Adsorption Of Alcohol Molecules Research Articles

Supported Nanometric Titanium Oxide Sols as a New Efficient Photocatalyst

We report on the first study of the photocatalytic performance of immobilized smallest titanium oxide oxoparticles of the size 2R = 5.0 nm on a glass support. The nanometric particles are prepared in the sol-gel reactor with rapid reagent mixing and temperature, atmosphere, and particle size control. The surface coverage is achieved by inserting the support into the reactor solution during the induction period, where chemically active nanoparticles are relatively stable. We show that this immobilized amorphous oxo phase of titanium oxide exhibits considerable activity toward photocatalytic degradation of trichloroethylene in the gas phase. Moreover, one of the important factors appears to be the catalyst surface preparation, which has to be free of the adsorbed alcohol molecules. UV-assisted exchange between propoxy and hydroxy groups is suggested as the surface activation mechanism. The film thickness is expected to strongly affect the material photocatalytic efficiency because of the internal traps population.

INS and IR and NMR Spectroscopic Study of C1−C4 Alcohols Adsorbed on Alkali Metal-Exchanged Zeolite X

The adsorption of short-chain (C1−C4) n-alcohols on alkali cation-exchanged X zeolites (Si/Al = 1.2) was studied by inelastic neutron scattering and infrared and NMR spectroscopy. Vibrational and NMR spectra of alcohols adsorbed on the zeolites were compared to those of solid alcohols and isolated alcohol molecules to describe the interactions between the sorbate molecule and the zeolite. The experimental results are compared to theoretically calculated INS spectra for one, two, and three alcohol molecule aggregates. For all alkali-metal cation-exchanged X zeolites, only physically adsorbed alcohol molecules were found on the catalyst's surface. The interactions in the channels of alkali cation-exchanged X zeolites of the short-chain C1−C4 alcohols were found to be similar and independent of the chain length. The alcohol oxygen atoms interact via their lone electron pairs with the exchanged alkali-metal cation, and hydrogen-bond formation was found between the alcohol OH protons and the negatively charged...

Simulating the effect of alcohol on the structure of a membrane

Adsorption of alcohol molecules or other small amphiphilic molecules in the cell membrane can induce significant changes in the structure of the membrane. To understand the molecular mechanisms underlying these structural changes, we developed a mesoscopic membrane model. Molecular simulations on this model nicely reproduce the experimental phase diagrams. We find that alcohol can induce an interdigitated structure in which the normal bilayer structure changes into a monolayer in which the alcohol molecules screen the hydrophobic tails from the water phase. We compute the effect of the chain length of the alcohol on the phase behaviour of the membrane. At low concentrations of alcohol, the membrane has domains of the interdigitated phase that are in coexistence with the normal membrane phase. We use our model to clarify some of the experimental questions related to the structure of the interdigitated phase and put forward a simple model that explains the alcohol chain length dependence of the stability of this interdigitated phase.

Kinetics of Cadmium Electrodeposition in Perchlorate Water-Ethanol Electrolytes

It is found that promotion of electrode process of Cd deposition is caused by the formation of unstable solvates of discharging ions with adsorbed alcohol molecules (zone of water structure stabilization) or by the ψ′ effect manifestation as a result of preferential adsorption of perchlorate anions (zone of alcohol structure stabilization). The minimum rate of cadmium ion electroreduction is observed in the mixtures with the maximum “loosening” of structure under the conditions of preferential adsorption of nonaqueous solvent molecules and is associated with the blockage of cathode surface and the variation in ψ′ potential under the adsorption of cation complexes with organic ligands.

Properties of Spreaded Collagen I Monolayers on the Surface of Aqueous tert-Butanol and n-Hexanol Solutions

Properties of the monolayers of collagen isolated from the sclera of pig's eye are studied at the air–water interface with increasing tert-butanol or n-hexanol concentrations in a subphase. In the case of aqueous n-hexanol solutions, its adsorption on the subphase surface results in the formation of mixed monolayer whose properties depend on n-hexanol concentration in the subphase and the ratio between the number of alcohol and collagen molecules in the monolayer. At higher n-hexanol surface concentration, the phase separation of the monolayer into the domains of the condensed phase of alcohol and fibrous collagen occurs. A decrease in water activity in the presence of tert-butanol leads to a drastic reduction of collagen surface activity. This effect can be explained by both the constrained collagen spreading on the surface of tert-BuOH solutions and adsorption of alcohol molecules on collagen resulting in macromolecule hydrophilization. Alcohol critical concentrations are disclosed above which collagen monolayers are not formed.

Kinetics study of esterification of acetic acid with isobutanol in the presence of amberlite catalyst

Kinetic data on the esterification of acetic acid with isobutanol have been obtained from both the uncatalyzed and heterogeneously catalyzed reactions using a stirred batch reactor in dioxane. The equilibrium constant, which is independent of temperature ranging from 318 to 368 K, was found to be 4. The uncatalyzed reaction was proved to be second-order reversible. In the presence of the catalyst, on the other hand, the reaction has been found to occur between an adsorbed alcohol molecule and a molecule of acid in the bulk fluid (Eley–Rideal model). It has also been observed that the initial reaction rate decreases with alcohol and water concentrations and it linearly increases with that of acid. The temperature dependency of the constants appearing in the rate expression were also determined.

DRIFT Studies for the Reaction and Adsorption of Alcohols and Isobutylene on Acidic Resin Catalysts and the Mechanism of ETBE and MTBE Synthesis

Diffuse reflectance FT-IR spectra of methanol and ethanol on Amberlyst 15 and on a synthesized acidic resin catalyst indicate that alcohol molecules are adsorbed by forming hydrogen bridges with the −SO3H sites of the catalyst and among themselves. Some of the alcohol molecules were found to be strongly chemisorbed by dissociation of one or two hydrogen atoms. Isobutylene was also found to be strongly adsorbed by forming a bridged structure between the adsorbed alcohol molecules and the −SO3H groups. DRIFT spectra verified the presence of adsorbed ether molecules formed as a result of surface reaction and supported a Langmuir−Hinshelwood-type reaction mechanism.

Chemical treatment of machined titanium surfaces. An in vitro study.

Microbial plaque accumulation on titanium dental implant surfaces can result in an inflammatory condition of the surrounding tissues. Cleaning of such a contaminated surface, in vivo, by means of a solution of amino-alcohol, following surgical exposure, has been proposed. However, the tissue healing following treatment resulted in formation of a fibrous capsule at the tissue-implant interface, i.e. improper implant re-integration. The present experiment was designed to investigate the possible influence of an amino-alcohol solution on machined titanium surface properties. Titanium samples with topography and chemical composition similar to the clinically used Brånemark implant surfaces were used in this experimental in-vitro study to investigate the adsorption of amino-alcohol to such surfaces, and the possibilities to chemically remove the adsorbed alcohols in order to recover a pristine titanium surface. The amino-alcohol solution was supplied to the sample surfaces and four different methods were subsequently used in order to remove the adsorbed alcohol molecules. It was shown that rinsing in water, saline solution, and 5% H2O2 did not remove the amino-alcohol from the surface. However, exposure to ozone produced by using a commercial mercury lamp in ambient air resulted in complete removal of the adsorbed amino-alcohol. The results show that the amino-alcohol used forms a stable and dense film at the implant surface in vitro. Presence of such a film most likely prevents re-integration to occur at the implant-tissue interface in vivo.

Alcohol-assisted growth of copper CVD films

We report the effect of various alcohols on the transport mechanism and reaction kinetics of Cu(hfac) 2 reduction for copper CVD. A variety of transport experiments are performed, all of which indicate that the presence of alcohol does nothing to increase the vapor phase transport rate of Cu(hfac) 2. In contrast, steady-state kinetic measurements reveal a significant increase in CVD growth rates upon addition of an alcohol co-reactant, which we therefore attribute to an alcohol-assisted enhancement of the intrinsic kinetics of Cu(hfac) 2 reduction. For the series of alcohols studied, the enhancement factor increases in the order: MeOH<EtOH< i-PrOH; this correlates with the p K a values of the alcohols. The dependence of the growth rate on alcohol partial pressure is first-order, which can be described using a simple modification of our earlier Langmuir–Hinshelwood rate expression for H 2 reduction of Cu(hfac) 2. The revised expression is consistent with a mechanism in which the rate limiting step involves H + transfer between an adsorbed alcohol molecule and the first dissociated (hfac) ligand from an adsorbed Cu(hfac) 2 molecule.

Streaming Current of Polystyrene Porous Plugs: Solvent Composition Effect

The main purpose of this work is to research the solvent composition effect on the streaming current of porous plug formed by monodisperse polystyrene microspheres. Polystyrene was selected as the disperse material because monodisperse, spherical polystyrene latexes have proved to be useful model systems, whose surface charge density can be conveniently controlled. A polystyrene latex was prepared by emulsifier-free emulsion polymerization, having a particle size of 1.2 μm and a surface charge density of −34.0 ± 1.0 mC/m2. Binary mixtures of ethanol– and 1-propanol–water were used to understand the effect of the liquid phase composition on the streaming current of polystyrene porous plugs. For the ethanol– and 1-propanol–water mixtures the streaming current depends nonlinearly on the molar alcohol fraction. This nonlinear dependence can be explained by the variation of the viscosity and dielectric permittivity of the liquid with solvent composition. The ζ-potential plays also an important role in the explanation of the above dependence, especially with binary mixtures low in alcohol where a minimum in the ζ-potential appears. The electrokinetic results obtained in this work suggest that the basically hydrophobic polystyrene surface is modified by the presence of hydrophilic sites. Adsorption of alcohol molecules on the charged hydrophilic sites leads to desorption of counterions from the inner part of the electrical double layer.

Adsorption of some normal aliphatic alcohols on a polycrystalline gold electrode

The adsorption of n-tetradecanol, n-hexadecanol and n-octadecanol on a polarized Au electrode from LiClO 4 methanolic solutions was studied by means of capacity measurements. The adsorption parameters for potentials near to the potential of maximum adsorption were calculated according to the Frumkin and Damaskin theory. The results are discussed in relation to literature data concerning the adsorption of alcohol molecules.

Kinetic evaluation of the direct synthesis of ethers from alcohols over sulfonated resin catalysts

The acidic Amberlyst-35 sulfonated resin effectively catalyzes the coupling of methanol + isobutanol and ethanol + isobutanol mixtures in the gas-phase to give methyl isobutyl ether and ethyl isobutyl ether, respectively. The reaction occurs via a S N2 reaction pathway involving two adsorbed alcohol molecules and is successfully described by a simple Langmuir-Hinshelwood kinetics.

Pulsed EPR for studying silver clusters

The cationic silver clusters of different nuclearity have been produced by radiolysis of zeolite A and SAPO molecular sieves containing Ag + as exchangeable cations. The pulsed EPR spectroscopy has been applied for studying the local environment of silver cluster in order to understand the mechanism of cluster formation and stabilization. The electron spin echo modulation (ESEM) results on Ag 6 n+ cluster in dehydration zeolite A indicate that the hexameric silver is stabilized only in sodalite cages which are surrounded by α-cages containing no water molecules. Trimeric silver clusters formed in hydrated A zeolites strongly interact with water, thus the paramagnetic center can be considered as a cluster-water adduct. In SAPO-molecular sieves, silver clusters are formed only in the presence of adsorbed alcohol molecules. From ESEM it is determined that Ag 4 n+ in SAPO-42 is stabilized in α-cages, where it is directly coordinated by two methanol molecules. Dimeric silver, Ag 2 + in SAPO-5 and SAPO-11 is located in 6-ring channels and interacts with three CH 3OH molecules, each in different 10-ring or 12-ring channels. The differences of Ag 2 + stability in SAPO-5 and SAPO-11 are also discussed.

Orientation of molecules of aliphatic alcohols adsorbed on a mercury electrode surface analysis of steric factors of inhibited electrode reactions and quantum-chemical calculations

The orientation of adsorbed aliphatic alcohols on mercury electrode surface is discussed on the basis of literature data concerning steric factors of electrochemical reactions inhibited by these alcohols and on quantum chemical calculations using the mopac program. Steric factors were evaluated from dependences of rate constants of electrochemical reactions of several model systems on alcohol concentration at total surface coverage. Theoretical calculations were made for a single alcohol molecule interacting with a 28-atomic mercury cluster. These two sets of data point to a vertical orientation of adsorbed alcohol molecules, even at incomplete coverage of the electrode surface.

水溶液中におけるシリカゲルへのアルコールの吸着

The adsorption of alcohol molecules on silica gel was investigated in a wide range of the alcohol concentrations in a water solution. Adsorption isotherms of ethanol and 1-propanol from the aqueous solutions were measured and analyzed in terms of the surface excess amount of adsorption. The composite adsorption isotherms were well expressed by a Dubinin-Radushkevich type equation. The individual isotherm, which was calculated by assuming a simple volume-filling model, showed that the pores of the silica were filled with the alcohol at a mole fraction higher than about 0.8.The surface hydroxyl groups of silica gel were partially alkoxylated to the alkoxyl groups even in contact with the alcohol in the presence of water. The number of formed alkoxyl groups increased with increase in the concentration of the alcohol in the solution. The equilibrium constant for the alkoxylation reaction was calculated.

Adsorption of n-aliphatic alcohols on mercury from aqueous solutions of low ionic strength: the problem of adsorbate orientation

The electrosorption behaviour of n-aliphatic alcohols from n-butanol to n-octanol on mercury from aqueous 0.1 M NaF and from aqueous 0.05 M Na 2SO 4 was determined from capacitive charge measurements by using a computerized chronocoulometric technique. The increase in the surface area occupied by one adsorbed alcohol molecule at maximum coverage by about 0.06 nm 2 per CH 2 group, the constancy of the differential capacity at maximum coverage for all alcohols investigated, an incipient second rise in all experimental adsorption isotherms as well as other trends, point to a flat orientation of the adsorbed alcohol molecules up to maximum coverage.

Methanol and 2-Methyl-1-Propanol (Isobutanol) Coupling to Ethers and Dehydration over Nafion H: Selectivity, Kinetics, and Mechanism

The dehydration of a mixture of methanol and isobutanol has been studied over the sulfonic acid Nafion H catalyst. Dehydration products consisted of dimethyl ether (DME), di-isobutyl ether (DIBE), methyl-isobutyl ether (MIBE), butenes, octenes, and traces of methyl-tertiarybutyl ether (MTBE). At low temperatures and high alcohol pressures (P ≥ 150 kPa), the dehydration product state was dominated by ether formation with selectivity within the ethers significantly in favor of the mixed ether, MIBE. The rates of ether and butene formation as a function of alcohol pressure could be described by Langmuir-Hinshelwood kinetics in which competitive adsorption of the two alcohols on the surface -SO3H sites was the dominant feature. The kinetics of isobutanol dehydration to isobutene were consistent with a dual-site mechanism involving the cooperative action of a free surface -SO3H site and an adjacent adsorbed alcohol molecule. Dehydration to ethers was consistent with the reaction of two adsorbed alcohols, also by a dual-site mechanism. As a consequence, dehydration to symmetric ethers showed saturation-type kinetics as a function of alcohol pressure, while the rate of isobutene formation went through a distinct maximum. Due to the competitive adsorption of methanol and isobutanol, the mixed ether MIBE was formed at a maximum rate with an optimum ratio of partial pressures of the two alcohols. The high selectivity to MIBE was explained by stronger adsorption of isobutanol on the catalyst surface as compared to methanol. The absence of MTBE and the predominance of products such as MIBE and 2,5-dimethylhexene suggests that dehydration to give "free" carbenium ions that subsequently rearrange to the more stable tertiary intermediate was not occurring. It was proposed that the alcohols react with the -SO3H groups to give oxonium ions or esters. These intermediates couple to give the product ethers or octenes.

Trends in the adsorption behaviour of n-aliphatic alcohols on mercury from aqueous 0.5 M Na 2SO 4

The electrosorption behaviour of n-aliphatic alcohols from n-butanol to n-octanol at the mercury/water interface was determined from capacitive charge measurements by using a computerized chronocoulometric technique. The surface area A occupied by one adsorbed alcohol molecule at maximum coverage was found to increase by about 0.06 nm 2 per each CH 2 group, thus suggesting strongly that the alcohols are adsorbed on mercury from aqueous solutions of 0.5 M Na 2SO 4 in a flat orientation up to maximum coverage. This interpretation is further supported by the approximate constancy of the differential capacity at maximum coverage for all alcohols investigated, and by the gradual increase in the coefficient ▪ with an increase in chain length, where Δ G o ads is the standard Gibbs energy of adsorption and σ m is the charge density of maximum adsorption. This adsorption behaviour differs from that from aqueous 0.1 M NaF as reported by B.B. Damaskin, A.A. Survila and L.E. Rybalka (Elektrokhimiya, 3 (1967)146); in fact, the latter behaviour suggests a vertical orientation of the hydrocarbon chains at maximum coverage.

Wettability of quartz by methanol and ethanol aqueous solutions

Measurements of the contact angle were carried out in the systems: quartz — droplet of methanol in aqueous solution — air and quartz — droplet of ethanol in aqueous solution — air. The measured contact angle values were correlated with those calculated theoretically. For calculations the values of the dispersion and nondispersion components of surface free energy of quartz with monolayer water film, and values of surface tension and its dispersion and nondispersion components of methanol and ethanol aqueous solutions, taken from the literature were used. For these calculations, values of surface tension components of the above mentioned solutions determined theoretically on the assumption that the alcohol adsorption at the interface solution — air is negligible were also used. From the calculations it was shown that the contact angles calculated and measured would be compatible if it is assumed that adsorption of alcohol molecules from solution on a quartz surface is smaller than at a solution-air interface.

XPS, UPS and thermal desorption studies of alcohol adsorption on Cu(110) : II. higher alcohols

Abstract Preceding work dealing with the adsorption of methanol on Cu(110) has been extended to include ethanol, n- and iso-propanol and a diol, ethylene glycol. In common with the simplest alcohol, all these molecules are able to form a stable alkoxy species on the surface, that is, the alcohol dissociated at the O-H group. However, in contrast to methanol on the clean surface for which the dissociated methoxy and hydrogen recombined to desorb as methanol, all the higher alcohols reacted further with the surface, dehydrogenating to yield the corresponding aldehyde or ketone in the gas phase. Ethylene glycol reacted to form the most strongly bound intermediate of all, decomposing near 390 K to produce the dialdehyde, glyoxal, with little evidence of monoaldehyde formation or C-C bond breakage. The influence of pre-adsorbed oxygen on these reactions was to generally increase the amount of alkoxy formed on the surface by enhancing the amount of dissociative adsorption (water is formed by the deprotonation of adsorbed alcohol molecules by oxygen atoms). The alkoxide decomposition peaks were shifted to slightly higher temperatures and considerably broadened in such experiments. The decomposition peak temperatures of the different surface alkoxides correlate fairly well with literature values of the αC-H bond strength, which is weaker in iso-propanol than in methanol. XPS showed broad O(1s) spectra for all the molecules adsorbed at 140 K, probably due to hydrogen-bonding effects in the adlayer, with peak emissions at around 533 eV. When the surface was warmed to 250 K, the O(1s) spectra narrowed to close to instrumental linewidths with a concomitant shift to a lower binding energy near 531 eV. C(1s) spectra showed little change between the adsorbed alcohol and alkoxy species. The UPS showed low temperature spectra similar to the gas phase, but the highest occupied orbitals, which are essentially O(2p) orbitals, showed a chemisorption bonding shift of several tenths of an electron volt. UPS for these molecules is shown to have considerable less utility than for the simplest molecule, methanol, due to the masking of possible orbital shifts during chemical changes on the surface by the presence of overlapping emissions in the spectra.