scholarly journals Methane adsorption onto silicas with various degree of hydrophobicity

Surface ◽  
2021 ◽  
Vol 13(28) ◽  
pp. 94-126
Author(s):  
V. V. Turov ◽  
◽  
V. M. Gun'ko ◽  
T. V. Krupska ◽  
◽  
...  
Keyword(s):  
Water Clusters ◽  
Chemical Shifts ◽  
Physical Adsorption ◽  
Bound Water ◽  
Adsorbed Water ◽  
Methane Adsorption ◽  
Methane Hydrates ◽  
Degree Of Hydration ◽  
Surface Condensation ◽  
Wide Range

The methane adsorption onto a hydrated surface of hydrophobic silica AM1 alone and impregnated by arginine, and silica gel Si-100 has been studied using low-temperature 1H NMR spectroscopy. It has been shown that the methane adsorption onto the AM1 surface depends on the degree of hydration and pretreatment type. The maximum adsorption (up to 80 mg/g) is observed for a sample hydrated after complete drying. It has been established that the adsorption is determined by a number of clusters of bound water of small radii. Based on a shape of the temperature dependence of the adsorption, it has been assumed that not only physical adsorption occurs, but also the quasi-solid methane hydrates are formed. It has been established that the amount of methane adsorbed onto a surface of a composite system AM1/arginine under isobaric conditions increases by tens of times (from 0.5 to 80 mg/g) in the presence of pre-adsorbed water pre-adsorbed at the surface. Probable mechanisms of the methane adsorption are physical adsorption on a surface, condensation in narrow voids between silica nanoparticles and nano-scaled (1-10 nm) water clusters, and the formation of solid (clathrate) methane hydrates. Water, adsorbed at a surface in a wide range of hydration, forms various clusters. This water is mainly strongly associated and characterized by chemical shifts in the range dH = 4-6 ppm. The hydrate structures with methane/water are quite stable and can exist even in the chloroform medium. However, in this case, a part of water transforms into a weakly associated state and it is observed at dH = 1.5-2 ppm.

scholarly journals Probing equilibrium of molecular and deprotonated water on TiO2(110)

2017 ◽  
Vol 114 (8) ◽  
pp. 1801-1805 ◽  
Author(s):  
Zhi-Tao Wang ◽  
Yang-Gang Wang ◽  
Rentao Mu ◽  
Yeohoon Yoon ◽  
Arjun Dahal ◽  
...  
Keyword(s):  
Molecular Beam ◽  
Bound Water ◽  
Adsorbed Water ◽  
High Energy ◽  
Ab Initio Molecular Dynamics ◽  
Water Dissociation ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Dissociation Equilibrium ◽  
Wide Range

Understanding adsorbed water and its dissociation to surface hydroxyls on oxide surfaces is key to unraveling many physical and chemical processes, yet the barrier for its deprotonation has never been measured. In this study, we present direct evidence for water dissociation equilibrium on rutile-TiO2(110) by combining supersonic molecular beam, scanning tunneling microscopy (STM), and ab initio molecular dynamics. We measure the deprotonation/protonation barriers of 0.36 eV and find that molecularly bound water is preferred over the surface-bound hydroxyls by only 0.035 eV. We demonstrate that long-range electrostatic fields emanating from the oxide lead to steering and reorientation of the molecules approaching the surface, activating the O–H bonds and inducing deprotonation. The developed methodology for studying metastable reaction intermediates prepared with a high-energy molecular beam in the STM can be readily extended to other systems to clarify a wide range of important bond activation processes.

Accurate prediction of 195Pt NMR chemical shifts for a series of Pt(ii) and Pt(iv) antitumor agents by a non-relativistic DFT computational protocol

2014 ◽  
Vol 43 (14) ◽  
pp. 5409-5426 ◽  
Author(s):  
Athanassios C. Tsipis ◽  
Ioannis N. Karapetsas
Keyword(s):  
Dft Calculations ◽  
Anticancer Agents ◽  
Antitumor Agents ◽  
Chemical Shifts ◽  
Accurate Prediction ◽  
Nmr Chemical Shifts ◽  
Relativistic Dft ◽  
Square Planar ◽  
Wide Range ◽  
Computational Protocol

Exhaustive benchmark DFT calculations reveal that the non-relativistic GIAO-PBE0/SARC-ZORA(Pt)∪6-31+G(d)(E) computational protocol predicts accurate 195Pt NMR chemical shifts for a wide range of square planar Pt(ii) and octahedral Pt(iv) anticancer agents.

The Role of Adsorbed Water on Pore Structure Characteristics and Methane Adsorption of Shale Clay

2018 ◽  
Author(s):  
Dong Feng ◽  
Xingfang Li ◽  
Chaojie Zhao ◽  
Jing Li ◽  
Qing Liu ◽  
...  
Keyword(s):  
Pore Structure ◽  
Adsorbed Water ◽  
Methane Adsorption ◽  
Structure Characteristics

Wide Range Two-Crystal Vacuum X-ray Spectrometer for Chemical State Analysis

1982 ◽  
Vol 36 (2) ◽  
pp. 171-174 ◽  
Author(s):  
Y. Gohshi ◽  
H. Kamada ◽  
K. Kohra ◽  
T. Utaka ◽  
T. Arai
Keyword(s):  
Coordination Number ◽  
Chemical Shifts ◽  
Fluorescence Analysis ◽  
Chemical State ◽  
X Ray ◽  
Wide Range ◽  
Scanning Range ◽  
Excellent Reproducibility ◽  
Design And Construction ◽  
State Analysis

The design and construction of a new two-crystal x-ray spectrometer are described together with the observed Mg Kα, Al Kα, Si Kα, S Kα, and Cu Kα1 spectra. The spectrometer is designed for x-ray fluorescence analysis and has a wide scanning range (2° to 146° 2θ) under vacuum. Excellent reproducibility of 0.4 s in arc is attainable, which makes possible the observation of chemical shifts in x-ray spectra. Magnesium Kα was found to be influenced by the coordination number, proving that the spectrometer is useful for chemical state analysis.

Determination of T2 cut-off for shale reservoirs: a case study from the Carynginia formation, Perth Basin, Western Australia

2017 ◽  
Vol 57 (2) ◽  
pp. 664 ◽  
Author(s):  
M. Nadia Testamanti ◽  
Reza Rezaee ◽  
Yujie Yuan ◽  
Dawei Pan
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Petroleum Industry ◽  
Bound Water ◽  
Invasive Technique ◽  
Sources Of Information ◽  
Vacuum Oven ◽  
Low Field ◽  
Wide Range

Over recent decades, the low-field Nuclear Magnetic Resonance (NMR) method has been consistently used in the petroleum industry for the petrophysical characterisation of conventional reservoirs. Through this non-invasive technique, the porosity, pore size distribution and fluid properties can be determined from the signal emitted by fluids present in the porous media. Transverse relaxation (T2) data, in particular, are one of the most valuable sources of information in an NMR measurement, as the resulting signal decay can be inverted to obtain the T2 distribution of the rock, which can in turn be correlated with porosity and pore size distribution. The complex pore network of shales, which can have a large portion of pore sizes in the nanopore and mesopore range, restricts the techniques that can be used to investigate their pore structure and porosity. The ability of the NMR technique to detect signals from a wide range of pores has therefore prompted the quest for more standardised interpretation methods suitable for shales. Using low-field NMR, T2 experiments were performed on shale samples from the Carynginia formation, Perth Basin, at different saturation levels. The shale samples were initially saturated with brine and the T2 spectrum for each sample was obtained. Then, they were placed in a vacuum oven and their weight monitored until a constant value was reached. T2 curves were subsequently obtained for each of the oven-dried samples and a cut-off value for clay-bound water was calculated.

scholarly journals Water inside β-cyclodextrin cavity: amount, stability and mechanism of binding

2019 ◽  
Vol 15 ◽  
pp. 1592-1600 ◽  
Author(s):  
Stiliyana Pereva ◽  
Valya Nikolova ◽  
Silvia Angelova ◽  
Tony Spassov ◽  
Todor Dudev
Keyword(s):  
Inclusion Complexes ◽  
Water Clusters ◽  
Bound Water ◽  
Thermodynamic Characteristics ◽  
Water Molecules ◽  
Native State ◽  
Hydrophobic Substances ◽  
Cyclodextrin Cavity ◽  
Stabilizing Factors ◽  
Native Host

Cyclodextrins (CDs) are native host systems with inherent ability to form inclusion complexes with various molecular entities, mostly hydrophobic substances. Host cyclodextrins are accommodative to water molecules as well and contain water in the native state. For β-cyclodextrin (β-CD), there is no consensus regarding the number of bound water molecules and the location of their coordination. A number of intriguing questions remain: (1) Which localities of the host’s macrocycle are the strongest attractors for the guest water molecules? (2) What are the stabilizing factors for the water clusters in the interior of β-CD and what type of interactions between water molecules and cavity walls or between the water molecules themselves are dominating the energetics of the β-CD hydration? (3) What is the maximum number of water molecules inside the cavity of β-CD? (4) How do the thermodynamic characteristics of β-CD hydration compare with those of its smaller α-cyclodextrin (α-CD) counterpart? In this study, we address these questions by employing a combination of experimental (DSC/TG) and theoretical (DFT) approaches.

Zur Struktur des Enols von Benzoylaceton / On the Structure of the Enol of Benzoylacetone

1979 ◽  
Vol 34 (11) ◽  
pp. 1606-1611 ◽  
Author(s):  
W. Winter ◽  
K.-P. Zeller ◽  
S. Berger
Keyword(s):  
Structural Model ◽  
Chemical Shifts ◽  
Ring System ◽  
Coupling Constants ◽  
Spin Coupling ◽  
X Ray ◽  
Wide Range ◽  
Spin Coupling Constants ◽  
C Nmr ◽  
Oxygen Atoms

Abstract A low temperature X-ray study of the enol of benzoylacetone indicates fixed positions of the C and O atoms within the enolic ring system and an extensive bond delocalisation over these atoms. The distribution of electron density between the two oxygen atoms shows that the enolic hydrogen is spread over a wide range. This is in accordance with a structural model proposed by de la Vega, whereupon the C and O atoms are kept fixed in their average positions during a tunneling process of the hydrogen between the two oxygen atoms. With this conception, the chemical shifts in the 17O and 13C NMR spectra, the 13C13C spin coupling constants and the temperature independance of these values can be explained.

scholarly journals Thermal and calorimetric investigations of titania–silica composites

2017 ◽  
Vol 35 (7-8) ◽  
pp. 706-713 ◽  
Author(s):  
B Charmas ◽  
J Skubiszewska-Zięba ◽  
H Waniak-Nowicka
Keyword(s):  
Free Energy ◽  
Porous Structure ◽  
Surface Free Energy ◽  
Bound Water ◽  
Chemical Vapor ◽  
Nitrogen Adsorption ◽  
Adsorbed Water ◽  
Silica Gels ◽  
Developed Surface ◽  
Calorimetric Investigations

The paper presents the studies of effects of TiO2 amount differentiation on the structural and thermal properties of titania–silica complex oxides prepared by chemical vapor deposition of TiCL4 onto the Si-40, Si-60, and Si-100 silica gels. The mesoporous materials, characterized by a varied pore structure with highly developed surface and large pore volume, were obtained. The porous structure of materials under investigations was characterized by the low-temperature nitrogen adsorption–desorption method as well as by power spectral density calculated from the calorimetric investigations of water confined in the pores. Moreover, the thermodesorption of water using the quasi-isothermal thermogravimetry was used to characterize their thermal and surface properties. The adsorbed water layers and the concentration of weakly and strongly bound water as well as the surface free energy on the adsorbent–water interfaces were calculated. It was stated that the increase of titania content causes a gradual decrease of specific surface area and has a significant effect on the porous structure formation. The water thermodesorption from the surface proceeds in few stages because of the porosity created by TiO2. The decrease in the total surface free energy (Δ GΣ) can be observed with the increasing TiO2 content. The largest Δ GΣ value at the adsorbent/strongly bound water interface is exhibited by the adsorbents of Si-100 series. The lowering of the freezing/melting points of water contained in the pores of the studied materials is strongly connected with their porous structure.

EELS of Niobium and Stoichiometric Niobium-Oxide Phases—Part I: Plasmon and Near-Edges Fine Structure

2009 ◽  
Vol 15 (6) ◽  
pp. 505-523 ◽  
Author(s):  
David Bach ◽  
Reinhard Schneider ◽  
Dagmar Gerthsen ◽  
Jo Verbeeck ◽  
Wilfried Sigle
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Chemical Shifts ◽  
Primary Electron ◽  
White Line ◽  
Wide Range ◽  
Experimental Parameters ◽  
Oxide Phases ◽  
Energy Convergence ◽  
Electron Energy Loss

AbstractA comprehensive electron energy-loss spectroscopy study of niobium (Nb) and stable Nb-oxide phases (NbO, NbO2, Nb2O5) was carried out. In this work (Part I), the plasmons and energy-loss near-edge structures (ELNES) of all relevant Nb edges (Nb-N2,3, Nb-M4,5, Nb-M2,3, Nb-M1, and Nb-L2,3) up to energy losses of about 2600 eV and the O-K edge are analyzed with respect to achieving characteristic fingerprints of Nb in different formal oxidation states (0 for metallic Nb, +2 for NbO, +4 for NbO2, and +5 for Nb2O5). Chemical shifts of the Nb-N2,3, Nb-M4,5, Nb-M2,3, and Nb-L2,3 edges are extracted from the spectra that amount to about 4 eV as the oxidation state increases from 0 for Nb to +5 for Nb2O5. Four different microscopes, including a 200 keV ZEISS Libra with monochromator, were used. The corresponding wide range of experimental parameters with respect to the primary electron energy, convergence, and collection semi-angles as well as energy resolution allows an assessment of the influence of the experimental setup on the ELNES of the different edges. Finally, the intensity of the Nb-L2,3 white-line edges is correlated with niobium 4d-state occupancy in the different reference materials.

scholarly journals NMR characterization of the interaction between the C-terminal domain of interferon-γ and heparin-derived oligosaccharides

2004 ◽  
Vol 384 (1) ◽  
pp. 93-99 ◽  
Author(s):  
Cécile VANHAVERBEKE ◽  
Jean-Pierre SIMORRE ◽  
Rabia SADIR ◽  
Pierre GANS ◽  
Hugues LORTAT-JACOB
Keyword(s):  
Electrostatic Interactions ◽  
Chemical Shifts ◽  
Heparan Sulphate ◽  
Interferon Γ ◽  
Activated T Cells ◽  
Terminal Domain ◽  
Physiological Processes ◽  
Nmr Characterization ◽  
Wide Range ◽  
Proliferation And Apoptosis

Interferons are cytokines that play a complex role in the resistance of mammalian hosts to pathogens. IFNγ (interferon-γ) is secreted by activated T-cells and natural killer cells. IFNγ is involved in a wide range of physiological processes, including antiviral activity, immune response, cell proliferation and apoptosis, as well as the stimulation and repression of a variety of genes. IFNγ activity is modulated by the binding of its C-terminal domain to HS (heparan sulphate), a glycosaminoglycan found in the extracellular matrix and at the cell surface. In the present study, we analysed the interaction of isolated heparin-derived oligosaccharides with the C-terminal peptide of IFNγ by NMR, in aqueous solution. We observed marked changes in the chemical shifts of both peptide and oligosaccharide compared with the free state. Our results provide evidence of a binding through electrostatic interactions between the charged side chains of the protein and the sulphate groups of heparin that does not induce specific conformation of the C-terminal part of IFNγ. Our data also indicate that an oligosaccharide size of at least eight residues displays the most efficient binding.

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