Hydrothermal Synthesis of Potassium Hexatitanates under Subcritical and Supercritical Water Conditions and Its Application in Photocatalysis

Abstract

Hydrothermal synthesis of potassium hexatitanate was carried out under various subcritical and supercritical water conditions using potassium hydroxide and titanium tetraisopropoxide as starting materials. Characterization of these hydrothermally synthesized potassium hexatitanates by XRD, SEM, TEM, and thermal analysis showed that long, felted-like fibers of potassium hexatitanates were formed and these fibers are thermally stable up to 1273 K. The use of these fibers as photocatalysts in water decomposition was investigated using ruthenium oxide as the catalytic active phase. Photocatalytic activitiy in the water decomposition reaction was found to be much higher in comparison with the solid state synthesized photocatalyst. Activites of more than 13-fold were obtained for the photocatalysts synthesized under subcritical water conditions and between 27- and 59-fold for those synthesized under supercritical water conditions for water decomposition.

Low‐temperature controllable calcination syntheses of potassium dititanate

“…Potassium dititanate is an important perovskite of the potassium titanate family (Bao, 2002a,b;Clearfield, 1988; or three-dimensionally bonded compounds (Clearfield, 1988;Ogawa, 1995;Sasaki, 1994;Schaak, 2002) with special photochemical applications of photoluminescence and photocatalysis (Inoue, 1991;Kudo, 1993Kudo, , 1997aKudo, , 1998Ogawa, 1995;Schaak, 2002;Yagi, 2001;Yahya, 2001;Yin, 2000). Potassium dititanate (K 2 Ti 2 O 5 ) exhibits the highest catalytic activity and photoluminescence, even at room temperature, compared to that of other layered titanates (Kudo, 1993(Kudo, , 1997a(Kudo, ,b, 1998Ogawa, 1995;Shibata, 1987;Uchida, 2001;Yin, 2000); from K 2 Ti 2 O 5 many host-guest compounds exhibiting strong blue luminescence and highly improved photochemical activity, even without Pt cocatalysts, have been prepared (Kudo, 1993(Kudo, , 1997a(Kudo, , 1998Shibata, 1987).…”

Rapid Production of Micro- and Nano-particles Using Supercritical Water

“…KTO has tunnel structure, which finds applications in photocatalytic materials. Alkali-metal haxatitanate is one of the semiconducting photocatalysts, which has the capability of invoking a photocatalytic decomposition of water to produce H 2 and O 2 [59][60][61]. Using the tunnels to accommodate the active phase (e.g., Ru) can enhance the catalytic activity further [62].…”

“…Yahya et al [59] synthesized KTO using potassium hydroxide and titanium tetraisopropoxide (molar ratio of K/Ti = 1/2) as starting materials in SubCW (623 K, 16 MPa) and SCW (673 K, 28 MPa; 723 K, 43 MPa) for 2, 5 and 25-h reaction times in an autoclave. The particles were compared with those synthesized by SSR method, that was carried out using potassium carbonate and titanium oxide (anatase) in a K/Ti molar ratio of 1.1/6 and heating at 1,403 K for 5 h. SEM and TEM observations revealed that the particulate morphology of products by hydrothermal synthesis is long and thin fibers (with diameter of 0.5 μm) while the particles by SSR method was mainly short thick fibers (with diameter of 3 μm) ( Fig.…”

Hydrothermal Synthesis of Potassium Titanate Powders in Sub/Supercritical Water and Its Cobalt Ion Sorption Properties

“…We have demonstrated hydrothermal synthesis of potassium titanates powders and fibrous potassium hexatitanate with relatively large surface area were achieved under subcritical and supercritical conditions. [6,7] It is expected that hydrothermally synthesized K2Ti6O13 could be used as heat-resistant ion-exchanger. In this paper, cobalt ion sorption properties of hydrothermally synthesized K2Ti6O13 under hydrothermal conditions (373-473 K) were compared with the conventional solid-state synthesized K2Ti6013.…”