Layered Titanates

While it is worthy to note that polyaniline-Ti02 nanocomposites have been synthesized and characterized [78-83], it should, however, be emphasized that these nanocomposites are not intercalated, but rather consist of Ti02 nanoparticles, in either the anatase or rutile phase, mixed with the polymer. 

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In characterizing layered silicate, including layered titanate (HTO), the surface charge density is particularly important because it determines the interlayer structure of the intercalants as well as the cation exchange capacity (CEC). Lagaly proposed a method of calculation consisting of total elemental analysis and the dimensions of the unit cell [15] ... 

Fig. 9.3 Illustration of a model of interlayer structure of intercalant N-(cocoalkyl)-N,N-[bis (2-hydroxyethyl)]-N-methyl ammonium cation (qCi4(OH)) in the gallery space of layered titanate (HTO). The average distance between exchange sites is 0.888 nm, calculated from the surface charge density of 1.26e /nm2. For qCi4(OH), the obtained molecular length,...

Fig. 3 Suggested scheme for the transformation of layered titanate to anatase Ti02 nanoroad. The structure models presented are the projection along the nanotube axis, i.e., the [010] of the titanate. The final TiOz nanorod product shown is the (010) face of the anatase phase. Elaborated from the picture reported by Nian and Teng.165...

Fig. 16.1 Idealized structures of some layered titanates and titanoniobates possessing edge- and corner-connected octahedra. 1...

The Kagome lattice structure clearly explains the non-symmetric nature of the band structure of the C0O2 layer. When the effect of the Kagome lattice becomes dominant, the bottom band, i.e., the flat band as shown in Fig, 3(a) will play a crucial role on the electronic state. Mielke [32] has shown that the flat band with the Coulomb interaction has the ferromagnetic ground state at around half filling. A prospective system for the ferromagnet will be dl transition metal oxides, i.e., the layered titanates with iso-structure of the cobalt oxides. 

The 0-d nanoparticles can be nano-metal oxides (such as silica,1 titania,2 alumina3), nano-metal carbide,4 and polyhedral oligomeric silsesquioxanes (POSS),5 to name just a few the 1-d nanofibers can be carbon nanofiber,6 and carbon nanotubes (CNT),7 which could be single-wall CNTs (SWCNT) or multiwall CNTs (MWCNT) etc. the 2-d nano-layers include, but are not limited to, layered silicates,8 layered double hydroxides (LDH),9 layered zirconium phosphate,10 and layered titanates,11 etc. 3-d nano-networks are rarely used and thus examples are not provided here. 

Sukpirom, N. and Lemer, M. M., Preparation of organic-inorganic nanocomposites with a layered titanate, Chem. Mater. (2001), 13, 2179-2185. 

Wang Q, Gao Q, Shi J (2004) Enhanced catalytic activity of hemoglobin in organic solvents by layered titanate immobilization. J Am Chem Soc 126 14346—14347... 

Layered compounds provide unique character for electron-transfer processes owing to their low dimensionality. Especially layered materials with ion-exchange and/or intercalation capabilities show behavior that is not seen in so-called bulk-type materials. Layered materials, which have been often used in studies of photoelectron transfer as well as photocatalysis, may be classified into two groups compounds in which the host layers work as an active component for the photoexcitation and electron-transfer reactions, and materials in which the layers are inert for electron-transfer processes. Examples of the former are layered titanates and niobates and of the latter are clays. In the latter case, photoactive materials are intercalated in the interlayer spaces. Recently, the exfoliation of various layered compounds has become possible and artificial assemblies consisting of these exfoliated sheets have been formed. Electron transfer in such assemblies is also an attractive subject in this field. 

Table 8. Catalytic activities of some layered titanates 64],...

S. Cheng and T. Wang, Pillaring of Layered Titanates by Polyoxo Cations of Aluminum. 

Nano-composite photocatalysts, CuOx-TiOa, were synthesized from Cu(OAc)2-intercalated fibrous layered titanates by thermal decomposition in different atmospheres (N2, air, and H2). The structural characterization using XRD, UV-vis, XPS, and SEM implied that the composite of partially reduced CuOx and anatase-t)q3e Ti02 in a waffle-like texture would be a reason for the excellent photocatalytic activity for H2 production from CH3OH/H2O mbttures. 

The reaction was also conducted using aqueous solutions of other transition-metal acetates in the same manner. As shown in Table 1, the M/Ti ratio for the as prepared composites was in the range of 0.10-0.47, suggesting that the bulk-type reaction took place between metal acetates and the layered titanate. No deposition of metal acetate was confirmed on the surface of the fibrous microcrystals by the SEM for all as prepared samples before calcination. These results demonstrated that metal acetates were accommodated in the interlayer. 

Fig. 4 shows SEM photographs of Cr-400-Nz and Cu-400-Nz. The Cr-400-Nz retained the fibrous morphology of pristine layered titanate as shown in Fig. 1. Since the deposition of amorphous Cr oxide was not observed, nm-scale slits formed between layers are responsible for the increased surface area. By contrast, fibrous particles of Cu-400-Nz...

Table 4 shows the photocatalytic activity of CuOx supported on the pristine samples of layered titanates. The loading (26 wt% Cu) corresponds to the Cu/Ti ratio (0.33) for the composite prepared by the intercalation process. The two pristine layered titanates showed very low activity without loading CuOx. In contrast, the activity of the CuOx-loaded samples was quite different the protonated phase produced ca. 18-times higher rate of Ha evolution. Copper oxides in these materials were deposited only on the surface of the fibrous crystals. However, the protonated phase was decomposed to produce anatase-type TiOa as in the case of the intercalated composite (Fig. 5). This result also supports that the formation of anatase is essential for the photocatalytic activity. 

Clays have also been pillared with polyoxometalate ions, such [(PW11VO40)4-].261 Other layered materials can also be pillared. Zirconium phosphate has been pillared with chromium(III) oxide.262 A layered titanate has been pillared with silica.263 The need for a separate pillaring step has been avoided in the preparation of some porous lamellar silicas which are structurally similar to pillared clays.264 Eight to twelve carbon diamines were used with tetra-ethoxysilane in ethanol with added water to make them in 18 h at room temperature. The template was recovered by solvent extraction before the silica was calcined. 

Weng et al. [113] studied the effect of tetramethylammonium cations (TMA"") on HO2 crystal morphology under hydrothermal conditions. The as-synthesized samples were characterized by XRD, TEM and SEM methods (see Table 2). The observed morphologies include besom-like particle, nanosheet and nanotubes. The mechanism to accelerate the formation of nanotube in the base of NaOH/TMAOH mixture is illustrated in Eigure 7. Bulk HO2 is first exfoliated to be layered protonic titanate by the mineralization effect of Na". In the presence of TMA"" cations, the separation of layered protonic titanate is accelerated by intercalating TMA"" cations in layered titanate. As a result of the presence of more layered titanate in the hydrothermal solution, nanotubes are formed ahead of schedule by curliness of layered titanate. Thus, the mechanism through which TMA cations affect crystal growth in the conditions of this study is different. 

The mesoporous structure, with high surface area could provide simple accessibility of guest molecules to the active sites and increase their chances to receive light. One research group fabricated mesoporous photocatalysts with delaminated structure. The exfoliated layered titanate in aqueous solution was reassembled in the presence of anatase Ti02 nanosol particles to make a great number of mesopores and increase the surface area of Ti02 [370] (see Table 6). 

T.P. Feist, P.K. Davies, The soft chemical synthesis of Ti02 (B) from layered titanates . Journal of Sohd State Chemistry, 101, 275-295, (1992). 

Riss A, Berger T, Stankic S et al (2008) Charge separation in layered titanate nanostructures effect of ion exchange induced morphology transformation. Angew Chem Int Ed 47 1496-1499... 

Riss A, Elser MJ, Bemardi J et al (2009) Stability and photoelectronic properties of layered titanate nanostructures. J Am Chem Soc 131 6198-6206... 

Inorganic or organic nanoparticles have been incorporated to enhance the mechanical, barrier and thermal properties of PLA. Over the past few years, various nanomaterials have been investigated for reinforcing PLA, including layered silicates, carbon nanotube, hydroxyapaite, layered titanate, aluminum hydroxide, etc. 

Harada and co-workers [88] investigated the flame retardancy of polyglycidyloxypropyl silsesquioxane layered titanate nanocomposites. The UL 94 test method [13] was used to investigate the burning properties of the nanocomposites. It was found that the spherical titanate-filled nanocomposite sample burned from one end to the other, whereas a fire extinguishing property was observed in the sheet-like titanate-filled nanocomposites. The latter nanocomposites were classified as UL 94 VO, even with a 5 wt% layered titanate content. 

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