Modified amorphous oxide surfaces

An alternative method to produce surface amorphous modified oxides (silica, titania, alumina, etc.) is to promote the reaction of the oxide precursor with the organic flmctionahzing agent. A typical example is shown in Fig. 3.3. 

In 1990, Choudary [139] reported that titanium-pillared montmorillonites modified with tartrates are very selective solid catalysts for the Sharpless epoxidation, as well as for the oxidation of aromatic sulfides [140], Unfortunately, this research has not been reproduced by other authors. Therefore, a more classical strategy to modify different metal oxides with histidine was used by Moriguchi et al. [141], The catalyst showed a modest e.s. for the solvolysis of activated amino acid esters. Starting from these discoveries, Morihara et al. [142] created in 1993 the so-called molecular footprints on the surface of an Al-doped silica gel using an amino acid derivative as chiral template molecule. After removal of the template, the catalyst showed low but significant e.s. for the hydrolysis of a structurally related anhydride. On the same fines, Cativiela and coworkers [143] treated silica or alumina with diethylaluminum chloride and menthol. The resulting modified material catalyzed Diels-Alder reaction between cyclopentadiene and methacrolein with modest e.s. (30% e.e.). As mentioned in the Introduction, all these catalysts are not yet practically important but rather they demonstrate that amorphous metal oxides can be modified successfully. 

The influence of the modification on the surface atomic ratios of Si Al as measured by ESCA is shown in Table 2. The enrichment of alumina was observed for modified HZSH-5. The surface Si Al ratio was decreased to about one half its original value. It seemed impossible for diazomethane modification to remove the framework alumina of the zeolite. Ve assumed that the enrichment was caused by the migration of the amorphous aluminum oxide to the surface of the zeolite. The mechanism should be studied further in detail. 

Several strategies have been employed in supporting metal complexes on oxide surfaces. For example, surface 0x0 and hydroxyl groups may be used as ligands the surface may be modified by reaction of the hydroxyl groups to introduce ligands to the surface, and more recently amorphous metal oxides, such as silica, have been imprinted via sol-gel techniques to generate shape selective cavities. ... 

Modified Amorphous Oxide Surfaces as Metal Cation Sequestrating Agents... 

Modified Amorphous Oxide Surfaces AS Electrochemical Sensors... 

The use of alkoxides as precursors to produce new materials [1] has increased in the last decade due to the advantages of the so-called sol-gel process [2] such as the preparation of compounds with high homogeneity, at room temperatures, in contrast with the typical high-temperature syntheses in solid-state chemistry. Such an experimental approach can lead not only to modified amorphous oxide surfaces, as discussed in Chapter 1, but also to nanostructured modified surfaces, as will be shown here. 

In an interesting interplay between GO and organosilanes (which are so extensively used to modify amorphous or nanostructured oxide surfaces), there are reports [33], of the preparation of intercalation compounds in which amino groups are inserted into the interlayer space of GO, using 3-aminopropylethoxysilanes. For such compounds, it was shown that the amino groups of... 

The term surface must be considered in a broad sense. If, for example, we are talking about an amorphous solid such as sihca gel, one understands immediately what is being considered as the surface, but when considering a lamellar solid, such as molybdenum oxide, both surfaces, that is, the external and internal (intrala-mellar) parts of the solid must be taken into accoimt. So, to promote intercalation is also to modify a surface, of course. 

In another study, the so-called sohd-liquid-solid (SLS) technique was used to prepare a silicon oxide nanofiber surface [64]. The amorphous sihcon oxide nanofibers shown in Fig. 10b were made by heating a silicon substrate coated with a thin gold layer at 1100°C for 3 h in a lutrogen atmosphere in contrast to the previous example, no additional source of silicon materials was used in this case. As before, the nanofiber growth starts at the interface of the Au/Si alloy droplet and the Si substrate and is maintained by the diffusion of the Si atoms from the substrate to the interface [65]. The surface was then UV/ozone-treated to generate surface hydroxyl groups that were subsequently reacted with perfluorodecyltrichlorosilane. The chemically modified nanofiber surface exhibited a WCA of 152°. 

In our previous study, the surface of commercial LiCoOj was modified by coating its surface with a thin layer of amorphous magnesium oxide (nano-... 

In both cases, we observe an amorphous pattern no crystallites of rare earth oxide appear even at 25% wt. loading. This indicates that oxide particles remain less than 30A in diameter. The surface area, pore volume and pore size distribution of the starting Si-Al support also change on impregnation. Table 1 lists the values for yttria-modified samples of... 

Komrska Satava (1970) showed that these accounts apply only to the reaction between pure zinc oxide and phosphoric acid. They found that the setting reaction was profoundly modified by the presence of aluminium ions. Crystallite formation was inhibited and the cement set to an amorphous mass. Only later (7 to 14 days) did XRD analysis reveal that the mass had crystallized directly to hopeite. Servais Cartz (1971) and Cartz, Servais Rossi (1972) confirmed the importance of aluminium. In its absence they found that the reaction produced a mass of hopeite crystallites with little mechanical strength. In its presence an amorphous matrix was formed. The amorphous matrix was stable, it did not crystallize in the bulk and hopeite crystals only grew from its surface under moist conditions. Thus, the picture grew of a surface matrix with some tendency for surface crystallization. 

ZnO displays similar redox and alloying chemistry to the tin oxides on Li insertion [353]. Therefore, it may be an interesting network modifier for tin oxides. Also, ZnSnOs was proposed as a new anode material for lithium-ion batteries [354]. It was prepared as the amorphous product by pyrolysis of ZnSn(OH)6. The reversible capacity of the ZnSn03 electrode was found to be more than 0.8 Ah/g. Zhao and Cao [356] studied antimony-zinc alloy as a potential material for such batteries. Also, zinc-graphite composite was investigated [357] as a candidate for an electrode in lithium-ion batteries. Zinc parhcles were deposited mainly onto graphite surfaces. Also, zinc-polyaniline batteries were developed [358]. The authors examined the parameters that affect the life cycle of such batteries. They found that Zn passivahon is the main factor of the life cycle of zinc-polyaniline batteries. In recent times [359], zinc-poly(anihne-co-o-aminophenol) rechargeable battery was also studied. Other types of batteries based on zinc were of some interest [360]. 

Some properties of palladium deposited on different amorphous or zeolitic supports were determined, including catalytic activity per surface metal atom (N) for benzene hydrogenation, number of electron-acceptor sites, and infrared spectra of chemisorbed CO. An increase of the value of N and a shift of CO vibration toward higher frequencies were observed on the supports which possessed electron-acceptor sites. The results are interpreted in terms of the existence of an interaction between the metal and oxidizing sites modifying the electronic state of palladium. 

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