Unilamellar titania crystallites of Ti 1-δ O 2 4δ-(δ ) 0.0875) and polydiallyldimethylammonium chloride have been alternately deposited layer-by-layer onto various substrates from their aqueous media. An atomic force microscopy (AFM) image visualized the adsorbed nanosheets, which gave efficient coverage of the substrate surface. The resulting multilayer film apparently displayed a very intense UV absorption ( ) 2.2 × 10 4 mol -1 dm 3 cm -1 at 265 nm) due to the titania nanosheets with a molecular thickness. X-ray diffraction (XRD) measurements detected a Bragg peak, which reflects a nanosheet/polycation nanostructure inside the film. Its multilayer repeat distance was 1.4-1.7 nm, being dependent on the surrounding humidity. Simulation on the XRD profile suggested that the obtained films have some structural disorder, involving about 20% of the mean displacement for the multilayer repeat spacing. Spectroscopic ellipsometry data can successfully be analyzed based on a multilayer assembly model composed of titania nanosheets that are ∼1.2 nm thick and polycations that are ∼0.7 nm thick, which is substantially compatible with the XRD and AFM data.
This paper reports on the synthesis and characterization of oversized titania nanosheets derived from single crystals of a potassium lithium titanate, K 0.8 Ti 1.73 Li 0.27 O 4 . The single crystals with a lateral size of over 1 mm were obtained via a melt and recrystallization process in a flux melt. The crystals were converted into an acid-exchanged form of H 1.07 -Ti 1.73 O 4 ‚H 2 O, and then was reacted with aqueous tetrabutylammonium (TBA) ions at various concentrations. X-ray diffraction analysis revealed that the titanate crystals exhibited high degrees of swelling, and exfoliated single sheets were obtained at a molar TBA dose of 0.5-1 with respect to the exchangeable protons in H 1.07 Ti 1.73 O 4 ‚H 2 O. Observations by transmission electron microscopy and atomic force microscopy detected very large nanosheet crystallites with a lateral size of several tens of micrometers. Some wrinkles and cracks within the crystallites indicated that they were highly flexible and also fragile.
A multilayer film of titania nanosheet crystallites and poly(diallyldimethylammonium chloride) has been modified via heat treatment or exposure to UV light. The resulting films in various chemical compositions and crystal structures have been characterized by X-ray diffraction, FT-IR spectroscopy, X-ray photoelectron spectroscopy, and spectroscopic ellipsometry. Thermal or photocatalytic decomposition of polycations in the nanosheet gallery was achieved by heating to 400 °C or UV irradiation, respectively, which produced inorganic multilayers composed of the nanosheets and charge-balancing cations such as ammonium and/or oxonium ions. The polycation removal brought about an improvement in the multilayer stacking order, accompanied by a decrease in inter-nanosheet distance by ∼35%. The nanosheet architecture as well as multilayer structure collapsed upon heating at 500 °C or higher, yielding ultrathin films of TiO 2 (anatase and then rutile). The films exhibited a wide range of optical and photochemical properties dependent on modifications.
Aims. We derive physical properties such as the optical depths and the column densities of 13 CO and C 18 O to investigate the relationship between the far ultraviolet (FUV) radiation and the abundance ratios between 13 CO and C 18 O. and 0.4 × 10 15 < N C 18 O < 3.5 × 10 16 cm −2 , respectively. The abundance ratios between 13 CO and C 18 O, X13 CO /X C 18 O , are found to be 5.7−33.0. The mean value of X13 CO /X C 18 O in the nearly edge-on photon-dominated regions is found to be 16.47 ± 0.10, which is a third larger than that the solar system value of 5.5. The mean value of X13 CO /X C 18 O in the other regions is found to be 12.29 ± 0.02. The difference of the abundance ratio is most likely due to the selective FUV photodissociation of C 18 O.
MPMS-5S) in an external field of 0.5 T. The Mössbauer spectrometer, with a 57 Co/Rh source, was driven in the transmission mode. The lowtemperature measurements were performed with a closed-cycle helium refrigerator (Iwatani Co., Ltd.).
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