Yoshinobu Fujishiro

Synthesis and microstructure of calcia doped ceria as UV filters

Fine particles of calcium oxide doped cerium dioxide, 2–4 nm in diameter, were prepared by the chemical reaction of CeCl3-CaCl2 mixed aqueous solution and NaOH aqueous solution at pH 6–12 and 40°C followed by the oxidation with hydrogen peroxide. Doping of CaO with CeO2 resulted in decreasing the particle size and consequently, increasing UV shielding efficiency and transparency to visible light. The particle shape of ceria changed significantly depending on the reaction condition, i.e., rod-like particles and spherical particles were formed by the H2O2 oxidation of cerium trihydroxide pH above 8 and below 7, respectively.

Intercalation of titanium oxide in layeredH2Ti4O9 andH4Nb6O17 and photocatalyticwater cleavage withH2Ti4O9/(TiO2,Pt) andH4Nb6O17/(TiO2,Pt) nanocomposites

Titanium oxide and platinum have been intercalated into nH n 2 nTi n 4 nO n 9 n and nH n 4 nNb n 6 nO n 17 n by the successive nreactions of H n 2 nTi n 4 nO n 9 n and nH n 4 nNb n 6 nO n 17 n with n[Pt(NH n 3 n) n 4 n]Cl n 2 n, nn-C n 3 nH n 7 nNH n 2 n and nacidic TiO n 2 n colloid solutions followed by UV nlight irradiation. The thicknesses of titanium oxide and nplatinum were less than 0.7 nm. The band gap energy of the ntitanium oxide incorporated was less than 3.4 eV. The rate nconstants for the charge injection from excited nTiO n 2 n into the conduction band of nH n 2 nTi n 4 nO n 9 n and nH n 4 nNb n 6 nO n 17 n were determined to nbe 0.11×10 n 9 n and 0.12×10 n 9 n ns n -1 n, respectively, by measuring the nTiO n 2 n emission lifetimes in TiO n 2 n nincorporatednanocomposites. nH n 2 nTi n 4 nO n 9 n/(TiO n 2 n, nPt) and nH n 4 nNb n 6 nO n 17 n/(TiO n 2 n n,Pt) nanocomposites (intercalated with both TiO n 2 n nand Pt) werecapable of water cleavage into hydrogen and noxygen without a hole scavenger, at 0.088–0.104 mmol nh n -1 n, following irradiation from a 450 W Hg lamp, nalthough no noticeable gas was evolved in the presence of nH n 2 nTi n 4 nO n 9 n/TiO n 2 n, nH n 4 nNb n 6 nO n 17 n/TiO n 2 n, nH n 2 nTi n 4 nO n 9 n/Pt, nH n 4 nNb n 6 nO n 17 n/Pt and unsupported nTiO n 2 n/Pt. The hydrogen and oxygen evolution was nlinear with time and the niobate system was fairly nefficient.

Intercalation of iron oxide in layered H2Ti4O9 and H4Nb6O17: visible-light induced photocatalytic properties

H2Ti4O9/Fe2O3·nH2O and H4Nb6O17/Fe2O3·nH2O nanocomposites containing intercalated Fe2O3·nH2O, particles of 400 nm) from a 450 W Hg lamp in the presence of Na2SO3 as a sacrificial donor. The hydrogen production activity of these nanocomposites was superior to that of unsupported Fe2O3·nH2O. The hydrogen production was enhanced to 11.3–13.6 cm3 over 5 h by doping Pt together with Fe2O3·nH2O in the interlayer. Hydrogen evolution was linear with time with the niobate system being slightly more efficient.

Crystallization of Titania in Liquid Media and Photochemical properties of Crystallized Titania

Titania gels in liquid media crystallized from amorphous to anatase at temperatures as low as 120 ±C, while the onset of crystallization in air was 370 ±C. The crystallization rate in water was much faster than in methanol and n-hexane, and the crystallite size of anatase prepared in water was larger than of those prepared in organic solvents. The crystallized powders were capable of efficient hydrogen evolution following band gap irradiation in the presence of a sacrificial hole acceptor such as methanol. The photocatalytic activity of powder crystallized in methanol was superior to those prepared in water and air.

Synthesis and photocatalytic properties of fibrous titania by solvothermal reactions

Abstract Fibrous titania was synthesized by the solvothermal reactions of fibrous H 2 Ti 4 O 9 ·0.25H 2 O precursor in different media. H 2 Ti 4 O 9 ·0.25H 2 O transformed in steps to H 2 Ti 8 O 17 , monoclinic TiO 2 , anatase and rutile. The phase transformation temperature and microstructure of the products changed significantly, depending on the heating environment. The critical temperature at which anatase appeared in liquid media was much lower than that in air, indicating that the phase transformation of the monoclinic TiO 2 to anatase proceeded by the dissolution–precipitation mechanism. Nanosize crystals of TiO 2 possessing high crystallinity could be obtained by the solvothermal reactions using water and methanol as reaction media. The crystallite size of the titania could be decreased using methanol as a reaction medium. The photocatalytic activity of titania changed with heat treatment media in the following sequence: methanol>water⪢air. The effects of the phase composition and microstructure of the TiO 2 powders on photocatalytic activity were also investigated. Titania powders crystallized by the solvothermal reaction in methanol possessed excellent photocatalytic activity and thermal stability.

Photocatalytic Properties of Layered Hydrous Titanium Oxide/CdS-ZnS Nanocomposites IncorporatingCdS-ZnS into the Interlayer

H 2 Ti 4 O 9 /Cd 0.8 Zn 0.2 S nanocomposites incorporating Cd 0.8 Zn 0.2 S particles, less than 1 nm in thickness, were fabricated by the chemical reaction between a Cd 2+ -Zn 2+ mixture and H 2 S in the interlayer of H 2 Ti 4 O 9 . H 2 Ti 4 O 9 /Cd 0.8 Zn 0.2 Z nanocomposites were capable of efficient hydrogen evolution following irradiation with visible light in the presence of Na 2 S as a sacrificial donor. The hydrogen production activity of the H 2 Ti 4 O 9 /Cd 0.8 Zn 0.2 Z nanocomposite was superior to those of unsupported Cd 0.8 Zn 0.2 S and the mixture of H 2 Ti 4 O 9 and Cd 0.8 Zn 0.2 S. The hydrogen production was enhanced by doping Pt together with Cd 0.8 Zn 0.2 S in the interlayer, but was depressed by depositing Pt on the outer surface of the H 2 Ti 4 O 9 /Cd 0.8 Zn 0.2 S nanocomposite.

Synthesis and photochemical properties of semiconductor pillared layered compounds

Abstract CdS and ZnS mixtures, Fe2O3 and TiO2 pillars were constructed in the interlayer of montmorillonite, layered double hydroxide, H4Nb6O17 and H2Ti4O9 by the intercalation reactions. The thicknesses of the semiconductors incorporated were less than 1 nm and the band gap energies of them were slightly larger than those of normal crystalline ones. The photocatalytic activities of the semiconductors incorporated were superior to those of unsupported ones. The incorporation of semiconductors in the interlayers of semiconducting layered compounds such as H2Ti4O9 and H4Nb6O17 was much more efficient in enhancing the hydrogen production activity than when an insulator such as montmorillonite and layered double hydroxide was used, since the recombination of photo-induced electrons and holes was depressed by the electron transfer from the incorporated semiconductors to the semiconducting host layer.

Synthesis of monodispersed LaPO4 particles using the hydrothermal reaction of an La(edta)− chelate precursor and phosphate ions

Abstract Homogeneous precipitation of LaPO 4 was carried out using the hydrothermal reaction of lanthanum(III) ethylenediamine tetraacetate complex (La(edta) − ) and phosphate ion in order to prepare directly monodispersed crystalline LaPO 4 particles. Monodispersed monazite-type LaPO 4 precipitated under conditions of 0.008xa0M La 3+ , [edta]/[La]≥2 and [PO 4 ]/[edta]=0.6 to 1 at 150xa0°C for 2xa0h. The particle consisted of fine crystals ca. 20xa0nm in length. The spherical particle of 0.3xa0μm diameter precipitated at pH 3, and the spindle-like particle precipitated with decreasing [edta]/[L 3+ ] molar ratio or increasing pH to 7. The monodispersed particle may be formed by control of the precipitation rate, depending on the stability of the La(edta) − chelate precursor determined by [edta]/[PO 4 ] and pH.

Synthesis of cadmium sulfide pillared layered compounds and photocatalytic reduction of nitrate under visible light irradiation

Abstract Layered compound/CdS nanocomposites incorporating CdS pillars in the interlayer of layered compounds such as hectorite, H2Ti4O9 and H4Nb6O17 were prepared by the stepwise ion exchange reactions of the layered compounds with C3H7NH3+ and Cd2+ followed by the reaction with H2S gas. The pillar height was less than 1 nm and the band gap energy was slightly larger than that of normal crystalline CdS. Although the host layered compounds were insulators or wide band gap semiconductors, CdS pillared layered compounds showed photocatalytic activity under visible light irradiation. Nitrate ion was photochemically reduced to nitrite, nitrogen and ammonia by irradiating visible light (λ>400 m) from a high pressure mercury lamp to nitrate solution containing H2Ti4O9/CdS and H4Nb6O17/CdS nanocomposites in the presence of a sacrificial hole acceptor such as methanol, whereas no photoreduction of nitrate proceeded in the presence of unsupported CdS and hectorite/CdS nanocomposite, indicating that the incorporation of CdS pillars in the interlayer of a semiconducting layered compound such as H2Ti4O9 and H4Nb6O17 was much more efficient in enhancing the nitrate reduction activity than when an insulator such as hectorite was used.

Hydrothermal synthesis of K4Nb6O17

A new approach for the synthesis of K4Nb6O17.3H2O by hydrothermal method was examined using different alkaline solutions such as Nb2O5-KOH-NaOH-H2O, Nb2O5-KOH-NH4OH-H2O and Nb2O5-KOH-H2O. K4Nb6O17.3H2O was formed as single phase in Nb2O5-KOH-H2O system in the region of KOH concentration 1.0-1.5 m and temperature 220-285°C. KNbO3 was also formed as single phase in 3.0 m KOH solutions above 250°C. Addition of methanol was useful to decrease the particle size and increase the specific surface area of K4Nb6O17.3H2O.