Adsorption Of Alcohol Molecules Research Articles

Single-Atom Co-N4 Sites Mediate C=N Formation via Reductive Coupling of Nitroarenes with Alcohols.

It remains challenging to construct C=N bonds due to their facile hydrogenation. Herein, a single Co atom catalyst was discovered to be active for the selective construction of C=N bonds toward the synthesis of imines and N-heterocycles via reductive coupling of nitroarenes with various alcohols, including inert aliphatic ones. DFT calculations and experimental data revealed that the transfer hydrogenation proceeded via the intramolecular hydride transfer and the transfer of H from the α-Csp3-H bond to the nitro group was the rate-determining step. The single Co atoms served as a bridge to transfer the electrons from the catalyst to the adsorbed alcohol molecules, resulting in the activation of the α-Csp3-H bond. Unlike metal nanoparticles, the C=N bonds in imine products can be reserved due to the large steric hindrance from substituents on C and N. DFT calculation also confirmed that transfer hydrogenation of the C=N bonds in imines is thermodynamically unfavored with a much higher energy barrier compared with the transfer hydrogenation of the -NO2 group (1.47 vs 1.15 eV).

Quasi-2D SnO2 Thin Films for Gas Sensors: Chemoresistive Response and Temperature Effect on Adsorption of Analytes

We performed in silico calculations of electrical conductivity of quasi-2D SnO2 thin films with a (110) surface-prospect material for sensitive element of gas sensors. Electronic structure, charge transfer and chemoresistive response of quasi-2D SnO2 thin films during adsorption of alcohol molecules (ethanol, methanol, isopropanol and butanol) and ketones (acetone, cyclopentanone and cyclohexanone) were calculated. It was found that the electrical conductivity of quasi-2D SnO2 thin films decreases within 4-15% during adsorption of analytes. The influence of temperature on the concentration of analytes on the surface of quasi-2D SnO2 thin films was explored in dependence analyte's type.

Free-standing and binder-free nickel polymeric nanofiber membrane for electrocatalytic oxidation of ethanol in alkaline solution

In-situ chemical reduction technique was exploited to fabricate free-standing and binder-free active nanocatalyst materials for direct ethanol fuel cells using nickel nanoparticles onto polyvinylidenefluoride-co-hexafluoropropylene membrane [Ni/PVdF-HFP]. Homogeneously distributed nickel nanoparticles with face-centered cubic structure were observed onto smooth membrane surfaces. Cyclic voltammetric measurements indicated the enhanced activity of Ni/PVdF-HFP membrane for oxidizing the alcohol molecules in NaOH solution. The measured oxidation current density increased with increasing the added ethanol concentration into the supporting electrolyte up to 0.64 M. Some kinetic parameters were calculated such as the charge transfer coefficient (α), Tafel slope and exchange current density values to record 0.468, 369 mV dec−1 and 1.28 μA cm−2, respectively. The three dimensional nanostructure of these fabricated metallic membranes and the increased number of their active voids could provide largely exposed surface areas for adsorbed alcohol molecules. The good stability of nickel nanoparticles onto PVdF-HFP membrane surface with minimum leaching level during prolonged ethanol oxidation in alkaline solution can offer unique possibilities for utilizing these polymeric electrocatalyst structures for energy production applications.

Influence of temperature, surface composition and electrochemical environment on 2-propanol decomposition at the Co[formula omitted]O[formula omitted] (001)/H[formula omitted]O interface

Ab initio molecular dynamics simulations of a single hydrated 2-propanol molecule were performed to study the role of temperature, surface structure and electrochemical environment for the oxidation of 2-propanol to acetone at the Co3O4 (001)/H2O interface. On the A-terminated and B-terminated surfaces, which differ in the relative number of Co2+ and Co3+ ions at the surface, 2-propanol adsorbs molecularly on the Co2+ and Co3+ sites, respectively. In both cases, no C-H bond cleavage is observed at room temperature. However, under oxidative conditions, which are modeled here by partial dehydrogenation of the mixed hydroxyl/water adsorbate layer, dehydrogenation of the alcoholic OH group is observed on both surface terminations. As a result, adsorbed 2-propanolate is formed. The reaction on the less hydroxylated B-terminated surface further proceeds with C-H bond cleavage at the 2-carbon atom. The oxidation product acetone remains adsorbed on the Co3+ site during the simulation period of approximately 20 ps. Both deprotonation steps are aided by the presence of the adsorbed hydroxyl groups in the vicinity of the adsorbed alcohol molecule, because both hydrogen atoms from the reactand molecule are transferred as protons to form adsorbed water molecules. Different from the case of the partially dehydrogenated environment, raising the system temperature from 300 to 450 K, which can be considered a simple model for high temperature thermal catalysis, does not lead to oxidation via C–H dehydrogenation of the 2-propanol molecule.

Adsorption of C2-C5 alcohols on ice: A grand canonical Monte Carlo simulation study.

In this paper, we report grand canonical Monte Carlo simulations performed to characterize the adsorption of four linear alcohol molecules, comprising between two and five carbon atoms (namely, ethanol, n-propanol, n-butanol, and n-pentanol) on crystalline ice in a temperature range typical of the Earth's troposphere. The adsorption details analyzed at 228K show that, at low coverage of the ice surface, the polar head of the adsorbed molecules tends to optimize its hydrogen bonding with the surrounding water, whereas the aliphatic chain lies more or less parallel to the ice surface. With increasing coverage, the lateral interactions between the adsorbed alcohol molecules lead to the reorientation of the aliphatic chains that tend to become perpendicular to the surface; the adsorbed molecules pointing thus their terminal methyl group up to the gas phase. When compared to the experimental data, the simulated and measured isotherms show a very good agreement, although a small temperature shift between simulations and experiments could be inferred from simulations at various temperatures. In addition, this agreement appears to be better for ethanol and n-propanol than for n-butanol and n-pentanol, especially at the highest pressures investigated, pointing to a possible slight underestimation of the lateral interactions between the largest alcohol molecules by the interaction potential model used. Nevertheless, the global accuracy of the approach used, as tested under tropospheric conditions, opens the way for its use in modeling studies also relevant to another (e.g., astrophysical) context.

Understanding the Highly Selective Methanol Sensing Mechanism of Electrodeposited Pristine MoS2 Using First Principle Analysis

In this paper, synthesis, characterizations and highly selective methanol sensing performance of pristine electrodeposited MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film is reported and correlated with the corresponding density functional theory (DFT) based computations. Pristine MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> was electrochemically deposited on conducting Indium doped Tin Oxide (ITO) glass substrate, and was annealed at three different temperatures viz. 350 °C, 450 °C and 550 °C. Sensing study was performed targeting primary alcohols i.e. methanol, ethanol, and 2-propanol. At room temperature (27 °C), pristine MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> annealed at 550 °C, was found to offer the most promising sensing performance with a response magnitude of ~17% (160%) with an appreciably high selectivity window (with the nearest interfering species ethanol) of 18% (78%) towards 10 ppm (400 ppm) of methanol. Adsorption mechanism was investigated with the help of DFT based simulation studies in terms of changes in structural (adsorption distances) and energetic (adsorption energies) features of MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> considering the adsorption of alcohol molecules on the same. Simulation results revealed that MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> offered enormous potential in terms of adsorption energy (~20 times) and the shortest adsorption distance (~1.2 times) for methanol compared to its nearest interfering species (ethanol), justifying the present experimental outcome.

A molecular to macro level assessment of direct contact membrane distillation for separating organics from water

The removal of water-soluble organics from aqueous feeds is required in numerous practical applications, including bioresource processing, fermentation, and wastewater treatment. To this end, direct contact membrane distillation (DCMD) has been proposed as a separation technology. DCMD utilizes hydrophobic membranes – typically, comprising perfluorocarbons – which, when placed between a warm feed and a cold permeate, prevent mixing due to the robust entrapment of air inside the (membranes') pores. Thus, the membranes allow only pure water vapor to transport across, following the thermal gradient. Here, we assessed DCMD for separating organics from aqueous feeds in light of organic fouling by utilizing ethanol and perfluorodecyltrichlorosilane (FDTS) as the surrogate organic and hydrophobic coating, respectively. We investigated the adsorption of ethanol onto FDTS-grafted surfaces and membranes exposed to alcohol-water mixtures. Using the surface force apparatus, we found that the magnitude of hydrophobic forces between ultra-smooth FDTS-grafted mica surfaces in water-alcohol mixtures decreased with the increasing alcohol content. To simulate a practical DCMD scenario, we utilized FDTS-grafted polycarbonate membranes to separate a pure water reservoir from another containing 0.6 M NaCl and alcohol. For the 0% alcohol case, the membranes robustly separated the reservoirs for over a week, whereas even for ≥0.1% ethanol content, the membranes leaked within <5 h. After the leakage, the membranes’ hydrophobicity could not be recovered by rinsing them with pure water and blow-drying; a heat treatment at 363 K for 1 h proved to be successful, however. Our molecular dynamics simulations revealed that ethanol molecules in water got preferentially stabilized at the interfaces of water and hydrophobic surfaces. Furthermore, this stabilization is significantly enhanced at higher alcohol concentrations due to the emergence of II-D interfacial networks comprising adsorbed alcohol molecules. Thus, this micro to macro-scale assessment demonstrates that DCMD with hydrophobic membranes is not suitable for separating organics from water, even at low alcohol concentrations. We also compare the efficacies of apparent advancing and receding contact angles towards a reliable characterization of fouled surfaces.

Alcohol molecules adsorption on graphane nanosheets – A first-principles investigation

The geometric structure, electronic and adsorption properties of methanol, ethanol and 1-propanol molecules on hydrogenated graphene (graphane) were investigated using first-principles calculations. The stability of graphane base material is confirmed using formation energy and phonon band structures. The adsorption of alcohol molecules on bare graphane and hydrogen vacant graphane nanosheet is found to be prominent and the selectivity of alcohol molecules can be achieved using bare or hydrogen vacant graphane nanosheet. Moreover, the interaction of alcohol molecules on bare and hydrogen vacant graphane nanosheets is studied using the adsorption energy, energy band gap variation, Bader charge transfer and average energy band gap variation. The adsorption energy ranges from -0.149 to −0.383 eV upon alcohol adsorption. The energy gap varies from 4.71 to 2.62 eV for bare graphane and from 4.02 to 3.60 eV for hydrogen vacant graphane nanosheets upon adsorption of alcohol molecules. The adsorption properties of alcohol molecules provide useful information for the possible application of graphane nanosheet as a base material for the detection of alcohol molecules.

Effect of Adsorbed Alcohol Layers on the Behavior of Water Molecules Confined in a Graphene Nanoslit: A Molecular Dynamics Study.

With the rapid development of a two-dimensional (2D) nanomaterial, the confined liquid binary mixture has attracted increasing attention, which has significant potential in membrane separation. Alcohol/water is one of the most common systems in liquid-liquid separation. As one of the most focused systems, recent studies have found that ethanol molecules were preferentially adsorbed on the inner surface of the pore wall and formed an adsorbed ethanol layer under 2D nanoconfinement. To evaluate the effect of the alcohol adsorption layer on the mobility of water molecules, molecular simulations were performed to investigate four types of alcohol/water binary mixtures confined under a 20 Å graphene slit. Residence times of the water molecules covering the alcohol layer were in the order of methanol/water < ethanol/water < 1-propanol/water < 1-butanol/water. Detailed microstructural analysis of the hydrogen bonding (H-bond) network elucidated the underlying mechanism on the molecular scale in which a small average number of H-bonds between the preferentially adsorbed alcohol molecules and the surrounding water molecules could induce a small degree of damage to the H-bond network of the water molecules covering the alcohol layer, resulting in the long residence time of the water molecules.

Mechanism and kinetics of 1-dodecanol etherification over tungstated zirconia

Growing interest in finding renewable alternatives to conventional fossil fuels and petroleum-derived specialty chemicals has motivated the investigation of biomass-derived alcohols to make ethers as diesel additives or lubricants. To optimize the direct etherification of long chain alcohols in the liquid phase, it is necessary to develop an understanding of the kinetics and mechanism of etherification and dehydration reactions. In this study, tungstated zirconia was identified asa selective solid-acid catalyst for the liquid-phase etherification of 1-dodecanol. Investigations of the mechanism and kinetics of this reaction suggest that cooperation between Brønsted- and Lewis-acid sites on tungstated zirconia enhances the selectivity to ether by increasing the surface concentration of adsorbed alcohol, thereby promoting bi-molecular ether formation relative to unimolecular alcohol dehydration. The suggested rate limiting step for etherification is the formation of a CO bond between two adsorbed alcohol molecules, and the suggested rate-limiting step for dehydration is the cleavage of the CH bond of the β-carbon atom in an adsorbed alcohol. Measurements of the kinetic isotope effects for etherification and dehydration support the proposed mechanism. A microkinetic model based on the proposed mechanism for dodecanol etherification and dehydration over tungstated zirconia accurately describes the observed effects of alcohol concentration and product inhibition.

Study of Alcohol and Aldehydes Interaction on the Surface of Silicane Nanosheet: Application of Density Functional Theory

The electronic properties of silicane and adsorption behavior of two distinct aldehyde and three various alcohol vapors on silicane nanosheet are investigated using density functional theory method. The present work gives the insight on possible applications of silicane nanosheet as a chemical nanosensor. The density of states spectrum provides vision on the electronic properties of silicane nanosheet. The variation in the band gap confirms the possible use of monolayer silicane for the detection of volatile organic compounds. The adsorption properties of aldehyde and alcohol vapors on silicane nanosheet are studied in terms of adsorption energy, Mulliken charge transfer, HOMO–LUMO gap and average energy gap variation. The most favorable adsorption sites of aldehyde and alcohol molecules on silicane nanosheet are studied at an atomistic level. The adsorption of alcohol molecules on silicane nanosheet is found to be more favorable than aldehyde molecules. The findings suggest that the monolayer silicane nanosheet can be used to detect the presence of alcohol vapors in the environment.

Sensing properties of monolayer borophane nanosheet towards alcohol vapors: A first-principles study

The electronic properties of borophane nanosheet and adsorption behavior of three distinct alcohol vapors namely methanol, ethanol and 1-propanol on borophane nanosheet is studied using density functional theory method for the first time. The state-of-the-art provides insights on to the development of new two dimensional materials with the surface passivation on boron nanostructures. The density of states spectrum provides a clear perception on charge transfer upon adsorption of alcohol vapors on borophane nanosheets. The monolayer of borophane band gap widens upon adsorption of alcohol vapors, which can be used for the detection for volatile organic vapors. The adsorption properties of alcohol vapors on borophane base material are analyzed in terms of natural bond orbital, average energy gap variation, adsorption energy and energy gap. The most suitable adsorption sites of methanol, ethanol and 1-propanol molecules on borophane nanosheet are investigated in atomistic level. The adsorption of alcohol molecules on borophane nanosheet is found to be more favorable. The findings suggest that the monolayer borophane nanosheet can be utilized to detect the presence of alcohol vapors in the atmosphere.

Visible light enhanced oxidant free dehydrogenation of aromatic alcohols using Au–Pd alloy nanoparticle catalysts

We find that visible light irradiation of gold–palladium alloy nanoparticles supported on photocatalytically inert ZrO2 significantly enhances their catalytic activity for oxidant-free dehydrogenation of aromatic alcohols to the corresponding aldehydes at ambient temperatures. Dehydrogenation is also the dominant process in the selective oxidation of the alcohols to the corresponding aldehydes with molecular oxygen. The alloy nanoparticles strongly absorb light and exhibit superior catalytic and photocatalytic activity when compared to either pure palladium or gold nanoparticles. Analysis with a free electron gas model for the bulk alloy structure reveals that the alloying increases the surface charge heterogeneity on the alloy particle surface, which enhances the interaction between the alcohol molecules and the metal NPs. The increased surface charge heterogeneity of the alloy particles is confirmed with density function theory applied to small alloy clusters. Optimal catalytic activity was observed with a Au : Pd molar ratio of 1 : 186, which is in good agreement with the theoretical analysis. The rate-determining step of the dehydrogenation is hydrogen abstraction. The conduction electrons of the nanoparticles are photo-excited by the incident light giving them the necessary energy to be injected into the adsorbed alcohol molecules, promoting the hydrogen abstraction. The strong chemical adsorption of alcohol molecules facilitates this electron transfer. The results show that the alloy nanoparticles efficiently couple thermal and photonic energy sources to drive the dehydrogenation. These findings provide useful insight into the design of catalysts that utilize light for various organic syntheses at ambient temperatures.

Effects of Vapor Environment and Counter-Surface Chemistry on Tribochemical Wear of Silicon Wafers

The effects of counter-surface chemistry and adsorption of water and alcohol from the environment on the tribological responses of silicon surfaces were investigated using atomic force microscopy. When scratching with SiO2 tips at contact pressures below the hardness of the materials, changing the environment yielded drastically different wear behaviors. In humid air, the adsorbed water molecules facilitated wear of the surface and material removal. In N2 environment, there was subsurface deformation but no wear, so the surface protruded outward in the rubbing region. In the ethanol vapor condition, the adsorbed alcohol molecules acted as a lubricant and prevented any discernible changes to the surface even at contact pressures above 1 GPa. These results extend upon previous studies of vapor-phase alcohol lubrication using even more protective longer-chain alcohols where failure was observed at much lower contact pressures in macroscale tests, probably due to high-pressure asperity contacts. Thus, the chemical environment can govern the response of silicon to mechanical rubbing. Rubbing with a diamond tip, however, yielded protrusions in all three environments, showing that the chemistry of the counter-surface also contributes to the tribological response; in this case, diamond is not tribochemically reactive toward Si surface. The protrusion formed by the diamond tip in ethanol vapor was only ~20 % the height of the one in humid air, even though the measured friction coefficients (and so the applied shear forces) were similar. These results clearly show that the surface chemistry at the tribological interface can substantially alter both the wear and subsurface damage processes.

Multicomponent Adsorption of Alcohols onto Silicalite-1 from Aqueous Solution: Isotherms, Structural Analysis, and Assessment of Ideal Adsorbed Solution Theory

Configurational-bias Monte Carlo (CBMC) simulations in the isobaric-isothermal version of the Gibbs ensemble (GE) were carried out to probe the adsorption from aqueous solutions of methanol and/or ethanol onto silicalite-1. This methodology does require neither specification of the chemical potential nor any reference to activity models based on experimental data. The CBMC-GE methodology can be applied to the complete range of mixture compositions from pure water to pure alcohols and can also be used when multiple solute types are present at high concentration. The simulations demonstrate high selectivities for the alcohols (α(ethanol) > α(methanol)) almost over the entire composition range. The ideal adsorbed solution theory is found to substantially underpredict the amount of sorbed water and leads to very large errors for low alcohol solution concentrations. The simulations indicate that, at lower loadings, the adsorbed alcohol molecules can serve as seeds for water adsorption but, at higher loadings, alcohols displace water molecules from their preferred region.

Reaction of Ferricyanide and Methyl Viologen with Free Radicals Produced by Ultrasound in Aqueous Solutions

The redox reactions of organic radicals, with Fe(CN)63− and methyl viologen, generated from the sonochemical decomposition of aliphatic alcohols in aqueous solutions, have been studied. The number of radicals produced was found to relate to the amount of adsorbed alcohol molecules (Gibbs surface excess) at the gas−aqueous solution interface for any bulk solution concentration of the alcohol. The majority of the radicals produced stem from the thermal degradation of the alcohol molecules that have entered imploding cavitation bubbles. The maximum rate of reduction at 355 kHz, of Fe(CN)63−, was 2.6 ± 0.3 μM min−1, whereas for methyl viologen, it was 1.2 ± 0.3 μM min−1 under the conditions used.The difference in the rates is attributed to the reaction of various pyrolytically produced organic radicals with the methyl viologen radical cation. The possible reactions occurring in the sonolysis of alcohol/water systems are discussed in detail.

Kinetic Study of the Esterification of Acetic Acid with 1-Butanol Catalysed by Alumina-Supported Tungstophosphoric Acid

The kinetics of the esterification of acetic acid with 1-butanol in the presence of alumina-supported tungstophosphoric acid (TPA) was studied. The uncatalysed reaction was shown to proceed by a second-order mechanism. In the presence of the catalyst, the reaction was found to occur between an adsorbed alcohol molecule and a molecule of acid in the bulk fluid (Eley–Rideal mechanism). It was found that alumina-supported TPA is suitable for this reaction because the activation energy was reduced from 58.0 to 37.3 kJ mol−1. The catalyst was characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscope, nitrogen adsorption study and IR spectroscopy.

Tribochemical Polymerization of Adsorbed n-Pentanol on SiO2 during Rubbing: When Does It Occur and Is It Responsible for Effective Vapor Phase Lubrication?

The origin and role of tribochemical reaction products formed while sliding silicon oxide surfaces in the presence of adsorbed alcohol molecules in equilibrium with the vapor phase were studied. Wear and friction coefficient studies with varying contact loads and n-pentanol vapor environments were used to determine under what operating conditions the tribochemical reaction species was produced. Imaging time-of-flight secondary ion mass spectrometry and microinfrared spectroscopy found that hydrocarbon species with a molecular weight higher than the starting vapor molecules are produced when there is wear of the SiO(2) surface. When the n-pentanol vapor lubrication is effective and the silicon oxide surface does not wear, then the tribochemical polymerization products are negligible. These results imply that the tribochemical polymerization is associated with the substrate wear process occurring due to insufficient adsorbate supply or high mechanical load. The tribochemical reactions do not seem to be the primary lubrication mechanism for vapor phase lubrication of SiO(2) surfaces with alcohol, although they may lubricate the substrate momentarily upon failure of the alcohol vapor delivery to the sliding contact.

A New Photoactive Crystalline Highly Porous Titanium(IV) Dicarboxylate

Titanium is a very attractive candidate for MOFs due to its low toxicity, redox activity, and photocatalytic properties. We present here MIL-125, the first example of a highly porous and crystalline titanium(IV) dicarboxylate (MIL stands for Materials of Institut Lavoisier) with a high thermal stability and photochemical properties. Its structure is built up from a pseudo cubic arrangement of octameric wheels, built up from edge- or corner-sharing titanium octahedra, and terephthalate dianions leading to a three-dimensional periodic array of two types of hybrid cages with accessible pore diameters of 6.13 and 12.55 A. X-ray thermodiffractometry and thermal analysis show that MIL-125 is stable up to 360 degrees C under air atmosphere while nitrogen sorption analysis indicates a surface area (BET) of 1550 m(2) x g(-1). Moreover, under nitrogen and alcohol adsorption, MIL-125 exhibits a photochromic behavior associated with the formation of stable mixed valence titanium-oxo compounds. The titanium oxo cluster are back oxidized in the presence of oxygen. This photochemical phenomenon is analyzed through the combined use of Electron Spin Resonance (ESR) and UV-visible absorption spectroscopies. The photogenerated electrons are trapped as Ti(III) centers, while a concomitant oxidation of the adsorbed alcohol molecules occurs. This new microporous hybrid is a very promising candidate for applications in smart photonic devices, sensors, and catalysis.

Calculation of the characteristics of ethanol and methanol adsorbed in a pore of activated carbon by the density functional method

Density functional theory was used to perform quantum-chemical calculations of changes in the energy and structure characteristics of methanol and ethanol molecules caused by their adsorption in model slitlike pores of activated carbon. The conclusion was made that changes in these characteristics (bond lengths, angles, charges on atoms, and harmonic vibration frequencies) is additional evidence of the validity of the Tolmachev thermodynamic model, in which adsorption is treated as a quasi-chemical reaction of the addition of adsorbate molecules to adsorption centers of an adsorbent. It was shown that the arrangement of alcohol molecules, when the C-O and C-C bonds were approximately parallel to pore walls and the hydrogen atom was directed toward a nearer pore wall, was most favorable energetically. Two adsorbed alcohol molecules are also arranged parallel to pore walls and form a hydrogen bond.