Capacity of Aqueous Solutions of the Ionic Liquid 1-Ethyl-3-methylimidazolium Acetate to Partially Depolymerize Lignin at Ambient Temperature and Pressure.

Lignin is a very attractive and abundant biopolymer with the potential to be a biorenewable source of a large number of value-added organic chemicals. The current state-of-the-art methods fail to provide efficient valorization of lignin in this regard without the involvement of harsh conditions and auxiliary substances that compromise the overall sustainability of the proposed processes. Making an original approach from the set of mildest temperature and pressure conditions, this work identifies and explores the capacity of an aqueous solution of the nonvolatile ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) to partially depolymerize technical lignin (Indulin AT) by means of a treatment consisting in the simple contact at ambient temperature and pressure. Among a considerable number of valuable phenolic molecules that were identified in the resulting fluid, vanillin (yield of about 3 g/kg) and guaiacol (yield of about 1 g/kg) were the monophenolic compounds obtained in a higher concentration. The properties of the post-treatment solids recovered remain similar to those of the original lignin, although with a relatively lower abundance of guaiacyl units (in agreement with the generation of guaiacyl-derived phenolic molecules, such as vanillin and guaiacol). The assistance of the treatment with UV irradiation in the presence of nanoparticle catalysts does not lead to an improvement in the yields of phenolic compounds.

Nanoparticles in Chemical EOR: A Review on Flooding Tests.

The use of nanofluids is showing promise as an enhanced oil recovery (EOR) method. Several reviews have been published focusing on the main mechanisms involved in the process. This new study, unlike previous works, aims to collect information about the most promising nano-EOR methods according to their performance in core-flooding tests. As its main contribution, it presents useful information for researchers interested in experimental application of nano-EOR methods. Additional recoveries (after brine flooding) up to 15% of the original oil in place, or higher when combined with smart water or magnetic fields, have been found with formulations consisting of simple nanoparticles in water or brine. The functionalization of nanoparticles and their combination with surfactants and/or polymers take advantage of the synergy of different EOR methods and can lead to higher additional recoveries. The cost, difficulty of preparation, and stability of the formulations have to be considered in practical applications. Additional oil recoveries shown in the reviewed papers encourage the application of the method at larger scales, but experimental limitations could be offering misleading results. More rigorous and systematic works are required to draw reliable conclusions regarding the best type and size of nanoparticles according to the application (type of rock, permeability, formation brine, reservoir conditions, other chemicals in the formulation, etc.).

Nanomaterial Synthesis in Ionic Liquids and Their Use on the Photocatalytic Degradation of Emerging Pollutants.

The unique properties of ionic liquids make them suitable candidates to prepare nanoscale materials. A simple method that uses exclusively a corresponding bulk material and an ionic liquid-in this case, [P6,6,6,14]Cl-was used to prepare AgCl nanoparticles and AgCl@Fe3O4 or TiO2@Fe3O4 magnetic nanocomposites. The prepared nanomaterials were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, ultraviolet-visible spectroscopy, and X-ray photoelectron spectroscopy. The photodegradation of atenolol as a model pharmaceutical pollutant in wastewater was investigated under ultraviolet-visible light irradiation using the different synthesized nanocatalysts. In the presence of 0.75 g·L-1 AgCl nanoparticles, a practically complete degradation of 10 ppm of atenolol was obtained after 30 min, following pseudo-first-order reaction kinetics. The effect of different variables (concentrations, pH, oxidant agents, etc.) was analyzed. The recyclability of the nanocatalyst was tested and found to be successful. A degradation mechanism was also proposed. In order to improve the recovery stage of the nanocatalyst, the use of magnetic nanocomposites is proposed. Under the same experimental conditions, a slightly lower and slower degradation was achieved with an easier separation. The main conclusions of the paper are the suitability of the use of ionic liquids to prepare different nanocatalysts and the effectiveness of these at degrading an emerging pollutant in wastewater treatment.

Photocatalytic degradation of methyl orange, methylene blue and rhodamine B with AgCl nanocatalyst synthesised from its bulk material in the ionic liquid [P6 6 6 14]Cl.

The photocatalytic degradation of wastewater containing three industrial dyes belonging to different families, methyl orange (MO), methylene blue (MB) and Rhodamine B (RhB), was studied under UV-Vis irradiation using synthesised silver chloride nanoparticles. The nanocatalyst was prepared by a dissolution/reprecipitation method starting from the bulk powder and the ionic liquid trihexyl(tetradecyl)phosphonium chloride, [P6 6 6 14]Cl, without addition of other solvents. The obtained catalyst was characterised by UV-Vis absorbance, X-ray powder diffraction, transmission electron microscopy and scanning electron microscopy. The decolourisation of the samples was studied by UV-Vis absorbance at the corresponding wavelength. Starting from 10 ppm dye solutions and 1 g L-1 of the synthesised AgCl nanoparticles, degradation efficiencies of 98.4% for MO, 98.6% for MB and 99.9% for RhB, were achieved in 1 h. The degradation mechanisms for the different dyes were studied. Comparison with other frequently used nanocatalysts, namely P-25 Degussa, TiO2 anatase, Ag and ZnO, highlights the strong catalytic activity of AgCl nanoparticles. Under the same experimental conditions, these nanoparticles led to higher (more than 10%) and faster degradations.

Preparation of AgX (X = Cl, I) nanoparticles using ionic liquids.

Nanoparticles of silver halides have been prepared by mixing silver halide powder with a single liquid phase consisting of an ionic liquid, isooctane, n-decanol and water. Much higher nanoparticle concentrations may be formed with ionic liquids using this new simple method than are found with conventionally applied surfactants. This method also emphasizes the applicability of ionic liquids as versatile components in microemulsions and as solvents for the synthesis of nanomaterials. The effect on the nanoparticles of changing the composition of the liquid mixtures and the nature of the ionic liquid is analysed. High nanoparticle concentrations were only found with chloride based ionic liquids, indicating the importance of the ionic liquid anion in the mechanism of the reaction.

A novel approach for the preparation of AgBr nanoparticles from their bulk solid precursor using CTAB microemulsions.

Microemulsions are suitable reaction media to prepare a wide variety of nanoparticles and provide control over their sizes. However, as typically used, microemulsions limit rates of rapid reactions and suffer from low reactant solubilization capacity. This work presents a new application of a novel approach aimed at minimizing these limitations. This approach, which was previously applied for AgCl nanoparticle preparation, involves solubilization of a bulk silver halide in the form of higher halides, by means of reaction with the surfactant counterion of a microemulsion, and the reprecipitation of silver halide nanoparticles in the water pools of individual reverse micelles. CTAB microemulsions were employed because they possess a reactive counterion and are known to have a high solubilization capacity for ionic reactants. Despite their high solubilization capacity, CTAB microemulsions achieved lower nanoparticles uptake (molar concentration of the colloidal nanoparticles) for the same surfactant concentration when compared to our previous study. The effect of the following variables on the nanoparticle uptake and the particle size was investigated: (1) operation variables, including rate of mixing and temperature; and (2) microemulsion variables, including CTAB and n-butanol concentrations, and water-to-surfactant mole ratio, R. These variables provide a comprehensive test to the proposed mechanism and expose the role of the surfactant layer rigidity. The nanoparticle uptake increased as the rate of mixing, temperature, and CTAB concentration increased, and decreased as n-butanol concentration and R increased. High n-butanol concentration and R values reduced the effective surfactant concentration and contributed to less surfactant layer rigidity and to particle aggregation.

A novel method for the preparation of silver chloride nanoparticles starting from their solid powder using microemulsions.

A novel method of preparing AgCl nanoparticles by mixing AgCl powder and a microemulsion consisting of dioctyldimethylammonium chloride/n-decanol/water/isooctane is introduced. This new method was discovered during the preparation of AgCl nanoparticles in single microemulsions by direct reaction with the dioctyldimethylammonium chloride surfactant counterion. The effect of the following variables on the concentration of the colloidal AgCl nanoparticles (the nanoparticle uptake) and the particle size were studied: (1) operating variables, including mixing and temperature; and (2) microemulsion variables, including surfactant and cosurfactant concentration, and water to surfactant mole ratio. Manipulating these variables provides an insight into the role of the surfactant surface layer rigidity on the phenomenon. The results were explained by the effect of these variables on reaction rates and the colloidal nanoparticle stability. Mixing had a significant effect on the nanoparticle uptake. At 300 rpm an equilibrium AgCl nanoparticle uptake was achieved in about 1 h, while without mixing only 5% of the equilibrium value was reached even after 24 h. An optimum temperature was found for which a maximum nanoparticle uptake was obtained. At higher temperatures, the nanoparticle uptake declined. The nanoparticle uptake increased linearly with the surfactant concentration, and the particle size increased as well. A monotonic decrease in the nanoparticle uptake accompanied by an increase in the particle size was observed when increasing n-decanol concentration or the water to surfactant mole ratio.

Formation of silver bromide precipitate of nanoparticles in a single microemulsion utilizing the surfactant counterion.

Silver bromide precipitate of nanoparticles was prepared by addition of silver nitrate aqueous solution to a single microemulsion system consisting of dioctyldimethylammonium bromide, n-decanol, and water in isooctane. The silver ion reacted readily with the surfactant counterion, bromide, to form the precipitate of nanoparticles, which was stabilized in the water pools. The use of the surfactant counterion as a reactant is a new approach to nanoparticle preparation in microemulsions. It is characterized by high reactivity and less dependency on the intermicellar exchange of solubilizate. The effects of the surfactant and the cosurfactant concentrations, the amount of silver nitrate, and the water to surfactant mole ratio, R, were evaluated. Increasing the surfactant concentration at fixed R and amount of silver nitrate enhanced the role of intermicellar nucleation and resulted in the formation of larger particles, while increasing the amount of silver nitrate at fixed values of all the other variables enhanced the direct nucleation and resulted in the formation of smaller particles. Particle aggregation and flocculation took place when the concentration of n-decanol or the value of R was increased. Particle aggregation and flocculation were attributed to the decrease in the interaction between the surfactant protective layer and the nanoparticles in the water pools.

Selective removal of gallium (III) from aqueous solutions containing zinc or aluminum using sodium di-(n-octyl) phosphinate.

Gallium was removed selectively from aqueous solutions containing zinc or aluminum using sodium di-(n-octyl) phosphinate as a ligand (NaL). At low pH or low mole ratios, the gallium was removed by complexation with the ligand as GaL(3(S)), while the zinc or the aluminum remained in the solution. Nearly complete separation of gallium was obtained. By increasing the amount of ligand or by increasing the pH, the zinc or aluminum remaining in the solution was then removed as a solid complex: ZnL(2(S)) or AlL(3(S)), respectively. At a pH between 1.5 and 2 and a mole ratio ligand to total metals of 0.75 for zinc solutions and 1.0 for aluminum solutions, more than 98% of the gallium was selectively removed with a high molar selectivity, alpha(Ga/Zn) and alpha(Ga/Al), respectively. Over 95% of gallium was recovered from the solid GaL(3(S)) complex by treatment of the complex with a 3M NaOH solution and diethyl ether. The gallium was concentrated in the aqueous solution to 4 times its initial concentration and the ligand was extracted into the ether phase. After evaporation of the ether, 95% of the ligand was regenerated in its sodium form as a solid.