An Ordered Water Molecular Assembly Structure in a Slit-Shaped Carbon Nanospace

Iiyama, Taku; Nishikawa, Keiko; Otowa, Toshiro; Kaneko, Katsumi

doi:10.1021/j100025a004

Cited by 181 publications

(137 citation statements)

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“…Several authors [15][16][17][18][19][20][21] have conducted studies to evaluate adequately and systematically porosity that develops in carbon materials by different methods, including the effect pore subtraction method (SPE) using the graphics high αs resolution, for N2 adsorption isotherms at 77 K by which they can properly evaluate the structure of micropores [15,19]. According to these authors, to apply the analysis of highresolution αs it is possible to find adequate information on the microporosity developed in the process of synthesis of aerogels, as well as of the mesoporosity [22] that are in good agreement with other methods that have been used for several decades [23][24][25].…”

Section: Introductionmentioning

confidence: 99%

Carbon Aerogels: a study with different models of the effect resorcinol/catalyst at different ratios after pyrolysis and the effect on textural properties

et al. 2017

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Eight samples of carbon aerogels were prepared at various resorcinol/catalytic (R/C) ratios (ranging from 25 to 1500) and followed the changes in structure after pyrolysis. Isotherms of N2 to 77 K were determined to calculate the textural parameters using Dubinin-Astakhov (DA), Barret Joyner and Halenda (BJH), Non-Local Density Functional Theory (NLDFT) and Quenched Solid Density Functional Theory (QSDFT) models. The results generated two series of samples. In series I, a single type of pores developed (microporous, at low R/C weight ratio). Series II developed mesoporosity to top gears of R/C (> 400). The specific areas ranged from 64 to 990 m 2 /g. Additional models were applied to the materials synthesized, which allowed for adjustment to a system of "cylinder-slit" pores by applying the QSDFT kernel, with an error percentage ranging from 0.03 to 0.74.

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Section: Introductionmentioning

confidence: 99%

Carbon Aerogels: a study with different models of the effect resorcinol/catalyst at different ratios after pyrolysis and the effect on textural properties

et al. 2017

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“…The ERDFs of bulk water and confined water exhibit three peaks and shoulder at 0.3, 0.45, and 0.7 nm, which can be attributed to the first, second, and third nearest-neighbor water molecules, respectively. 8,20,21 We have shown that the water confined in carbon micropores has the highest peak of the 2nd nearest neighbor. 8,20 Caminiti et al have previously demonstrated detailed analyses of the 2 M sulfuric acid solution under the bulk condition, 22 and they concluded that the hydration radii of the sulfate ions is 0.367 nm.…”

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confidence: 97%

“…8,20,21 We have shown that the water confined in carbon micropores has the highest peak of the 2nd nearest neighbor. 8,20 Caminiti et al have previously demonstrated detailed analyses of the 2 M sulfuric acid solution under the bulk condition, 22 and they concluded that the hydration radii of the sulfate ions is 0.367 nm. Hence, the ERDF peaks at 0.31 and 0.41 nm for the bulk solution (Figure 2) can be derived from the hydration structures of the ions as well as the intermolecular structure of the water molecules.…”

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Small- and Large-angle X-ray Scattering Studies of Nanometer-order Sulfuric Acid Solution in Carbon Micropores

et al. 2012

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The structure of nanometer-order sulfuric acid solution in carbon micropores is investigated by large-and small-angle X-ray scattering experiments. The electron radial distribution function of the nanosolution is different from that of bulk solution. The intermolecular structure of nanosolution does not change with fractional filling. These results and the dependency of density fluctuations of the system with fractional filling showed that the nanometer-order sulfuric acid solutions in carbon micropores form a small molecular assembly with a hydration structure at low fractional filling.In recent times, the rapid progress in nanoscience and nanotechnology 1 has led to the design, development, and application of various new porous materials to many scientific and industrial fields. Furthermore, extensive investigations of the adsorbate behaviors on the surfaces as well in the pores have been ongoing over the last few decades.2,3 The in situ measurements have been performed to examine the structures and behaviors of adsorbed molecules. 48Multicomponent adsorptions, for example, the adsorption of a solution in micropores, are not only of scientific interest but also extremely attractive for many industrial applications. The adsorption of nanometer-order sulfuric acid solution in micropores is important in environmental chemistry 9 and electric double-layer capacitor (EDLC) applications.10 EDLCs are one of the most attractive next-generation energy storage devices because they have high electrical power and can be used almost indefinitely. However, a microscopic understanding of the formation of the electrical double layers in carbon micropores is required for improving the capacitance performance. 10,11 Chmiola et al. 11 and Lin et al. 12 have demonstrated the possibilities of desolvation or distortion of the solvation structures of ions in carbon micropores by electrochemical measurements. These results indicate that the solution structures in carbon micropores could be considerably different from those under bulk conditions.Computer simulations have been employed for investigating nanometer-sized solutions 1315 primarily because of experimental difficulties. A few experimental studies have also been conducted; for example, Kittaka et al. investigated the phase behavior of water and acetonitrile mixtures in MCM-41 by employing infrared spectra (IR), 16 while Ohkubo et al. investigated the hydration structure of metal ions in carbon micropores by extended X-ray absorption fine structure (EXAFS). 17However, even though their results have shown the importance of understanding multicomponent states in nanometer-order spaces, such experimental approaches are rare.X-ray scattering curves directly provide wide-ranging geometric information from intermolecular to colloidal distances; hence, they are indispensable to describe multicomponent adsorption behaviors in nanospaces. In this paper, we describe our investigations into nanosized sulfuric acid solutions in carbon micropores by employing X-ray scattering methods; we...

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“…3 One reason for such phenomena is that the adsorbed phase comprises a small number of molecules. This effect is more pronounced in micropores whose width is less than 2 nm.…”

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confidence: 99%

Structure Determination of Hydrogen-bonding Network of Water in Hydrophobic Nanospace by Neutron and X-ray Diffractions

Iiyama¹,

Fujisaki²,

Futamura³

et al. 2012

Chemistry Letters

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The structure of the hydrogen-bonding network of water in carbon micropores was investigated by X-ray diffraction (XRD) and neutron diffraction (ND). ND provided positional information about both oxygen and hydrogen. A reverse Monte Carlo simulation was performed to combine the XRD and ND data. The results of ND from the adsorbed water showed that the hydrogen-bonding structure resembled that of bulk water when the pore width was 1 nm but was distorted at the 2nd nearestneighbor distance.Molecules in a confined space show unique phenomena such as unusual phase transition 1,2 and ordered-structure formation.3 One reason for such phenomena is that the adsorbed phase comprises a small number of molecules. This effect is more pronounced in micropores whose width is less than 2 nm. Water shows intermolecular hydrogen bonding, which is the main reason for its unique physical properties. The hydrogen bonds are strongly distorted, and the number and direction of bonds change at the interface of the water phase. Therefore, water is strongly affected by the size effect induced by space restriction. The small space comprising the hydrophobic surface is suitable for investigating such a size effect, because of hydrogen bonding between the water molecules.We have applied X-ray techniques for the structural analysis of water assemblies in carbon micropores. Since the micropores of activated carbon fibers (ACFs) are considerably uniform and since they have a smaller number of surface functional groups than do conventional activated carbons, 4,5 they can be regarded as hydrophobic slit-shaped nanospaces. X-ray small-angle scattering (SAXS), which clarifies the structure of molecular assemblies, provides evidence for cluster formation in water. 6,7 Recently, we applied SAXS to determine the density of molecular assemblies in pores and confirmed that water shows negative thermal expansion over a wide temperature range (from 20 K to room temperature).8 X-ray diffraction (XRD), which clarified the intermolecular structure of water, revealed the formation of an ordered structure at room temperature and the disappearance of the liquidsolid phase transition. 8,9 Although X-rays can be a powerful tool for structure determination, they are scattered by electrons; hence, it is very difficult to use X-rays for detecting hydrogen in water molecular assemblies. Therefore, we employed neutron diffraction (ND) to analyze the waterACF adsorption system. Neutrons are scattered by the nucleus of an atom, and therefore, they can be used for detecting hydrogen isotopes, especially deuterium. This method was used for the structural analysis of adsorbed water in porous silicas. 10 We used activated carbon as the hydrophobic nanospace and D 2 O as adsorbate, and attempted to combine the ND and XRD results by performing a reverse Monte Carlo (RMC) simulation for segregating the oxygen data and deuterium data. Activated carbon A20 (Ad'all Co., Ltd., Uji, Japan) was used as the adsorbent. The micropore structure of A20 was determined by N 2 adsorption i...

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An Ordered Water Molecular Assembly Structure in a Slit-Shaped Carbon Nanospace

Cited by 181 publications

References 1 publication

Carbon Aerogels: a study with different models of the effect resorcinol/catalyst at different ratios after pyrolysis and the effect on textural properties

Carbon Aerogels: a study with different models of the effect resorcinol/catalyst at different ratios after pyrolysis and the effect on textural properties

Small- and Large-angle X-ray Scattering Studies of Nanometer-order Sulfuric Acid Solution in Carbon Micropores

Structure Determination of Hydrogen-bonding Network of Water in Hydrophobic Nanospace by Neutron and X-ray Diffractions

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