34 research outputs found

    FDIONIC18 Interactions and stabilisation of acetone, sulfur dioxide and water with 1-octyl-3-methylimidazolium tetrafluoroborate at low temperatures

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    The interactions between three small molecules, water (H2O) , sulfur dioxide (SO2) and acetone ( (CH3)2CO ) with the ionic liquid (IL) 1-octyl-3-methylimidazolium tetrafluoroborate, [OMIM][BF4], have been determined using line of sight temperature programmed desorption (LOSTPD) from a gold surface. Multilayers of the IL were deposited by physical vapour deposition with multilayers of the small molecular species (adsorbed from the gas phase) at 90 K. LOSTPD was then carried out with the small molecular species desorbing first from the mixed multilayer, followed at higher temperatures by desorption of the IL from the gold surface. The IL had a high activation energy for desorption of 126(6) kJ mol-1 . Pure acetone showed a desorption activation energy of 38(2) kJ mol-1, which increased to 45 - 61 kJ mol-1 when it was pre-adsorbed below an overlying porous layer of the ionic liquid at 90 K. The stabilised acetone is thought to be associated with pores containing ionic moieties. Destabilised acetone was also observed and thought to originate from pores containing octyl chains. The quantity of stabilised acetone scaled with the amount of IL, being ≈ 1.1 molecules per IL ion pair. SO2 and H2O were co-adsorbed with the IL at 90 K leading to an intimate mixture of the two. For pure SO2 the desorption energy was 32(2) kJ mol-1, which increased to 40 - 50 kJ mol-1 for relative concentrations up to 6 SO2 molecules per IL ion pair. For pure water the activation energies were 49(5) kJ mol-1 and 43(1) kJ mol-1 for amorphous and crystalline ice respectively. When co-adsorbed with the IL the stabilisation energies were 42 - 49 kJ mol-1, but up to 505 water molecules per IL ion pair could be stabilised to some degree. The desorption mechanisms and the reasons for these interactions are discussed

    Ionic Liquids on Oxide Surfaces

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    Ionic liquids supported on oxide surfaces are being investigated for numerous applications including catalysis, batteries, capacitors, transistors, lubricants, solar cells, corrosion inhibitors, nanoparticle synthesis and biomedical applications. The study of ionic liquids with oxide surfaces presents challenges both experimentally and computationally. The interaction between ionic liquids and oxide surfaces can be rather complex, with defects in the oxide surface playing a key role in the adsorption behaviour and resulting electronic properties. The choice of the cation/anion pair is also important and can influence molecular ordering and electronic properties at the interface. These controllable interfacial behaviours make ionic liquid/oxide systems desirable for a number of different technological applications as well as being utilised for nanoparticle synthesis. This topical review aims to bring together recent experimental and theoretical work on the interaction of ionic liquids with oxide surfaces, including TiO2, ZnO, Al2O3, SnO2 and transition metal oxides. It focusses on the behaviour of ionic liquids at model single crystal surfaces, the interaction between ionic liquids and nanoparticulate oxides, and their performance in prototype devices

    Lubricant Degradation Monitoring with AI-Assisted Sensors

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    The value of machine lubrication is well understood, but all lubricants must be periodically tested to verify their condition. This has driven intense research towards the development of efficient, low cost and timely degradation monitoring solutions. However, the periodic testing currently used results in a difficult decision between the labour and downtime costs of testing more frequently and the risk of inter-inspection faults if testing is delayed. A series of six metal oxide semiconductor gas sensors has been used within an artificial olfactory system (e-nose) to monitor the volatile compounds released by samples of mineral oil at different levels of thermal degradation. Data collected from the sensors has been used to train an artificial intelligence pattern recognition system based on principal component analysis and a support vector machine for both classification and regression predictions. The classifier achieved a 95.5% accuracy and the regression was accurate within a root-mean-square error of 2.47 showing the effective performance of an e-nose when applied to oil condition monitoring

    Thin film structural analysis using variable-period x-ray standing waves

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    Variable-period x-ray standing wave (VPXSW) studies have been carried out using 3 keV x rays and photoelectron detection. Two model surfaces have been used, a native SiO2 layer (20 Å thick) on bulk silicon, and a purpose-built multilayer surface comprising a chloroform/water marker layer (12 Å thick) on an ionic liquid spacer layer (211 Å thick) deposited on a SiO2/Si substrate at 90 K. By using photoelectron detection, both chemical and elemental sensitivity were achieved. The surfaces were modeled using dynamic x-ray scattering for x-ray intensity, and attenuation of photoelectrons transmitted through the layers, to produce simulations which accurately reproduced the experimental VPXSW measurements. VPXSW measurements made using the substrate, spacer layer, and marker layer photoelectron signatures produced consistent structural values. This work demonstrates that VPXSW can be used to determine chemically specific layer thicknesses within thick (≲300Å) surface structures composed of the light elements B, C, N, O, F, and Cl with an accuracy of 10 to 15 Å, perpendicular to the surface

    Reversible Reaction of CO2 with Superbasic Ionic Liquid [P66614][benzim] Studied with in Situ Photoelectron Spectroscopy

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    Ionic liquids (ILs) are of significant interest as CO2 capture agents, and one subgroup of ILs that has shown particular promise is that of superbasic ILs. They can absorb large quantities of CO2 in the dry state, but some will have a diminished CO2 capacity when prewetted. In the work presented here, the superbasic IL trihexyl-tetradecylphosphonium benzimidazolide, or [P66614][benzim], was exposed to 3 mbar of CO2, 2 mbar of H2O vapor, and a CO2 + H2O gas mixture and was investigated using near-ambient pressure X-ray photoelectron spectroscopy. The results show that the IL reacts with CO2 to form carbamate and that the reaction is reversible through reduction of the surrounding gas pressure. Regardless of whether the IL was exposed to CO2 or H2O vapor first, the presence of H2O under these experimental conditions does not significantly hinder the IL’s ability to absorb and react with CO2. Furthermore, the IL appears to preferentially react with CO2 over H2O vapor

    Water-Induced Reordering in Ultrathin Ionic Liquid Films

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    Water-induced reordering in ultrathin ionic liquid films has been observed using in situ X-ray photoelectron spectroscopy. An ultrathin layer of 1-butyl-3-methylimidazolium tetrafluoroborate ([C4C1Im][BF4]) was deposited on a rutile TiO2 (110) single crystal and exposed to water vapour at a relative humidity of ~70% in an in situ cell. Water was found to adsorb onto the ionic liquid surface, causing a reordering of the ions at the interface. Water initially remained trapped on the ionic liquid surface as the in situ cell was evacuated. This could have negative implications for supported ionic liquid phase catalysis, where reactants and products move in and out of an ionic liquid containing the catalyst. This insight into the behaviour at the water/ionic liquid interface provides a basis for understanding interfacial behaviour in more complex gas/ionic liquid systems

    Structure and Reactivity of a Model Oxide Supported Silver Nanocluster Catalyst Studied by Near Ambient Pressure X-ray Photoelectron Spectroscopy

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    The photocatalytic activity of anatase TiO2 decorated with metal clusters has been widely documented, but the nature of the metal-metal oxide interface and reaction intermediates in catalytic processes are still not well understood. This in part is due to the fact that use of photoelectron spectroscopy to deduce the surface chemistry of catalytic systems has long been hampered by the huge pressure difference between real-world operation and the requirement of high vacuum for electron detection. Here, the in situ growth of silver nanoparticles on a model metal-oxide catalyst support and their reactivity with a CO/H2O gas mixture has been investigated in detail. Using synchrotron X-ray photoelectron spectroscopy, near-ambient pressure X-ray photoelectron spectroscopy and scanning tunneling microscopy, the interaction of Ag with the anatase TiO2 surface leads to metal-surface charge transfer and low mobility of Ag on the surface. Upon exposure to a 1.5 mbar CO/1.5 mbar H2O gas mixture, partial oxidation of the Ag clusters is observed. There is also evidence suggesting that a Ag-carbonyl species is formed during exposure of the Ag/TiO2 surface to a CO/H2O gas mixture

    An Experimental Investigation of the Adsorption of a Phosphonic Acid on the Anatase TiO2(101) Surface

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    A combination of synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy has been used to study the adsorption of phenylphosphonic acid (PPA) on anatase TiO2(101) single crystal at coverages of 0.15 monolayer (ML) and 0.85 ML. The photoelectron spectroscopy data suggest that at 0.15 ML coverage PPA adsorbs in a bidentate geometry following deprotonation of both phosphonate hydroxyl groups, leaving the P═O group unbound. At 0.85 ML there is a shift to a mixed bidentate/monodentate binding mode. The carbon K-edge NEXAFS spectra were recorded at two azimuths. Our calculations show that for PPA on anatase TiO2(101) the phenyl ring is oriented 65 ± 4° away from the surface plane with an azimuthal twist of 57 ± 11° away from the [101] azimuth

    In situ XPS of Competitive CO2/H2O Absorption in an Ionic Liquid

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    Superbasic ionic liquids (SBILs) are being investigated as potential CO2 gas capture agents, however, the presence of H2O in the flue stream can inhibit the uptake of CO2. In this study a thin film of the SBIL trihexyltetradecylphosphonium 1,2,4-triazolide ([P66614][124Triz]) was deposited onto rutile TiO2 (110) using in situ electrospray deposition and studied upon exposure to CO2 and H2O using in situ near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). The molar uptake ratio of gas in the electrosprayed SBIL (ngas:nIL) was calculated to be 0.3:1 for CO2, 0.7:1 for H2O, and 0.9:1 for a CO2/ H2O mixture. NAP-XPS taken at two different depths reveals that the competitive absorption of CO2 and H2O in [P66614][124Triz] varies with sampling depth. A greater concentration of CO2 absorbs in the bulk layers, while more H2O adsorbs/absorbs at the surface. The presence of H2O in the gas mixture does not inhibit the absorption of CO2. Measurements taken during exposure and after the removal of gas indicate that CO2 absorbed in the bulk does so reversibly, whilst CO2 adsorbed/absorbed at the surface does so irreversibly. This is contrary to the fully reversible CO2 reaction shown for bulk ILs in literature and suggests that irreversible absorption of CO2 in our highly-structured thin films is largely attributed to reactions at the surface. This has potential implications on IL gas capture and thin film IL catalysis applications
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