Ionic Properties of Oxide Gels

1988 ◽  
Vol 135 ◽  
Author(s):  
J. Livage ◽  
P. Barboux ◽  
M. Nabavi ◽  
P. Judeinstein
Keyword(s):  
Ion Exchange ◽  
Water Adsorption ◽  
Mixed Valence ◽  
Adsorbed Water ◽  
Proton Diffusion ◽  
Hydrous Oxides ◽  
Solution Interface ◽  
Sheet Silicates ◽  
New Compounds ◽  
Ionic Devices

AbstractOxide gels are actually hydrous oxides. Water adsorption and dissociation occur at the surface of the oxide network leading to charged particles surrounded by an acid or basic aqueous medium. They can be considered as particle hydrates. Fast proton conduction is observed arising from proton diffusion through the adsorbed water layers. Proton conductivity is actually strongly related to the water adsorption isotherm.Ion exchange readily occurs at the oxide-solution interface when the gel is dipped inside an aqueous solution. Some inorganic gels exhibit a layered structure similar to that of sheet silicates. Ion exchange can then be described as an intercalation process. It can be used as a synthetic route toward new compounds.Electrochemical insertion within the oxide network is highly reversible. This is due to the open structure of the gel and the mixed valence behavior of the transition metal oxide. Reversible cathodes or electrochromic layers have been made from V2 O5, W03or TiO2gels. Thin films or pressed pellets can be easily made from oxide gels. They are therefore good candidates for making "all gel" micro-ionic devices.

Ionic Properties of Vanadium Pentoxide Gels

1988 ◽  
Vol 121 ◽  
Author(s):  
J. Livage ◽  
P. Barboux ◽  
J. C. Badot ◽  
N. Baffier
Keyword(s):  
Vanadium Pentoxide ◽  
Water Adsorption ◽  
Mixed Valence ◽  
Adsorbed Water ◽  
Water Molecules ◽  
Proton Diffusion ◽  
Hydrous Oxides ◽  
Solution Interface ◽  
Ionic Devices ◽  
Acid Aqueous Medium

ABSTRACTVanadium pentoxide gels V2O5·nH2O are actually hydrous oxides. Water adsorption and dissociation occurs at the surface of the oxide leading to negatively charged oxide particles surrounded by an acid aqueous medium. Ionic conductivity is observed, arising from proton diffusion through the water molecules. This process mainly depends on the nature of adsorbed water molecules. Proton conductivity is strongly related to the water adsorption isotherm.Ion exchange readily occurs at the oxide-solution interface when the gel is dipped into an aqueous solution of a metal chloride. New vanadium bronzes have been obtained upon heating such gels around 300° C. They exhibit interesting properties as reversible cathodes.Electrochemical insertion of Li* into the gel phase is quite easy. This is due to the very open structure of the gel and the mixed valence behavior of the vanadium oxide.Transition metal oxide gels could then be used as thin films or pressed pellets for making micro-ionic devices.

scholarly journals Calorimetric and Spectroscopic Studies of Water Adsorption onto Alkaline Earth Fluorides

2005 ◽  
Vol 23 (6) ◽  
pp. 425-436
Author(s):  
Toshinori Mori ◽  
Yasushige Kuroda ◽  
Ryotaro Kumashiro ◽  
Koji Hirata ◽  
Hidehiro Toyota ◽  
...  
Keyword(s):  
Alkaline Earth ◽  
Water Adsorption ◽  
Adsorbed Water ◽  
Spectroscopic Studies ◽  
Water Molecules ◽  
Earth Fluoride ◽  
Alkaline Earth Fluoride ◽  
Pretreatment Temperature ◽  
Argon Adsorption ◽  
Ir Bands

Interactions between the surfaces of alkaline earth fluorides (CaF2, SrF2 and BaF2) and water molecules were investigated by calorimetric and spectroscopic methods. The exposed surfaces of the alkaline earth fluoride samples, with which the (100) crystalline plane is mainly associated, were found to be fully covered with strongly adsorbed water molecules, resulting in characteristic IR bands at 3684, 2561, 1947 and 1000 cm−1, respectively. This surface was homogeneous towards further water adsorption. The strongly adsorbed water molecules were almost completely desorbed from the surface on evacuating the sample up to 473 K. The heat of immersion in water also increased with increasing pretreatment temperature; this may be attributed to surface rehydration of the alkaline earth fluorides. The state of the surface changed drastically as the pretreatment temperature was increased and stabilized towards incoming water molecules. Thus, the surface formed after evacuation at temperatures greater than 473 K was resistant to hydration even after immersion in water at room temperature. This surface was relatively heterogeneous towards water adsorption, although it behaved homogeneously towards argon adsorption. These facts indicate that strongly adsorbed water molecules appear to be somewhat specific towards the adsorption of further incoming water molecules. The adsorption properties of the (100) plane of alkaline earth fluorides towards water and argon molecules depend strongly on both the electrostatic field strength and the extent of rehydration of the alkaline earth fluoride surface.

ESCA and Vibrational Spectroscopy of Alkali Cation Exchanged Manganic Acids with the 2×2 type Tunnel Structure Synthesized via Different Chemical Routes

2000 ◽  
Vol 658 ◽  
Author(s):  
Masamichi Tsuji ◽  
Hirofumi Kanoh ◽  
Kenta Ooi
Keyword(s):  
Ion Exchange ◽  
Vibrational Spectroscopy ◽  
Mixed Valence ◽  
Redox Process ◽  
Alkali Cation ◽  
Exchange Mechanism ◽  
Uptake Mechanism ◽  
Alkali Cations ◽  
Xrd Patterns ◽  
Mixed Valence Compounds

ABSTRACTManganese dioxides have received much attention over the last two decades as ion exchangers. Actually these are typically mixed-valence compounds and the terminology of ‘dioxide’ is not appropriate. The mechanisms for their variety of chemical reactivities are still open for study. On the cation uptake mechanism there are strong claims that a redox process is involved in cation uptakes by manganic acids synthesized by substituting H+ for alkali cations incorporated in ‘hydrous manganese dioxides’. The present work was carried out to physically demonstrate the alkali cation exchange mechanism on tunnel-structured manganic acids and to study the ion exchange with lattice vibrational spectroscopy. Manganic acids were prepared through the redox process using KMnO4 and MnSO4, and thermal decomposition of (CH3)3COK and MnCO3 at 530°C. ESCA spectra of their alkali cation exchanged forms indicated no evidence of redox process and supported the ion exchange mechanism on these materials. Their infrared absorption spectra strongly depended on their preparation routes and are closely related to their ion-exchange selectivity of each material. Thus, the vibrational spectra of manganic acids take an important role as a synthesis index together with XRD patterns.

Changes in Water Adsorption Desorption Isotherms of Cement Mortars Caused by Carbonation Coupled with Humidification-Drying Cycles

2014 ◽  
Vol 989-994 ◽  
pp. 705-709
Author(s):  
Tung Pham Son
Keyword(s):  
Water Adsorption ◽  
Coupling Effect ◽  
Adsorbed Water ◽  
Water Vapor Adsorption ◽  
Adsorption Method ◽  
Cement Mortars ◽  
Pore Size Distributions ◽  
Low Humidity ◽  
Desorption Isotherms ◽  
Adsorption Desorption

The objective of this work was to examine the influence of carbonation on the water vapor adsorption desorption isotherms of cement materials. Two types of Portland mortars, which were CEM I and CEM II, were carbonated at 20°C, 65% relative humidity and 20% of CO2concentration. The pore size distributions were determined from the water adsorption method. We also studied the coupling effect between carbonation and humidification-drying cycles. The results showed a reduction in microporosity and a small increase in the mesoporosity. The pores clogging due to formation of calcium carbonate was highlighted by the reduction of the quantity of adsorbed water and the decrease in the hysteresis isotherms. The results of this study also indicated that the humidification-drying cycles coincide only from the second cycle because of a difficult evacuation of water during desorption, even at low humidity.

Molecular Orbital Modeling of Water Adsorption on a Tetrasiloxane Ring

1990 ◽  
Vol 180 ◽  
Author(s):  
J. K. West ◽  
S. Wallace
Keyword(s):  
Water Molecule ◽  
Molecular Orbital ◽  
Water Adsorption ◽  
Adsorbed Water ◽  
Metal Alkoxide ◽  
Sioh Group ◽  
Vibrational Overtone ◽  
Neglect Of Differential Overlap ◽  
Mo Theory ◽  
Hydrogen Bonded

ABSTRACTA water molecule hydrogen bonded to a surface SiOH group produces an IR vibrational transmission peak (ν3) at 2.82 μm. Water was adsorbed into the pores of a metal alkoxide derived silica gel monolith, and the increase in the wavelength of the first vibrational overtone (2ν3) of this peak was measured as a function of the adsorbed water content W (g H2O/g SiO2). The peak shifted from 1.390 to 1.420 μm as W increased by 0.14 g/g. Intermediate Neglect of Differential Overlap (INDO) Molecular Orbital (MO) theory was used to model this process. The effect of a H2O molecule, hydrogen bonded to a hydroxylated tetrasiloxane ring, on the structure of the ring and the water molecule was investigated. The bond length of the O-H group H-bonded to the water molecule increased, as expected from the increase in wavelength of the 2ν3 IR peak.

scholarly journals Synthesis, structure and water sorption in Zr metal-organic frameworks

2014 ◽  
Vol 70 (a1) ◽  
pp. C1240-C1240
Author(s):  
Felipe Gándara ◽  
Hiroyasu Furukawa ◽  
Zhang Yue-Biao ◽  
Juncong Jiang ◽  
Wendy Queen ◽  
...  
Keyword(s):  
Water Adsorption ◽  
Metal Organic Frameworks ◽  
Adsorbed Water ◽  
Neutron Diffraction Study ◽  
Water Molecules ◽  
Remote Areas ◽  
Adsorption Sites ◽  
Thermal Batteries ◽  
Secondary Building Units ◽  
Metal Organic

Metal-organic frameworks (MOFs) based on zirconium secondary building units (SBUs) have proven to have great thermal and chemical stability,[1,2] which make them ideal for their use in different applications. We have prepared a series of six new MOFs made from the Zr6O4(OH)4(-CO2)nsecondary building units (n = 6, 8, 10, or 12) and variously shaped carboxyl organic linkers to make extended porous frameworks, with the aim of studying their performance as water adsorbents. Thus, we have evaluated the water adsorption properties of these new MOFs and other reported porous materials to identify the compounds with the most promising materials for use in applications such as thermal batteries or delivery of drinking water in remote areas. An X-ray single-crystal and a powder neutron diffraction study reveal the position of the water adsorption sites in one of the best performing materials, and highlight the importance of the intermolecular interactions between adsorbed water molecules within the pores.

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