New insight in the role of modifying ligands in the sol-gel processing of metal alkoxide precursors: A possibility to approach new classes of materials

Kessler, Vadim G.; Spijksma, G.I.; Seisenbaeva, Gulaim A.; Håkansson, Sebastian; Blank, David H.A.; Bouwmeester, Henny J.M.

doi:10.1007/s10971-006-9209-6

Cited by 188 publications

(142 citation statements)

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“…It was reported that the rate of hydrolysis and the extent of cross-linking in the formed network are decreased as a result of chelation [32]. Kessler et al [33] stated that hydrolysis and polycondensation reactions of metal alkoxides facilitated by the chemical modification and their kinetics have no direct relation to the sol-gel transformation. In the IR spectrum of EAA, two characteristic bands located at 1,720 and 1,650 cm -1 were assigned to the C-O stretching vibrations of the ketonic and enolic forms, respectively [34].…”

Section: Polymeric Solsmentioning

confidence: 99%

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Sol–gel derived mesoporous and microporous alumina membranes

Topuz

Çiftçioğlu

2010

J Sol-Gel Sci Technol

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Stable polymeric and colloidal boehmite sols were prepared by sol-gel process through controlled hydrolysis/condensation reactions. The particle sizes of the colloidal sols were in the 12-25 nm range depending on the process parameters and about 2 nm for polymeric sols. The presence of a significant increase in the microporosity content of the heat treated polymeric membranes relative to the mesoporous colloidal membranes might make the design of thermally stable microporous alumina membranes with controlled pore structures possible. The phase structure evolution in the 600-800°C range had shown that the crystallization of the gamma alumina in the amorphous matrix starts at about 800°C. This indicated that the pore structure stability may be enhanced through processing up to this relatively high temperature in polymeric alumina derived unsupported membranes. The permeance values of the two and three layered colloidal alumina membranes were observed to be independent of pressure which implies that the dominant gas transport mechanism is Knudsen diffusion in these structures. This was also supported by the 2.8 nm BJH pore sizes of the colloidal membranes. The Knudsen diffusion equation derived permeances of the polymeric alumina membranes with thicknesses of about 300 nm were determined to be very close to the experimentally determined permeance values.

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Section: Polymeric Solsmentioning

confidence: 99%

“…This may be due to the influence of the increasing chelating agent content on the gelation and consolidation behaviour of the sol particles during drying. Kessler et al [33] reported that the use of chelating only ligand (e.g. acetylacetonate) results in dense film because of ligand mobility.…”

Section: Polymeric Solsmentioning

confidence: 99%

Sol–gel derived mesoporous and microporous alumina membranes

Topuz

Çiftçioğlu

2010

J Sol-Gel Sci Technol

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“…Ligands such as -diketonates are hydrophobic, and helps in the stabilization of the inorganic colloids in organic solvents, [34] thus they can stabilize dispersions in essentially the same way as surfactants. [35] This chelation increases the reactivity of the alkoxides in hydrolysis-polycondensation, resulting in facile formation of self-assembled micelar aggregates, that can explain the morphology and textural properties of the materials. Thus, porosity can be achieved through the retention of ligands inside the volume of micelles and thus requires inmobilization of ligands.…”

Section: Resultsmentioning

confidence: 99%

Key insights on the structural characterization of textured Er2O3–ZrO2 nano-oxides prepared by a surfactant-free solvothermal route

Julián‐López

Luz

Gonell

et al. 2012

Journal of Alloys and Compounds

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Keywords: structural resolution / Er 2 O 3 -ZrO 2 / HRTEM / fluorite / solvothermal route Zirconia-mixed oxides can exhibit cubic fluorite and pyrochlore structure. Their discrimination is not easy in nanooxides with a crystal size close to that of a few unit cells. In this work, High Resolution Transmission Electron Microscopy (HRTEM) has been employed to provide key insights on the structural characterization of a nanometric and porous mixed Er 2 O 3 -ZrO 2 oxide. The material was prepared by a simple template-free solvothermal route that provided nanocrystalline powders at low temperature (170 ºC) with spherical morphology, and high surface area (280 m 2 /g). The porosity was mainly originated from the assembling of organic complexing agents used in the synthesis to limit the crystal growth and to control hydrolysis and condensation reaction rates. The samples were characterized by thermal analysis, X-ray Diffraction, Scanning Electron Microscopy and N 2 adsorption measurements.A detailed study by HRTEM was conducted on microtomed samples. It was observed that the material was made of nanocrystals packed into spherical agglomerates. HRTEM simulations indicated that it is not possible to identify the pyrochlore phase in nanoparticles with diameter below 2 nm. In our samples, the analysis of the HRTEM lattice images by means of Fast Fourier Transform (FFT) techniques revealed well defined spots that can be assigned to different planes of a cubic fluorite-type phase, even in the raw material. Raman spectroscopy was also a powerful technique to elucidate the crystalline phase of the materials with the smallest nanoparticles. HREM and Raman results evidenced that the material is constituted, irrespective of the temperature of the final calcination step, by an ensemble of randomly oriented nanocrystals with fluorite structure. This study opens new perspectives for the design of synthetic approaches to prepare nanooxides (fluorites and pyrochlores) and the analysis of their crystalline structure.____________ [a]

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“…[1][2][3][4] Nowadays, the preparation of these oxides is often performed by chemical methods. 3,[5][6][7] In particular, the sol-gel process, either hydrolytic or non-hydrolytic, has been widely employed due to its advantages over conventional solid state methods. These advantages include lower processing temperatures and better control over microstructure, uniformity and stoichiometry of the final material.…”

Section: Introductionmentioning

confidence: 99%

“…[12][13][14][15] Depending on a number of factors, such as ligand composition, choice of solvents, stability in processing and metal stoichiometry with respect to the desired product, the use of SSPs can allow the synthesis of pure and homogeneous mixed metal oxides. [5][6][7] In earlier reports 16,17 we presented our first results on the sol-gel synthesis of iron-titanium oxides using the structurally characterised Fe II /Ti IV SSP, [FeCl{Ti 2 (OPr i ) 9 }] (1, Figure 1). 18 This precursor contains two titanium(IV) centres, each coordinated to six isopropoxide groups, and one iron(II) centre coordinated to four isopropoxides and one chloride.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of Fe/Ti oxides from a single source alkoxide precursor under inert atmosphere

Camargo¹,

Nunes²,

Luis³

et al. 2008

J. Braz. Chem. Soc.

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O alcóxido heterometálico [FeCl{Ti 2 (OPr i ) 9 }] (1) foi utilizado como um precursor de fonte única para a preparação de óxidos de Fe/Ti sob atmosfera inerte. Três procedimentos sintéticos distintos foram adotados no processamento de 1, com o emprego de soluções aquosas ácidas (HNO 3 ou HCl), ou na ausência de ácido mineral. Os produtos foram caracterizados por difratometria de raios X (pó), microscopia eletrônica de varredura combinada com espectroscopia de dispersão de raios X (MEV/EDS) e espectroscopias Raman, de ressonância paramagnética eletrônica (RPE) e Mössbauer. Os óxidos produzidos contêm titânio(IV) e ferro(III) (ou ferro(II)), dependendo das condições de reação e das temperaturas de tratamento térmico. Uma interessante redução de ferro(III) a ferro(II), que levou à obtenção de ilmenita (FeTiO 3 ), foi observada a 1000 o C no sistema contendo HNO 3 . Estudos por MEV/EDS revelaram uma distribuição altamente heterogênea dos metais em todos os produtos, possivelmente relacionada com a presença de um conteúdo significativo de carbono e de defeitos estruturais (vacâncias de oxigênio) nos sólidos.The heterometal alkoxide [FeCl{Ti 2 (OPr i ) 9 }] (1) was employed as a single source precursor for the preparation of Fe/Ti oxides under inert atmosphere. Three different synthetic procedures were adopted in the processing of 1, either employing aqueous HNO 3 or HCl solutions, or in the absence of mineral acids. Products were characterised by powder X-ray diffractometry, scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM/EDS) and Raman, electron paramagnetic resonance (EPR) and Mössbauer spectroscopies. Oxide products contained titanium(IV) and either iron(III) or iron(II), depending on reaction conditions and thermal treatment temperatures. An interesting iron(III)→iron(II) reduction was observed at 1000 o C in the HNO 3 -containing system, leading to the detection of ilmenite (FeTiO 3 ). SEM/EDS studies revealed a highly heterogeneous metal distribution in all products, possibly related to the presence of a significant content of carbon and of structural defects (oxygen vacancies) in the solids.Keywords: oxides, sol-gel, single source precursor, inert atmosphere, electron microscopy IntroductionMultimetal oxide systems play an important role in materials science. They have been extensively investigated for the development of high performance ceramics and (nano)composites, aiming at applications in optics, electronics, magnetism and catalysis. The development of structural components, energy conversion devices, sensors and MRI contrast agents has also benefited from heterometal oxide research. [1][2][3][4] Nowadays, the preparation of these oxides is often performed by chemical methods. 3,[5][6][7] In particular, the sol-gel process, either hydrolytic or non-hydrolytic, has been widely employed due to its advantages over conventional solid state methods. These advantages include lower processing temperatures and better control over microstructure, uniformity and stoichiometry o...

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New insight in the role of modifying ligands in the sol-gel processing of metal alkoxide precursors: A possibility to approach new classes of materials

Cited by 188 publications

References 34 publications

Sol–gel derived mesoporous and microporous alumina membranes

Sol–gel derived mesoporous and microporous alumina membranes

Key insights on the structural characterization of textured Er2O3–ZrO2 nano-oxides prepared by a surfactant-free solvothermal route

Synthesis of Fe/Ti oxides from a single source alkoxide precursor under inert atmosphere

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