Water concentrations and hydrogen isotope compositions of alkaline basalt-hosted clinopyroxene megacrysts and amphibole clinopyroxenites: the role of structural hydroxyl groups and molecular water

2016 ◽  
Vol 171 (5) ◽  
Author(s):  
István Kovács ◽  
Attila Demény ◽  
György Czuppon ◽  
Christophe Lécuyer ◽  
Francois Fourel ◽  
...  
Keyword(s):  
Hydrogen Isotope ◽  
Molecular Water ◽  
Hydroxyl Groups ◽  
Alkaline Basalt ◽  
Structural Hydroxyl ◽  
Clinopyroxene Megacrysts

Investigation of structural and optical properties of zirconia dioxide nanoparticles by radiation and thermal methods

2020 ◽  
pp. 2150050
Author(s):  
G. T. Imanova ◽  
T. N. Agayev ◽  
S. H. Jabarov
Keyword(s):  
Zirconium Hydride ◽  
Molecular Water ◽  
Hydroxyl Groups ◽  
Peroxide Radical ◽  
Absorption Bands ◽  
Thermal Methods ◽  
Surface Hydroxyl ◽  
Radiation Induced ◽  
Decomposition Of Water

The X-ray diffraction (XRD) spectrum of the nano-ZrO2 compound was drawn, the crystal structure was determined at room temperature and under normal conditions. Radiation-thermal decomposition of water on nanosized ZrO2 in the temperature range of [Formula: see text]–673 K has been studied by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. It has been shown that nanosized zirconium dioxide adsorbs water via the molecular and dissociative mechanisms. Intermediate products of the radiation-induced heterogeneous decomposition of water, namely, the molecular oxygen and hydrogen peroxide radical ions, zirconium hydride, and hydroxyl radicals have been detected. A comparative analysis of changes in the absorption bands (ABs) of molecular water and surface hydroxyl groups with temperature has been conducted, and the stimulating role of radiation in the radiation-thermal process of water decomposition has been revealed. With the participation of nano-ZrO2 during the radiation-heterogeneous decomposition of water to reveal the role of unbalanced cargo carriers that play the role of energy carriers under the influence of gamma-quantities in nano-ZrO2 and nano-[Formula: see text] systems paramagnetic centers, their origin and acquisition kinetics learned by the EPR method.

scholarly journals Role of structural hydroxyl groups in enhancing performance of electrochemically-synthesized bilayer V2O5

Nano Energy ◽  
2018 ◽  
Vol 53 ◽  
pp. 449-457 ◽  
Author(s):  
Sanja Tepavcevic ◽  
Justin G. Connell ◽  
Pietro P. Lopes ◽  
Mukesh Bachhav ◽  
Baris Key ◽  
...  
Keyword(s):  
Hydroxyl Groups ◽  
Structural Hydroxyl

The role of secondary alcoholic groups of D-galacturonan in its degradation with exo-D-galacturonanase

1980 ◽  
Vol 45 (2) ◽  
pp. 427-434 ◽  
Author(s):  
Kveta Heinrichová ◽  
Rudolf Kohn
Keyword(s):  
Acetyl Derivative ◽  
Competitive Inhibitor ◽  
Hydroxyl Groups ◽  
Pectic Acid ◽  
Substrate Complex ◽  
Enzyme Substrate ◽  
The Individual ◽  
Degradation Degree ◽  
Derivatives Of

The effect of exo-D-galacturonanase from carrot on O-acetyl derivatives of pectic acid of variousacetylation degree was studied. Substitution of hydroxyl groups at C(2) and C(3) of D-galactopyranuronic acid units influences the initial rate of degradation, degree of degradation and its maximum rate, the differences being found also in the time of limit degradations of the individual O-acetyl derivatives. Value of the apparent Michaelis constant increases with increase of substitution and value of Vmax changes. O-Acetyl derivatives act as a competitive inhibitor of degradation of D-galacturonan. The extent of the inhibition effect depends on the degree of substitution. The only product of enzymic reaction is D-galactopyranuronic acid, what indicates that no degradation of the terminal substituted unit of O-acetyl derivative of pectic acid takes place. Substitution of hydroxyl groups influences the affinity of the enzyme towards the modified substrate. The results let us presume that hydroxyl groups at C(2) and C(3) of galacturonic unit of pectic acid are essential for formation of the enzyme-substrate complex.

scholarly journals F/OH ratio in a rare fluorine-poor blue topaz from Padre Paraíso (Minas Gerais, Brazil) to unravel topaz’s ambient of formation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
N. Precisvalle ◽  
A. Martucci ◽  
L. Gigli ◽  
J. R. Plaisier ◽  
T. C. Hansen ◽  
...  
Keyword(s):  
Supercritical Fluids ◽  
Fluorine Content ◽  
Minas Gerais ◽  
Hydroxyl Groups ◽  
Exchange Reactions ◽  
Silicate System ◽  
Mullite Phase ◽  
Anomalous Water

AbstractTopaz [Al2SiO4(F,OH)2] is one of the main fluorine-bearing silicates occurring in environments where variably acidic (F)/aqueous (OH) fluids saturate the silicate system. In this work we fully characterized blue topaz from Padre Paraíso (Minas Gerais, Brazil) by means of in situ synchrotron X-Ray and neutron powder diffraction measurements (temperature range 298–1273 K) combined with EDS microanalyses. Understanding the role of OH/F substitution in topaz is important in order to determine the hydrophilicity and the exchange reactions of fluorine by hydroxyl groups, and ultimately to characterize the environmental redox conditions (H2O/F) required for mineral formation. The fluorine content estimated from neutron diffraction data is ~ 1.03 a.f.u (10.34 wt%), in agreement with the chemical data (on average 10.0 wt%). The XOH [OH/(OH + F)] (0.484) is close to the maximum XOH value (0.5), and represents the OH- richest topaz composition so far analysed in the Minas Gerais district. Topaz crystallinity and fluorine content sharply decrease at 1170 K, while mullite phase starts growing. On the basis of this behaviour, we suggest that this temperature may represent the potential initial topaz’s crystallization temperature from supercritical fluids in a pegmatite system. The log(fH2O/fHF)fluid (1.27 (0.06)) is coherent with the fluorine activity calculated for hydrothermal fluids (pegmatitic stage) in equilibrium with the forming mineral (log(fH2O/fHF)fluid = 1.2–6.5) and clearly different from pure magmatic (granitic) residual melts [log(fH2O/fHF)fluid < 1]. The modelled H2O saturated fluids with the F content not exceeding 1 wt% may represent an anomalous water-dominant / fluorine-poor pegmatite lens of the Padre Paraíso Pegmatite Field.

Role of Hydroxyl Groups in Low-Temperature CO Catalytic Oxidation over Zn4Si2O7(OH)2 Nanowire-Supported Gold Nanoparticles

2018 ◽  
Vol 122 (44) ◽  
pp. 25456-25466 ◽  
Author(s):  
Jing-Jing Li ◽  
Bao-Lin Zhu ◽  
Gui-Chang Wang ◽  
Zun-Feng Liu ◽  
Wei-Ping Huang ◽  
...  
Keyword(s):  
Gold Nanoparticles ◽  
Low Temperature ◽  
Catalytic Oxidation ◽  
Hydroxyl Groups ◽  
Co Catalytic Oxidation ◽  
Supported Gold Nanoparticles ◽  
Supported Gold

scholarly journals Hydrogen Speciation in Hydrated Layers on Nuclear Waste Glass

1986 ◽  
Vol 84 ◽  
Author(s):  
Roger D. Aines ◽  
Homer C. Weed ◽  
John K. Bates
Keyword(s):  
Nuclear Waste ◽  
Vapor Phase ◽  
Waste Glass ◽  
Hydroxyl Group ◽  
Molecular Water ◽  
Hydroxyl Groups ◽  
Phase Layer ◽  
Nuclear Waste Storage ◽  
Nuclear Waste Glass ◽  
Saturated Atmosphere

AbstractThe hydration of an outer layer on nuclear waste glasses is known to occur during leaching, but the actual speciation of hydrogen (as water or hydroxyl groups) in these layers has not been determined. As part of the Nevada Nuclear Waste Storage Investigations Project, we have used infrared spectroscopy to determine hydrogen speciations in three nuclear waste glass compositions (SRL-131 & 165, and PNL 76-68), which were leached at 90°C (all glasses) or hydrated in a vapor-saturated atmosphere at 202°C (SRL-131 only). Hydroxyl groups were found in the surface layers of all the glasses. In addition, molecular water was found in the surface of SRL-131 and PNL 76-68 glasses that had been leached for several months in deionized water, and in the vapor-hydrated sample. The water/hydroxyl ratio increases with increasing reaction time; molecular water makes up most of the hydrogen in the thick reaction layers on vapor-phase hydrated glass while only hydroxyl occurs in the least reacted samples. Using the known molar absorptivities of water and hydroxyl in silica-rich glass the vapor-phase layer contained 4.8 moles/liter of molecular water, and 0.6 moles water in the form hydroxyl. A 15 micrometer layer on SRL-131 glass formed by leaching at 90°C contained a total of 4.9 moles/liter of water, 2/3 of which was as hydroxyl. The unreacted bulk glass contains about 0.018 moles/liter water, all as hydroxyl.The amount of hydrogen added to the SRL-131 glass was about 70% of the original Na + Li content, not the 300% that would result from alkali-hydronium ion (H30+) interdiffusion. If all the hydrogen is then assumed to be added as the result of alkali-H+ interdiffusion, the molecular water observed may have formed from condensation of the original hydroxyl groups according to:20H = H20 molecular + 00where 00 refers to a bridging oxygen, and OH refers to a hydroxyl group attached to a silicate polymer. The hydrated layer on the nuclear waste glasses appears to be of relatively low water content (4 to 7% by weight) and is not substantially hydroxylated. Thus, these layers do not have many of the properties associated with “gel” layers.

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