Silica films mesoporous

Similarly, monometallic Rh, Pd, and Au and bimetallic Pt-Rh and Pt-Pd nanowires were prepared in FSM-16 or HMM-1 by the photoreduction method [30,33,34]. The bimetallic wires gave lattice fringes in the HRTEM images, and the EDX analysis indicated the homogeneous composition of the two metals. These results show that the wires are alloys of Pt-Rh and Pt-Pd. Mesoporous silica films were also used as a template for the synthesis of uniform metal particles and wires in the channels [35,36]. Recently, highly ordered Pt nanodot arrays were synthesized in a mesoporous silica thin film with cubic symmetry by the photoreduction method [37]. The... 

Dourdain, S. Gibaud, A. 2005. On the capillary condensation of water in mesoporous silica films measured by x-ray reflectivity. Appl. Phys. Lett. 87 223105. 

Fattakhova-Rohlfing, D. Wark, M. Rathousky, J. 2007. Electrode layers for electrochemical applications based on functionalized mesoporous silica films. Sens. Actual B-Chem. 126 78-81. 

Fattakhova-Rohlfing, D. Rathousky, J. Rohlfing, Y. Bartels, O. Wark, M. 2005. Functionalized mesoporous silica films as a matrix for anchoring electrochemically active guests. Langmuir 21 11320-11329. 

Synthesis ofPt and Au Nanoparticle Arrays in Mesoporous Silica Films 631... 

Synthesis ofPt and Au Nanoparticle Arrays in Mesoporous Silica Films and their Electric/Magnetic Properties in Terms of the Quantum-Size Effect... 

Figure 15.28 TEM images of (a) Au nanoparticle arrays in mesoporous silica film (b) superlattice of extracted Au nanoparticles stabilized with 1-dodecanethiol.

From above experimental results, Pt nanoparticle arrays were similarly formed in the mesoporous silica film by the photoreduction of H2PtCl6/mesoporous silica film/Si in the presence of vapors of water and methanol. As shown in Figure 15.29, Pt nanoparticles (diameter 3 nm) are packed close to each other in the one-dimensional mesopores, and in some part the arrays of Pt nanoparticles show an ordered structure [27]. 

Figure 15.30 TEM and electron diffraction images of Pt nanoparticles (diameter 2.5 nm) with mesoporous frameworks of mesoporous silica thin films from different planes [100] (a) and [210] (b) (c) cross-section structure of a single electron soliton device of Pt nanoparticle/mesoporous silica film on a Si substrate connected with two Al electrode.

Figure 15.31 Coherent oscillation in l-V characteristics observed on a Pt nanoparticle/mesoporous silica film at 4.2 K.

Structural Analysis of Hexagonal Mesoporous Silica Films Produced from Triblock-Copolymer-Structuring Sol-Gel... 

Aida and coworkers developed poly(pyrrole)-containing mesoporous silica films in both hexagonal and lamellar phases.34 The polypyrrole chains are highly constrained and insulated when incorporated within hexagonal mesoscopic channels and the possibility of the polarons recombining into bipolarons is significantly suppressed. In contrast, the two-dimensional lamellar phase affords spatial freedom for electron recombination. 

From the viewpoint of supramolecular chemistry, behavior of noncovalent supramolecular assemblies confined in mesopores would be a more interesting target. Aida and coworkers reported the first example of immobilization of one-dimensional columnar charge-transfer (CT) assemblies in a mesoporous silica film through sol-gel... 

It has also been demonstrated that mesoporous materials are viable candidates for optical devices [90]. Silicon nanoclusters were formed inside optically transparent, free-standing, oriented mesoporous silica film by chemical vapor deposition (CVD) of disilane within the spatial confines of the channels. The resulting silicon-silica nanocomposite displayed bright visible photoluminescence and nanosecond lifetimes (Fig. 2.12). The presence of partially polymerized silica channel walls and the retention of the surfactant template within the channels afforded very mild 100-140°C CVD conditions for the formation of... 

Figure 2.18. Scanning electron microscopy (a) and transmission electron microscopy (b) images of a free-standing mesoporous silica film grown at the air-water interface.

The early preparations of mesoporous silica film were conducted by growth from solution.[20,276]. The basic principle for the synthesis of ordered mesoporous films by growth from solution is to bring the synthesis solution (including a solvent, surfactant, and inorganic precursor) into contact with a second phase, e.g. solid (ceramic), gas (air), or another liquid (oil). The two-phase system is kept under specific conditions and the ordered film is formed at the interface. When the second phase is solid, it is the support on which the ordered film or membrane is grown. When the second phase is air or oil, the solid films are self-standing. 

H. Yang, N. Coombs, I. Sokolov, and G.A. Ozin, Free-standing and Oriented Mesoporous Silica Films Grown at the Air-Water Interface. Nature (London), 1996, 381, 589-592. 

S. Besson, C. Ricolleau, T. Gacoin, C. Jacquiod, and J.P. Boilot, Highly Ordered Orthorhombic Mesoporous Silica Films. Microporous Mesoporous Mater., 2003, 60, 43-49. 

The synthesis of mesoporous silica films typically begins with the preparation of precursor solutions. These solutions contain a silica source (typically an alkoxide, although chloride and colloidal precursors can be used), a surfactant molecule used to template the mesostructure, an acid or base catalyst, and solvents. The nanoscale structure is then formed by a cooperative self-assembly of monomeric or partially... 

The chemistry involved in the formation of mesoporous silica thin films is qualitatively well understood. However, specific reaction mechanisms of the individual steps are still debated. In addition, owing to the complexity of the sol-gel reaction pathways and cooperative self-assembly, full kinetic models have not been developed. From the time of mixing, hydrolysis reactions, condensation reactions, protonation and deprotonation, dynamic exchange with solution nucleophiles, complexation with solution ions and surfactants, and self-assembly, all occur in parallel and are discussed here. Although the sol-gel reactions involved may be acid or base catalyzed, mesoporous silica film formation is carried out under acidic conditions, as silica species are metastable and the relative rates of hydrolysis and condensation reactions lead to interconnected structures as opposed to the stable sols produced at higher pH. Silicon alkoxides are the primary silica source (tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, etc.) and are abbreviated TMOS, TEOS, and TPOS, respectively. Starting from the alkoxide, Si(OR)4, in ROH and H2O solution, some of the general reactions are ... 

Fig. 4 Critical packing parameters and characteristic structure typical to mesoporous silica films. The top shows a cross-section of a micelle, displaying the parameters used to calculate the CPP. The spherical head group for the surfactant represents the effective cross-sectional area that the head group occupies. (View this art in color at www.dekker.com.)...

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