Influence Of Chemisorption Research Articles

Influence of chemisorption on the double hysteresis phenomenon during reactive sputtering

Process curves that are obtained during reactive magnetron sputtering can exhibit a double S-shape, also termed a double hysteresis. A previous study mainly focused on the relationship between the double shape behavior and the reaction kinetics of implanted reactive ions, although chemisorption also defines the target condition. As a follow-up study, the influence of chemisorption on double hysteresis is computationally studied by high-throughput calculations using a state-of-the-art model for reactive sputtering. The analysis reveals that the magnitude of the double hysteresis is a conserved quantity for the chemisorption driven reactions at the substrate level. At the target level, a balance between compound formation by direct reactive ion implantation and chemisorption is established. A minimal condition for double hysteresis is derived and process conditions are identified for which the double hysteresis can be measured for target materials prone to strong chemisorption of the reactive gas. The condition can assist to further explore the close interplay between chemisorption and implantation during reactive sputtering.

Activated carbon fibers prepared from cellulose and polyester–derived residues and their application on removal of Pb2+ ions from aqueous solution

In the present work, cellulose and cellulose/polyester-derived denim residues were successfully used as carbon precursors for preparation of H3PO4-activated carbon fibers (ACFs), which were applied on removal of Pb2+ ions from aqueous solutions. ACFs were prepared under conditions of slow pyrolysis, leading to the obtaining of materials with high BET surface area values (SBET). The materials were characterized from several analytical techniques and the results showed that they have well-developed porous structures, with SBET of 1714 and 1743 m2 g−1, for ACFs obtained from the cellulose (ACFC) and cellulose/polyester denim residues (ACFCP), respectively. Additionally, the materials showed a well-developed mesoporous structure. The thermogravimetric analysis confirmed the thermal stability of materials, while SEM images attested the fibrous character. The surface groups were explored via FTIR, Boehm titration and pHPZC, which demonstrated the predominance of acidic groups on the surface of both materials. The Pb2+ adsorption efficiency from aqueous solution was investigated, evaluating the effect of solution pH, time, adsorbate initial concentration and temperature. The results confirmed the good performances of materials for Pb2+ removal, showing monolayer adsorption capacities of 361.54 and 385.77 mg g−1 for ACFC and ACFCP, respectively. Additionally, the thermodynamic studies confirmed the spontaneity and exothermic nature of adsorption, suggesting a synergistic mechanism with influence of chemisorption and ion exchange.

Synthesis of microporous organic polymers with high CO2-over-N2 selectivity and CO2 adsorption

A series of microporous organic polymers (MOPs) were synthesized by Schiff base condensation of 1,3,5-tris(4-aminophenyl)benzene and a number of dialdehyde monomers. The polymers were structurally characterized by in situ infrared and ex situ solid state 13C{1H} nuclear magnetic resonance (NMR) spectroscopy. Synthesis conditions were optimized to enhance CO2 uptake by the MOPs. Synthesis at low temperatures results in the MOPs being linked by imine groups. Heating of the MOPs reduces the number of imine groups and after heating to >300 °C nitrile groups were found to be present in the MOPs. The MOPs have specific surface areas up to 614 m2 g−1 and narrow pore size distributions of ∼4 to 8 A. The selectivity of CO2-over-N2 at 273 K and 1 bar was 56–77, which requires either an influence of chemisorption on CO2 or a molecular sieving (or kinetic selection) of CO2-over-N2. The materials had also heats of adsorption typical for physisorption of CO2.

Influence of chemisorption on the thermal conductivity of graphene nanoribbons

The thermal conductivity of graphene nanoribbons (GNRs) functionalized by the chemical attachment of methyl and phenyl groups at random positions is calculated using reverse nonequilibrium molecular dynamics. The GNRs exhibit a rapid drop in thermal conductivity with increasing degree of functionalization; a functional group coverage regime of as little as 1.25% of GNR atoms reduces the thermal conductivity by about 50%. The thermal conductivity of nanoribbons with zigzag edges is more sensitive in the degree of functionalization than nanoribbons with armchair edges. The simulation results indicate that the rapid drop in thermal conductivity is a consequence of the higher angular momentum of functional groups, which rotate the unsupported sp 3 bonds and thus reduce the phonon mean free paths.

Atomic and electronic properties of tert-butanol on the Si(001)-(2×1) surface

The atomic and electronic properties of the adsorption of tert-butanol [(CH3)3OH] molecule on the Si(001)-(2×1) surface have been studied by using the ab-initio density functional theory (DFT) based on pseudopotential approach. We have found that tert-butanol bonded the Si(001) surface by oxygen atom, cleaving a O–H bond and producing a Si-H bond and tert-butoxy surface species. We have also investigated the influence of chemisorption of tert-butanol on the electronic structure of the clean Si(001)-(2×1) surface. Two occupied surface states situated entirely below the bulk valence band maximum have been identified, which means that the clean Si(001)-(2×1)surface was passivated by the chemisorption of tert-butanol. In order to explain the nature of the surface components we have also plotted the total and partial charge densities at the \(\bar{K}\) point of the surface Brillouin zone (SBZ).

The chemisorption of CO on a disordered binary alloy (NixCu1－x) and the mutual influence of chemisorption and surface segregation

The atomic structural model of the NixCu1-x disordered binary alloy was set up for the cases with or without consideration of surface segrega tion by computer program ming.Then the model of the chemisorption of CO on the surface of the material wa s set up with a coverageθ=05. The electronic structure of CO chemisorpti on on the top and hollo w sites of the NixCu1-xdisordered binary alloy was calculated (considering and not considering the segregation).The calculated results show that (1) the CO ad sorbd at top site on the surface is stable and, (2) the chemisorp tion makes the surface density of states of the disordered binary alloy lowered, the ener gy ba nd widened and the localization of d orbital weakened and, (3) the chemisorpti on of CO on the surface restricts the surface segregation of Cu, then the mutual influence of chemisorption and multiplayer surface segregation is discussed at an electronic level.

Target poisoning during reactive magnetron sputtering: Part II: the influence of chemisorption and gettering

As generally accepted gettering of the reactive gas by the sputtered target material plays an important role for most reactive gas/target combinations. The influence of the gettering process and the chemisorption of reactive gas on the target have been modelled by Berg et al. (J. Vac. Sci. Technol. A 5(2) (1987) 202–207). However, in this model the effect of ion implantation was not included. Therefore, a model is proposed which takes ion implantation into account. The model is used to understand the target voltage behaviour during reactive sputtering of aluminium in an argon/oxygen mixture. At high pumping speed or low current, a target voltage increase is noticed before the critical point. This can be attributed to chemisorption of oxygen on the aluminium target. Chemisorption of oxygen reduces the erosion rate of the target, which enhances the poisoning of the aluminium target by reactive ion implantation. At low pumping speed or high current, i.e. when gettering dominates the reactive sputtering process, the effect of chemisorption on the target voltage is less pronounced due to the competition between reactive ion implantation and chemisorption.

Spectra of surface-enhanced Raman scattering of 1-propanethiol and 3-mercaptopropionic acid chemisorbed on thin silver films

The influence of chemisorption and intermolecular Van der Waals interactions on the formation of surface-enhanced Raman spectra of 1-propanethiol and 3-mercaptopropionic acid coated as self-organized monolayers on vacuum-deposited thin silver films and thin silver films annealed at high temperatures is studied. Optical properties of films of both types are found to be strongly affected by the chemical modification, which is associated with peculiarities of the monolayer formation. It is shown that the reorganization of the substrate surface can be associated with intense repulsion between alkane chains of thiol when the distance between them decreases in comparison with the distance typical of crystalline paraffins. Conclusions on the presence and the nature of packing defects of short-chain thiols on the substrate surface are made on the basis of the analysis of Raman and surface-enhanced Raman spectra. It is shown that the interaction between the first (propanethiol) and the second (pyruvate) monolayers near the silver surface in the water phase results in the reorganization of the first monolayer, in which conformers of propanethiol in the gauche-conformation with respect to the C(1)-C(2) bond prevail.

The influence of chemisorption on the defect equilibrium of metal oxide thin films

Using the exact charge density of intrinsic point defects of metal oxides (MOs), the phenomenological electron theory of chemisorption, developed by Volkenstein, is applied to acceptorlike and donorlike chemisorption on MO thin films for the whole ξ region (where ξ=D/LD, D is the film thickness, and LD is Debye length). The experimental temperature and oxygen partial pressure dependence of the averaged electron concentration 〈n〉(pO2,T)∝e−EA/kTpO2−m(T) for polycrystalline ZnO films are discussed on the bases of three different models: the Schottky-defect model, the Volkenstein model for electronic equilibrium, and the comprehensive model for complete equilibrium. It turns out that a Schottky-defect model that uses single-crystal-mass action constants will not yield the experimental high temperature limit (T=1000 K: EA=1.6 eV, m=0.26). This limit is obtained using a higher averaged concentration of oxygen vacancies for polycrystalline films (due to the presence of grain boundaries). The comparison between the electronic and complete equilibrium shows that the screening of the surface charge through mobile positively charged oxygen vacancies has a tremendous reducing effect of about 30% of the surface potential in the temperature range considered.

A MODEL FOR THE MUTUAL INFLUENCE OF CHEMISORPTION AND MULTILAYER SEGREGATION

The Green function method and the chemisorption theory of Einstein and Schrieffer are used to calculate the chemisorption energies of O and CO on the multilayer segregated Ni-Cu disordered binary alloy within the many-coupled self-consistent coherent potential approximation. In general cases, the chemisorption-induced surface segregation can change the surface component and the chemisorption property to varying degrees. When the mutual influence of chemisorption and multilayer segregation is considered, the changes appear slightly mild. The chemisorption energy for O/Ni-Cu (CO/Ni-Cu) depends sensitively on O(CO) coverage θ, and decreases with increasing θ.

Influence of chemisorption on the photodecomposition of salicylic acid and related compounds using suspended titania ceramic membranes

The adsorption and photodecomposition on semiconducting membranes of molecules with different functional groups were studied. Ceramic membranes, prepared by a sol-gel technique, were employed because this technique provides some control over surface area, porosity, and crystal form of these materials, properties which affect their photochemical behavior. Salicylic acid was chosen as a prototype molecule. 3-Chlorosalicylic acid, benzoic acid, phenol, and 4-chlorophenol were also investigated. The adsorption densities of salicylic and 3-chlorosalicylic acids decreased with both increasing solution pH and membrane firing temperature, in correlation with the number of positive adsorption sites on TiO2 surface. No adsorption for benzoic acid, phenol, and 4-chlorophenol was observed. Photodecomposition rates were found to depend on the adsorption characteristics of the organic compound; for salicylic acid the degradation rate diminished with increasing pH. Benzoic acid, whose degradation products adsorb on the oxide surface, showed a similar trend. No dependence on pH was detected for phenols. Methanol was found to affect the degradation rate of salicylic acid only under conditions of high pH. It is proposed that, for chemisorbing organics, the initial step of the photodecomposition process is governed by two different mechanisms that depend on the adsorption behavior of the organic compound at a particular pH. For adsorbed salicylate, an orbital configuration of the chelate ring is proposed to interpret direct electron transfer from the organic molecule to the semiconductor.

Carbon monoxide and hydrogen chemisorption studies on small supported iron carbide particles

The influence of chemisorption of CO and H2 has been studied on small iron carbide particles by Mossbauer spectroscopy. The line with is increased by 2–3 times upon evacuation and also the values of isomer shift and magnetic hyperfine field were increased in vacuum. The effect is attributed to the chemisorption induced uniformization of the magnetic exchange interaction among the particles.

Additions and corrections. Quantum Chemical Investigation of Support-Metal Interactions and Their Influence of Chemisorption

ADVERTISEMENT RETURN TO ISSUEPREVArticleAdditions and corrections. Quantum Chemical Investigation of Support-Metal Interactions and Their Influence of ChemisorptionHelmut Haberlandt and Friedrich RitschlCite this: J. Phys. Chem. 1984, 88, 7, 1454Publication Date (Print):March 1, 1984Publication History Published online1 May 2002Published inissue 1 March 1984https://doi.org/10.1021/j150651a044RIGHTS & PERMISSIONSArticle Views11Altmetric-Citations-LEARN 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 (96 KB) Get e-Alerts

Charging of pre-existing slow states of the real surface of epitaxial CdSe films during adsorption of acceptor molecules

The influence of chemisorption of NO2 on the electrical conductivity of epitaxial CdSe films treated in various ways was investigated. It was found that the profile of the Δσ(t) kinetic curves of the CdSe films during chemisorption is determined by the concentration and nature of the “biographical” (pre-existing) slow states on their surface. It was found that the effective relaxation time τs does not depend on the thickness d of the oxide film, and is entirely determined by the nature and concentration of the biographical slow states. It is shown that chemisorption of gases can be used as a method to investigate the biographical slow states of the real surface of CdSe films.

The Influence of Chemisorption on Oxygen on the Microporosity of Chromia

The Influence of Chemisorption on Oxygen on the Microporosity of Chromia

Ferromagnetic resonance of nickel thin films influenced by H 2 and CO adsorption

Nickel thin films prepared in UHV on quartz glass substrates are shown by means of ferromagnetic resonance (FMR) to be either superparamagnetic (for d < 30 × 10 -10 m) or ferromagnetic (for d > 30 × 10 -10 m). Under UHV conditions the FMR-data change reversibly with H 2 or CO pressure and temperature. From the magnetic behaviour of d = 13 × 10 -10 m films chemisorption isotherms can be obtained, which are in good agreement with well known thermodynamical data. H 2 as well as CO adsorption on d = 150 × 10 -10 m films lead to non-monotonous shifts in the resonance field and microwave absorption. The results (resonance field, linewidth, lineshape and microwave absorption after different pretreatments) are discussed in terms of the FMR-theory of thin films. The influence of chemisorption on the magnetic moment, magnetic surface anisotropy and surface stress is estimated.

The influence of chemisorption on the electrical conductivity of thin semiconductors

The influence of chemisorption on the electrical conductivity of thin semiconductors

The influence of chemisorption on photoconductivity in CdS crystals

The action of chemisorbed oxygen on photoconductivity in highly insulating CdS-monocrystals has been studied. For all wavelengths, the photosensitivity is increased by several orders of magnitude after desorption by electron bombardment. The intensity dependance of the photo-current is sublinear for a clean crystal surface. With chemisorbed oxygen at the surface, the intensity dependance is linear and supralinear. The experimental results are accounted for by means of a theory of Stöckmann. Finally it is shown that quenching characteristics are also affected by surface states.