Soluble metal oxide precursors

Utilizes inkjet printing of overlapping patterns of soluble metal oxide precursors onto a conductive substrate. Metal nitrate salts have been the most widely printed... 

Among various methods to synthesize nanometer-sized particles [1-3], the liquid-phase reduction method as the novel synthesis method of metallic nanoparticles is one of the easiest procedures, since nanoparticles can be directly obtained from various precursor compounds soluble in a solvent [4], It has been reported that the synthesis of Ni nanoparticles with a diameter from 5 to lOnm and an amorphous-like structure by using this method and the promotion effect of Zn addition to Ni nanoparticles on the catalytic activity for 1-octene hydrogenation [4]. However, unsupported particles were found rather unstable because of its high surface activity to cause tremendous aggregation [5]. In order to solve this problem, their selective deposition onto support particles, such as metal oxides, has been investigated, and also their catalytic activities have been studied. 

The arrows show the isotherm evolution for continual addition of dissolved Me. The initial isotherm with the slope of 1 (in the double logaritmic plot) corresponds to a Langmuir isotherm (surface complex formation equilibrium). [Me]S0 = solubility concentration of Me for the stable metal oxide [Me]p = solubility concentration of Me for a metastable precursor (e.g., a hydrated Me oxide phase). 

Solvothermal reaction (thermal decomposition) of metal aUcoxides in toluene usually yields the corresponding metal oxides (see Section III.B.l). Aromatic hydrocarbons are favored for this reaction over aliphatic hydrocarbons because of the higher solubility of the precursors in the former than those in the latter. Xylenes (dimethylbenzenes) are also suitable solvents for the solvothermal synthesis. 

Figure 13.29. Schematic sorption isotherms of a metal ion (Me) on an oxide (XO ) at constant pH (a) adsorption only (H) adsorption and surface precipitation via ideal solid solution (c) adsorption and heterogeneous nucleation in the absence of a free energy nucleation barrier (AG 0) adsorption and heterogeneous nucleation of a metastable precursor (e) same as in (3) but with transformation of the precursor into the stable phase. The arrows show the isotherm evolution for continual addition of dissolved Me. The initial isotherm with the slope of 1 (in the double logarithmic plot) corresponds to a Langmuir isotherm (surface complex formation equilibrium). [Me]s , = solubility concentration of Me for the stable metal oxide [Me]p = solubility concentration of Me for a metastable precursor (e.g., a hydrated Me oxide phase). (From Van Cappellen, 1991.)...

Well ordered mesoporous silicate films were prepared in supercritical carbon dioxide.[218] In the synthesis in aqueous or alcoholic solution, film morphology of preorganized surfactants on substrate cannot be fully prescribed before silica-framework formation, because structure evolution is coincident with precursor condensation. The rapid and efficient preparation of mesostructured metal oxides by the in situ condensation of metal oxides within preformed nonionic surfactants can be done in supercritical CCU- The synthesis procedure is as follows. A copolymer template is prepared by spin-coating from a solution containing a suitable acid catalyst. Upon drying and annealing to induce microphase separation and enhance order, the acid partitions into the hydrophilic domain of the template. The template is then exposed to a solution of metal alkoxide in humidified supercritical C02. The precursor diffuses into the template and condenses selectively within the acidic hydrophilic domain of the copolymer to form the incipient metal oxide network. The templates did not go into the C02 phase because their solubility is very low. The alcohol by-product of alkoxide condensation is extracted rapidly from the film into the C02 phase, which promotes rapid and extensive network condensation. Because the template and the metal oxide network form in discrete steps, it is possible to pattern the template via lithography or to orient the copolymer domains before the formation of the metal oxide network. 

Oligomerization becomes more and more important as the N-Z difference increases, that is, as the oxidation state Mz+ decreases. Divalent metals give insoluble polymeric alkoxides [Af(OR)2]n (Af2+ = Fe, Co, Ni, Cu,. ..). This was a real drawback for the sol-gel synthesis of high-Tc superconducting ceramics, such as YBa2Cu307-e. Bulky ligands, such as 2-(2-ethoxy-ethoxy)ethoxide had then to be used to prevent oligomerization and obtain soluble copper oxide molecular precursors [11]. 

Sirio, C Poncelet, O., Hubert-Pfaizgraf, L. G., Daran, J. C., and Vaissermann, J., Reactions between copper p-diketonates and metal alkoxides as a route to soluble and volatile copper(II) oxide precursors Synthesis and molecular structure of Cu4( J-3,n -0C2H40iPr)4(acac)4 and (acac)Cu(p-OSiMe3)2Al(OSiMe3)2, Polyhedron, 11, 177 (1992). 

Another potential source of processlble precursors Is the citric acid/ethylene glycol system which has been esiployed previously in the preparation of highly dispersed perovskite, spinel and related complex oxides. This method provides soluble, metal-organic, polymer precursors which have been used for the fabrication of oxide thin films as well as for the production of oxide powders with excellent homogeneity, good stoichiometry control and uniform sizes at relatively low temperatures(13,14). 

One of the advantages of starting with a silica sol is that when such colloidal solutions are dried, the surface of the silica particles becomes coated with the metal or metal oxide or their soluble precursors, in molecular dimensions, and little, if any, excess metal modifier will be present in locations other than on said particle surfaces. Thus, the metal modifier is located in such a manner as to exert its maximum influence on catalytic activities and harmful excesses are not concentrated in isolated areas. 

Ozin and coworkers recently extended the supra-molecular I S+ assembly into the synthesis of binary mesoporous yttrium oxide-stabilized-zirconium oxide materials.These materials were synthesized by a modified sol-gel method under basic conditions, where zirconium ethoxide and yttrium acetate were used as the precursors for the transition metal oxides, and CTAB was used to form the supramolecular templates. The use of ethylene glycol with coordinating capability as a cosolvent may play a role in controlling the hydrolysis rate and solubility of zirconium(IV) and yttrium(III). This synthesis strategy is similar to that of so-called polymerizable-complex method, which was widely used to prepare multicomponent single-phase oxides. The yttrium content in these binary materials can be tuned from 12-56 wt%, and no phase segregation of yttrium and zirconium oxides was observed. These materials could be applied in designing new solid oxide fuel-cell electrode materials. 

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