Tetrabutylphosphonium Bromide Research Articles

Phase Stability Conditions of the Methane + Tetrabutylphosphonium Bromide + Water Semiclathrate Hydrate System in the Presence and Absence of NaCl and/or MgCl2: Experimental Measurements and Thermodynamic Modeling

Gas hydrate, or clathrate hydrate, technology is considered to be one of the promising solutions for natural gas storage and transportation. Tetrabutylphosphonium bromide (TBPB) is capable of sorting out stability issues of hydrate formation effectively. On the other hand, using water from natural resources such as sea, river, or well instead of pure water is essential for hydrate formation in the industrial scale. The current study was organized to investigate the hydrate phase behaviors of CH4 + TBPB formed in saline solutions, which are necessary for potential industrial applications. For this purpose, we first generated hydrate dissociation conditions data of the CH4 + TBPB aqueous solution system over TBPB mass fractions of 0.05 and 0.2. It should be mentioned that there is some discrepancy between hydrate dissociation condition data of the CH4 + TBPB + water system reported in literature, which necessitates generation of accurate and reliable data in this work. Afterward, the effects of the presence of NaCl, MgCl2, and NaCl + MgCl2 in aqueous solutions on the hydrate dissociation conditions of the CH4 + TBPB + water system were studied. All equilibrium points were obtained using a reliable constant-volume pressure-search method in the pressure and temperature ranges of 1–5.5 MPa and 280–292 K, respectively. The experimental results show that the aforementioned salts have dual effects on the hydrate phase stability, depending on TBPB concentration in the aqueous solution. In the case of 0.05 mass fraction of TBPB in the aqueous solution, the presence of NaCl (0.05 mass fraction), MgCl2 (0.05 mass fraction), and NaCl + MgCl2 (0.05 + 0.05 mass fractions) can boost the hydrate stability conditions of the CH4 + TBPB + water system and can act as thermodynamic promoters. However, by increasing the TBPB mass fraction in aqueous solution to 0.20 mass fraction, the aforementioned salts can shift the hydrate stability conditions to high pressures/low temperatures and can act as thermodynamic inhibitors. Furthermore, the experimental results show that the thermodynamic inhibition effects of the mineral salts are higher when the pressure of hydrate formation increases. A thermodynamic model based on the van der Waals–Platteeuw (vdW–P) solid solution theory was also developed for the aforementioned systems. The model employs the Soave–Redlich–Kwong equation of state and the Bromley equations for the gas phase and the aqueous phase, respectively. Results show that the thermodynamic model is capable of predicting the hydrate dissociation conditions with acceptable accuracy.

Phytotoxicity and Effect of Ionic Liquids on Antioxidant Parameters in Spring Barley Seedlings: The Impact of Exposure Time

The influence of the ionic liquids (ILs) tetrabutylammonium bromide [TBA][Br], 1-butyl-3-methylimidazole bromide [BMIM][Br], and tetrabutylphosphonium bromide [TBP][Br] added at different concentrations to the soil were studied for the growth and development of spring barley seedlings. Samples were harvested at three different time points: day 7, 14, and 21 after addition of ILs. The results show that [TBP][Br] was the most toxic. The introduction of this IL at the dose of 100 mg kg−1 of soil DM decreased the growth of seedlings at all test dates. The addition of the studied ILs to the soil in higher doses resulted in an increase in peroxidase and catalase activity, which may indicate the occurrence of oxidative stress in plants. An increase in the content of plant dry matter weight, contents of H2O2 and proline and a decrease in the content of photosynthetic pigments in barley seedlings were also observed. The malondialdehyde content and superoxide dismutase activity fluctuated randomly during the experiment. As a result, it was found that the phytotoxicity of ILs and the magnitude of oxidative stress in seedlings depended more on the added doses of these compounds than on the measurement date.

Synthesis and Structural Analysis of Novel Phosphonium Hexatungstate Complexes

Sodium tungstate reacted with tetramethyl- and tetrabutyl-phosphonium bromide in presence of hydrochloric acid to afford two new phosphonium hexatungstate compounds ((CH3)4P)2W6O19, 1, and ((CH3CH2CH2CH2)4P)2W6O19, 2, respectively. Under similar conditions, sodium tungstate reacted with methyltriphenyl-, allyltriphenyl-, butyltriphenyl- and benzyltriphenyl-phosphonium bromides to yield four new phosphonium hexatungstate compounds (CH3Ph3P)2W6O19, 3, (CH2CHCH2Ph3P)2W6O19, 4, (CH3CH2CH2CH2Ph3P)2W6O19, 5, and (C6H5CH2Ph3P)2W6O19, 6, respectively. All six compounds appeared to be stable in air, and were structurally characterized by a combination of FTIR, elemental analyses, and single-crystal X-ray diffraction analyses. The steric effect of the phosphonium cation was investigated and found to cause no significant change on the average bond distances of the hexatungstate anion. The crystal structure analyses of these compounds showed that hexatungstate anions were isolated and the distance between the anions increases with increase in the bulkiness of the surrounding phosphonium cations. Moreover, thermal stability and heat absorption of all six compounds were evaluated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).

Tuned extraction and regeneration process for separation of hydrophobic compounds by aqueous ionic liquid

Abstract A process concept for separation of hydrophobic compounds tuned by aqueous ionic liquid was developed and demonstrated by two typical cases, namely extractive desulfurization of fuel and separation of detergent range alcohol-alkane mixture. The ionic liquid tetrabutylphosphonium bromide (TBPB) and water, which present opposite interactions with hydrophobic solutes, were used to tune the separation process by adjusting their ratio. A small amount of water was favorable for extraction, while a large amount of water was beneficial for regeneration. For each separation case, the 1:2 M ratio of TBPB and water gave an effective extraction performance; further introducing water decreased hydrophobic solute solubility and promoted regeneration. The regenerated aqueous TBPB had an extraction efficiency close to that of fresh one. This tunable separation process relying on water is therefore environmentally friendly and can be extended for other hydrophobic compounds separation.

Investigation on the Synergistic Effect of Tetra Butyl Phosphonium Bromide with Poly(N-isopropylacrylamide) Based Kinetic Hydrate Inhibitor

The problem of clathrate hydrate plugging in flow pipes has been the most important issue in the off-shore exploitation since hydrates were found in transport facilities. In recent years, low dosage hydrate inhibitors have attracted much interest among researchers in place of thermodynamic hydrate inhibitors such as methanol and mono ethylene glycol (MEG). Poly-vinyl caprolactam and poly-isopropylacrylamide (PNIPAM) are among the hydrate inhibitors that are typically used for polymers containing amide groups. Furthermore, various kinds of polymer inhibitors containing amide group including tetrabutylphosphonium bromide(TBPB), which is a quaternary salt, were synthesized and studied in a methane gas hydrate environment. In this experiment, the injection of 0.1 wt% inhibitor at 276 K and 5 MPa was followed by stirring the water to induce nucleation. From the result, when PNIPAM alone was used as a single KHI, PNIPAM exhibited worst performance among the KHIs tested in this study. But the mixing of TBPB with PNIPAM further extended the induction time and reduced the CH4 hydrate growth rate. The real-time in situ Raman system used to understand the inhibition principle was recorded during CH4 hydrate formation, as a result, PNIPAM showed that the large hydrate cage affected, while TBPB prevented the CH4 molecule from occupying the small cage. TBPB was excellent synergist in blends with PNIPAM for kinetic hydrate inhibition of structure I forming CH4 hydrate.

Extractive separation of tetralin-dodecane mixture using tetrabutylphosphonium bromide-based deep eutectic solvent

Separation of components of light cycle oil (LCO) into aromatic-rich and nonaromatic-rich fractions is the essential step for upgrading LCO to produce benzene, toluene, xylene enriched fraction, and high-quality diesel. In this work, extractive separation of model LCO which contains 70 wt% tetralin and 30 wt% dodecane was performed using deep eutectic solvent (DES) as the extractant and water as the anti-extractant. Tetrabutylphosphonium bromide (TBPB) and levulic acid (LA) at a molar ratio of 1:4 was determined as the extractant, due to its high and stable performance during extraction and regeneration processes. The liquid-liquid equilibrium data of ternary systems involving TBPB:LA(1:4) were then experimentally determined and fitted using non-random two-liquid model. The continuous extraction process was simulated and optimized, high mass purity (0.980 for tetralin and 0.987 for dodecane) and high recovery ratio (0.994 for tetralin and 0.954 for dodecane) were achieved.

Experimental investigation on the effect of ionic liquids (C<SUB align="right">16H<SUB align="right">36BrP and C<SUB align="right">16H<SUB align="right">36BrN) on the tribological performance of neem oil

Ionic liquids are liquid salts, widely used in the chemical processing industry and have excellent lubricating properties. The present study focuses on the tribological performance of three different lubricants, pure neem oil, neem oil with 0.5 wt.% of ionic liquid tetrabutylammonium bromide (C16H36BrN) and neem oil with 0.5 wt.% of ionic liquid tetrabutylphosphonium bromide (C16H36BrP) in steel to steel interface. Considerable friction reduction and anti-wear capabilities have been confirmed when neem oil is added with 0.5 wt.% tetrabutylphosphonium bromide. The use of this fluid has reduced the frictional force at a uniform rate, and deep, broad wear scars or blisters or eruptions on the sides of the wear scars are not seen. The viscosity, density and wear resistance values also support this conclusion. The outcome of the research shows that neem oil along with tetrabutylphosphonium bromide can replace the existing conventional, unsustainable hydrocarbon and synthetic-based lubricants.

Experimental investigation on the effect of ionic liquids (C<SUB align="right">16H<SUB align="right">36BrP and C<SUB align="right">16H<SUB align="right">36BrN) on the tribological performance of neem oil

Ionic liquids are liquid salts, widely used in the chemical processing industry and have excellent lubricating properties. The present study focuses on the tribological performance of three different lubricants, pure neem oil, neem oil with 0.5 wt.% of ionic liquid tetrabutylammonium bromide (C16H36BrN) and neem oil with 0.5 wt.% of ionic liquid tetrabutylphosphonium bromide (C16H36BrP) in steel to steel interface. Considerable friction reduction and anti-wear capabilities have been confirmed when neem oil is added with 0.5 wt.% tetrabutylphosphonium bromide. The use of this fluid has reduced the frictional force at a uniform rate, and deep, broad wear scars or blisters or eruptions on the sides of the wear scars are not seen. The viscosity, density and wear resistance values also support this conclusion. The outcome of the research shows that neem oil along with tetrabutylphosphonium bromide can replace the existing conventional, unsustainable hydrocarbon and synthetic-based lubricants.

Selective Oxidation of Benzyl Halides to Benzaldehydes by Phase Transfer Catalyzed Monochromate Ions in Non-Polar Solvents

Benzyl chloride, benzyl bromide and their para substituted derivatives were selectively oxidized to corresponding benzaldehydes by acidified monochromate in toluene and ethyl acetate with the help of phase transfer catalysts like tetrabutylphosphonium bromide (TBPB), tetrabutylammonium bromide (TBAB), tetrabutylammonium hydrogen sulphate (TBAHS), cetyltrimethylammonium bromide (CTMAB) and tricaprylmethylammonium chloride (TCMC). The reaction was carried out by simple magnetic stirring for about 2 h at 60 ºC. The products were recrystallized and analyzed by infrared and UV-visible spectral techniques. Benzaldehyde and substituted benzaldehydes were formed in good yield (> 90%) on oxidation of benzyl chlorides and benzyl bromides. The reaction is proved to be highly selective due to the absence of acids or any other products during the reaction. All the phase transfer catalysts were highly effective in bringing out the reaction in both the solvents. This is highly significant as the oxidation reaction will not occur in non-polar solvents without the presence of phase transfer catalysts.

Development of novel hydrophilic ionic liquid membranes for the recovery of biobutanol through pervaporation

This paper aims to develop novel hydrophilic ionic liquid membranes using pervaporation for the recovery of biobutanol. Multiple polyvinyl alcohol (PVA) membranes based on three commercial ionic liquids with different loading were prepared for various experimental trials. The ionic liquids selected for the study include tributyl (tetradecyl) phosphonium chloride ([TBTDP][Cl]), tetrabutyl phosphonium bromide ([TBP][Br]) and tributyl methyl phosphonium methylsulphate ([TBMP][MS]). The synthesized membranes were characterized and tested in a custom-built pervaporation set-up. All ionic liquid membranes showed better results with total flux of 1.58 kg/m2h, 1.43 kg/m2h, 1.38 kg/m2h at 30% loading of [TBP][Br], [TBMP][MS] and [TBTDP][Cl] respectively. The comparison of ionic liquid membranes revealed that by incorporating [TBMP]MS to PVA matrix resulted in a maximum separation factor of 147 at 30 wt% loading combined with a relatively higher total flux of 1.43 kg/m2h. Density functional theory (DFT) calculations were also carried out to evaluate the experimental observations along with theoretical studies. The improved permeation properties make these phosphonium based ionic liquid a promising additive in PVA matrix for butanol-water separation under varying temperature conditions.

Extraction of caffeine using aqueous two-phase systems containing ionic liquid and sorbitol

In this study, a new aqueous two-phase system consisting of tetrabutylphosphonium bromide ionic liquid and sorbitol was selected. The partitioning of caffeine as a substance having many applications in the food and pharmaceutical industries was evaluated in this system. The effect of the variables such as the weight percentages of the ionic liquid and carbohydrate on the partitioning of caffeine was shown. The results indicated that by increasing the ionic liquid weight fraction and the sorbitol weight fraction, the partition coefficient of caffeine increased. Nevertheless, in all stages, the caffeine had a tendency to migrate towards the ionic liquid-rich phase. Also, the results indicated that the temperature had not an effect on the partitioning of caffeine. The recovery percentage of caffeine was reported in this system. The experimental results of the partition coefficient of caffeine were fitted by different regression models, and the most efficient regression model was selected based on the statistical analysis.

Efficient separation of curcumin using tetra butyl phosphonium bromide / carbohydrates (sorbitol, fructose) aqueous two-phase system

Curcumin, a natural polyphenol, is a main constituent of turmeric, which is frequently used in food industries as well as pharmaceutical and medicine fields. This bioactive compound is sensitive to high temperature, light, high concentrations of salt, organic solvents, and pH. An economical benign method to extract this precious polyphenol is what seems to be required especially for industrial applications. Aqueous two-phase systems (ATPSs) have demonstrated their potentials for the extraction and separation of bioactive agents. In recent years, researchers have taken a keen interest in the use of green biocompatible components capable of forming biphasic systems. In this study, the ATPSs consisting of carbohydrates (sorbitol, fructose) and tetra butyl phosphonium bromide (IL) were chosen to extract curcumin. To evaluate the efficiency of the system, the partition coefficient and recovery of curcumin were calculated. Furthermore, some factors affecting the curcumin partitioning such as temperature, pH and weight percent of carbohydrates and IL were taken into account. The results indicate that curcumin has a tendency to migrate towards the IL-rich phase. The highest values of the curcumin recovery (≈99%) and partitions coefficient suggest the ability of our proposed ATPS to meaningfully enhance the extraction of curcumin.

Effect of cationic-surfactant-modified Saudi bentonite on the thermal and flammability properties of poly(vinyl alcohol)-based nanocomposite films

ABSTRACTIn this study, poly(vinyl alcohol) (PVA)-modified Saudi bentonite nanocomposite films were prepared using the solution method. Two surfactants, cetylpyridinium chloride and tetrabutyl phosphonium bromide, were used to modify the clay after the ion-exchange process by Na+ ions. The effect of the addition of modified Saudi bentonite (2.5%) on the thermal and flammability properties of the nanocomposite films was investigated. The prepared samples were characterized using Fourier-transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. Thermogravimetric analysis and differential scanning calorimetry were carried out to observe the thermal behaviour of the PVA-based nanocomposite films. Vertical flammability tests (UL94 VB) were also carried out to study the flame retardancy behaviour of the nanocomposite films. The nanocomposite films showed better flammability than pure PVA, wherein the ignition time of the nanocomposites increased and flame propagation rate decreased. The thermal stability of the nanocomposites increased by approximately 10% for the onset and endset temperature of decomposition. The type of surfactant played an important role in dispersion of the clay into the polymeric matrix and enhancing the flammability properties of the films wherein the tetrabutyl phosphonium bromide was better flame retardant than cetylpyridinium chloride.

Synergy Effect Study of Poly(N-isoacrylamide) with Tetra Butyl Phosphonium Bromide on Methane Hydrate Formation

Natural gas hydrate plugging is one of the costly and challenging problems for the oil and gas industry, especially for subsea fields. One way to prevent gas hydrate formation at low cost is the use of low-dosage hydrate inhibitors (LDHI). Poly(N-isopropylmethacrylamide) (PNIPAM) with amide group have previously been shown to be an outstanding low-dosage hydrate inhibitor (LDHI). PNIPAMs are usually polymerized via radical polymerization, which can allow control over the molecular weight. We have synthesized PNIPAMs using control radical polymerization giving a fairly high degree of polymerization control. Additionally various Kinetic Hydrate Inhibitors (KHIs) were tested as CH4 hydrate inhibitors with polymeric hydrate inhibitor, PNIPAM. Furthermore, to check the synergetic effects of tetra butyl phosphonium bromide (TBPB), PNIPAM and their mixture TBPB-PNIPAM were tested as KHIs for methane gas hydrate formation. In this paper we present results on the performance of various polymeric inhibitors in KHI tests on methane gas in stirred autoclaves and on structure I hydrate formation. When PNIPAM alone was used as a single KHI, PNIPAM exhibited worst performance among the KHIs tested in this study. However the mixing of TBPB with PNIPAM further extended the induction time and reduced the CH4 hydrate growth rate. TBPB was an excellent synergist in blends with PNIPAM for kinetic hydrate inhibition of structure I forming CH4 hydrate. In summary, the mixture TBPB-PNIPAM was proven that great synergist for prevent the CH4 hydrate and good potential in achieving the industrial application of Oil & Gas production technology and therefore was a significantly meaningful discovery in the field of energy production.

Direct Aldolization of Unprotected Fructose to Bio-Based Surfactants

A new alkylation mode of fructose was developed by direct aldolization of unprotected fructose with fatty aldehydes as alkylating agents. The reaction occurs in the presence of a base in a mixture of water/EtOH at 60 °C under microwave irradiation. Trimethylamine was found the most effective base for the aldolization of fructose with short chain aldehydes (C4–C8) while better results were obtained with K2CO3 in association with tetrabutylphosphonium bromide (TBPB) for long chain aldehydes (C8–C12). The corresponding alkylated fructose were obtained as mixture of 3 main tautomers (the β-pyranoid form being the predominant isomer) and were isolated with 31–46% yield. These aldolization products were also reduced under hydrogen to give the corresponding alkylated heptaols with 84–96% isolated yields.

Hydroxyl functionalized renewable polyesters derived from 10-undecenoic acid: Polymer structure and post-polymerization modification

A simple synthetic route is used for the preparation of hydroxyl functionalized polyesters from an AB-type monomer carrying an epoxy and carboxylic acid group. A systematic study of the reaction conditions suggested that tetrabutylphosphonium bromide was the better polymerization catalyst to obtain the highest conversion of linear polymers with moderate molecular weights. Enzymatic catalyst (CALB), in contrast, yielded branched polymers with polyether units. The synthesized polymers were structurally characterized in detail, using model compounds previously synthesized, by 1H, 13C, and 19F NMR. Polyesters were characterized by FTIR, SEC, DSC and TGA too. The post-polymerization modification of the reactive hydroxyl sites present along the polymer backbone with N-Boc protected l-phenylalanine and l-serine was essayed to test the ability of these polyesters to prepare polymer bioconjugates.

Surface concentration or surface excess, which one dominates the surface tension of multicomponent mixtures?

This work is to answer an important question: which parameter, surface concentration or surface excess, dominates the surface tension of multicomponent mixtures? Two series of solutions have been chosen to inspect the dependence of solution surface tension on surface concentration and surface excess of the solutes. The solutions are separately 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in 3-hydroxypropionitrile and tetrabutylphosphonium bromide (TBPBr) in formamide. The surface tension data of these two series of binary solutions have been respectively correlated to the Gibbs surface excess and the surface concentration of the solutes. Both surface excess and surface concentration are experimentally determined by Neutral Impact Ion Scattering Spectroscopy (NICISS). The surface tension of POPC solutions is linearly dependent on the surface concentrations of POPC; whereas, the surface tension of TBPBr solutions depends piecewise linearly on surface concentration but irregularly upon surface excess of TBPBr. The intrinsic linear relationships between surface tension and surface concentration found in those two series of solutions are consistent to those results found in previous work. This observation evidences that the dominant factor to the surface tension of solutions is the surface concentration of solute to which both the surface fraction and the molecular orientation are subject.

TBHP/n-Bu4PBr-Promoted Oxidative Cross-Dehydrogenative Coupling of Aryl Methanols: A Facile Synthesis of Symmetrical Carboxylic Anhydride Derivatives

A transition-metal-free oxidative cross-dehydrogenative coupling reaction has been developed for the preparation of symmetrical carboxylic anhydrides through self-coupling dual C–O bond formations of aryl methanols. In the presence of a catalytic amount of tetrabutylphosphonium bromide (TBPB) as transfer agent and aqueous tert-butyl hydroperoxide (TBHP) as oxidant and reactant, methylene groups of aryl methanols were efficiently oxidized to C=O and coupled with the peroxide oxygen from TBHP to form a diverse array of symmetrical carboxylic anhydride derivatives.

Remote Imaging of the Buried Interface Using AFM-IR

The degradation of corrosion-resistant organic coatings continues to present an analytical challenge to corrosion scientists. This is because failures in corrosion protection are localised events, whereas coating analysis is predominately performed using bulk methodologies (e.g., vibrational spectroscopy, thermal analysis). This is compounded by the paucity of non-destructive techniques capable of detecting and characterising localised coating failure in the early stages (i.e., able to pinpoint the appearance of buried pitting sites, de-adhesion processes or blistering). Ex-situ microscopy has conventionally been used to characterise corrosion phenomena beneath organic coatings. However, physical sectioning precludes meaningful chemical analysis of the polymer at failure sites. Emerging non-destructive approaches that allow direct detection of corrosion at the buried interface include: acoustic microscopy, local electrochemical techniques (e.g. scanning Kelvin probe microscopy, the scanning vibrating electrode and local electrochemical impedance measurements) and can be employed to monitor corrosion of a buried substrate in situ. Whilst these can examine buried corrosion phenomena, little or no information is obtained about the overlying coating. Alternative techniques with improved resolution utilise scanning probe microscopy (SPM) methods (e.g. Kelvin probe force microscopy, KPFM) whilst detailed topographic images of the overlying coating may be simultaneously collected. More recently, SPM has been coupled to vibrational spectroscopy and allows direct nanoscale mapping of functional group chemistry. AFM-IR is a particularly versatile approach, whereby sub-diffraction limit detection of infrared absorbance is achieved by monitoring the deflection of an AFM probe in response to photo-thermal expansion of the sample. During AFM-IR measurements, the sample is illuminated by a rapidly pulsed tuneable infrared source, (an optical parametric oscillator, 10 ns pulses at a repetition rate of 1 KHz.) Upon absorbance of the infrared radiation, transient thermal expansion of the sample induces a contact-mode AFM probe to oscillate at its resonant frequency. A plot of the amplitude of oscillations as a function of infrared wavelength yields spectra that closely match conventional transmission-mode FTIR. Here we examine the degradation of model epoxy-phenolic can coatings on electrolytic chrome-coated steel (ECCS). Substrate materials were mechanically abraded successively to 1200 grit, then polished to 0.25 µm diamond paste to achieve a mirror-like surface finish. Stoichiometric epoxy-phenolic coatings were prepared by adding 1,1,1-tris(4-hydroxyphenyl) ethane to bisphenol-A diglycidyl ether (epoxide equivalent weight 172-176 g mol-1) using tetrabutylphosphonium bromide as catalyst. Coatings were spin-coated onto the substrates at 2000 rpm then cured at 150 °C for 60 min. The final coating thickness was around 7 µm. AFM-IR was performed on a NanoIR2 system (Anasys Instruments). In order to induce corrosion the polished ECCS samples were contaminated by spraying with a saturated sodium chloride solution in ethanol prior to coating. Corrosion was then initiated by placing a droplet of deionised water on the coating surface for 5 minutes, after which it was dried. Examination of the sample by optical microscopy subsequently revealed isolated patches of underfilm discolouration discernible through the coating (a). However, no corresponding change in the coating morphology was observed in AFM height images (b), and infrared amplitude maps obtained at 1260 cm-1 (c) and 1604 cm-1 (d) also remained featureless, indicating that significant deformation of the coating had not taken place. In contrast, infrared maps gathered at 916 cm-1 (e) and 1800 cm-1(f) showed an enhanced signal at the locus of discolouration. Preliminary results using AFM-IR mapping has been shown to detect the steel-polymer interface buried beneath an epoxy-phenolic coating. Generated infrared absorbance maps are sensitive to the substrate composition and morphology, opening up a new avenue for the detection of buried corrosion phenomena. Detection of the interface is dependent upon both the wavelength and power of incident infrared illumination. This is a result of the variable penetration depth of the radiation, in turn dependent on the infrared wavelength and laser power employed. Thus, judicious selection of infrared parameters permits the selective probing of the infrared absorbance of the coating alone, or a combination coating heterogeneity and interfacial reflectance. Figure 1

Deep eutectic solvents as green absorbents of volatile organic pollutants

Volatile organic compounds are a major source of air pollutants. Absorption is an effective solution to treat polluted air loaded with volatile organic compounds, but most actual absorbents are often toxic and non-biodegradable. Here, we tested eutectic solvent mixtures for the absorption of volatile organic compounds for the first time. The affinity of solvent mixtures for toluene, acetaldehyde and dichloromethane was determined by measuring vapour–liquid partition coefficients and liquid phase absorption capacities. Results show that the vapour–liquid partition coefficients vary, at 30 °C, from close to zero for acetaldehyde in the mixtures choline chloride:urea, choline chloride:glycerol and tetrabutylphosphonium bromide:glycerol to 0.124 for dichloromethane in the choline chloride:urea eutectic mixture. These values are similar or even superior to those published for ionic liquids and organic solvents. Solvents based on choline chloride, a food additive, and urea, can solubilize up to 500 times more volatile organic compounds compare to water. Moreover, deep eutectic solvents are easier to prepare and more biodegradable than ionic liquids, which are also toxic. Deep eutectic solvents are more biodegradable than silicone oils, which are also expensive. Furthermore, in terms of recycling, the absorption capacities of the tested solvents remained unchanged during five absorption–desorption cycles. These findings are patented.