytic activity in several reaction systems. The preparation conditions were optimized.3. Isolation of anatase and rutile crystallites from Degussa P25: From Degussa P25, a representative commercial titania powder with anatase and rutile mixed crystallites, anatase and rutile crystallites were isolated through newly developed method. The isolated samples were used for making calibration curves of each crystal phase to obtain, for the first time, exact composition of P25 and for reconstruction of P25 from two kinds of isolated pure crystallites and commercial amorphous titania. Comparison of physical properties and photocatalytic activities between original and reconstructed samples revealed that there seems to be no synergetic effects by mixing anatase and rutile on the photocatalytic activity.