Solvothermal syntheses of semiconductor photocatalysts of ultra-high activities

Abstract Thermal treatment of titanium(IV) butoxide dissolved in 2-butanol at 573 K under autogenous pressure (alcohothermal treatment) yielded microcrystalline anatase-type titanium(IV) oxide (TiO 2 ). Thermal treatment of oxobis(2,4-pentanedionato-O,O′)titanium (TiO(acac) 2 ) in ethylene glycol (EG) in the presence of sodium acetate and a small amount of water at 573 K yielded microcrystalline brookite-type TiO 2 . Tungsten(VI) oxide (WO 3 ) powders of monoclinic crystal structure with high crystallinity were synthesized by hydrothermal treatment (HTT), at 523 or 573 K, of aqueous tungstic acid (H 2 WO 4 ) solutions prepared from sodium tungstate by ion-exchange (IE) with a proton-type resin. Anatase and brookite TiO 2 products were calcined at various temperatures and then used for photocatalytic mineralization of acetic acid in aqueous solutions under aerated conditions and dehydrogenation of 2-propanol under deaerated conditions. Almost all the anatase-type TiO 2 samples showed the activities more than twice higher than those of representative active photocatalysts, Degussa P-25 and Ishihara ST-01 in both reactions. A brookite sample with improved crystallinity and sufficient surface area obtained by calcination at 973 K exhibited the hydrogen evolution rate almost equal to P-25. HTT WO 3 powders with various physical properties were used as photocatalyst for evolution of oxygen (O 2 ) from an aqueous silver sulfate solution. WO 3 powder of high crystallinity, e.g., IE-HTT-WO 3 synthesized at 573 K, gave much higher O 2 yield than commercially available WO 3 samples.