Adsorption Of Cl Research Articles

DFT study of chlorine adsorption on bimetallic surfaces - Case study of Pd3M and Pt3M alloy surfaces

Chlorine adsorption on Pd3M and Pt3M alloy surfaces (M=Fe, Co, Ni, Rh, Pd, Pt) with ideal bulk surface composition and Pt and Pd-skin type surfaces was analyzed by means of spin-polarized periodic Density Functional Theory calculations. The Pd-based surfaces tended to adsorb chlorine more strongly than the Pt-based surfaces. On bimetallic surfaces, Cl preferred to adsorb on the high-coordination sites. The ratio of surface stabilities, that is the preference of non-segregated surfaces or the skin-type ones, can be inverted under chlorine chemisorption conditions. The relative surface stability was linked to catalytic activity of Pt3Ni surfaces towards the oxygen reduction reaction in chloride-containing solutions. The charge transfer from metallic substrate to the Cl adatom was found to become more pronounced when the position of the solute M in the Periodic Table of Elements moved upward and left. However, the degree of bond ionicity did not exceed 20% in any case. In order to contribute to the comprehension of the adsorption trends, the Cl adsorption energy was correlated to the charge transfer parameters and to the electronic structure of the investigated bimetallic surfaces.

Adsorption of Cl−, Br−, and I− ions from 0.1 M solutions in methanol on Ga, (In-Ga), and (Tl-Ga) electrodes

Adsorption of Cl−, Br−, and I− (Hal−) ions from 0.1 M solutions in methanol (MeOH) is studied on the liquid renewable Ga, (In-Ga), and (Tl-Ga) electrodes by the methods of differential capacitance and jet electrode. It is shown that the adsorption parameters and the series of surface activity of halide ions in MeOH essentially depend on the metal nature. On the (In-Ga) and (Tl-Ga) electrodes, as well as on the Hg electrode, the surface activity of halide ions increases in the series: Cl− < Br− < I−; on the Ga electrode, it varies in another series: Br− < Cl− < I−. The data for the Ga/MeOH interface support the result, which was first obtained on the Ga/N-methyl formamide (N-MF) interface, that the effect of inversion of surface activity series can be observed not only in the aprotic solvents, but also in the protic solvents. The data, which were obtained in MeOH, are compared with the corresponding data, which were obtained in N-MF, dimethyl formamide (DMF), acetonitrile (AN), and water. For Ga, (In-Ga), and (Tl-Ga) electrodes, the adsorption of Hal− varies in the series: H2O < MeOH ≈ N-MF < DMF < AN. The data obtained in MeOH indicate that the energy of metal-Hal− interaction (ΔGM-Hal) increases in the series (Tl-Ga) < (In-Ga) < Ga as the electronic work function increases. This is in agreement with the data, which were obtained in other solvents, and is the evidence for the donor-acceptor nature of metal-Hal− interaction, where the Hal− ions are the donors of electron pair with respect to the metal.

The anticorrosive properties of sol-gel films doped with hydrotalcite nanoparticles applied on tinplate

The use of two-layer system based on the sol-gel technology is proposed as the inner lacquer for tinplate food cans. The primer was a hybrid film based on tetra-n-propoxyzirconium (TPOZ) and 3-Glycydoxypropyltrimethoxysilane (GPTMS) precursors. The topcoat was also a hybrid film based on tetraethyl orthosilicate (TEOS) and vinyltrimethilsiloxane (VTMS) precursors. The topcoat is intended to be in contact with foodstuff, thus, hydrotalcite nanoparticles were incorporated as dopants to increase the film barrier properties. The types of hydrotalcite nanoparticles studied were as-synthesized (HT) and thermally activated (CHT). The zeta potential measurements performed on the hydrotalcite suspensions indicated that they were stable in the acidic conditions used to synthesize the sol-gel solution; therefore, the particles disperse well into the sol-gel.The electrochemical behaviour was evaluated by means of Electrochemical Impedance Spectroscopy (EIS). The results showed better performance of tinplate samples coated with doped sol-gel film than undoped films. However, there were not significant differences between the hydrotalcite types, indicating that the mechanism of inhibition has to be the same in both cases. The zeta potential evolution of HT and CHT suspensions with the NaCl concentration revealed the adsorption of Cl— anion on the particles surface, removing the chloride ions from the surrounding environment.

First-Principles Study on the Corrosion Mechanism of Degradable Medical Mg Alloys in the Medium Containing Cl-

A first-principles plane-wave pseudopotential method based on Density Functional Theory (DFT) has been used to perform a comparative theoretical study of the adsorption H2O and Cl- on a degradable medical Mg alloy (0001) surface. It is found that H2O molecules bind preferentially at atop sites with a large tilt angle away from the surface normal, Cl- ions are energetically favoured adsorbed on hcp hollow sites. In the aqueous solution containing Cl-, the preferential adsorption of Cl- over H2O on Mg surface prevents the Mg surface passivation and induces the corrosion of degradable medical Mg alloys. For H2O adsorption, the ineraction between H2O molecule and Mg surface makes Mg hydration, and thereby Mg alloy surface passivates and the formation of the protective Mg(OH)2. For Cl- ion adsorption, a 0.44e charge translation from Cl- ion to the Mg alloy surface makes the corrosion potential of Mg alloy surface negativly shifted. Thereby, the activity and the corrosion of magnesium alloy are enhanced. This can explain why degradable medical magnesium alloys corrode quickly in physiological media containing high concentrations of chloride ions.

The Effect of Surface Geometry of Copper on Adsorption of Benzotriazole and Cl. Part I

The adsorption of benzotriazole and Cl on low Miller index surfaces of copper and under-coordinated defects thereon was characterized using density functional theory calculations; the former is an outstanding corrosion inhibitor and the latter a corrosion promoter. We find that adsorption bonding of intact benzotriazole (BTAH), dehydrogenated benzotriazole (BTA⊙), and Cl becomes stronger as the coordination number of surface Cu atoms involved in the adsorption site decreases, whereas the adsorption energy of H—considered as a side-product of BTAH dehydrogenation—is rather insensitive to surface geometry. The Cl binds the strongest, and the binding energy ranges from −3.3 eV on Cu(111) to −3.9 eV on very low-coordinated defects, and BTA⊙ binds somewhat weaker, from −2.8 to −3.8 eV, whereas BTAH binds considerably weaker, from −0.6 to −1.3 eV. The bonding enhancement due to reduced coordination of surface Cu atoms is hence the strongest for BTA⊙, which indicates its ability to passivate the reactive under-c...

Removal of Cl adsorbed on Mn–Ce–La solid solution catalysts during CVOC combustion

Mn–Ce–La oxide-mixed catalysts prepared by the method of complexation followed by calcination at 750°C were tested in the catalytic combustion of chlorobenzene (CB) taken as a model of chlorinated aromatics. XRD analyses show that Mn and La enter CeO2 matrix with a fluorite-like structure to form solid solution. The catalysts with high ratio of Mn/Mn+Ce+La exhibit high activity for CB combustion, due to high oxygen mobility. For all Mn–Ce–La catalysts, deactivation due to Cl adsorption is observed at different temperatures, depending on composition. At 330°C or higher temperature, the removal of Cl species from the surface in the forms of Cl2 (produced through Deacon reaction) and HCl (produced through hydrolysis of Cl) occurs and the activity of catalysts for CB combustion becomes thus stable. Either the addition of water or the increase in gaseous oxygen concentration can promote the removal of Cl species, and thus to increase the activity for CB combustion. High stable activity of Mn–Ce–La catalysts can be related to the combination of good oxidation and Deacon reaction performances.

Effect of metal nature on specific adsorption of Cl−, Br−, and I− ions from N-methylformamide solutions

The differential capacitance curves were measured with an ac bridge in the M/[N-MF+0.1m M KCl+0.1(1−m) M KClO4], M/[N-MF+0.1m M KBr+0.1(1−m) M KClO4], and M/[N-MF+0.1m MKI+0.1(1−m) M KClO4] systems (where M=In–Ga, Tl–Ga) at the following values of molar fraction m of the surface–active anion: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1. The I−, Br− and Cl− (Hal−) anions specific adsorption in the above systems can be described quantitatively by the Frumkin isotherm. The main parameters of adsorption of the I−, Br−, and Cl− anions were determined for the studied interfaces. Unlike Ga/N-MF interface, where the adsorption energy (ΔGads) increased in the sequence Br−≈I−<Cl−, at the (In–Ga)/N-MF and (Tl–Ga)/N-MF interfaces, same as at the Hg/N-MF interface, it increased in the reverse sequence: Cl−<Br−<I−. It is found that the values of ΔGads, energy of metal–Hal− interaction (ΔGM-Hal-), and difference (ΔGM-Hal1--ΔGM-Hal2-) grow in the series of (Tl–Ga)<(In–Ga)<Ga. The metal–Hal− interaction energy increase in the sequence of ΔGM-Cl->ΔGM-Br->ΔGM-I-. The values of difference (ΔGM-Hal1--ΔGM-Hal2-) are higher for the Ga electrode and lower for the (In–Ga) and (Tl–Ga) electrodes than the values of difference between the Hal− solvation energies (ΔGS-Hal1--ΔGS-Hal2-), which determines the sequences of Hal− adsorption.

First-Principles Study on Cl Adsorption on γ-TiAl(100) Surface

The adsorption of Cl on the γ-TiAl (100) surface is studied by using the first-principles calculations based on the density-functional theory. The calculated result show that the most stable site for Cl adsorption is the four-fold-hollow site denoted by HFa. The binding energy per Cl atom increases when the coverage is more than 0.75ML. The Cl atoms are more likely to interact with the Ti atoms than the Al atoms from not only the electronic structure but also the atomic structure.

Adsorption of Benzyldimethylhexadecylammonium Chloride at the Hydrophobic Silica–Water Interface Studied by Total Internal Reflection Raman Spectroscopy: Effects of Silica Surface Properties and Metal Salt Addition

The adsorption of the cationic surfactant benzyldimethylhexadecylammonium (BDMHA(+)) chloride was studied at an octadecyltrichlorosilane (OTS)-monolayer-modified silica-water interface by Raman spectroscopy in total internal reflection (TIR) geometry. The present study demonstrates the capabilities of this spectroscopic technique to evaluate thermodynamic and kinetic BDMHA(+)Cl(-) adsorption properties at the hydrophobic silica surface. The surface coverage of BDMHA(+) decreased by 50% at the hydrophobic OTS-silica surface relative to the surface coverage on bare silica; the dominating driving mechanisms for surfactant adsorption were identified as hydrophobic effects and head group charge screening by the electrolyte counterions. Addition of magnesium metal salt (MgCl2) to the aqueous solution (∼ neutral pH) lowered the surface coverage and moderately increased the Langmuir adsorption constants relative to those of the pure surfactant. These trends were previously observed at the hydrophilic, negatively charged silica surface but with a smaller change in the Gibbs free energy of adsorption at the hydrophobic silica surface. The hydrophobic OTS-silica surface properties resulted in shorter times for the surfactant to reach steady-state adsorption conditions compared to the slow adsorption kinetics previously seen with the surfactant at the hydrophilic surface. Adsorption isotherms, based on Raman signal intensities from spectral analysis, were developed according to the Langmuir adsorption model for the pure surfactant at the OTS-silica-water interface; the modified Langmuir model was applied to the surfactant adsorption in the presence of 5, 10, 50, and 100 mM magnesium chloride. Spectral analysis of the Raman scattering intensities and geometric considerations suggests a hemimicelle-type surface aggregate as the most likely surfactant structure at the OTS-silica surface. The different kinetics observed at the hydrophilic versus the hydrophobic silica surface further indicate that the surface charge and potential influence the surfactant diffusion and kinetic rates of adsorption at the silica-water interface.

DFT calculations for Au adsorption onto a reduced TiO2 (110) surface with the coexistence of Cl

Residual chlorines, which originate from HAuCl4, enhance the aggregation of gold (Au) nanoparticles and clusters, preventing the generation of highly active supported Au catalysts. However, the detailed mechanism of residual-chlorine-promoted aggregation of Au is unknown. Herein to investigate this mechanism, density functional theory (DFT) calculations of Au and Cl adsorption onto a reduced rutile TiO2 (110) surface were performed using a generalised gradient approximation Perdew, Burke, and Ernzerhof formula (GGA–PBE) functional and plane-wave basis. Although both Au and Cl atoms prefer to mono-absorb onto oxygen defect sites, Cl atoms have a stronger absorption onto a reduced TiO2 (110) surface, abbreviated as rTiO2 (110) in the following, than Au atoms. Additionally, co-adsorption of a Cl atom and a Au atom or Au nanorod onto a rTiO2 surface was investigated; Cl adsorption onto an oxygen defect site weakens the interaction between a Au atom or Au nanorod and rTiO2 (110) surface. The calculation results suggest that the depletion of interaction between Au and rTiO2 surface is due to strong interaction between Cl atoms at oxygen defect sites and neighbouring bridging oxygen (OB) atoms.

Soil Salinity Changes in the Jordan Valley Potentially Threaten Sustainable Irrigated Agriculture

The integrated effect of irrigation and agricultural practices on soil salinity in the Jordan Valley (JV), where over 60% of Jordan's agricultural produce is grown, was investigated in this study during 2009–2010. Due to the differences in agricultural operations, cropping patterns, irrigation management, and weather conditions, 206 top- and sub-soil samples were taken every 1 to 3 km from representative farms along a north-south (N-S) transect with 1 to 2 km lateral extents. Soil electrical conductivity of saturated extract (ECse), Ca, Mg, K, Na, Cl, and Na adsorption ratio (SAR) were determined in saturated paste extracts. Results indicated that about 63% of soils in the JV are indeed saline, out of which almost 46% are moderately to strongly saline. Along the N-S transect of the JV, ECse increased from 4.5 to 14.1 dS m−1 in top-soil samples. Similar increase was observed for the sub-soil samples. The major chemical components of soil salinity; i.e., Ca, Mg, and Cl, also showed a similar increase along the N-S transect of the valley. Moreover, compared to previous field sampling, results showed that changes in soil salinity in the JV were dramatic. In addition, it was found that Cl imposed an existing and potential threat to sensitive crops in 60% of the soils in the JV, where Cl concentrations were greater than 710 mg L−1. Under the prevalent arid Mediterranean conditions, improving the management of irrigation water, crops, and nutrient inputs and increasing water and fertilizer use efficiencies should be indispensable to conserve and sustain the already fragile agricultural soils in the JV.

Efficient polymer solar cells with a solution-processed gold chloride as an anode interfacial modifier

The use of a solution-processed gold chloride (AuCl3) as an anode interfacial modifier was investigated for high-performance polymer solar cells (PSCs). Kelvin probe, 4-point probe, and X-ray photoelectron spectroscopy studies demonstrated that AuCl3 increases the indium-tin-oxide (ITO) work-function and decreases the ITO sheet resistance, because of Au nanoparticle formation and Cl adsorption by the AuCl3 treatment to induce a p-doping effect, thereby improving the built-in potential and interface resistance. As a result, the introduction of AuCl3 by simple solution processing remarkably improved cell-performances, indicating that AuCl3 is an efficient anode interfacial modifier for enhancing PSC-performance.

Efficient Pt/carbon electrocatalysts for proton exchange membrane fuel cells: Avoid chloride-based Pt salts!

The catalytic layers of Proton Exchange Membrane (PEM) fuel cells use carbon-supported Pt-based nanoparticles, which are classically synthesized by impregnation with a metal precursor usually based on chloride counter-ions. However, the literature points out that chloride ions poison the catalytic activity. The purpose of this work is to compare the surface reactivity and the electrocatalytic activity of Pt/carbon xerogel nanoparticles contaminated with different amount of chlorine. The catalysts were synthesized using the Strong Electrostatic Adsorption (SEA) method and H2PtCl6 as a metal precursor. The Cl content in the catalysts was changed by varying the gas atmosphere and the duration of the reduction step. The effect of Cl contamination was investigated on two model reactions: the electrochemical COads oxidation and the O2 reduction. Evidences are provided that the Cl− ions issued from the incomplete decomposition/removal of the metal precursor partially block the Pt catalytic sites, and limit the rate of the COads + OHads recombination and of the diffusion of COads molecules in CO stripping experiments. The adsorption of Cl− ions also depreciates the ORR kinetics. In search for efficient catalysts, chloride-containing metal precursors must therefore be avoided.

Selective adsorption behavior of BC2N nanotubes toward fluoride and chloride

By using density functional theory calculations, the adsorption of Cl− and F− ions on a BC2N nanotube was investigated. Adsorption energies in the most stable configurations are about −0.36 and −5.65eV for Cl− and F− ions, respectively. The adsorption of F− ion much more influences the electronic properties of the tube, in comparison with the Cl− ion, so that it is transformed from an intrinsic semiconductor with HOMO/LUMO energy gap of 2.57eV to an extrinsic n-type semiconductor with the gap of 0.67eV. It was found that the adsorption of both anions on the tube would facilitate the field electron emission from its surface by shifting the Fermi level to higher energies and decreasing the work function, significantly.

Tuning of the Surface-Exposing and Photocatalytic Activity for AgX (X = Cl and Br): A Theoretical Study

The underlying physical mechanism and dynamics of crystal growth in tuning the crystal morphology and surface exposing by adjusting the concentration of the precursor NaCl are elucidated by examining the surface energies, adsorption energy, and total energy for several surfaces upon adsorption of Cl in AgCl based on first-principles calculations. Our results indicate that the specific surface structures of different surfaces and the nature of ionic interactions between Ag and adsorbed Cl atoms in AgCl facilitate the reversal of relative surface energy upon adsorption of Cl, enabling the possibility of tuning the crystal morphology and surface exposing by adjusting the concentration of precursor NaCl. Two critical concentrations of NaCl at which the morphology of crystal changes are predicted, in satisfactory accordance with the experimental observations. Moreover, for the first time, we propose that the morphology and surface exposing of AgBr can be controlled by subtly tuning the concentration of precurs...

Application of multivariate statistical techniques in the assessment of groundwater quality in seawater intrusion area in Bafra Plain, Turkey

Multivariate statistical techniques such as cluster analysis and principal component analysis were performed on 28 groundwater wells in Bafra Plain. Cluster analysis results show that the groundwater in the study area is classified into three groups (A, B, and C), and factor analysis indicates that groundwater is composed of 89.64% of total variance of 12 variables and is mainly affected by three factors. Factor 1 (seawater salinization) includes concentrations of electrical conductivity, TDS, Cl(-), Na(+), and sodium adsorption ratio, factor 2 (mixing water) includes δ(18)O, δD, and T, and factor 3 (fresh) includes Ca(2+). For determination of the source of water, Ca/Cl, Cl/HCO(3), Mg/Cl, and Ca/Na as initials and Mg/Ca and SO(4)/Cl as molar rates which were identified, the rates had been found to be very useful. Cluster analysis was made by using these rates and the waters were classified in two groups (group 1 and group 2). First group waters were affected by seawater, and the second group were very less affected by freshwater or seawater. According to the comparison of two different parameters, group 1 comprised group A and group B-2, -3, and -4 from the same wells, and group 2 comprised group B-1 and group C from the same well. As a result of this study, it could be said that multivariate statistical methods gave very useful results for the determination of the source.

Synthesis and photocatalytic activity of monodisperse single crystalline NiO octahedrons by the selective adsorption of Cl− ions

Monodisperse NiO octahedrons have been synthesized by heating NiCl2 solutions on the Si substrates at 400–500°C for 1h. The NiO octahedrons are single-crystalline with the body-centered cubic structure and have controllable sizes in the range of 166–257nm. Control over the size of NiO octahedrons was achieved by adjusting the heating temperature. The formation of NiO octahedrons results from the selective adsorption of Cl– ions on unsaturated Ni(II) sites of NiO (111) surface. The NiO octahedrons with exposed {111} facets show higher intrinsic photocatalytic activity than Degussa P25 TiO2, and the photocatalytic activity was enhanced with a decrease on the size of NiO octahedrons.

Ions near the air/water interface. II: Is the water/air interface acidic or basic? Predictions of a simple model

A simple modified Poisson–Boltzmann model, compatible with zeta potential experiments, is used to calculate the concentrations of ions on the interface. It is shown that, for most pH values and salt concentrations, both H+ and OH− accumulate on the interface, making their interfacial concentrations larger than in the bulk. However, at extreme pH values, the interfacial concentrations of both H+ and OH− have been found to be lower than in bulk, which might explain some contradictory results from literature. The ratio between H+ and OH− concentrations is smaller at the interface than in bulk for most (but not all) pH values and salt concentrations. Recent experimental results, which show that H+ is present on the interface only at very low pH values, are explained on the basis of this model. It is shown that, when the adsorption of Cl− on the interface is sufficiently large compared to that of OH−, the number of H+ ions adsorbed on the interface passes through a maximum with salt concentration, also in agreement with experiment. The concentration at which the maximum occurs is of the order of the adsorption equilibrium constant of Cl− on the interface.

Improving the pore structure and adsorption properties of industrial active carbons

The paper describes the possibility of improving the pore structure and adsorption properties of industrial active carbons (AC) by means of their modification with ɛ-caprolactam (CL). Application of ɛ-caprolactam (a product of large-scale organic synthesis) as a modifying substance allows the targeted regulation of the specific surface area and volume of AC mesopores, while the conditions of modification change the chemical composition of the surface of carbon adsorbents and, as a result, their adsorption properties. The process of modification includes three stages. The first is the adsorption of CL from aqueous solution and heating at 300°C in the presence of atmospheric oxygen. The second is carbonization in an argon flow at 900°C, and the third is the vapor-gas activation of the resultant adsorbents at 900°C. Each stage is followed by determining the parameters of the pore structure by N2 adsorption and the adsorption parameters with respect to benzene, iodine, aqueous solutions of ɛ-caprolactam, and copper sulfate (CuSO4). When modifying the carbonized samples with an initial ɛ-caprolactam content of 2%, we observe the growth of mesopores over 100% of volume, relative to AG-OV-1 original industrial activated carbon. Depending on the stage of modification, an increase in adsorption is observed, relative to the AG-OV-1 original carbon: benzene adsorption rises by 50%, the adsorption of iodine from aqueous solution rises by 20%, the adsorption of ɛ-caprolactam from aqueous solution grows by more than 30%, and the adsorption of copper(II) ions rises by more than 70%. The procedure for the production of the described modified adsorbent has no rivals abroad; it is protected by a patent and can be used in industry. It is possible to use inexpensive industrial carbons as the original material. The procedure allows the production of carbon adsorbents with predetermined structural and adsorption properties.

Global Model of &lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;$\hbox{Cl}_{2}\hbox{/Ar}$&lt;/tex&gt; &lt;/formula&gt; High-Density Plasma Discharge and 2-D Monte-Carlo Etching Model of InP

A multiscale approach has been developed in order to simulate the etch process of InP in an inductive coupled plasma (ICP) Cl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ar plasma discharge. The model consists of three modules: a global kinetic model of the Cl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ar plasma discharge, a sheath model, and a 2-D Monte-Carlo etching model. The densities and the fluxes of all neutral and charged species considered in the reaction scheme as well as the electron temperature are calculated from the global model. The angular and energy distribution functions of ions are computed from the sheath model. The output parameters of both the global kinetic model and the sheath model in terms of particle fluxes, ion angular distribution function and ion energy distribution function are used as input parameters in the 2-D etching model. The latter allows tracking in time the evolution of the etched surface. The ultimate goal of the multiscale approach is to predict the etch rate, the etched surface chemical composition, and the etch profile as a function of the operating conditions (power, pressure, gas flow rates, etc). In this paper, the results from the global model are first compared to the measurements carried out in the ICP etching tool, showing a satisfactory agreement. The etching model is then used to simulate the etching of narrow trench and small-diameter hole in InP. The mechanisms involved in the development of undercut below the mask and in the bowing effect are analyzed. The comparison between simulated and experimental etch profiles evidences the important role of Cl adsorption probability on the development of the undercut, and the significant impact of the redeposition of the etched species on the etch rate variation and on the narrowing in the bottom of the etched hole/trench.