Combining Nitrogen, Argon, and Water Adsorption for Advanced Characterization of Ordered Mesoporous Carbons (CMKs) and Periodic Mesoporous Organosilicas (PMOs)

Thommes, Matthias; Morell, Jürgen; Cychosz, Katie A.; Fröba, Michael

doi:10.1021/la402832b

Cited by 149 publications

(152 citation statements)

References 58 publications

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“…They found that adsorption of water is very sensitive to surface heterogeneity but the physical structure has limited effects in the low pressure region. Similar conclusions were also drawn by Thommes et al [25,26], who proposed water as a probe to characterize the surface chemistry of carbon materials.…”

Section: Introductionsupporting

confidence: 85%

Novel approach to the characterization of the pore structure and surface chemistry of porous carbon with Ar, N2, H2O and CH3OH adsorption

Fan

Nguyen

Zeng

et al. 2015

Microporous and Mesoporous Materials

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Characterization of porous carbon for its pore size distribution is traditionally carried out with simple pore models of well-defined geometry (slit or cylinder) with both ends opened to the gas surroundings. These idealised models do not adequately describe the inherently complex structure of porous carbons. An improved model should be sufficiently simple, not only for characterization, but also for the design of separation and purification processes. The following factors should be included: (1) energetic variation along the pore axis due to constrictions or strong energy sites, (2) connectivity between adjacent pores and (3) the presence of functional groups. In this work, we report results from computer simulations, using argon and nitrogen as non polar or weakly polar adsorbates and water and methanol as examples of associating fluids. The new model is able to produce all hysteresis loops classified by the IUPAC as well as loop types reported earlier by de Boer [1], Experimental isotherms are commonly measured at 77K and 87K (nitrogen and argon boiling points, respectively), but in recent years cryostats have become increasingly available in characterization laboratories and our simulations show that by measuring isotherms at different temperatures new insights about the porous structure can be gained from the variation of the hysteresis loop with respect to temperature which may change, for example, from a single-loop to a double-loop via a fused-loop as the temperature is varied.

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Section: Introductionsupporting

confidence: 85%

Novel approach to the characterization of the pore structure and surface chemistry of porous carbon with Ar, N2, H2O and CH3OH adsorption

Fan

Nguyen

Zeng

et al. 2015

Microporous and Mesoporous Materials

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“…Another consequence of confinement effects is the formation of water clusters, which play a significant role in the stabilization of water in hydrophobic carbon micro and mesopores. [31,32] By forming clusters of 5 or more water molecules (cluster size of ∼ 1 nm), [31,[33][34][35]] the affinity of the water molecules can be transformed from hydrophillic to hydrophobic, [33] making their interaction with the CNT walls more favorable. While many previous studies have explored the mechanics, kinetics, and energetics of the entry of water molecules into uncapped single walled CNTs, [30,[36][37][38] the likelihood that a water molecule can enter the 3 inner region of a capped multiwalled CNT via wall defects is low (since the openings in the CNT walls are likely smaller than the cluster size), meaning that the exohedral physisorption of water is expected.…”

mentioning

confidence: 99%

Exohedral Physisorption of Ambient Moisture Scales Non-monotonically with Fiber Proximity in Aligned Carbon Nanotube Arrays

et al. 2014

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Here we present a study on the presence of physisorbed water on the surface of aligned carbon nanotubes (CNTs) in ambient conditions, where the wet CNT array mass can be more than 200% larger than that of dry CNTs, and modeling indicates that a water layer > 5 nm thick can be present on the outer CNT surface. The experimentally observed non-linear and non-monotonic dependence of the mass of adsorbed water on the CNT packing (volume fraction) originates from two competing modes. Physisorbed water cannot be neglected in the design and fabrication of materials and devices using nanowires/nanofibers, especially CNTs, and further experimental and ab initio studies on the influence of defects on the surface energies of CNTs, and nanowires/nanofibers in general, are necessary to understand the underlying physics and chemistry that govern this system.One dimensional nanoscale systems, such as nanowires, nanofibers, and nanotubes, are well known for their phenomenal electrical, [1][2][3][4] thermal, [5][6][7][8] and mechanical properties, [9][10][11] which could enable the design and manufacture of next-generation materials with unprecedented properties. [12][13][14][15][16][17][18] However, while many studies have previously explored the synthesis of new architectures and devices using one dimensional nanomaterials, specifically carbon nanotubes (CNTs), the properties they reported were far lower than the properties of predicted using current theory.[12] Some of the main reasons why existing models cannot accurately predict the behavior of CNTs in scalable architectures, such as aligned CNT arrays, are the various CNT morphology and proximity effects, [13][14][15]19] which can strongly impact properties, but are not well understood and cannot be properly integrated into theoretical frameworks. Here we report the presence of a commonly neglected morphological effect, an unexpectedly large (compared to the CNT mass) amount of moisture located on the surface of CNTs in aligned CNT (A-CNT) arrays at ambient conditions; show the non-linear and non-monotonic dependence of this effect on array porosity, which suggests two competing mechanisms; and discuss the strong impact such an effect can have on the structure and properties of nanocomposite architectures composed of A-CNTs.Previous studies on how water interacts with the outer surface of a CNT illustrated that the water molecules form a layer-like shell surrounding the CNTs, [20][21][22][23] and that the water layer density varies greatly and non- * wardle@mit.edu.monotonically with its thickness. [21,22] A recent study on the physisorption of water onto the external surface of a suspended ∼ 1.1 − 1.2 nm diameter single walled CNT showed that more than one layer of water is present on the CNT surface in water vapor, and that water molecules more easily adsorb onto larger diameter CNTs.[24] However, this study was limited to isolated and defect-free CNTs, [24,25] meaning that the interaction of moisture present in ambient air with multiwalled CNTs, which normally have nativ...

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“…However, we do not understand the validity of the cluster-associated filling mechanism to mesoporous carbons, although adsorption of water in mesopores of 30 nm in the width cannot be observed below P/P 0 = 0.95 (Hanzawa and Kaneko 1997). A recent study on water adsorbed on ordered mesoporous carbon showed a unique stepwise adsorption isotherm which can be ascribed to adsorption in micropores and mesopores (Thommes et al 2013). We need to clarify the applicability of the cluster-associated filling mechanism to small mesopores.…”

Section: Introductionmentioning

confidence: 72%

“…Then, understanding of the interaction of water with nanoporous carbon can contribute to develop a new water related technology. However, the water-carbon interaction is not necessarily understood regardless of active studies for a long time (Thommes et al 2013;Müller et al 2013;Mowla et al 2003;Lie et al 2007;Striolo 2011;Nguyen and Bhatia 2011).…”

Section: Introductionmentioning

confidence: 99%

Cluster-associated filling of water molecules in graphene-based mesopores

2016

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Graphene monoliths were prepared through unidirectional freeze-drying method of graphene oxide colloids-KOH mixed solution and successive reduction by heating at 573 K in Ar. The porosity-and crystallinitycontrolled graphene monoliths were prepared by the KOH activation at different temperature and the post-heating in Ar. These activated graphene monoliths were characterized by N 2 adsorption at 77 K, X-ray diffraction and Raman spectroscopy. Water adsorption isotherms show a typical hydrophobicity below P/P 0 = 0.5 and a marked hydrophilicity above P/P 0 = 0.6, which depends on the pore width. In the water adsorption isotherms of porous graphene monoliths activated at different temperature, the higher the activation temperature, the larger the rising P/P 0 . No essential change in the shape of the water adsorption isotherm for the post-heated nanoporous graphene monoliths is observed except for the decrease in water adsorption amount with higher post-heating temperature. The linear relationship between the saturated water adsorption and pore volume whose width is smaller than 4 nm indicates clearly that water molecules are adsorbed in small mesopores by the clusterassociated filling mechanism.

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Combining Nitrogen, Argon, and Water Adsorption for Advanced Characterization of Ordered Mesoporous Carbons (CMKs) and Periodic Mesoporous Organosilicas (PMOs)

Cited by 149 publications

References 58 publications

Novel approach to the characterization of the pore structure and surface chemistry of porous carbon with Ar, N2, H2O and CH3OH adsorption

Novel approach to the characterization of the pore structure and surface chemistry of porous carbon with Ar, N2, H2O and CH3OH adsorption

Exohedral Physisorption of Ambient Moisture Scales Non-monotonically with Fiber Proximity in Aligned Carbon Nanotube Arrays

Cluster-associated filling of water molecules in graphene-based mesopores

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