Mesoporous coatings

The photoisomerization of the azobenzene on polymer films has been also exploited to devise controlled release drug delivery systems. In this regard, researchers have recently directed their attention to the development of photo-controlled drug delivery platforms based on dendron-modified surfaces [274] and mesoporous coatings [274—276]. Mei et al. [276] tethered 6-CD to hollow MSNs via... 

A variant of the enhanced reaction zone concept is to utilize as catalyst support various porous three-dimensional electrodes with thickness between 200 to 2,000 pm. Thus, the electric contact resistance between the individual layers is eliminated. The three-dimensional matrix (such as various graphite felts, reticulated vitreous carbon, metal mesh, felt, and foam) supporting uniformly dispersed electrocatalysts (nanoparticles or thin mesoporous coating) could assure an extended reaction zone for fuel (methanol, ethanol, and formie aeid) electrooxidation, providing an ionic conductor network is established to link the catalytically active sites and the proton exchange membrane. The patent by Wilkinson et al. also suggests such electrode configurations (e.g., carbon foam, expended metal and reticulated metal) but experimental results were not provided [303]. 

Figure 4.63 compares the effect of the novel extended reaction zone supports on the electrocatalytic activity of PtRu for methanol electrooxidation. The catalyst characteristics arc presented in Table 4.3. The catalyst surface morphology on all three supports could be characterized as predominantly mesoporous coating composed of nanoparticle agglomerates (Figure 4.64). 

The deposition of films from a liquid phase whose precursor solution has been synthesized via sol-gel chemistry has widely been applied to produce coatings of different compositions and structures, such as oxides, hybrids, nanocomposites, and mesoporous coatings. Chemical-physical methods, such as plasma-enhanced chemical vapor deposition (PECVD) or chemical vapor deposition (CVD), are still fevored for most of the industrial applications. The sol-gel route to films, however, even if has not been able to challenge these techniques in terms of mass production, has occupied an important niche in the field. 

Examples of dense silica, hybrid silica, metal oxides, solid-state metal oxide solutions, or colloidal self-assembly are unlimited. However, the recent developments to accurately control processing conditions (e.g., atmosphere, temperature, and motion) led to films with unique properties (see Figure 9.6) [52,53]. These progresses concern mesoporous coatings with controlled pore size and structure [26], hard template infiltration and/or replication [54-58], nanostructured epitaxial low-quartz thin films [59], ultrathin nanostructured supported networks [60,61], ultrathick porous Ti02 layer prepared from aqueous solutions [51], coatings with hierarchical porosity [62], multilayer porous stacks [63], colloidal MOF layers [64,65], pillar planar nanochannels (PPNs) for nanofluidics [66], and so on. 

At the point where capillary condensation commences in the finest mesopores, the walls of the whole mesopore system are already coated with an adsorbed film of area A, say. The quantity A comprises the area of the core walls and is less than the specific surface A (unless the pores happen to be parallel-sided slits). When capillary condensation takes place within a pore, the film-gas interface in that pore is destroyed, and when the pore system is completely filled with capillary condensate (e.g. at F in Fig. 3.1) the whole of the film-gas interface will have disappeared. It should therefore be possible to determine the area by suitable treatment of the adsorption data for the region of the isotherm where capillary condensation is occurring. 

Possible applications include optical coatings [98], catalysts [99-101], substrates for Surface Enhanced Raman spectroscopy [102] or biosensor electrodes [103], Mesoporous gold can be prepared by de-aHoying a suitable precursor such as a... 

Of the various semiconductors tested to date, Ti02 is the most promising photocatalyst because of its appropriate electronic band structure, photostability, chemical inertness and commercial availability. But currently, a variety of nanostmctured Ti02 with different morphologies including nanorods, nanowires, nanostmctured films or coatings, nanotubes, and mesoporous/nanoporous structures have attracted much attention. 

Fig.4.30 Immobilization ofthe bacterial photosynthetic reaction center on tailored three-dimensional wormlike mesoporous W03-Ti02 films for artificial photosynthetic systems (A) procedure of film coating (B) proposed scheme of photoelectric conversion. Reprinted with permission from [229], Y. Lu et at., Langmuir 2005, 21, 4071. 2005, American Chemical Society.

Surface coating of mesoporous silicas provides an effective and flexible way for controlled release due to the high drug loading possible and the easy control of release rate. A drug-containing core or tablet is... 

The effects of organosilane type on the VB1 release are large and show that for tablets coated twice and dried at 60 °C, the samples coated with bis(trimethoxysilyl)hexane (TSH), bis(triethoxysilyl)octane (TSO), bis (trimethoxysilylpropyl)amine (TSPA) and bis[3-(trimethoxysilyl)propyl]-ethylenediamine (enTMOS) give slower release than the other samples including uncoated mesoporous silica used for a comparison (Figure 2.16). 

Z. Wu, Y. Jiang, T. Kim and K. Lee, Effects of surface coating on the controlled release of vitamin B1 from mesoporous silica tablets, J. Controlled Release, 2007, 119, 215. 

B. D. Hatton, K. Landskron, W. Whitnall, D. D. Perovic and G. A. Ozin, Spin Coated Periodic Mesoporous Organosilica Thin Films Towards a New Generation of Low-Dielectric-Constant Materials, Adv. Fund. Mater., 2005, 15, 823. 

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