Condensation‐ and Crystallinity‐Controlled Synthesis of Titanium Oxide Films with Assessed Mesopores

Abstract

Materials with controlled microstructures based on solgel science have been widely applied to intelligent adsorbents, catalyst supports, photocatalysts, and ceramics in highperformance electronic, photonic, and magnetic devices. Sol-gel reactions of metal alkoxides, such as hydrolysis and condensation, in general lead to the formation of inorganic oxide networks. Compositional design in the frameworks is possible in mixed alkoxide systems. Non-hydrolytic routes have often facilitated the fabrication of mixed metal oxides [1] and inorganic-organic hybrid materials.[2] Likewise, self-adjusted reactions between appropriate inorganic acidity and alkalinity pairs are a powerful method of constructing not only single and/or mixed metal oxides but also metal phosphates.[3] Although these studies have only focused on the initial formation of inorganic networks, subsequent condensation has not been discussed as adequately. Condensation reactions of transition-metal oxides are too fast and it is still difficult to control microstructures atomically in the final metal oxides. Control of the sol-gel reactions has been investigated further by using chemical modification of metal alkoxides with organic chelating agents; the hydrolysis reaction rates of the hydrophobic metal species are lower than those of the original precursors.[4] However, once the designed alkoxides have been hydrolyzed by the presence of water, it becomes difficult to manage subsequent condensation reactions between the metal species, which is a limitation of using sol-gel chemistry with highly reactive transition-metal chlorides and alkoxides.Herein we demonstrate an effective way for preventing from continuous condensation of transition-metal species in solution by the addition of phosphites.

Highly Photoactive Porous Anatase Films Obtained by Deformation of 3D Mesostructures

“…Upright adsorption was not observed for the Im3 m-derived nanoparticle film, but the end of desorption from the mesospaces was confirmed at P/P 0 = 0.72. [17] This result suggests that intercrystalline mesospaces in the P6 3 /mmc-derived nanoparticle film are larger than those observed for the reported Im3 m-derived films.…”

“…In this case, deformation of the gridlike structure led to decreased photocatalytic performance, which is also simi- lar to that observed for our Im3 m derivative films. [17] In contrast, in the present study, the deformation of regular nanopillars to nanocrystals with formation of intercrystalline mesospaces leads to drastic improvement of photocatalytic performance. Such intercrystalline mesospaces surrounded by highly crystallized anatase nanoparticles are designed through deformation of regular anatase nanopillars with long lateral distance.…”

“…[15,16] Recently, we reported full characterization data such as TEM images, GISAXS patterns, and Kr adsorption/desorption isotherms. [17] The structural transformation (including the deformation to anatase nanocrystal film with sufficient porosity) during calcination of the Im3 m mesostructured titania film was documented adequately. Here, we therefore needed P6 3 /mmc-derived porous anatase films with similar film thickness (< 100 nm) to those observed for our reported Im3 m derivative films, because photocatalytic performance over porous anatase films was discussed on the basis of crystallinity, porosity, diffusivity, and so on.…”

“…Crystallinity of the present P6 3 /mmc-derived and our reported Im3 m-derived anatase nanocrystal films [17] was compared by using the synchrotron XRD data. On the basis of the (101) peak area, the crystallinities of the titania frameworks were estimated to be almost same.…”

Nanoarchitectonics for Mesoporous Materials

“…454 This approach is based on the poor reactivity of phosphites with transition-metal species for preventing the continuous condensation of metal species in solution. Yamauchi and co-workers reported the extraordinary antibacterial properties of mesoporous titania films.…”