Adsorption Of Methyl Iodide Research Articles

Model for the growth and reactivity of metal films on oxide surfaces: Cu on ZnO(0001̄)–O

In the many studies of vapor deposition of late transition metals on single-crystal oxide surfaces, never has a low-energy electron diffraction superstructure been observed in the first layer. Although layer-by-layer behavior is often reported at ≤300 K, annealing the films generally leads to irreversible clustering into thick islands that cover a tiny part of the oxide. We discuss here a growth model that explains these general observations and is also consistent with the expected energetics for metal atom diffusion over oxide and metal terraces and up and down over the edges of metal islands. We briefly review our recent studies which led to this model, in which the structural, electronic, and chemical properties of Cu films on the oxygen-terminated ZnO(0001̄)–O surface were examined. At coverages beyond a few percent, vapor-deposited Cu adatoms become nearly neutral. Their chemical behavior indicates that they form two-dimensional (2D) islands with metal-like Cu–Cu distances, much shorter than the substrate lattice parameter. Further deposition of Cu leads to spreading of these 2D islands without forming thicker layers, until about 55% of the surface is covered. Thereafter, these Cu islands grow thicker without filling the voids between islands, except at a rate much slower than the rate at which Cu vapor strikes in these voids. Our new model shows that a large fraction of an oxide surface will first be covered by 2D islands during metal deposition at low temperatures due to a kinetic effect. This occurs even when the metal’s adsorption energy on itself significantly exceeds its adsorption energy on the oxide (i.e., when 3D clustering is thermodynamically favored), provided the difference in these energies does not exceed the energy of 2D evaporation from island edges onto terraces. As soon as islands nucleate in the second layer, 2D spreading ceases and energetic pathways open that allow metal atoms to migrate up from the oxide terrace into this new layer. This can lead to thick, flat-topped islands. Atom-thin (2D) Cu islands on ZnO(0001̄)–O react with CO, O2, H2O, HCOOH, and CH3OH very much like Cu(110), although there are some differences: The transiently adsorbed H and CO2 products of HCOOH dissociation migrate off or under the Cu islands and interact strongly with ZnO sites, and Oa is not as good a Bro/nsted base as on Cu(110). Annealed 3D islands behave much like Cu(111). We present here new results for methyl iodide adsorption and methyl dissociation on these Cu islands which further support this general picture.

Adsorption and desorption of gaseous methyl iodide in a triethylenediamine-impregnated activated carbon bed

As a relevant technique for controlling radioactive organic iodines, the adsorption and desorption of methyl iodide was investigated in a (triethylenediamine-impregnated activated carbon bed. The amount of adsorption was quantitatively divided into two parts: reversible physical adsorption and strongly bonded chemisorption. The physical adsorption obeyed the Langmuir equation and the amount of chemisorption was stoichiometrically proportional to the amount of impregnant. Furthermore, a non-equilibrium dynamic model was developed based on both the physical adsorption and the bimolecular reaction between adsorbate and impregnant. The dynamic model successfully simulated the adsorption and desorption behavior of methyl iodide.

Use of gas chromatography to study the adsorption at zero surface coverage of CH 3I on active carbons

Four active carbons were prepared by carbonization of polyfurfuryl alcohol. From these, other four samples were prepared by impregnation with KI (1%). All these samples were characterized by adsorption of nitrogen and carbon dioxide at 77 K and 298 K, He density and mercury porosimetry. Gas-solid chromatography was used to study the adsorption of methyl iodide at zero surface coverge (Henry's law region). The thermodynamic functions of adsorption of methyl iodide at zero surface coverge ( ΔH A 0, ΔG A 0 and ΔS A 0) were obtained.

Spectroscopic study on the adsorption and dissociation of CH 3I on Pd(100): thermal and photo effects

The adsorption of methyl iodide on a Pd(100) surface has been investigated by temperature programmed desorption (TPD), work function change Δφ, ultraviolet and X-ray photoelectron (UPS and XPS) spectroscopies at 85–425 K. By means of TPD only one adsorption state is identified, T p = 129 K, which is formed only at high exposures and attributed to multilayer. Adsorption of CH 3I is characterized by a significant decrease in the work function (1.54 eV at monolayer) indicating that adsorbed CH 3I has a positive outward dipole moment. UPS, XPS and TDS measurements suggest that CH 3I adsorbs dissociatively at submonolayer even at 85–90 K yielding adsorbed CH 3 and I species. The dissociation of the monolayer is complete below 200 K. This process is accompanied by a decrease in the binding energy of the I(3d 5 2 ) core electrons. The decomposition of adsorbed CH 3 started above 160 K and is completed below 250 K. The primary product of the decomposition is CH 4 which desorbs with T p = 170 K. C 2H 6, C 2H 4 and H 2 were detected only in trace amounts. Illumination of the adsorbed layer at 85–90 K enhanced the extent of the dissociation which is ascribed to the generation of photoelectrons.

Gas chromatographic study of the adsorption of methyl iodide on several types of carbons

Gas chromatography has been used to measure the adsorption at zero surface coverage of methyl iodide on different types of carbon. The effect on the adsorption of methyl iodide of adding potassium iodide to the carbon samples was also studied. The differences observed in the behaviour of these samples for the adsorption of methyl iodide are explained on the basis of the textural characteristics of the samples. Thermodynamic functions of adsorption of methyl iodide at zero surface coverage are obtained.

Determination of the activation energy for the dissociation of the carbon–iodine bond in methyl iodide adsorbed on Ni(100) surfaces

The chemistry of methyl iodide on Ni(100) surfaces has been studied by using x-ray photoelectron spectroscopy (XPS). Methyl iodide adsorption is molecular below 100 K, but the C–I bond begins to cleave around 120 K and is completely broken by 160 K. The activation energy for the C–I bond scission was estimated to be about 3.5 kcal/mol based on results from isothermal XPS experiments.

Thermal stability of the methyl group adsorbed on Si( 100): CH 3I surface chemistry

The adsorption and thermal behavior of methyl iodide on Si(100)-(2 × 1) have been studied by kinetic uptake measurements, Auger electron spectroscopy (AES) and temperature-programmed desorption (TPD) mass spectroscopy. Methyl iodide adsorbs on Si(100) at room temperature with high efficiency (initial reaction probability of unity). From the kinetic uptake measurements and the AES measurements an average saturation coverage of (2.9 ± 0.3) × 10 14 methyl iodide molecules cm 2 is calculated, i.e., about one methyl iodide molecule per two silicon surface atoms. Experimental evidence is presented indicating that the molecule dissociates into a covalently bonded methyl group and an iodine atom upon adsorption. Heating causes the decomposition of the methyl group. The hydrogen atoms liberated from the methyl group mainly desorb as molecular hydrogen. The adsorbed iodine desorbs in the form of atomic iodine and possibly some small amount of hydrogen iodide as detectable by line-of-sight mass spectrometry. Less then 1% of the carbon desorbs in the form of C 2 hydrocarbon species. Neither the desorption of methane nor the desorption of methyl iodide is observed.

Dynamic adsorption of methyl iodide on activated carbons

The adsorption at the Henry's law region of CH 3I on several activated carbons was studied by gas-solid chromatography. The thermodynamic functions at zero surface coverage were obtained. The difference between the standard differential enthalpy of adsorption for each carbon, ΔH° A , and the heat of liquefaction of the adsorptive, ΔH° L , indicates that the adsorption takes place on micropores whose sizes are commensurate with the size of CH 3I, although adsorbent-adsorbate interactions are nonspecific. Finally, from the ΔH° A and ΔG° A values, the evolution of the microporosity of the samples with the increase of the period of treatment was established.

Adsorption of methyl iodide and n-hexane on fibrous carbon materials

Adsorption isotherms of n-hexane and methyl iodide on fibrous carbon material (FCM), both uncoated and coated with 5% w/w triethylene diamine (TEDA), were determined in the temperature span from 303 to 318 K using gas-chromatographic technique. The isotherms obtained are of the BET IV type, suggesting multilayer adsorption. Monolayer capacities were determined for unmodified adsorbents only. Due to the mixed adsorption mechanism acting on the modified FCM, the monolayer capacity of this solid has not been possible to evaluate. It was shown that the adsorption of methyl iodide is greater than for n-hexane. Methyl iodide, in addition, has almost four times larger adsorption on FCM-TEDA compared to the bare solid presumably due to the specific reaction between the adsorbate and TEDA. Isosteric heat of adsorption of the two adsorbates exhibits a maximum in the vicinity of the corresponding monolayer surface capacity, approaching the limiting value of the heat of liquefaction at higher surface loadings.

Thermodynamic Evaluation of Activated Charcoal as a Poison Antidote by High-Performance Liquid Chromatography I: Derivation and Validation of an Equation for Gibbs Free Energy of Liquid–Solid Adsorption

An in vitro method utilizing high-performance liquid Chromatography (HPLC) was developed in order to investigate the adsorptive process between activated charcoal and various drugs and toxic chemicals by measuring their Gibbs free energy of adsorption from various acetonitrile: water mobile phases. This report details the derivation and validation of the equation for calculating the Gibbs free energy of liquid-solid adsorption via HPLC. The derived equation incorporates the following experimental parameters: specific surface area of the adsorbent, specific retention volume of the solute, molar volume of the mobile phase, and surface concentration of the solute in a predefined standard state. This equation was validated by means of a closed thermodynamic cycle composed of three segments. Each segment represents a different physical process: gas-solid adsorption of methyl iodide on activated charcoal, gas-liquid solution of methyl iodide in n-hexadecane, and liquid-solid adsorption of methyl iodide on activated charcoal from n-hexadecane. The Gibbs free energy for each of these thermodynamic processes was determined by the appropriate chromatographic technique. Since the cycle did not balance because it did not account for the interaction of n-hexadecane and activated charcoal, it was altered to include a gas-liquid-solid chromatographic technique. When the Gibbs free energies of solution and gas-solid adsorption determined by this chromatographic technique were incorporated into the cycle, the resulting imbalance was only 0.213 kJ/mol (1.1%), thereby validating the derived equation.

ChemInform Abstract: PHYSICAL AND CHEMICAL PROPERTIES OF INACTIVE SURFACE HYDROGEN‐BONDED HYDROXYL GROUPS

AbstractDie Eigenschaften von H‐gebundenen Oberflächen‐OH‐Gruppen, die durch hydrothermale Reaktion von SiO2‐Hydrogelen, Xerogelen, gefällten Kieselsäuren (ausgehend von Na‐silicat in flüssiger Phase bei pH 11 und > 373 K) sowie Aerosilen gebildet werden, werden untersucht.

Adsorption and reaction of iodine and methyl iodide with uranium monocarbide surfaces

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAdsorption and reaction of iodine and methyl iodide with uranium monocarbide surfacesJ. G. Dillard, H. Moers, H. Klewe-Nebenius, G. Kirch, G. Pfennig, and H. J. AcheCite this: J. Phys. Chem. 1984, 88, 22, 5345–5352Publication Date (Print):October 1, 1984Publication History Published online1 May 2002Published inissue 1 October 1984https://doi.org/10.1021/j150666a048RIGHTS & PERMISSIONSArticle Views93Altmetric-Citations10LEARN 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 (928 KB) Get e-Alerts

The adsorption of methyl iodide on uranium and uranium dioxide: Surface characterization using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES)

The adsorption of methyl iodide on uranium and on uranium dioxide has been studied at 25 °C. Surfaces of the substrates were characterized before and after adsorption by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The XPS binding energy results indicate that CH 3I adsorption on uranium yields a carbide-type carbon, UC, and uranium iodide, UI 3. On uranium dioxide the carbon electron binding energy measurements are consistent with the formation of a hydrocarbon, —CH 3-type moiety. The interpretation of XPS and AES spectral features for CH 3I adsorption on uranium suggest that a complex dissociative adsorption reaction takes place. Adsorption of CH 3I on UO 2 occurs via a dissociative process. Saturation coverage occurs on uranium at approximately two langmuir (1 L = 10 −6 Torr s) exposure whereas saturation coverage on uranium dioxide is found at about five langmuir.

Physical and chemical properties of inactive surface hydrogen-bonded hydroxyl groups

The physical and chemical properties of surface hydrogen-bonded OH groups, formed by the hydrothermal reaction of silica hydrogels, xerogels, precipitated silicas (made with sodium silicate in the liquid phase at pH 11 and > 373 K) and aerosils, have been studied. In contrast to free OH groups, surface hydrogen-bonded OH groups, having an absorption band at 3500 cm–1, have low enthalpies of adsorption of water, methanol and methyl iodide, can be reversibly dehydroxylated and rehydroxylated by the adsorption of water vapour, and can be easily changed to OD groups by the adsorption of heavy water. These OH groups cannot be methoxylated with chlorotrimethylsilane or methanol. Cations such as Co2+ do not seem to be ion exchanged with the protons of these OH groups.

Application of Zeolites to Remove Iodine from Dissolver Off-Gas, (III) Adsorption of Methyl Iodide (CH3I) on Zeolite 13X

Click to increase image sizeClick to decrease image sizeKEYWORDS: Iodinesilver-free zeolitemethyl iodidenitrogen dioxidezeolite 13Xdissolver off-gasiodine 131adsorption

Application of zeolites to remove iodine from dissolver off-gas, (III). Adsorption of methyl iodide (CH3I) on zeolite 13X.

Click to increase image sizeClick to decrease image sizeKEYWORDS: Iodinesilver-free zeolitemethyl iodidenitrogen dioxidezeolite 13Xdissolver off-gasiodine 131adsorption

Studies by ESCA of supported rhodium catalysts related to activity for methanol carbonylation

Various solid preparations containing rhodium have been examined using ESCA in an attempt to provide a basis for understanding their activities in carbonylation of methanol to acetic acid. High activity is apparently associated with the use of molecular sieve zeolites as supports. With use of the pentammine rhodium salt [Rh(NH 3) 5Cl]Cl 2 the dispersion of rhodium in the zeolite framework is superior to that found using RhCl 3 All active preparations contain rhodium predominantly in the +3 state. The realization of this oxidation state in the initial catalyst may be a necessary but insufficient requirement for subsequent activity for carbonylation. RhCl 3 MgO also contains Rh(III) but no catalyst activity is seen. For RhCl 3 SiO 2 and RhCl 3 SnO 2 , there is a clear tendency for Rh(I) species to be produced in the initial material and these supports also lead to inactive catalysts. There is evidence that the zeolite framework assists in producing active sites by enabling the ligands originally surrounding the rhodium centre to be easily removed so that coordination with the reactants present under reaction conditions can proceed with comparative ease. A further positive effect of the zeolite lattice operating under carbonylation reaction conditions in assisting the dissociative adsorption of methyl iodide is also suggested.

Oxidation of iodides by silica-alumina catalysts

Aqueous solutions of iodide ion liberate iodine in a continuing reaction in the presence of a silica-alumina catalyst, suitably activated by heat treatment, provided molecular oxygen is present. A similar reaction occurs in benzene solutions of tetramethylammonium iodide. Pure alumina and pure silica are both inactive for the oxidation. Hydrogen Y zeolite has an activity comparable with that of the most active of the amorphous silica-aluminas. The catalytic activity of both the amorphous and crystalline silica-aluminas for the iodide ion oxidation is related to their Bronsted acidity. In the presence of water, the Bronsted sites on the oxide surface are continuously regenerated as the oxidation proceeds. Although silica-aluminas are active for the oxidation of methyl iodide to iodine, the reaction occurs much more readily on the surface of pure alumina. Alumina samples dehydrated at about 630 °C show maximum oxidizing activity and maximum Lewis acid activity. The production of methyl peroxy radicals shows that basic sites are also involved. Dissociative adsorption of methyl iodide probably occurs on the alumina surface and is followed by association of the halogen atoms to produce molecular iodine. Bronsted acid sites are not involved.

488. 活性炭による放射性ヨウ素の除去に関する研究,(I)

In order to obtain adsorption data for iodine and methyliodide at low partial pressures, helium gas containing iodine or methyliodide was passed through a small activated carbon bed, and the amount of iodine and methyliodide adsorbed was measured. The specific adsorption of both iodine and methyl iodide at temperatures from 50° to 400°C was determined, together with the rate of desorption and the amounts irreversibly adsorbed.From these results it was found that the rate of adsorption can be, expressed by the equation given by Bangham, and the isotherms by that of Freundlich. The differential heats of adsorption were obtained through the use of Clausius-Clapeyron's equation.