Direct Determination of the Intermolecular Structure of the Adsorbed Phase Using <i>in situ</i> X-Ray Diffraction and Reverse Monte Carlo Methods

Iiyama, Taku; Aragaki, Rei; Urushibara, Takafumi; Ozeki, Sumio

doi:10.1260/026361706781388941

Cited by 17 publications

(18 citation statements)

References 17 publications

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“…As noted above, clustering of water in hydrophobic nanopores at moderate loading has been experimentally observed in [19,21] by in situ SAXS and in situ XRD. In simulations, this effect can be qualitatively observed through direct visualisation of the water molecules within the pore, and can be quantitatively characterised by calculation of the radial distribution function g(r) that for two particles of the same species is,…”

Section: Water Structure and Transport Propertiesmentioning

confidence: 56%

“…Both experimental and simulation results have identified that water in hydrophobic and/or nanoporous structures forms clusters at some loadings [19][20][21]. Small-angle x-ray scattering (SAXS) experiments and grand canonical Monte Carlo (GCMC) studies have shown that water molecules begin to form clusters that are 6 Å in diameter at 0.6 relative pressure (P/P 0 ) within a 11 Å width slit-pore and the cluster size becomes bigger with increasing the pressure (higher water loading) due to combination of clusters [19].…”

Section: Introductionmentioning

confidence: 99%

“…Small-angle x-ray scattering (SAXS) experiments and grand canonical Monte Carlo (GCMC) studies have shown that water molecules begin to form clusters that are 6 Å in diameter at 0.6 relative pressure (P/P 0 ) within a 11 Å width slit-pore and the cluster size becomes bigger with increasing the pressure (higher water loading) due to combination of clusters [19]. Also, it has been found that water assemblies of 15 Å diameter are formed and the structure has ice-like order in slit-pores of 16.3 Å in width at P/P 0 = 0.6 using x-ray diffraction (XRD) measurements and reverse Monte Carlo simulations [21]. Recently, some interesting studies have been carried out for slit-pores of different widths (7 and 11 Å) and at different pressures (P/P 0 ), revealing that the kinetics of water assembly is dominantly influenced by the pore width at low pressure (under P/P 0 = 0.5) and water adsorption rate is faster for the narrower pores at just above the critical pressure (0.4 for 7 Å width and 0.6 for 11 Å) [22].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Water diffusion in zeolite membranes: Molecular dynamics studies on effects of water loading and thermostat

Han

Bernardi

Wang

et al. 2015

Journal of Membrane Science

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Molecular dynamics simulations were employed to investigate diffusion and structural properties of water molecules confined in one-dimensional zeolites. Several water loadings and thermostatting methods were used, and insight into the effects of these was obtained by comparing diffusion and structural properties. Water diffusion was characterised via mean square displacements (self and collective diffusivities) and radial distribution functions enabled the structural ordering of water for different pore sizes and loadings to be compared. Interestingly at lower loadings, molecules tend to form clusters and move collectively, while at higher loadings, the self-diffusion coefficient in the pores is similar to that in bulk water. The length of the simulation cell was varied to determine the system size effects on the results, and narrow pores were also investigated in order to examine how this affected the effectiveness of water transport through the zeolite.

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Section: Water Structure and Transport Propertiesmentioning

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Water diffusion in zeolite membranes: Molecular dynamics studies on effects of water loading and thermostat

Han

Bernardi

Wang

et al. 2015

Journal of Membrane Science

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“…Recently, we reported preliminary results of the RMC simulation for water adsorbed in micropores of an activated carbon fiber [28].…”

Section: Introductionmentioning

confidence: 99%

Direct determination of intermolecular structure of ethanol adsorbed in micropores using X-ray diffraction and reverse Monte Carlo analysis

Iiyama

Hagi

Urushibara

et al. 2009

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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The intermolecular structure of C 2 H 5 OH molecules confined in slit-shaped graphitic micropore of activated carbon fiber was investigated by in situ X-ray diffraction (XRD) measurement and reverse Monte Carlo (RMC) analysis.The pseudo-3-dimensional intermolecular structure of C 2 H 5 OH adsorbed in the micropores was determined by applying the RMC analysis to XRD data, assuming a simple slit-shaped space composed of double graphene sheets.The results were consistent with conventional Monte Carlo simulation; e.g., bilayer structure formed by hydrogen bonds among C 2 H 5 OH adsorbed at low fractional filling. The RMC method based on experimental XRD data may be a useful tool to estimate the 3-dimensional structure of adsorbed phase confined in pores.

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“…13,14 In this case, geometrical parameters of the adsorbent and adsorbate were used to deduce the molecular arrangement, which reproduces the experimental scattering profiles. 15,16 We used this technique for separating the intra-and intermolecular OO, OD, and DD contributions, and the contributions of carbon and D 2 O. The detailed procedure and three-dimensional structure analysis using a snapshot of the RMC simulation will be described in a future article.…”

Section: 8mentioning

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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Direct Determination of the Intermolecular Structure of the Adsorbed Phase Using in situ X-Ray Diffraction and Reverse Monte Carlo Methods

Cited by 17 publications

References 17 publications

Water diffusion in zeolite membranes: Molecular dynamics studies on effects of water loading and thermostat

Water diffusion in zeolite membranes: Molecular dynamics studies on effects of water loading and thermostat

Direct determination of intermolecular structure of ethanol adsorbed in micropores using X-ray diffraction and reverse Monte Carlo analysis

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

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