Cobalt–silicon mixed oxide nanocomposites by modified sol–gel method

Esposito, Serena; Turco, Maria Caterina; Ramis, Gianguido; Bagnasco, G.; Pernice, P.; Pagliuca, C.; Bevilacqua, Maria; Aronne, Antonio

doi:10.1016/j.jssc.2007.09.032

Cited by 89 publications

(65 citation statements)

References 54 publications

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“…31 Codoped SiO 2 showed excellent stability under hydrothermal conditions and in a reductive/oxidative atmosphere that was attributed to the doped Co, which could be impregnated in the silica matrix as metal ions, 41 covalently bound compounds 42 such as SiAOACoA, or as tiny crystals that cannot be detected by XRD. The densification of the silica network under hydrothermal conditions can be explained by the disruption of the siloxane network, generation of silanol groups, and subsequent recombination and rearrangement of silanol groups into the siloxane network.…”

Section: Resultsmentioning

confidence: 99%

Permeation properties of hydrogen and water vapor through porous silica membranes at high temperatures

et al. 2011

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Silica and cobalt-doped silica membranes that showed a high permeance of 1.8 Â 10 À7 mol m À2 s À1 Pa À1 and a H 2 /N 2 permeance ratio of $730, with excellent hydrothermal stability under steam pressure of 300 kPa, were successfully prepared. The permeation mechanism of gas molecules, focusing particularly on hydrogen and water vapor, was investigated in the 300-500 C range and is discussed based on the activation energy of permeation and the selectivity of gaseous molecules. The activation energy of H 2 permeation correlated well with the permeance ratio of He/H 2 for porous silica membranes prepared by sol-gel processing, chemical vapor deposition (CVD), and vitreous glasses, indicating that similar amorphous silica network structures were formed. The permeance ratios of H 2 /H 2 O were found to range from 5 to 40, that is, hydrogen (kinetic diameter: 0.289 nm) was always more permeable than water (0.265 nm).

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Section: Resultsmentioning

confidence: 99%

Permeation properties of hydrogen and water vapor through porous silica membranes at high temperatures

et al. 2011

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“…Over the last decade, several studies [24][25][26][27][28][29] have focused on the preparation of nanospheres. Silica nanobottles [38], silica nanospheres with a magnetic core and charged surface [39], fluorescent silica nanospheres [40], polypyrrolemagnetite-silica particles [41], CdS-SiO 2 core-shell particles [42] and silica nanospheres encapsulating enzymes [43] are among some of the most interesting examples in this area.…”

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confidence: 99%

Sol–gel encapsulation of binary Zn(II) compounds in silica nanoparticles. Structure–activity correlations in hybrid materials targeting Zn(II) antibacterial use

Halevas

Nday

Kaprara

et al. 2015

Journal of Inorganic Biochemistry

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“…Figure 2.4. Structure evolution of (a) acid and (b) base catalysed sol-gel during calcination [48] In terms of silica membranes, the silica sol-gel method has been further improved by incorporating extra species/reactants, such as transitional metal alkoxides [53][54][55][56], surfactants [57,58] or metal salts [59][60][61][62][63] to functionalise the resultant materials. These reactants play various roles during the sol-gel method.…”

Section: Sol-gel Methodsmentioning

confidence: 99%

“…In addition, the specific states of cobalt in xerogels are not very clear, though cobalt tetroxide, cobalt hydroxide and cobalt silicate in xerogels have been reported [46,60,61,106,107].…”

Section: Hydrothermal Stability Of Silica Based Membranesmentioning

confidence: 99%

“…However, the formation of cobalt tetroxide in the xerogels is not only determined by cobalt loading, it also depends on specific sol gel conditions [60,61,106,107]. It is clear that there is a significant research gap regarding the correlation between cobalt phase and hydrothermal stability of cobalt doped silica matrices.…”

Section: Hydrothermal Stability Of Silica Based Membranesmentioning

confidence: 99%

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Development of microporous cobalt oxide silica membrane for CO2/H2 separation

Liu¹

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Hydrogen as a clean energy carrier is proposed as a long term solution to address issues related to global warming, energy security and air pollution. H2 production is currently fossil fuel based and this is expected to remain the case during the transition to cleaner sources. Hence, high performance H2 separation from CO2 is required to meet purity production targets, whilst the CO2 can be transported and stored in safe geological sites. Microporous silica membranes are a promising technology for processing syngas streams because of the simplicity of the sol-gel synthesis coupled with great pore size tailorability at molecular sieving dimensions. However, poor hydrothermal stability of silica membranes remains a contributing factor to the delay of the commercial deployment of this technology, particularly for processing wet syngas streams at high temperature (500-600 °C).Recent improvements have been attained by doping metal oxides in the silica matrix. Cobalt oxide silica membranes show excellent separation performance and improved hydrothermal stability.However, there are significant knowledge gaps associated with the fundamental understanding of the influence of cobalt dopant on the hydrothermal stability of silica matrices. To address these gaps, this thesis systematically investigated the physicochemical properties and hydrothermal stability of cobalt oxide silica materials and the performance of resultant membranes.The first key contribution of this thesis is the finding that the hydrothermal stability of cobalt doped silica materials is highly dependent on the cobalt phase, particularly Co 3+ as cobalt tetroxide (Co3O4).The Co3O4 silica materials resulted in less than 25% surface area loss whilst maintaining microporous structures when exposed to harsh hydrothermal conditions of 75 mol% H2O(v) at 550 °C for 40 h.Contrary to this, silica samples without Co3O4 completely densified under the same testing conditions. It is postulated that Co3O4 nanoparticles 'shielded' the silica matrix and inhibited to a certain degree the hydrolysis and condensation of the silica in the pores walls, thus conferring improved hydrothermal stability.A second key contribution is evidenced by sol-gel conditioning, thus aiding the formation of the Co3O4 in the silica network. By increasing the water ratio and decreasing the ethanol ratio, Co3O4 was formed at a much lower loading (Co/Si=0.1) than previously reported. The cobalt silica materials synthesised from the new sol-gel conditions showed a lower surface area loss after hydrothermal treatment (HT). The local structures around cobalt atoms were probed by X-ray absorption spectroscopy (XAS). For the low cobalt loading sample (Co/Si=0.05), the XAS results showed that the cobalt was highly dispersed in the silica network in a tetrahedral coordination (Co 2+ ) with oxygen and a small proportion of Co-Co interactions in the second shell. Co3O4 long range order was ii observed for higher cobalt loading samples (Co/Si=0.10, 0.25), which suggests that Co3O4 acts as a ph...

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Cobalt–silicon mixed oxide nanocomposites by modified sol–gel method

Cited by 89 publications

References 54 publications

Permeation properties of hydrogen and water vapor through porous silica membranes at high temperatures

Permeation properties of hydrogen and water vapor through porous silica membranes at high temperatures

Sol–gel encapsulation of binary Zn(II) compounds in silica nanoparticles. Structure–activity correlations in hybrid materials targeting Zn(II) antibacterial use

Development of microporous cobalt oxide silica membrane for CO2/H2 separation

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