Immobilization layered metal oxides

Preparation of metal oxide thin film by means of stepwise absorption of metal alkoxide has been carried out in the past for the activation of heterogeneous catalysts [13]. For example, Asakura et al. prepared one-atomic layer of niobium oxide by repeating chemisorption of Nb(OEt)5 on silica beads. The catalyst obtained by immobilizing platinum particles on a niobum oxide layer showed improved reactivity for hydrogenation of ethylene in comparison with... 

Surface redox reactions — or surface -> electrode reactions, are reactions in which both components of the -> redox couple are immobilized on the electrode surface in a form of a -> monolayer. Immobilization can be achieved by means of irreversible -> adsorption, covalent bonding, self-assembling (- self-assembled mono-layers), adhesion, by Langmuir-Blodgett technique (- Langmuir-Blodgett films), etc. [i]. In some cases, the electrode surface is the electroactive reactant as well as the product of the electrode reaction is immobilized on the electrode surface, e.g., oxidation of a gold, platinum, or aluminum electrode to form metal oxide. This type of electrode processes can be also considered as surface electrode reactions. Voltammetric response of a surface redox reaction differs markedly from that of a dissolved... 

The immobilization of metal complex catalysts on polymers and inorganic oxides has received considerable attention as a means of combining the best advantages of homogeneous and hetereo-geneous catalysis (1-6). The swelling layer lattice silicates known as smectite clay minerals have added an important new dimension to metal complex Immobilization. These compounds have mica-type structures in which two-dimensional silicate sheets are separated by monolayers of alkali metal or alkaline earth cations (7). The structure of a typical smectite, hectorite, is illustrated in Figure 1. 

Metal oxide semiconductor electrodes also differ from bare metal electrodes with respect to interactions with water. Interfacial region in which water properties differ significantly from those found in the bulk phase is generally more extensive than for metal electrodes. Significant interfacial water structure can extend to several molecular layers from oxide surfaces. Also, the inner monolayer of water can be rotationally immobile due to hydrogen bonding, a feature that is absent at pure metal surfaces. 

Ruthenium phthalocyanine 49 (R = -H, M = Ru(II)) monolayers were obtained by self-assembly on pyridyl-functionalized SiOa or AI2O3 substrates by coordination between Ru and the pyridino group to obtain 63 [155]. The pyridino-functionalized metal oxides were dipped into a solution containing the more soluble benzonitrile derivative of the phthalocyanine RuPc(NC-C6H5)2, and ligand exchange reactions led to 63. Strategies have been described to immobilize a second layer of a Ru-phthalocyanine or a Co tetraphenyl-porphyrin. 

The aim of the present study was to immobilize PEG on metal oxide surfaces such as silicon dioxide, titanium dioxide, and niobium pentoxide. The adsorption behavior of polyelectrolytes on such metal oxide surfaces has been characterized, " and polycations, in particular, were found to form stable adsorbed layers on negatively charged oxides such as silicon dioxide and titanium dioxide. 

Among the various techniques for the immobilization of PEG on surfaces, - - graft copolymers of poly(L-ly sine) and poly(ethylene glycol) (PLL- -PEG) are particularly attractive. PLL- -PEG copolymers spontaneously adsorb from aqueous solutions as dense, monomolecular layers onto a rangeofnegatively charged surfaces such as various metal oxides and tissue-culture polystyrene, protecting them against nonspecific protein adsorption moreover,... 

---