Chemisorption Of Water Research Articles

Surface acidity and reactivity of β-FeOOH/Al2O3 for pharmaceuticals degradation with ozone: In situ ATR-FTIR studies

The surface acidity and reactive activity of β-FeOOH, mesoporous alumina (MA), β-FeOOH/MA were investigated in catalytic ozonation of pharmaceutically active compounds (PhACs) aqueous solution. β-FeOOH/MA showed high efficiency for the degradation and mineralization of ibuprofen and ciprofloxacin. Its surface Lewis acid sites on β-FeOOH/MA were more greatly enhanced compared with those on MA and β-FeOOH. In situ attenuated total reflection FTIR (ATR-FTIR) spectroscopy was used to investigate the interaction of D2O and O3 with the catalysts in aqueous phase under various conditions. The dissociative chemisorptions of D2O occurred at the surface Lewis acid sites of the catalyst. Furthermore, O3 interacted with the surface hydrogen-bonded –O–D and D2O to initiate reactive oxygen species (ROS). The stronger Lewis acid sites of β-FeOOH/MA caused the more chemisorbed water enhancing the interaction with ozone, resulting in higher catalytic reactivity. The observations verified that the Lewis acid sites were reactive centers for the catalytic ozonation of PhACs in water.

A mechanism of changes in the electron work function upon water chemisorption on a Si(100) surface

Based on an analysis of observed changes, experimentally obtained by the methods of thermal and radiation processing, in the electron work function (EWF) of a monocrystalline silicon (100) surface upon water chemisorption, a physical mechanism associated with the concept of the energy action of the coherent phase of sorbed water on a surface is proposed for the decrease and increase in the EWF.

A shortcut for evaluating activities of TiO2 facets: water dissociative chemisorption on TiO2-B (100) and (001)

By means of density functional theory (DFT) calculations, we study the water adsorption behavior on two common surfaces, (001) and (100) TiO(2)-B, which maintains the monoclinic structure as high as approximately 550 degrees C or higher in ambient conditions. The two surfaces show totally different activity for water dissociation. The dissociative chemisorption of water on TiO(2)-B (100) is identified at both submonolayer and monolayer coverages, which indicates considerable reactivity. In contrast, the non-dissociative molecular adsorption of water is the most stable state on TiO(2)-B (001) which suggests no special activity. Furthermore, we compare the structural features of different surfaces with diverse crystal structures, such as rutile, anatase, brookite, TiO(2)-B etc. Keeping a close eye on the exposed atoms on the surface, we conclude a more general criterion for a quick evaluation of reactivities of different TiO(2) surfaces merely based on local surface structure features.

Selectivity problem of metal oxide based sensors in the presence of water vapors

We report our recent results on comparative analysis of sensing properties for two-component nanodispersed oxide systems: SnO2–MetOx (Met=Ti, Zr, Hf, Y and La) and SnO2-noble metals (Pt, Pd, Rh). The sensor signals towards 20 ppm H2 as a function of temperature (50–550∘C) and ambient humidity (0, 20, 50 and 80% RH at 25∘C) were compared in the light of surface hydroxylation degree, estimated by FTIR and TGA. Poor selectivity of SnO2 doped with noble metals was found and explained by interaction of H2 and H2O with the same surface species (most probably surface oxygen). Rather good selectivity of blank SnO2 and SnO2–MetOx (especially doped with IVB elements) seems to be related with H2 interaction with surface hydroxyls, which are supposed to be inactive for direct water chemisorption.

The Heat of Chemisorption of Water on Metal Oxides

The Heat of Chemisorption of Water on Metal Oxides

Chemisorption of water and carbon dioxide on nanostructured BaTiO3–SrTiO3(001) surfaces

The interaction of water and carbon dioxide with nanostructured epitaxial (Ba,Sr)TiO3(001) thin film and bulk single crystal SrTiO3(001) surfaces was studied using x-ray photoemission spectroscopy (XPS), thermal desorption spectroscopy (TDS), and density functional theory (DFT). On both surfaces, XPS and TDS indicate D2O and CO2 chemisorb at room temperature with broad thermal desorption peaks (423–723 K) and a peak desorption temperature near 573 K. A comparison of thermal desorption Redhead activation energies to adsorption energies calculated using DFT indicates that defect surface sites are important for the observed strong adsorbate-surface reactivity. Numerical calculations of the competetive adsorption/desorption equilibria for H2O and CO2 on SrTiO3(001) surfaces show that for typical atmospheric concentrations of 0.038% carbon dioxide and 0.247% water vapor the surfaces are covered to a large extent with both adsorbates. The high desorption temperature indicates that these adsorbates have the potential to impact measurements of the electronic structure of BaTiO3–SrTiO3(001) surfaces exposed to air, or prepared in high vacuum deposition systems, as well as the electrical properties of thin film ATiO3-based devices.

Comparative study of the hydrophobicity of BEA, HZSM-5 and HY zeolites determined by competitive adsorption

A hydrophobicity study was realized for a series of siliceous and steamed BEA, HZSM-5 and HY zeolites. The hydrophobicity was assessed according to the Weitkamp method by performing water and toluene competitive adsorption experiments. The Weitkamp hydrophobicity indexes (HI) were determined for each sample. The BEA samples were the most hydrophobic samples and there was a linear correlation between HI values and the Brønsted acidity. This was explained by a water preferential adsorption on the Brønsted acidic sites. On the contrary for the HZSM-5 and HY samples the decrease of HI with the Brønsted acidity was not linear. This was explained by a water preferential condensation in the available porous volume of the zeolites instead of water chemisorption on the Brønsted acidic sites. For the highly mesoporous samples the water adsorption was essentially localized in the mesopores so the hydrophobicity of these samples remained almost constant despite important variations of the Brønsted acidity. Due to their microporous structure, the HZSM-5 samples were more hydrophobic than the HY samples for a same value of Brønsted acidity and Si/Al ratio, despite a lower toluene adsorption for HZSM-5 samples because of steric hindrance of toluene. In the case of the competitive adsorption of water and toluene, the values of HI were essentially depending on the localization of water molecules and the global water uptake, despite a noteworthy increase of the toluene uptake.

Adsorption and dissociation ofH2Oon in-plane-polarizedBaTiO3(001)surfaces and their relation to ferroelectricity

Density-functional calculations have been performed on ${\text{BaTiO}}_{3}(001)$ bare, with adsorbed molecular water and hydroxylated surfaces in the case of surfaces having in-plane polarization. We show that in-plane-polarized ${\text{BaTiO}}_{3}(001)$ flat surfaces have very strong interaction energies with water and that ${\text{H}}_{2}\text{O}$ is chemisorbed on both BaO and ${\text{TiO}}_{2}$ terminations in that case. The adsorption results into surface hydroxyl groups OH with electric dipoles that couple to ferroelectricity in the materials (imprint effect) and point preferentially in the same direction as the polarization in the slab or into molecular water strongly bound to the surface. Moreover we find that the in-plane polarization in the last ${\text{TiO}}_{2}$ layer is pinned by the dipoles of the OH groups adsorbed for both terminations (especially in the case of the ${\text{TiO}}_{2}$ one). The influence of strain on hydroxylation is also examined in the case of ${\text{TiO}}_{2}$ terminations, and tensile strain is found to increase the reactivity of ${\text{TiO}}_{2}$-terminated ${\text{BaTiO}}_{3}(001)$ surfaces with respect to water dissociation. The evidence of spontaneous water chemisorption on in-plane-polarized ${\text{BaTiO}}_{3}$ surfaces in ambient moisture conditions might partly explain screening mechanisms on ferroelectric films.

Dissociative Chemisorption of Water onto Silica Surfaces and Formation of Hydronium Ions

Dissociative Chemisorption of Water onto Silica Surfaces and Formation of Hydronium Ions

Complementary Active Sites Cause Size-Selective Reactivity of Aluminum Cluster Anions with Water

The reactions of metal clusters with small molecules often depend on cluster size. The selectivity of oxygen reactions with aluminum cluster anions can be well described within an electronic shell model; however, not all reactions are subject to the same fundamental constraints. We observed the size selectivity of aluminum cluster anion reactions with water, which can be attributed to the dissociative chemisorption of water at specific surface sites. The reactivity depends on geometric rather than electronic shell structure. Identical arrangements of multiple active sites in Al16-, Al17-, and Al18- result in the production of H2 from water.

Water on Rutile TiO2(110) and Au/TiO2(110): Effects on Au Mobility and the Isotope Exchange Reaction

The behavior of adsorbed water on rutile TiO2 (110) and 0.05 ML-equivalent Au/TiO2 (110) have been probed over the temperature range from 110 to 800 K using a combination of temperature-programmed desorption (TPD), ion scattering spectroscopy (ISS), and X-ray photoelectron spectroscopy (XPS). Water, either predosed in order to hydroxylate vacancy sites on the surface prior to Au deposition, or dosed after Au deposition onto clean vacuum-annealed TiO2, results in more facile agglomeration of the initially dispersed Au atoms compared to Au deposited on vacuum-annealed TiO2. TPD indicates that the presence of Au binding at oxygen vacancy sites blocks dissociative chemisorption of water.

EPR and Mössbauer characterization of RTV polysiloxane foams and their constituents

We have used electron paramagnetic resonance (EPR) and 57Fe Mössbauer spectroscopies to investigate potential aging mechanisms in filled RTV polysiloxane foams, diatomaceous earth, and their other constituents. Intense, broad EPR resonances in the RTV foams were recorded at room temperature as a function of microwave power. These signals were shown to come from the diatomaceous earth filler (Celite ® 350) in the RTV foams. 57Fe Mössbauer measurements for neat Celite ® 350 showed the presence of iron compounds in the form of lepidocrocite. Further EPR measurements showed that the intense, broad signals from Celite ® 350 and the RTV foams were due to lepidocrocite that has been annealed to 175 °C and is in an excited state. EPR measurements of annealed samples of Celite ® 350 also indicated that structural (chemisorbed) water is not easily released by the lepidocrocite. Therefore, the presence of intermediate forms of iron oxides in Celite ® 350 and RTV foams indicates that water is not active in these materials.

Dissociative Chemisorption of Water onto Silica Surfaces and Formation of Hydronium Ions

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionDissociative Chemisorption of Water onto Silica Surfaces and Formation of Hydronium Ions and S. H. GarofaliniCite this: J. Phys. Chem. C 2008, 112, 14, 5694Publication Date (Web):March 13, 2008Publication History Published online13 March 2008Published inissue 1 April 2008https://doi.org/10.1021/jp8015134Copyright © 2008 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views424Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (5 KB) Get e-Alerts Get e-Alerts

Surface characterization and SO 2 removal activity of activated semi-coke with heat treatment

The activity of SO 2 removal by activated semi-coke is influenced by the precursor and surface modification processes. Raw semi-coke was modified by heat treatment at 800 °C in a nitrogen flow, and its activity for SO 2 removal was tested in a fixed bed reactor. The surface chemical properties of both raw semi-coke and activated semi-coke were characterized by acid-base titration, XPS, and FTIR. Graphitic carbon was the major component of carbon functional groups in the surface of both raw semi-coke and activated semi-coke. Surface C=O groups in the forms of ketone, lactone, carbonyl, or quinone were the main surface oxygen functional groups, and pyrrolic and/or pyridon-N groups were the main nitrogen functional groups in raw semi-coke. The heat treatment resulted in the decomposition of surface oxygen functional groups and the redistribution of surface oxygen and nitrogen functional groups. The content of the surface carbon groups, such as C=O decreased dramatically after heat treatment. However, the content of surface oxygen functional groups, such as ethers and chemisorbed oxygen or water increased on the surface of activated semi-coke. The number of pyridine-like structures was increased by the removal of pyrrolic and/or pyridon-N groups in the activation process. The increase of ethers group and π-π* transitions in aromatic systems, and the change of the nitrogen functional groups increased the surface basicity for activated semi-coke. Activated semi-coke had the higher activity for SO 2 removal than did raw semi-coke. The surface features influencing the activity for SO 2 removal for activated semi-coke may be ethers, aromatic carbons and nitrogen functional groups with basicity.

Dissociative Chemisorption of Water onto Silica Surfaces and Formation of Hydronium Ions

Molecular dynamics (MD) computer simulation of the adsorption of water molecules onto the vitreous silica surface was performed using a new dissociative water potential.58 The simulations showed dissociative chemisorption of water molecules onto the silica surface, forming silanol (SiOH) groups at a concentration consistent with experimental data. Water penetration and silanol formation ∼7−8 Å below the outermost oxygen are observed. Because of the dissociative nature of the water potential, formation of hydronium ions is allowed, and, whereas seldom observed in the simulations of bulk water, hydronium ions are formed during the reactions causing the formation of the silanols. The formation of hydronium ions has also been observed in ab initio calculations of water adsorption onto silica surfaces. The time evolution of the reactions involving hydronium ions in our MD simulations is similar to that observed in first-principles MD calculations. Hydronium ions offer a mechanism by which initially singly coordinated terminal oxygen (Si−O-) receives a H+ ion from a relatively distant chemisorbed H2O molecule via multiple H+ ion transfer, creating two SiOH sites.

Mechanistic aspects of the water–gas shift reaction on alumina-supported noble metal catalysts: In situ DRIFTS and SSITKA-mass spectrometry studies

Steady-state isotopic transient kinetic analysis (SSITKA) experiments coupled with mass spectrometry were performed for the first time to study essential mechanistic aspects of the water–gas shift (WGS) reaction over alumina-supported Pt, Pd, and Rh catalysts. In particular, the concentrations (μmol g −1) of active intermediate species found in the carbon-path from CO to the CO 2 product gas (use of 13CO), and in the hydrogen-path from H 2O to the H 2 product gas (use of D 2O) of the reaction mechanism were determined. It was found that by increasing the reaction temperature from 350 to 500 °C the concentration of active species in both the carbon-path and hydrogen-path increased significantly. Based on the large concentration of active species present in the hydrogen-path (OH/H located on the alumina support), the latter being larger than six equivalent monolayers based on the exposed noble metal surface area ( θ > 6.0), the small concentration of OH groups along the periphery of metal-support interface, and the significantly smaller concentration (μmol g −1) of active species present in the carbon-path (adsorbed CO on the noble metal and COOH species on the alumina support and/or the metal-support interface), it might be suggested that diffusion of OH/H species on the alumina support towards catalytic sites present in the hydrogen-path of reaction mechanism might be considered as a slow reaction step. The formation of labile OH/H species is the result of dissociative chemisorption of water on the alumina support, where the role of noble metal is to activate the CO chemisorption and likely to promote formate decomposition into CO 2 and H 2 products. It was found that there is a good correlation between the surface concentration and binding energy of CO on the noble metal (Pt, Pd or Rh) with the activity of alumina-supported noble metal towards the WGS reaction.

Electronically induced modification of thin layers on surfaces

Interactions of thermally and electronically stimulated reactions in thin layers on surfaces are investigated. For self-assembled monolayers, thermal activation promotes many processes primarily induced by electronic excitations. We demonstrate that the film temperature is an important parameter for steering these reactions towards different final products. Using chemisorbed water on Ru(001) as an example, we investigate how the products of an irradiation induced reaction catalyze thermally stimulated dissociation of water molecules.

Volume and surface oxidation of basalt

Natural, Fe2+-rich basalt glass (quenched lava) was heat treated as glass pieces and glass powder in air, in 6.0 Ar and in a 9×10−6 mbar vacuum below temperatures of significant crystallization to access volume and surface oxidation by 57Fe Mossbauer spectroscopy. While no oxidation occurs upon heating in vacuum, the amount of Fe3+ formed in powder (surface oxidation) is about 10 times higher than in pieces (volume oxidation), and surface oxidation is of the same order in air and Ar. This effect is assigned to chemisorption of water or CO2. Crystalline basalt, investigated by wet chemistry, includes five glass pieces treated above T of crystallization in air and in 6.0 Ar, and three lava samples of increasing depth up to 9 cm of lava lobes. The high Fe2O3 of all these crystalline samples is explained as a stabilization of Fe3+ due to the change of the local electronic environment in the course of crystallization; volume oxidation therefore appears to be independent on the environmental atmosphere.

Electronic structure calculations of physisorption and chemisorption on oxide glass surfaces

A description of the physisorption and subsequent chemisorption of water on silica glass surfaces is presented that combines electronic structure calculations with classical molecular dynamics simulations. The method associates the strength of the physisorption sites with the gradient of the electrostatic potential, and the chemical reactivity with the chemical hardness of the surface. The physisorption results are compared with those of more classical physisorption energy mappings, and to ab initio calculations of water molecules physisorbing at specific sites. The chemisorption reactivity index is compared with calculated chemisorption energy barriers. The techniques are applied to two types of silica glass surfaces: a fracture surface with high energy coordination defects and a low energy defect-free ``melt surface.'' The mappings show that the strongest sites for physisorption are network coordination defects, but that a high physisorption energy is not necessarily an indicator of a reactive site. The physisorption and chemisorption mappings were converted to energy distributions and reactivity distributions for a direct comparison between the melt and fracture surfaces. Altogether, this approach combines the efficiency of classical molecular dynamics for structural determinations, with the chemical degrees of freedom provided by electronic structure calculations, to yield a semiquantitative map of chemical reactivity across a surface.

Evidence for emission and transfer of energy from excited edge sites of MgO smokes by photoluminescence experiments

New features are observed in photoluminescence spectra of MgO smokes produced in controlled conditions, an experiment inspired by previous measurements on cleaved MgO(1 0 0). Upon photoexcitation at 5.17–5.45 eV, most luminescence spectra observed can be decomposed into two bands, peaking at 3.82–3.86 eV (the highest energy ever recorded in such experiment) and 3.20 eV, respectively. It is assumed that the 3.82–3.86 eV band is related to the luminescence at four-coordinated (4C) defect-free edge sites and that the 3.20 eV band arises from the excitation transfer from 4C edge sites towards less-coordinated 3C sites. A minor contribution to the 3.20 eV band observed upon excitation with 4.6 eV photons is assigned to a direct excitation of 3C sites. Within these assumptions, water chemisorption–desorption is suggested to produce less-coordinated sites (the 3.20 eV band increases in intensity) at the expense of 4C sites (the 3.84 eV band decreases). The huge sensitivity of the 3.84 eV/3.20 eV branching ratio to the formation of defects on 4C edges is suggested to explain the lack of consensus about the photoluminescence of MgO.