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 2WO 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.