Negative thermal expansion of water in hydrophobic nanospaces

The density and intermolecular structure of water in carbon micropores (w = 1.36 nm) are investigated by small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD) measurements between 20 K and 298 K. The SAXS results suggest that the density of the water in the micropores increased with increasing temperature over a wide temperature range (20-277 K). The density changed by 10%, which is comparable to the density change of 7% between bulk ice (I(c)) at 20 K and water at 277 K. The results of XRD at low temperatures (less than 200 K) show that the water forms the cubic ice (I(c)) structure, although its peak shape and radial distribution functions changed continuously to those of a liquid-like structure with increasing temperature. The SAXS and XRD results both showed that the water in the hydrophobic nanospaces had no phase transition point. The continuous structural change from ice I(c) to liquid with increasing temperature suggests that water shows negative thermal expansion over a wide temperature range in hydrophobic nanospaces. The combination of XRD and SAXS measurements makes it possible to describe confined systems in nanospaces with intermolecular structure and density of adsorbed molecular assemblies.ArticlePHYSICAL CHEMISTRY CHEMICAL PHYSICS. 14(2):981-986 (2012)journal articl

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

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.ArticleCOLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS. 347(1-3):133-141 (2009)journal articl

Tcnq-based Porous Coordination Polymers Synthesis and Sorption Properties Study in Magnetic Field

Porous coordination polymers (PCPs) were synthesized with used TCNQ anion that acts as cross linker connecting and bipyridine to form a 3D framework. In these study, we use zinc and manganese metal ion as centre of complex coordination. Green crystal of Zn(TCNQ-TCNQ)bpy.1.5 benzene and Mn(TCNQ-TCNQ)bpy.1.5 benzene was successfully synthesized in no under magnetic field (0T) and under magnetic field 6T. XRD patterns of Zn(TCNQ-TCNQ)bpy.1.5 benzene 0T and 6T shown not significant different pattern that indicate no different crytal formed. XRD patterns of Mn(TCNQ-TCNQ)bpy.1.5 benzene also shown not significant different but we found five different intensity ratio peaks that possibility it was a little bit changing of crystal structure. To investigate the pores properties, adsorption isotherm was performe for oxygen gas in 77 K and the guest of benzene were removed at 413 K for 3 hours under low pressure. Zn(TCNQ-TCNQ)bpy}1.5benzene 0T and 6T oxygen adsorption isotherms shows the unique sorption isotherms by gate pressure profile. On other hand, Mn(TCNQ-TCNQ)bpy}1.5 benzene 0T and 6T shows type 1 adsorption isotherms for micropores materials. Adsorption isotherm was also determined in magnetic field 6T for all crystal, and shows shift of gate pressure for Zn compounds and enhance the amount of oxygen adsorbed for all kind of compounds

Configurational evidence for antiferromagnetic interaction in disordered magnetic ionic liquids by X-ray scattering-aided hybrid reverse Monte Carlo simulation

Published online: 11 May 2020Magnetic ionic liquids (MIL) are a new type of ionic liquids that show paramagnetic response to magnetic fields. Here, we elucidate a plausible 3D liquid structure of the 1-ethyl-3-methyl-imidazolium tetrachloroferate (Emim[FeCl4]) and 1-butyl-3-methyl-imidazolium tetrachloroferate (Bmim[FeCl4]) MILs by X-ray scattering-aided hybrid reverse Monte Carlo simulations. Bmim[FeCl4] showed anomalously continuous structural changes over a wide temperature range (90–523 K) without crystallization, while Emim[FeCl4] displayed a melting point at 291 K with no glass transition.Conventional electron radial distribution function (ERDF) analysis provides misleading information about the structures of these MILs due to the mutual cancelation of the partial anion-anion and anion-cation ERDFs. Subsequent hybrid reverse Monte Carlo (HRMC) analysis revealed the precise coordination structures of both ionic liquids, and the alternating periodic arrangement of the anions and cations was visualized based on the HRMC simulation results. The results clearly revealed that the 1st coordination structure of the FeCl4 anion around the Bmim cation was widespread compared to that of the Emim cation, resulting in the absence of crystallization. In addition, we obtained new insights into the antiferromagnetic interaction between the FeCl4− ions of Bmim[FeCl4] even in the absence of the crystallization at low temperatures. Our results shed new light on the development of MILs not only for practical applications but also for the advancing the basic science of pure liquids with a high magnetic response.ArticleJournal of Molecular Liquids.311(1):113321(2020)journal articl

Negative thermal expansion of water in hydrophobic nanospaces

The density and intermolecular structure of water in carbon micropores (w = 1.36 nm) are investigated by small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD) measurements between 20 K and 298 K. The SAXS results suggest that the density of the water in the micropores increased with increasing temperature over a wide temperature range (20-277 K). The density changed by 10%, which is comparable to the density change of 7% between bulk ice (I(c)) at 20 K and water at 277 K. The results of XRD at low temperatures (less than 200 K) show that the water forms the cubic ice (I(c)) structure, although its peak shape and radial distribution functions changed continuously to those of a liquid-like structure with increasing temperature. The SAXS and XRD results both showed that the water in the hydrophobic nanospaces had no phase transition point. The continuous structural change from ice I(c) to liquid with increasing temperature suggests that water shows negative thermal expansion over a wide temperature range in hydrophobic nanospaces. The combination of XRD and SAXS measurements makes it possible to describe confined systems in nanospaces with intermolecular structure and density of adsorbed molecular assemblies.ArticlePHYSICAL CHEMISTRY CHEMICAL PHYSICS. 14(2):981-986 (2012)journal articl

TCNQ-BASED POROUS COORDINATION POLYMERS SYNTHESIS AND SORPTION PROPERTIES STUDY IN MAGNETIC FIELD

Porous coordination polymers (PCPs) were synthesized with used TCNQ anion that acts as cross linker connecting and bipyridine to form a 3D framework.  In these study, we use zinc and manganese metal ion as centre of complex coordination.  Green crystal of Zn(TCNQ-TCNQ)bpy.1.5 benzene and Mn(TCNQ-TCNQ)bpy.1.5 benzene was successfully synthesized  in no under magnetic field (0T) and under magnetic field 6T.  XRD patterns of Zn(TCNQ-TCNQ)bpy.1.5 benzene 0T and 6T shown not significant different pattern that indicate no different crytal formed.  XRD patterns of Mn(TCNQ-TCNQ)bpy.1.5 benzene also shown not significant different but we found five different intensity ratio peaks that possibility it was a little bit changing of crystal structure.   To investigate the pores properties, adsorption isotherm was performe for oxygen gas in 77 K and the guest of benzene were removed at 413 K for 3 hours under low pressure.  Zn(TCNQ-TCNQ)bpy}1.5benzene 0T and 6T oxygen adsorption isotherms  shows the unique sorption isotherms by gate pressure profile.  On other hand, Mn(TCNQ-TCNQ)bpy}1.5 benzene 0T and 6T shows type 1 adsorption isotherms for micropores materials.  Adsorption isotherm was also determined in magnetic field 6T for all crystal, and shows shift of gate pressure for Zn compounds and enhance the amount of oxygen adsorbed for all kind of compounds. Key words: porous coordination polymers, polymers synthesis, magnetic fiel

Effects of Al³⁺ Ions on Formation of Silica Framework and Surface Active Sites for SO₄^2– Ions

Al³⁺ ions were introduced into silica framework at 318 K in order to make active Al sites for SO₄^2– by the addition of aqueous sodium silicate solution to aqueous sulfuric acid solution of Al₂(SO₄)₃. The ²⁷Al and ²⁹Si NMR spectra of aluminosilicates were measured at 278 K with reaction time. ²⁹Si NMR spectra were analyzed by the multivariate curve resolution. The addition of Al³⁺ ions to aqueous silicate solution promoted gel formation. Small amounts of Al³⁺ ions were incorporated as a four-coordinated complex at early stage of polymerization reaction of silicates and during subsequent reaction six-coordinated Al complex increased, suggesting reversible conversion between 4- and 6-coordinated complexes. SO₄^2– ions interact with positive surfaces of aluminosilicates and are specifically adsorbed on the surface sites of 6-coordinated Al³⁺ species, which may be stabilized on silicate surfaces as [Al­(H₂O)₅SO₄]⁺

Magnetic field effects on electric behavior of [Fe(CN)6]3− at bare and membrane-coated electrodes

The cyclic voltammetric behavior of [Fe(CN)6]3− was investigated under homogeneous magnetic fields perpendicular to the electrode surface in order to determine the effects of magnetic fields on the distribution of an Fe2+/Fe3+ redox couple. The cathodic current was enhanced much more than the anodic current by a homogeneous magnetic field, suggesting that the concentration gradient of paramagnetic [Fe(CN)6]3− and diamagnetic [Fe(CN)6]4− formed at an electrode surface may also contribute to the asymmetric current. The apparent diffusion coefficient of the redox couple increased by over 30% in both cathodic and anodic processes upon applying a magnetic field. For a gold electrode coated with dioctadecyldimethylammonium, the application of a magnetic field perpendicular to the surface increased the peak-to-peak separation, and enhanced the asymmetric current. It is inferred that the application of a magnetic field promotes the electron-tunneling process by tilting chain molecules in the barrier membrane