Design and Development of Unique Photocatalytic Systems for the Decomposition of NOx

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Until now, photocatalytic reactions involving TiO2 photocatalysts for the decomposition of NOx were known to proceed only under UV light irradiation. In this research project, by the application of advanced metal ion-implantation with various transition metal ions such as V and Cr, it was found that novel TiO2 photocatalysts which absorb and operate efficiently under visible light irradiation for the decomposition of NOx could be developed. In-situ ESR and XAFS investigations revealed that the implanted V ions which exist as VィイD14+ィエD1 at the lattice position in place of TiィイD14+ィエD1 ion play a significant role in the shift in the absorption bands of TiO2 toward visible light regions. On the other hand, highly dispersed TiO2 catalysts anchored within the pore structure of the Y-zeolite by an ion-exchange method (Ti-Y zeolite) exhibited higher photocatalytic activity as compared to powdered TiO2. V or Cr ion-implantation on the Ti-Y zeolite also leads to a shift in the absorption band of the catalyst toward visible light regions and it was found that these V or Cr ion-implanted Ti-Y zeolites successfully decompose NOx under irradiation with visible light longer than 450nm, while maintaining just as a high photocatalytic activity as observed before applying ion-implantation. Furthermore, in-situ ESR and FT-IR investigations *lucidated the electron transfer from the photo-excited active site of the photocatalyst into the p anti-bonding molecular orbital of NO which led to a weakening of the N-O bond and initiated the decomposition of the NO molecule. It can be said that the present research has opened the way to many innovative possibilities, significantly to address urgent environmental problem and also as an important breakthrough in the utilization of solar energy.