CONSTRUCTION OF PHOTO-CATALYTIC REACTION SYSTEMS IN EFFICINENT CONVERSION OF CARBON DIOXIDE TO METHANOL BY UTILIZING SOLAR ENERGY

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1. Preparation of chormophore / titania catalysts(1) Two-step polymer modification of colloidal titania of 100 nm size, with poly(maleic anhydride-styrene) (P(MA-ST)) and RuCl_2( 2,2' -bipyridyl)_3 (Ru(II)-bpy)-anchored poly(2-methyl-2-oxazoline), successfully gave chromophore-grafted titania composite particles (1) ; the maximum amounts of introduced Ru(II)- complex was 3.42 x 10^<-4> mol/g, i.e. 14.2 Ru-atom/nm^2.(2) In order to prepare stable titania composite particles in aqueous solution, incorporation of Ru(II)-(bpy)/silica, which was made from P(MA-ST)-modified colloidal silica of 20 nm size into titania resulted in photo-catalytically active Ru(II)(bpy)/silica/titania composite (2) of 40-70 nm size.2. Photocatalytic activity of the titania composite catalyst by visible light irradiation(1) Irradiation of visible light to the aqueous suspension containing Catalyst 1 led to efficient electron transfer from Ru(II)(bpy) to methyl viologen as a electron transfer in the presence of ethylenediaminetetraactic acid ; The maximum quantum yield was 1.5 %. Kinetic analysis of the photo-catalytic reaction showed the electron transfer took place via two rotes, one was direct one and another was indirect one via titania surface. The kinetic studies also showed the direct electron transfer was controlled by diffusion of the donor and involved with reverse electron transfer, and that the indirect electron transfer predominantly took place in low concentration of the donor.(2) Catalyst 2 was stably dispersible in aqueous solution and showed stable photo-catalytic activity by visible light, but 10% of the activity of Catalyst 1. It is required to improve the photo-catalytic activity of Catalyst 2, because of practically promising for photo-catalytic conversion of carbon dioxide to methanol.