Hydrogen Adsorption Isotherms: Modelling of Experimental Data

Tibus, Stefan; Klier, Jürgen; Leiderer, Paul

doi:10.1007/s10909-005-9412-9

Cited by 2 publications

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“…From a theoretical point of view, the influence of capillary fluctuations on wetting phenomena has attracted much attention as it could lead to nonuniversal wetting behavior with critical exponents depending explicitly on temperature [7,8]. Experimentally, the observation of this entropic repulsion in typical liquid layers is challenging, but some observations have shown that a correct description of adsorption isotherms of molecularly thin films could be achieved if one takes the entropic interaction into account [9][10][11][12].Similarly to simple liquids, mixtures of colloidal particles with nonadsorbing polymer can phase separate into a dense colloidal fluid phase (colloidal liquid) and a dilute one (colloidal gas) [13]. This phase separation is due to the depletion attraction that the polymer mediates between the colloids [14 -16].…”

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confidence: 99%

Fluctuation Forces and Wetting Layers in Colloid-Polymer Mixtures

et al. 2008

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We present confocal microscopy experiments on the wetting of phase-separated colloid-polymer mixtures. We observe that an unusually thick wetting layer of the colloid-rich phase forms at the walls of the glass container that holds the mixture. Because of the ultralow interfacial tension between the colloid-rich and the polymer-rich phases, the thermally activated roughness of the interfaces becomes very big and measurable. We observe that close to the critical point the roughness of the interface between the wetting layer and the polymer-rich phase decreases with decreasing layer thickness: large excursions of the interface are confined in the wetting layer. The measured relationship between the roughness and the thickness of the wetting layer is in qualitative agreement with the predictions of renormalization group theory for short-range forces and complete wetting. DOI: 10.1103/PhysRevLett.100.178305 PACS numbers: 82.70.Dd, 68.08.Bc, 68.35.Ct, 68.37.ÿd Wetting layers are ubiquitous in both nature and industry [1,2] and occur in a wide range of systems. For two coexisting phases, Cahn first proposed an argument that explains the formation of a wetting layer of one of the two phases onto a substrate (complete wetting) when approaching the critical point [3]. One classical example is a demixed (two-phase) binary liquid mixture in which the dense phase intrudes between the lighter fluid phase and the vapor. However, once the wetting conditions are set, the remarkable density inversion can only be maintained if forces act between the two film interfaces. For ordinary liquids, these forces are generally van der Waals forces [1,2] which, given their range, invariably lead to wetting layer thicknesses of the order of 100 Å .Liquid interfaces are also rough-they are locally fluctuating due to thermally excited capillary waves [4]. Consequently, the confinement of interface fluctuations in a wetting layer can in principle create an entropic interaction that enters the force balance between surface forces and gravity [5]. The existence of such an entropic force was first established by Helfrich [6] in the case of tensionless membranes. For liquid interfaces, where surface tension dominates, the situation is more complex. From a theoretical point of view, the influence of capillary fluctuations on wetting phenomena has attracted much attention as it could lead to nonuniversal wetting behavior with critical exponents depending explicitly on temperature [7,8]. Experimentally, the observation of this entropic repulsion in typical liquid layers is challenging, but some observations have shown that a correct description of adsorption isotherms of molecularly thin films could be achieved if one takes the entropic interaction into account [9][10][11][12].Similarly to simple liquids, mixtures of colloidal particles with nonadsorbing polymer can phase separate into a dense colloidal fluid phase (colloidal liquid) and a dilute one (colloidal gas) [13]. This phase separation is due to the depletion attraction that the polymer m...

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Fluctuation Forces and Wetting Layers in Colloid-Polymer Mixtures

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“…The critical limitation of their development remains so far the processing and exposure of large surface areas of metallic NPs within highly porous matrices composed of a naturally high specific surface area material to optimize the surface to volume ratio. The adsorption [17][18][19][20][21] and catalytic 11,15,[22][23][24][25] properties of gold are well documented following Haruta's work in the 90's 25 and sub-10 nm NPs were shown to be suitable adsorption sites due to their electronic d-bands becoming harder to saturate, creating semi-metallic structures more sensitive to selective gas adsorption. 14,26 The oxidation of CO by various sizes of gold NPs was found to be up to 100 times higher with sub-2 nm NPs when compared to sub-12 nm NPs, therefore highlighting the importance of exposed surface area on catalytic reactions.…”

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Activation of gold decorated carbon nanotube hybrids for targeted gas adsorption and enhanced catalytic oxidation

et al. 2012

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10Free standing assemblies of carbon nanotubes (CNTs), known as bucky-paper, (BP) have been functionalised through the in-situ plating of gold nanoparticles within the interstitial spaces in the BP. The nanoparticles are extremely small and well distributed at short plating times, so much so that the specific surface area of the BP is actually 15 increased by the gold incorporation. These well distributed nanoparticles exhibit high enthalpy hydrogen storage and selective carbon dioxide adsorption over other gases, in particular methane. In concert with the conductive BP substrate, it has been demonstrated that these materials can also act as high turnover heterogeneous catalysts. (Graphical abstract)Keywords 25 gold decorated carbon nanotube; composite bucky-paper; specific gas storage; catalytic activity Self-supporting BPs were processed from chemical vapour deposition grown multi walled CNTs as described in a previous study 51 . Research highlightsIn short, the functionalized CNTs were then suspended in propan-2-ol by 5 repeated cycles of freezing at -17 ºC followed by bath sonication as per the method developed in 50 . The CNT suspension was then filtered on top 10 of a porous poly(ether sulphone) membrane to form a self-supporting BP.BPs were exposed for 10 min to a flow of UV induced ozone in order to form hydroxyl groups at the surface of outer CNT walls 52, 53 . These groups are needed to both facilitate wetting of the CNTs by the plating solutions and as anchors for the initial plating reactions. 15The procedure of electroless gold deposition within porous materials has been described by Martin et al. 54 and was previously used to fabricate pure gold nanotubes 48 in a three step protocol. During the first step, BP properties analysisThe gold content in the structure was determined by Thermo Scanning Electron Micrographs (SEM) at 5 keV, 52 º of tilt and 5 cm working distance. The Gallium (Ga) milling was performed with an initial beam current of 7 nA followed by cleaning steps at 0.1 nA. Eventually, pore size distribution was determined by perm-porometry on a capillary flow porometer from Porous Materials Inc. in wet-up/dry-up mode. 50Galwick and N2 were respectively used as the wetting liquid and to pressurize the BP pores up to 500 psi. Gas adsorptionThe adsorption of N2, CH4 and CO2 was performed at room Catalytic activity determinationBPs were exposed to pure analytical grade pentanal at 70 ºC in oxygenated CDCl3 for times of either 2 or 24 h. The composition of the solution before and after being exposed to the catalytic influence of the 65 BPs were analysed using Nuclear Magnetic Resonance (NMR) on aBruker 400 MHz spectrometer. TGA performed on the series of samples showed an initial diminished thermal stability which was attributed to the ozone treatment inducing defects on the CNT walls. However, after 10 h of plating the 90 stability, compared to a non treated sample, was recovered and improved. C. Results and DiscussionThe samples were all stable up to 400 ºC. The gold content c...

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Hydrogen Adsorption Isotherms: Modelling of Experimental Data

Cited by 2 publications

References 18 publications

Fluctuation Forces and Wetting Layers in Colloid-Polymer Mixtures

Fluctuation Forces and Wetting Layers in Colloid-Polymer Mixtures

Activation of gold decorated carbon nanotube hybrids for targeted gas adsorption and enhanced catalytic oxidation

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