Synthesis of silver nanoparticles colloids in imidazolium halide ionic liquids and their antibacterial activities for gram-positive and gram-negative bacteria.

Four 1-butyl-3-methylimidazolium halide ionic liquids were synthesized via metathesis and anion exchange reactions. Silver nanoparticles (AgNPs) colloids were synthesized in four ionic liquids in the pressurized reactor by reduction of silver nitrate with hydrogen gas, without adding solvents or stabilizing agents. Antibacterial activities of base ionic liquids and AgNPs colloids in ionic liquids were reviewed by well-diffusion method for gram-positive Bacillus cereus (NCIM-2155) and gram-negative Escherichia coli (NCIM-2931) bacteria. Antibacterial activities of ionic liquids and AgNPs colloids in ionic liquids were observed to be controlled by ionic liquids anions and AgNPs particle size. The 1-butyl-3-methylimidazolium iodide ionic liquid exhibited higher antibacterial activities among the studied ionic liquids. Further, the presence of AgNPs in 1-butyl-3-methylimidazolium iodide, ionic liquid enhanced its antibacterial activity for Bacillus cereus and Escherichia coli bacteria.

Quantitative analysis of free water in ionic liquid-water mixtures.

The purpose of this paper is to determine the amount of water in ionic liquid aqueous solutions that does not form hydrogen bonds (that is to say, free water). Here, the amount of free water was determined in mixtures of water and four ionic liquids based on the imidazolium cation: 1-Butyl-3methylimidazolium acetate, 1-Butyl-3methylimidazolium bromide, 1-Butyl-3methylimidazolium chloride, and 1-3, dimethyl-imidazolium chloride. Their ionic liquid mass fraction was between 0% and 80%. The amount of free water in the mixtures was determined from the concentration profiles obtained by analysing the near infrared spectra of the mixtures between 800 and 1070 nm using multivariate curve resolution-alternating least squares. The absorption band characteristic of the OH- group in the water is present in the spectral region considered. The analysis was done at three temperatures: 298.15, 313.15 and 333.15 K. The major conclusions obtained from a comparative analysis of the results are these: a) the length of the alkyl chain significantly affects the hydrophobicity of the cations when the molality of the ionic liquid in the solutions is higher than 1.435 mol/kg. b) for the solutions with the same cation, the amount of free water in the chloride solutions is lower than in the acetate and bromide solutions when the temperature is lower than 333.15 K. At this temperature, the capacity of acetate and bromide solutions to interact with water is the same. Between 298.15 and 333.15 K, the ionic liquid concentration at which there is no free water in the solutions ranges between 62.70% and 59.59% for the 1-3, dimethylimidazolium chloride, 66.72% and 87.75% for the 1-Butyl-3methylimidazolium chloride, 69.76% and 78.36% for the -1-Butyl-3methylimidazolium bromide and between 69.77% and 78.26% for the 1-Butyl-3methylimidazolium acetate. So, the ionic liquid with the greatest capacity to retain water is the 1-3, dimethylimidazolium chloride.

Ranking the solubility of ammonia in ionic liquids using near infrared spectroscopy and multivariate curve resolution.

We rank the expected solubilities of ammonia in three hydroxyl ionic liquids - [HOEMIm][BF4], [HOEMIm][NTf2] and [Ch][NTf2] - in the temperature range 20-105 °C by analyzing the cations and anions available for interaction with ammonia. As this availability depends on ion-pair formation in ionic liquids, in this paper it is evaluated using the concentration and spectral profiles recovered in the analysis of their near infrared spectra by the multivariate resolution curve - alternating least squares method. The results indicate that the main effect of temperature on ion pairs is to decrease the number of structural configurations with cooperative hydrogen bonds between cation and cation, although in a lesser extent the number of cation-anion interactions increases. Regardless of the type of ionic liquid cation, the cation-anion interactions are higher in the tetrafluorborate ionic liquid than in the imide ionic liquid, hydroxyl imidazolium or choline. Assuming that the solubility of ammonia is limited by the concentration profile values representative of the cation-cation interactions, we deduce that at temperatures higher than 80 °C, ammonia solubility increases in the following order [HOEMIm][BF4] < [HOEMIm][NTf2] < [Ch][NTf2]. At lower temperatures, this order varies with the ammonia concentration in the NH3/ILs mixtures considered. We deduce that if the ammonia concentration is relatively low, the ammonia solubility will be governed by the evolution of cation-anion interaction in the ionic liquids and the solubility order is the same as at higher temperatures. However, when the ammonia concentration is higher, the ammonia solubility in the [Ch][NTf2] ionic liquid is lower than in the hydroxyl-ionic liquids. This conclusion is supported by the experimental vapor-liquid equilibria (VLE) data of ammonia-/ILs mixtures with ammonia mass fractions between 0.2 and 0.8.

A method based on near-infrared spectroscopy for the in-situ determination of the ammonia concentration in ammonia/water mixtures in an absorber test bench.

This paper discusses the development and implementation of a method based on NIR spectroscopy for the in-situ determination of the ammonia mass fraction of ammonia/water mixtures in an absorber test bench. The calibration model was established using a static measuring system. A cell was designed and constructed to prepare and measure samples at the ammonia mass fractions (0.332-0.482), pressures (3.4-4.6), bar and temperatures (25.0-35.5) °C typical in absorption refrigeration systems. A quadratic model for absorbance at 1041nm was established and validated. The root-mean-square deviation (RMSD) of the results was 2.1%. To implement NIR spectroscopy in the absorber test bench, a new flow cell was designed. The calibration model was transferred and used in the conditions of the absorber test bench. In these experimental conditions, the model was statistically validated using density measurements as a reference method for measuring the ammonia mass fraction. The root-mean-square deviation between the ammonia mass fractions obtained using the two methods was 1.1%.

Quantitative analysis of the hydration of lithium salts in water using multivariate curve resolution of near-infrared spectra.

The hydration process of lithium iodide, lithium bromide, lithium chloride and lithium nitrate in water was analyzed quantitatively by applying multivariate curve resolution alternating least squares (MCR-ALS) to their near infrared spectra recorded between 850 nm and 1100 nm. The experiments were carried out using solutions with a salt mass fraction between 0% and 72% for lithium bromide, between 0% and 67% for lithium nitrate and between 0% and 62% for lithium chloride and lithium iodide at 323.15 K, 333.15 K, 343.15 K and 353.15 K, respectively. Three factors were determined for lithium bromide and lithium iodide and two factors for the lithium chloride and lithium nitrate by singular value decomposition (SVD) of their spectral data matrices. These factors are associated with various chemical environments in which there are aqueous clusters containing the ions of the salts and non-coordinated water molecules. Spectra and concentration profiles of non-coordinated water and cluster aqueous were retrieved by MCR-ALS. The amount of water involved in the process of hydration of the various salts was quantified. The results show that the water absorption capacity increases in the following order LiI < LiBr < LiNO3 < LiCl. The salt concentration at which there is no free water in the medium was calculated at each one of the temperatures considered. The values ranged between 62.6 and 65.1% for LiBr, 45.5-48.3% for LiCl, 60.4-61.2% for LiI and 60.3-63.7% for LiNO3. These values are an initial approach to determining the concentration as from which crystal formation is favored.

Determining the composition of ammonia/water mixtures using short-wave near-infrared spectroscopy.

This paper proposes a methodology based on short-wave near-infrared spectroscopy to determine the ammonia content of ammonia/water mixtures with ammonia mass fraction in the range 0.35-0.65. Establishing this methodology meant modeling the relationship between the pressure bar (15-25)bar, temperature (20-50)°C and composition of the ammonia-water in the mixture (0.35-0.65 in ammonia mass fraction) with absorbance at 1033nm. The experiments were designed to optimize experimental work. A 2(3) factorial design+3 center points was used to establish and analyze the significance of the variables in the absorbance using analysis of variance (ANOVA). A linear model for absorbance was obtained using the least squares method. The trueness of the results versus the values obtained was assessed using a reference method; density measurement was chosen for this study. The accuracy of the results in terms of root-mean-square deviation (RMSD) was 3.7%. The methodology proposed represents a fast alternative for the "in-situ" measurement of the ammonia composition of ammonia-water mixtures in absorption refrigeration systems.

Reduced Graphene Oxide Composite with Oxidizable Manganese/Cobalt Mixed Oxide for p-Cresol Oxidation by Using Molecular Oxygen.

A composite of graphene oxide (GO) with mixed oxide (MnCo) was prepared by using a solvothermal method. During the synthesis, both the reduction of GO and growth of metal oxides took place simultaneously. The as-prepared composite material was highly selective for the liquid-phase oxidation of p-cresol to form p-hydroxybenzaldehyde in 71 % yield within 1 h. The composite material was characterised by SEM, X-ray photoelectron spectroscopy, high-resolution TEM and cyclic voltammetry (CV). A CV study revealed that the increase in the redox potential of the mixed oxide after being supported on GO, led to its higher activity of the catalyst for the oxidation reaction. The stability of the catalyst under the reaction conditions was studied by its successful reuse in three cycles.

Viscosity mixing rules for binary systems containing one ionic liquid.

In this work the applicability of four of the most commonly used viscosity mixing rules to [ionic liquid (IL)+molecular solvent (MS)] systems is assessed. More than one hundred (IL+MS) binary mixtures were selected from the literature to test the viscosity mixing rules proposed by 1) Hind (Hi), 2) Grunberg and Nissan (G-N), 3) Herric (He) and 4) Katti and Chaudhri (K-C). The analyses were performed by estimating the average (absolute or relative) deviations, AADs and ARDs, between the available experimental data and the predicted ideal mixture viscosity values obtained by means of each rule. The interaction terms corresponding to the adjustable parameters inherent to each rule were also calculated and their trends discussed.