Adsorption Of Iodide Research Articles

Density Functional Theory Study of Methyl Iodide Adsorption and Dissociation on Clean and K-Promoted β-Mo2C Surfaces

We have studied the effect of K on the adsorption and dissociation of methyl iodide on the β-Mo2C(001) surface using density functional theory calculations, and the results were compared with experimental data. The most favorable sites for methyl iodide adsorption are 3-fold sites on both clean and K-promoted surface. The changes in the work function fit our model as the molecule withdraws charge from the surface. The C−I bond weakens when the molecule adsorbs on the surface, and this effect is more noticeable on the K-promoted surface. The dissociation to an I adsorbed atom and a methyl group adsorbed is energetically favorable for both surfaces, but there is a lower activation barrier on the K-doped surface.

Clean and modified substrates for direct detection of living cells by surface-enhanced Raman spectroscopy

Iodide adsorption and electrochemical negative potential desorption were proposed and compared to obtain clean SERS substrates. The two methods can effectively eliminate the interference of surface impurities in the SERS detection. SERS signals of membranes of living cells with a good reproducibility have been obtained.

ChemInform Abstract: The Effect of Tin(II) Chloride Adsorption on the Electrochemical Oxidation of Tin(II) and Other Reactions at Gold and Platinum Electrodes

Abstract During a study of the electrooxidation of tin(II) chloride at gold and platinum electrodes by cyclic voltammetry, a remarkable hysteresis was associated with the oxidation of tin(II) chloride that is attributed to the adsorption of tin(II) chloride on the gold electrode. The adsorbed tin(II) chloride inhibits the oxidation of the bulk tin(II) chloride and therefore shifts the potential for oxidation to more positive values. However, once the adsorbed tin(II) chloride is oxidized, the dissolved tin(II) chloride is oxidizable at less positive potentials. This inhibition by adsorbed tin(II) chloride also affects other inner-sphere electrode reactions (e.g., oxidation of I−), but not outer-sphere reactions. This inhibition is explained in terms of the need of a bridging ligand to facilitate electron transfer in inner sphere reactions. This inhibition is even more pronounced on Pt electrodes, where no oxidation wave for tin(II) chloride is observed. However, adsorption of chloride ions, 2-mercaptoethanol, or iodide causes desorption of the tin(II) chloride and the appearance of an irreversible wave for oxidation of the tin(II) in solution.

Chloride and iodide electrosorption on Ag(1 1 1)

Chloride and iodide adsorption on Ag(1 1 1) was investigated from mixed c M KX + (0.02 − c) M KPF 6, with X = Cl, I, using the potential-step chronocoulometric technique. Measurements were carried out at potentials negative of –0.5 V/SCE, where STM does not provide images of ordered adlayers of these halides. Their adsorption behavior was compared with that of bromide ion on Ag(1 1 1), reported in a previous work. The plot of the applied potential E, decreased by the potential difference ϕ d across the diffuse layer, shows a maximum when plotted against the specifically adsorbed charge density σ i of the halides, at constant charge density σ M on the metal. This behavior is explained by an appreciable contribution from reorientation and displacement of adsorbed water molecules by the adsorbing halides. The minimum of the E − ϕ d vs. σ i plot is much shallower for iodide than for chloride and bromide. The σ i vs. log c plots at σ M = 0 are linear, thus satisfying the Temkin isotherm. The resulting interaction factor is appreciably less repulsive for iodide than for chloride and bromide. These results indicate that partial charge transfer from iodide to Ag(1 1 1) is appreciable even at negative potentials at which adsorption is random, as distinct from chloride and bromide.

Adsorption and desorption of iodine by various Chinese soils: II. Iodide and iodate

It is important to understand iodine availability in various soils in China to efficiently manage and control environmental iodine. A series of batch experiments was conducted on a variety of Chinese soils in order to determine the adsorption characteristics of iodide and iodate. For five soils, the sorption isotherms of iodide were determined, while for all 17 soils, iodide adsorption was studied under one initial concentration to evaluate its sorption capacity. Furthermore, iodate sorption isotherms on two soils at five different initial concentrations were determined in this study, to complement the earlier work of Dai et al. (2004a). From the sorption isotherm results, five Chinese soils were ranked in terms of their capacity for iodate adsorption: Perudic Ferrisols soil, HN > Orthic Aridisols soil, XJ1 > Udic Ferrisols soil, JX2 > Usdic Luvisols soil, BJ > Udic Isohumisols soil, JL. As a comparison, iodide adsorption was ranked as follows: Udic Ferrisols soil, JX2 > Perudic Ferrisols soil, HN > Udic Isohumisols soil, JL > Usdic Luvisols soil, BJ > Orthic Aridisols soil, XJ2. It was also found that the desorbed amounts demonstrated a significant positive correlation with the adsorption of the XJ1 and BJ soils for iodate, and also did the HN and JX2 soils for iodide. At an initial iodide concentration of 4 mg L − 1 , the values of the sorption distribution coefficient, K d, ranged between 0.78 and 6.59 mg kg − 1 soil in 17 soils from China, and iodide adsorption was significantly correlated with soil organic matter and cation exchange capacity. K d exhibited a linear relationship with soil organic matter, a polynomial relationship with free iron oxide content and a logarithmic relationship with cation exchange capacity. Furthermore, results from iodate and iodide adsorption from 17 Chinese soils, except for Fimic Anthrosols soil (GX) showed that the adsorption capacities of iodate were greater than those of iodide, and organic matter in soil environments plays an important role in controlling iodine geochemistry.

Iodide in CTAB Prevents Gold Nanorod Formation

The gold nanocrystal seed-mediated approach using cetyltrimethylammonium bromide (CTAB) as a stabilizing surfactant is commonly used to make large quantities of monodisperse gold nanorods. This method, however, has been at times difficult to reproduce in different laboratories. We recently showed [Smith, D. K.; Korgel, B. A. Langmuir 2008, 24, 644-649] that a very low concentration impurity in CTAB obtained from some suppliers prevents nanorod growth but were not able to identify the impurity. Here, we report that the impurity is iodide. Inductively coupled plasma mass spectroscopy (ICP-MS) revealed that iodide concentrations vary in CTAB from different suppliers, from less than 2.75 ppm up to 840 ppm. When CTAB with iodide concentrations greater than 50 ppm is used, nanorods do not form and the product consists entirely of spherical nanocrystals. Iodide slows the reduction of Au(III) to Au0. Iodide adsorption on Au {111} surfaces inhibits nanorod growth.

Adsorption and photodissociation dynamics of methyl iodide on magnesia supported gold nano-particles

Methyl iodide represents a classical model for photodissociation and photoreaction of polyatomic molecules. Here, a new experimental approach is used to study the surface photoreaction dynamics of methyl iodide on magnesia and on magnesia supported gold particles employing pump-probe laser mass spectrometry. The adsorption of methyl iodide at submonolayer coverage on these substrates is investigated via temperature programmed desorption spectroscopy. Two distinct desorption peaks of molecular methyl iodide are identified corresponding to molecules bound to magnesia and more strongly bound to gold, respectively. This permits to selectively investigate the photoreaction of methyl iodide on the gold particles by choosing the appropriate temperature at which all molecules have been desorbed from MgO but not yet from the gold particles. The temperature dependent transient methyl fragment signal reveals the direct photoinduced dissociation dynamics on magnesia, whereas a quenching of the expected dissociation is observed on gold particles.

Prediction of iodide adsorption on oxides by surface complexation modeling with spectroscopic confirmation

A deficiency in environmental iodine can cause a number of health problems. Understanding how iodine is sequestered by materials is helpful for evaluating and developing methods for minimizing human health effects related to iodine. In addition, 129I is considered to be strategically important for safety assessment of underground radioactive waste disposal. To assess the long-term stability of disposed radioactive waste, an understanding of 129I adsorption on geologic materials is essential. Therefore, the adsorption of I − on naturally occurring oxides is of environmental concern. The surface charges of hydrous ferric oxide (HFO) in NaI electrolyte solutions were measured by potentiometric acid–base titration. The surface charge data were analyzed by means of an extended triple-layer model (ETLM) for surface complexation modeling to obtain the I − adsorption reaction and its equilibrium constant. The adsorption of I − was determined to be an outer-sphere process from ETLM analysis, which was consistent with independent X-ray absorption near-edge structure (XANES) observation of I − adsorbed on HFO. The adsorption equilibrium constants for I − on β-TiO 2 and γ-Al 2O 3 were also evaluated by analyzing the surface charge data of these oxides in NaI solution as reported in the literature. Comparison of these adsorption equilibrium constants for HFO, β-TiO 2, and γ-Al 2O 3 based on site-occupancy standard states permitted prediction of I − adsorption equilibrium constants for all oxides by means of the Born solvation theory. The batch adsorption data for I − on HFO and amorphous aluminum oxide were reasonably reproduced by ETLM with the predicted equilibrium constants, confirming the validity of the present approach. Using the predicted adsorption equilibrium constants, we calculated distribution coefficient ( K d ) values for I − adsorption on common soil minerals as a function of pH and ionic strength.

Modified Nanodiamonds for Adsorption of Propidium Iodide and Aflatoxin

AbstractNanodiamonds (NDs) have desirable chemical, physical and biological properties that lend them to a wide range of applications. ND’s facile surface chemistry, for example, can be used to create a high affinity for adsorbing various biological molecules. However, NDs, which are commercially available from multiple vendors, show inconsistencies with surface groups, aggregate sizes and impurity contents that may limit adsorption. We explore adsorption mechanisms of molecules to NDs in efforts to expand ND applications to drug delivery agents, bio-labels and enterosorbents. In doing so, several types of NDs and modification methods are evaluated to increase adsorption capacity and selectivity of propidium iodide and aflatoxin B1. Capacities and binding strengths of target molecules are assessed by Langmuir isotherms and transform calculations. UV-Vis spectroscopy shows our modification treatments are successful in increasing ND adsorption capacities. Additionally, cyclic voltammetry measurements, used to monitor in-situ adsorption, show electrochemical detection even after binding.

Adsorption and Reaction of Methyl and Ethyl Iodide on Potassium-Promoted Mo2C/Mo(100) Surface

X-ray photoelectron spectroscopy (XPS) studies revealed that potassium on Mo 2 C/Mo(100) induced cleavage of the C-I bond in adsorbed CH 3 I even at ∼100 K. The temperature of complete C-I bond breaking occurred 60-80 K lower compared to the clean surface. Preadsorbed potassium also influenced the reaction pathway of adsorbed CH 3 formed. It decreased its self-hydrogenation into methane and facilitated the coupling reactions into ethane and ethylene below 200 K. High-resolution electron energy loss spectroscopy (HREELS) confirmed formation of adsorbed CH 3 species and revealed its thermal stability. Potassium exerted a similar influence on the chemistry of C 2 H 5 I on Mo 2 C/Mo(100) surface. Rupture of the C-I bond also occurred more easily on K-covered surface. Ethyl species, the primary product of the dissociation, dehydrogenated into ethylene on one hand and hydrogenated into ethane on the other. Rupture of the C-C bond was not observed even at high potassium coverage. Illumination of coadsorbed layers promoted further dissociation of the C-I bond in both compounds at ∼100 K.

Adsorption of iodide and iodate on colloidal silver surface

‘Chemically pure’ silver colloids were prepared by laser ablated method to investigate their adsorption-induced spectral and morphologic changes, using UV–visible absorption, Raman and transmission electron microscopy (TEM) techniques, when nucleophilic different anions (IO 3 − and I −) were added into sols. It reveals that the adsorption of nucleophiles on silver surfaces leads to an excess negative charge in the metal interior and modifies both surface charge density and the Fermi levels of metal, which is responsible for the colloidal aggregation, reconstruction and appearance of new resonance absorption bands or with wavelength shift. In addition, two models regarding different adsorption effects of these two anions on silver surfaces were proposed to explain their variant spectral and TEM phenomena.

Influence of Iodide Ions on the Growth of Gold Nanorods: Tuning Tip Curvature and Surface Plasmon Resonance

This paper describes morphological and optical changes induced by seed-mediated growth of gold nanorods in the presence of iodide ions. Addition of small amounts of iodide to the growth solution results in the growth of nanoparticles with dumbbell-like structure, meaning that gold salt reduction takes place preferentially at the rod tips. However, when excess iodide is added, homogeneous rod growth is observed, and therefore the original shape is retained. By controlling the experimental conditions, the position of the longitudinal plasmon band of grown nanorods can be shifted up to as much as 250 nm. These optical effects were also simulated by means of the boundary element method (BEM), achieving an excellent agreement with the experimental spectra. X-ray photoelectron spectroscopy (XPS) and surface enhanced Raman spectroscopy (SERS) analysis of the gold nanorods before and after iodide addition revealed the presence of AuI and AgI at the particles surface. A growth mechanism is proposed on the basis of preferential iodide adsorption at the tips {111} facets, leading to the formation of AgI, followed by reduction of gold salt precursor due to a decrease in the surface redox potential.

In situ observation of wall effects in activated carbon filters by X-ray microtomography

X-ray microtomography is a powerful non-invasive visualisation technique which can be advantageously used to get a better understanding of dynamic adsorption processes. In the present work, this technique is shown to be able to detect wall effects during the dynamic adsorption of methyl iodide on activated carbon filters. The analysis of transversal cross-sections along the filter height clearly shows the existence of radial concentration profiles. These radial adsorption profiles are directly linked to velocity profiles due to a higher permeability at the wall. Obtaining such in situ information constitutes a real progress in order to validate simulation models allowing predicting reliable breakthrough times.

Clean Substrates Prepared by Chemical Adsorption of Iodide Followed by Electrochemical Oxidation for Surface-Enhanced Raman Spectroscopic Study of Cell Membrane

Surface-enhanced Raman spectroscopy (SERS) has received renewed interest in recent years in fields such as trace analysis, biorelated diagnosis, and living cell study. However, the interference of impurities left on the surface from the preparation process of substrates or adsorbed from the ambient environment limits to some extent the application of SERS for analysis of trace or unknown samples. In the present paper, we propose a method to prepare clean SERS substrates by a combined method of chemical adsorption of iodide on the Au surface to remove the surface impurities and electrochemical oxidation of the adsorbed iodide to obtain a clean and impurity-free surface for SERS measurement. Time-dependent control experiment of untreated and treated substrate reveals that this method is very effective in obtaining substrates free of impurities. SERS mapping demonstrates the SERS activity of the substrate is homogeneous over the whole surface. The obtained clean substrate enables us to study the structures of the cell membrane with SERS and even to perform SERS mapping to visualize the distribution of amino acids over the membrane of a living cell.

Sluggish σ-Bond Formation between sp-Hybridized Carbons: Acetylide Coupling on Ag(111)

Chemisorbed methylacetylide intermediates were generated on clean Ag(111) to study the mechanism and kinetics of C−C σ-bond formation between sp-hybridized carbon centers. Following the adsorption of propynyl iodide (C3H3I) at 110 K, surface heating led to the cleavage of the C−I bond at 200 K, and the resulting surface Cα⋮Cβ−CH3 species were tilted and coordinated to the surface via a metal−carbon σ-bond with weak π-interactions, confirmed by reflection absorption infrared spectroscopy and theoretical calculations. Temperature programmed reaction (TPR) showed that a Csp−Csp coupling reaction occurred at ∼500 K to afford 2,4-hexadiyne through head-to-head dimerization involving Cα carbons. We attribute the relatively slow acetylide−acetylide coupling rate against those from vinyl−vinyl (Csp2−Csp2) and alkyl−alkyl (Csp3−Csp3) couplings to the stronger metal−carbon (M−Cα) bond strength as well as the anionic character bestowed upon the adsorbed acetylides, which all correlate with the increased s-character ...

Shape-Controlled Syntheses of Gold Nanoprisms and Nanorods Influenced by Specific Adsorption of Halide Ions

This paper describes the effect of halide ions during the seed-mediated growth of gold nanoparticles employing cetyltrimethylammonium bromide (CTAB) as a cationic surfactant system. With the addition of a small amount of iodide ion (∼20 μM) in a growth solution, the major product of the gold nanostructures formed were notably changed into triangular nanoprisms in the presence of excessive bromide ion (∼0.1 M); otherwise, in its absence, nanorods with an aspect ratio of ∼11 were the main products. The major role of the iodide ion was in retarding the overall rate of crystal growth, and the iodide adsorption appeared to repress the crystal growth along Au(111) direction, resulting in Au(111)-faced triangular nanoprisms. When the counteranions of the surfactant were replaced with chloride ions, a novel nanostructure (i.e., nanorice) was manufactured, which demonstrates the effectiveness of the adsorption of halide ions. However, this finding is quite contrasted with the work of the Sastry group (J. Nanosci. ...

X-ray Diffraction and STM Study of Reactive Surfaces under Electrochemical Control: Cl and I on Cu(100)

The surface structure of Cu(100) modified by chloride and iodide has been studied in an electrochemical environment by means of in-situ scanning tunneling microscopy in combination with in-situ surface X-ray diffraction with a particular focus on adsorbate and potential dependent surface relaxation phenomena. For positive potentials close to the on-set of the copper dissolution reaction, the X-ray data disclose an extraordinarily large Cu-Cl bond length of 2.61 A for the c(2 x 2)-Cl phase. This finding points to a largely ionic character of the Cu-Cl interaction at the Cu(100) surface, with chloride particles likely to retain their full charge upon adsorption. Together with the positive surface charging at these high potentials, this ionic Cu-Cl bond drives the observed 2.2% outward relaxation between the first two copper layers. These results indicate that the bond between the first and the second copper layer is significantly weakened which appears as the crucial prerequisite for the high surface mobility of copper-chloride species under electrochemical annealing conditions at these high potentials. With 2.51 A the Cu-I bond is 4% shorter than the Cu-Cl bond implying that the nature of the Cu-I bond is mainly covalent. Accordingly, we observe a significant inward relaxation of the top Cu layers upon substituting chloride by iodide at the same electrode potential, which suggests that the iodide adsorption involves charge transfer from the halide to the copper substrate.

Bromide and iodide removal from waters under dynamic conditions by Ag-doped aerogels

The objective of this study was to analyze the efficiency of Ag-doped aerogels in the removal of bromide and iodide from water. To test the applicability of these aerogels in water treatment, adsorption of bromide and iodide was studied under dynamic conditions using waters from Lake Zurich and a mineral water. The results obtained by using these waters showed a high breakthrough volume ( V 0.02 = 0.4 L ) of the columns, while the height of the mass transfer zone ( H MTZ = 6.8 cm ) was low, regardless of the anion under study. Bromide- and iodide-saturated columns were regenerated with NH 4OH. No change in the column characteristics was observed after two regeneration treatments, regardless of the type of water considered.

Influence of temperature pre-treatment and high-molar saline solutions on the adsorption capacity of organo-clay minerals

Clays play an important role in the design of HLW repositories. Serving as a buffer material between waste container and host rock, clays provide mechanical stability and radionuclide retardation due to advantageous hydrological and chemical properties. A crucial limitation, however, results from the fact that the affinity of natural clays for anionic species is very low. Modification of the clays with certain organic cations results in organo-clays, which have already proved high adsorption capacities for anions under laboratory conditions. In order to test the adsorption performance under various near-field conditions of a waste repository, experiments on the retention of radioiodide by different organo-clays were carried out under the influence of elevated temperatures and high-molar saline solutions. The results show that most of the investigated organo-clays exhibit stable structures and adsorption performances under the tested near-field conditions. Iodide adsorption remains at high levels in the temperature range under consideration for radioactive waste repositories. Adsorption reductions above 160 °C can be explained by both, losses of organo-cations and decreases of basal spacings. Under the impact of high-molar saline solutions, the organo-clays were able to adsorb considerable amounts of iodide in spite of extremely high concentrations of competing anions in the applied solutions.

About the possible upgrade of bentonite with respect to iodide retention capacity

Compacted bentonites are currently investigated as geotechnical barrier in high level radioactive waste (HLRW) repositories due to their low permeability, high swelling pressure, and cation adsorption capacity. In contrast, anions are repelled by the negatively charged smectite surfaces due to electrostatic forces. Therefore anion diffusion through bentonites is particularly slow (‘anion exclusion’). However, in case of crack formation bentonites do not possess anion retention capacity. In this case anions, neutral or negatively charged molecules or colloidal particles can pass the technical barrier faster. One of the hazardous anions is 129I − which is particularly dangerous due to its long half life, mobility, and biological relevance. In this context several studies concerning iodide adsorption by a variety of solids are available. The selection of an applicable bentonite additive for the improvement of iodide retention capacity of HLRW technical barriers is still subject to discussion. The optimum bentonite additive should possess high selectivity towards iodide, thermal stability, should not affect bentonite properties, and should be inexpensive. In this study we compare different potential iodide adsorbents using standardized conditions since it is well known that experimental parameters (concentration, time, precursor material, solid liquid ratio…) significantly influence the results of adsorption experiments. Therefore, only the application of standardized conditions allow for the direct comparison of a set of potential I − adsorber materials. Obtained results indicate that organoclays (bentonites modified by organic surfactants) are supposed to represent the most suitable bentonite additive with respect to the upgrade of iodide retention capacity. Additionally, we could show that the addition of 5 wt.% hexadecylpyridinium treated bentonite did not affect the swelling pressure of compacted MX80 bentonite. However, long term tests and/or natural analogue studies have to be performed in order to be able to answer the open questions.