Aqueous Acid Systems Research Articles

Ionic‐Liquid‐Based Acidic Aqueous Biphasic Systems for Simultaneous Leaching and Extraction of Metallic Ions

AbstractThe first instance of an acidic aqueous biphasic system (AcABS) based on tributyltetradecyl phosphonium chloride ([P44414][Cl]) and an acid is here reported. This AcABS exhibits pronounced thermomorphic behavior and is shown to be applicable to the extraction of metal ions from concentrated acidic solutions. Metal ions such as cobalt(II), iron(III), platinum(IV) and nickel(II) are found to partition preferentially to one of the phases of the acidic aqueous biphasic system and it is here shown that it successfully allows the difficult separation of CoII from NiII, here studied at 24 and 50 °C.

Mechanism of ionic-liquid-based acidic aqueous biphasic system formation.

Ionic-liquid-based acidic aqueous biphasic systems (IL-based AcABS) represent a promising alternative to the solvent extraction process for the recovery of critical metals, in which the substitution of the inorganic salt by an acid allows for a 'one-pot' approach to the leaching and separation of metals. However, a more fundamental understanding of AcABS formation remains wanting. In this work, the formation mechanisms of AcABS are elucidated through a comparison with traditional aqueous biphasic systems (ABS). A large screening of AcABS formation with a wide range of IL identifies the charge shielding of the cation as the primary structural driver for the applicability of an IL in AcABS. Through a systematic study of tributyltetradecylphosphonium chloride ([P44414]Cl) with various chloride salts and acids, we observed the first significant deviation to the cationic Hofmeister series reported for IL-based ABS. Furthermore, the weaker than expected salting-out ability of H3O+ compared to Na+ is attributed to the greater interaction of H3O+ with the [P44414]+ micelle surface. Finally, the remarkable thermomorphic properties of [P44414]Cl based systems are investigated with a significant increase in the biphasic region induced by the increase in the temperature from 298 K to 323 K. These finding allows for the extension of ABS to new acidic systems and highlights their versatility and tunability.

Redox behavior and chemical species of arsenic in acidic aqueous system

Abstract Arsenic (As) removal from smelting acidic wastewater is an urgent task. The most common method is oxidation of trivalent As(III) to pentavalent As(V) subsequently precipitated by ferric (Fe(III)) salts. Foundations of redox behavior and chemical species are of great importance for understanding As removal. In this work, cyclic voltammetry (CV) and UV-Vis spectroscopy were used for laboratory observation; meanwhile HSC and MINTEQ software were employed for theoretical analyses. It is found that As(III) oxidation, a multiple electron transfer reaction, is diffusion-controlled. The oxidation over-potential is very high (about 0.9 V) in sulfuric acid solutions (pH 1.0). In addition, Fe(III)-As(V) complexes are evidenced by UV-Vis spectra and chemical species analyses in series of Fe(III)-As(V)-H2SO4-H2O solutions. Therefore, the Fe(III) and As(V) species distribution against pH values are determined and a new φ–pH diagram with inclusion of Fe-As complexes is consequently compiled based on thermodynamic data predicted by other researchers.

Acidithiobacillus ferrooxidans enhanced heavy metals immobilization efficiency in acidic aqueous system through bio-mediated coprecipitation

This study investigated the promotion effect of A. ferrooxidans on complex heavy metals coprecipitation process. A. ferrooxidans significantly enhanced the ferrous oxidation, which also promoted the formation of iron-oxyhydroxysulphate. Cu(II) concentration reduced to 0.058 mmol/L in A. ferrooxidans inoculated system, and Cd also reduced to the lowest concentration (0.085 mmol/L). Pb was mainly immobilized as anglesite and iron-oxyhydroxysulphate promoted the removal of remanent Pb in solution. The precipitates are characterized by XRD, SEM, and FTIR analysis. The main component of the iron-oxyhydroxysulphate was well crystallized jarosite. A. ferrooxidans contributed to the formation of schwertmannite in later monovalent cation lack stage. Higher ferrous iron oxidation rate and Fe(III) supply rate in A. ferrooxidans inoculated system facilitated polyhedron crystal formation and the increase of particle diameter. Complex heavy metals could be incorporated into iron oxyhydroxysulphate crystal, and efficiently removed from acidic wastewater through A. ferrooxidans mediated coprecipitation.

Photo absorption of p-coumaric acid in aqueous solution: RISM-SCF-SEDD theory approach.

Photo absorption properties of p-coumaric acid, the chromophore of photoactive yellow protein, in aqueous solution were investigated by means of reference interaction site model self-consistent field with spatial electron density distribution (RISM-SCF-SEDD) method. RISM-SCF-SEDD is a combination methodology of electronic structure theory and statistical mechanics for molecular liquids. Here, time-dependent density functional theory was coupled with RISM equation to study the electronic structure of p-coumaric acid in aqueous system. Excitation energies of the chromophore in its neutral, two monoanionic and dianionic forms were computed to elucidate the effect of the deprotonation and solvation on the spectroscopic properties. We found that solvation strongly affects the excitation character of the chromophore, especially for phenolate anion and dianion. The free energy difference among the four protonation states is also discussed. © 2017 Wiley Periodicals, Inc.

Evaluation of the Capability of Ionic Liquid-Amino Acid Aqueous Systems for the Formation of Aqueous Biphasic Systems and Their Applications in Extraction.

To obtain further experimental evidence for a better understanding of the molecular mechanisms responsible for the soluting-out effect phenomena in ternary systems composed of an ionic liquid (IL), amino acid, and water, systematic studies on the vapor-liquid, liquid-liquid, and solid-liquid equilibrium behavior of aqueous solutions of several ILs were carried out in the presence of a range of amino acids. Water activities for binary and ternary aqueous solutions containing 1-butyl-3-methylimidazolium chloride, [C4mim]Cl, 1-hexyl-3-methylimidazolium chloride, [C6mim]Cl, 1-butyl-3-methyl-imidazolium trifluoromethanesulfonate, [C4mim][CF3SO3], l-Ser, Gly, Ala, and l-Pro were measured using both vapor pressure osmometry and isopiestic methods. All of the ternary IL + amino acid + water systems show negative deviations from semi-ideal behavior and therefore soluting-out effects have been observed in these systems. In the case of the [C4mim][CF3SO3] + amino acids aqueous systems, the IL is soluted-out by the amino acids and the soluting-out effect appears by aqueous biphasic system formation. For these systems, the phase diagram and partition coefficient of caffeine were measured at 298.15 K. However, for the [C4mim]Cl and [C6mim]Cl containing systems, the amino acids are soluted-out by the ILs and the soluting-out effect appears by precipitation of the amino acids from the solution, and the solubilities of the amino acids in the aqueous solutions decrease in the presence of [C4mim]Cl and [C6mim]Cl.

Development of a novel oral delivery system of edaravone for enhancing bioavailability

Edaravone (EDR), a strong free radical scavenger, is known for its promising therapeutic potential in oxidative stress (OS) associated diseases, however poor oral bioavailability is the major obstacle in its potential use. Oral liquid dosage form is the most preferred delivery method in paediatric, geriatric and specialised therapies. The present research discusses the development of a Novel Oral Delivery System (NODS) of EDR to enhance oral bioavailability. From preformulation study, solubility, and stability were identified as key challenges and the requirement of an acidic environment and protection against oxidation were found to be critical. The NODS made up of a mixture of Labrasol (LBS) and an acidic aqueous system, was optimized on the basis of solubility and stability study. It can be stored ≤40°C for at least one month. Drug release from NODS was slow, sustained and significantly better as compared to suspension. The significant reduction in metabolism and improvement in permeability across the small intestine were observed with NODS compared to free EDR. The oral pharmacokinetic study showed 571% relative bioavailability with NODS compared to EDR suspension. From the results obtained, NODS is a promising candidate for use in OS associated diseases.

PH‐Regulated Aqueous Catalytic Hydrogenation of Biomass Carbohydrate Derivatives by Using Semisandwich Iridium Complexes

AbstractSemisandwich Ir complexes [Cp*Ir‐(di‐OMe‐bpy)(OH2)][SO4] (di‐OMe‐bpy=4,4′‐dimethoxyl‐2,2′‐bipyridine) and [Cp*Ir‐(di‐OH‐bpy)(OH2)][SO4] (di‐OH‐bpy=4,4′‐dihydroxyl‐2,2′‐bipyridine) are excellent efficient catalysts for the aqueous hydrogenation reactions of biomass carbohydrate derivatives. We show that pH value plays an important role in the hydrogenation reaction. By adjusting the pH value of the solvent, we can improve the catalytic efficiency and control the product distribution. The turnover frequencies (TOF) of hydrogenation of furfural up to 13 877 h−1 and TOF of hydrogenation of levulinic acid up to 12 200 h−1 at 120 °C were achieved. Converting furfural into γ‐valerolactone in one step is observed at strong acidic aqueous system, which makes it easy to achieve a distribution‐controlled product by pH adjustment.

Salting-out effect in polypropylene glycol-amino acid aqueous solutions revealed by vapor pressure osmometry

Precise vapor pressure osmometry measurements at T = 303.15, 308.15 and 313.15 K have been performed for low concentrations of different binary and ternary aqueous solutions including: amino acids (glycine, alanine, serine and proline) in pure water, PPG725 in pure water and amino acids in aqueous solutions of 0.01 w/w PPG725. In order to study the salting effects occurring in polymer-amino acid aqueous systems, deviations from the semi-ideal behavior have been evaluated. The results indicate that because of unfavorable interactions between PPG and amino acids, they are preferentially hydrated in aqueous media. Therefore, the amount of free water molecules in the PPG + amino acid + water solutions is less than that expected based on the semi-ideal behavior. Hence, under condition that solutes molalities in the ternary solutions are the same as those in the corresponding binary solutions, the values of aw+1−awp°+awa° and Δp−(Δpp°+Δpa°) are negative and become more negative by increasing temperature and hydrophilicity of amino acids side chain.

The Species of Fehling's Solution

AbstractA species model for the copper(II)/L‐(+)‐tartaric acid (LH2, tartH2) aqueous system between pH 1.9 and 12.3 has been established by potentiometric, UV/Vis spectroscopic, solubility and crystallographic studies. Eight species were detected, including the oligonuclear major species Cu8L6H–10 in the neutral region and the mononuclear major species CuL2H–4 in the alkaline region, the latter being associated with Fehling's solution. The octanuclear complex was isolated as its lithium salt Li7[Cu8(L‐tartH–2)4(L‐tartH–1)2(H2O)6]NO3·19H2O (1). The “Fehling species” CuL2H–4 was crystallized as its sodium, potassium and caesium salts, namely K2Na4[Cu(L‐tartH–2)2]·12H2O (2), Na6[Cu(L‐tartH–2)2]·9H2O (3), Na6[Cu(L‐tartH–2)2]·14H2O (4), and Cs6[Cu(L‐tartH–2)2]·8H2O (5). Each of them shows a distorted square‐planar environment of copper(II), similar to the related non‐chiral cuprate [Cu(rac‐tartH–2‐κ2O2,O3)2]6– (S. Albrecht, P. Klüfers, Z. Anorg. Allg. Chem. 2013, 639, 280–284). By comparing the components of the UV/Vis spectra of Fehling's solution and the solids, we confirmed the identity of the major solution species.

ChemInform Abstract: Water Mediated Domino Knoevenagel‐Michael‐Cyclocondensation Reaction of Malononitrile, Various Aldehydes and Barbituric Acid Derivatives Using Boric Acid Aqueous Solution System Compared with Nano‐Titania Sulfuric Acid.

Nano-titania sulfuric acid (TSA) and boric acid [B(OH)3] were efficiently utilized for domino Knoevenagel-Michael-cyclocondensation reaction of malononitrile, various aldehydes and barbituric acid derivatives to synthesis of pyrano[2,3-d]pyrimidine diones. It is interesting that in boric acid aqueous solution system, H+ which abstracted from water by the interaction with B(OH)3, efficiently catalyzed the reaction.

A facile route to aqueous phase synthesis of mesoporous alumina with controllable structural properties

Mesoporous aluminas (MAs) with tunable structural properties, including BET surface area, pore volume and pore size, were successfully synthesized based on a sol–gel process via hydrolysis of aluminium isopropoxide associated with a structure-directing agent (SDA) as template in an acidic aqueous system. The effect of template type, template addition amount and inorganic aluminium precursor doping on the structural properties of the resulting MAs were systematically investigated. Four templates, including two non-ionic triblock copolymers P123 and F127, an amine based cationic quaternary surfactant cetyltrimethylammonium bromide (CTAB) and an anionic surfactant sodium dodecyl sulfate (SDS) were examined at varying amount. Three inorganic aluminium precursors, viz aluminium sulfate, aluminium nitrate and aluminium chloride, were used as the substitution aluminium sources to aluminium isopropoxide. The MAs synthesized were characterized using thermogravimetry – differential thermal analysis (TG–DTA) for decomposition and mass loss characteristics upon calcination, X-ray diffraction (XRD) for bulk crystallinity, transmission electron microscopy (TEM) for nano-scale morphology and N2 physisorption techniques for porous structural properties. For a given SDA, increasing the amount of surfactant addition markedly improved the porosity of the MA synthesized. In terms of the ability to influence the structural properties of the resulting MAs such as BET surface area, pore volume and pore size, the SDAs tested followed a descending order of F127 > P123 > CTAB > SDS. MAs with the greatest pore volumes and pore sizes with narrow PSDs were obtained when the doping ratios of Al(NO3)3, AlCl3 and Al2(SO4)3 were 15%, 30% and 2%, respectively. Depending on the type and addition amount of SDA and the aluminium precursor composition, the BET surface area, pore volume and pore size of MAs could be adjusted in the ranges of 178 m2 g−1 ∼ 358 m2 g−1, 0.4 cm3 g−1 ∼ 1.9 cm3 g−1 and 5.5 nm–30.1 nm, respectively.

A regenerable precipitant-solvent system for CO2 mitigation and metals recovery

This work describes a new resource engineering process for greenhouse gas control and metals recovery, and reports initial progress in its development. Central to this process is a regenerable solvent-precipitant system that enables pH-swing via a change in operational temperatures. In this particular contribution, various liquid-phase aliphatic tertiary amines and acids were examined to identify the suitable components that afford pH control between 10 and 2, deemed necessary for metal hydroxide precipitation and leaching metals from magnesium-bearing solids, respectively. Within the desired operational constraints (Tmax≤110°C, Pmax≤1bar, tmax≤2h), we found the triethylamine–sulphuric acid aqueous system (Et3N–H2SO4–H2O) has sufficiently covered the pH regimes of interest, affording a pH swing (at 25°C) between 10.5 and 1.9. Triethylamine (Et3N) provided the highest acid neutralising capacity of 7mol H+L−1 Et3N, capable of aqueous alkalisation to pH>10.5 (25°C, 1bar), and recoverable at ≤105°C (1.0bar) via fractional distillation. As for the acid component, H2SO4 allows for the formation of an acidic aqueous solution (pH 1.9, 25°C, 1bar) resulting from the partial liberation of Et3N from the acid-bound Et3N·H+ and HSO4− counter anion dissociation.

Water Mediated Domino Knoevenagel‐Michael‐cyclocondensation Reaction of Malononitrile, Various Aldehydes and Barbituric Acid Derivatives Using Boric Acid Aqueous Solution System Compared with Nano‐titania Sulfuric Acid

AbstractNano‐titania sulfuric acid (TSA) and boric acid [B(OH)3] were efficiently utilized for domino Knoevenagel‐Michael‐cyclocondensation reaction of malononitrile, various aldehydes and barbituric acid derivatives to synthesis of pyrano[2,3‐d]pyrimidine diones. It is interesting that in boric acid aqueous solution system, H+ which abstracted from water by the interaction with B(OH)3, efficiently catalyzed the reaction.

Synthesis of mesoporous alumina with tunable structural properties

Mesoporous aluminas (MAs) with tunable structural properties including BET surface area, pore volume and pore size were successfully synthesized. The synthesis method was based on a sol–gel process via hydrolysis of aluminium isopropoxide associated with non-ionic block copolymer P123 as the structure-directing template in an acidic aqueous system. The MAs were characterized using thermogravimetry – differential thermal analysis (TG-DTA) for decomposition and mass loss characteristics during calcination, X-ray diffraction (XRD) for bulk crystallinity, transmission electron microscopy (TEM) for nano-scale morphology, selected area electron diffraction (SAED) for local crystallinity and N2 adsorption–desorption techniques for porous structural properties. By tailoring the amount of P123 and HNO3 addition, inorganic aluminium precursor Al(NO3)3 doping ratio and calcination temperature, MAs with controllable structural properties were obtained, leading to regular variations in the surface area (up to 409 m2g−1), pore volume (0.4 cm3g−1 ∼ 2.8 cm3g−1) and pore size (5.0 nm ∼ 33.1 nm). Bovine serum albumin (BSA) was employed to evaluate the adsorption capability of the synthesized MAs. It was found that the structural properties of MA had a crucial effect on the BSA adsorption capability, increasing dramatically with increasing surface area, pore volume and pore size. For the sample MA4P15AlN (surface area 287 m2g−1, pore volume 2.8 cm3g−1 and pore size around 33.1 nm), the BSA adsorption amount reached 182.7 mgg−1 in 2 h, higher than other MA samples as well as a silicon based reference sorbent material, SBA-15 (133.3 mgg−1).

On the Mechanism of Corrosion in Presence of Organic Acids

Theories on the role of organic acids in general, and acetic acid in particular, in carbon steel corrosion were initiated in 1940s with the reports on the significant effect of acetic acid in pipeline corrosion in oil and gas industry1. It was reported that even small amounts of acetic acid (300 ppm) can cause severe corrosion of pipeline steel1. Later on, several studies on the concentration of organic acids in formation water of oil and gas wells have been reported up to 3000 ppm of acetic acid1–4. Despite numerous studies on the mechanism of acetic acid corrosion of pipeline steel, details of the mechanism are still debated. Acetic acid is known as a week acid which is partially dissociate in water. It is also known that weak acids act as a reservoir for hydrogen ions in the corrosion process. This phenomenon known as “buffering effect”, describes the enhanced limiting current in presence of acetic acid compared to the case of strong acids at a similar pH. Additionally, it is suggested that the undissociated acetic acid is also a proton donor and is able to be reduced at the surface of the steel, which is known as “direct reduction” mechanism. The direct reduction mechanism has been used for years5,6. Also, many other studies on the combined effect of acetic acid and carbon dioxide on carbon steel have adopted the same mechanism7–9. However, recent studies suggest that undissociated acetic acid is only involved in the corrosion process as a buffer for hydrogen ions. Tran et al.10 report a series of polarization curves on SS304 stainless steel, showing that the concentration of acetic acid does not affect the charge transfer portion of the cathodic sweeps. Therefore, they have concluded that acetic acid is not involved in charge transfer processes directly and that the buffering effect is the main mechanism. In that study, authors suggest that the same mechanism is valid for carbon steel. In the present study an iron electrode was used instead of carbon steel in order to minimize the effect of impurities such as carbon. Figure 1 presents the experimental data collected in the present work and the comparison with the results of the mathematical simulations. The experimental data are collected using a rotating disk electrode made from pure iron exposed in a two liter, three electrode glass cell in deoxygenated aqueous solution. The mathematical simulation is the solution of Nernst Plank equation for an acetic acid aqueous system. These equations are solved with finite difference method, using Newman’s BANDJ11 algorithm in FORTRAN with a MATLAB user interface. Figure 1 shows a clear linear cathodic charge transfer behavior at both pH values. Additionally the charge transfer part of the cathodic reactions is insensitive to changes in concentration of acetic acid which is the indication that free acetic acid in the system is not directly reduced at the surface of iron. Current results confirm that the proposed mechanism by Tran et al. applies to pure iron which has great similarity to pipeline steel. The mathematical calculations proposed here also support the same conclusion. Additionally, comparison of the calculated charge transfer rates based on these results suggests that the rate of dissolution of iron is slightly retarded in presence of acetic acid.

Self-organized TiO2 nanotube arrays in the photocatalytic degradation of methylene blue under UV light irradiation

Nanostructured titanium dioxide (NTiO2) is known to possess efficient photocatalytic activity and to have diverse applications in many fields due to its chemical stability, high surface area/volume ratio, high transmittance, and high refractive index in the visible and the near-ultraviolet regions. These facts prompted us to develop TiO2 nanotube (TiO2 NT) arrays through electrochemical anodic oxidation involving different electrolytes comprised of phosphoric acid — hydrofluoric acid aqueous systems by varying the voltage and the time. The annealing temperature of the nanotubes, TiO2 NTs, were varied to modify the surface morphology and were characterized by using X-ray diffraction and scanning electron microscopy. Scanning electron microscopy and X-ray diffraction results showed that the samples had uniform morphologies and good crystalline structures of the anatase phase at lower annealing temperatures and of the rutile phase at higher annealing temperatures. A secondary-ion mass-spectrometry analysis was used to investigate the surface atoms and to conduct a depth profile analysis of the TiO2 NTs. The efficiency of the photocatalytic activity of the TiO2 NT arrays in degrading methylene blue (MB) was investigated under UV-Vis light irradiation. The maximum photocatalytic activity was achieved for the samples with lower annealing temperatures due to their being in the anatase phase and having a higher surface area and a smaller crystal size, which play important roles in the degradation of organic pollutants.

Solvent Extraction of Perrhenate Anion from Sulfuric Acid Aqueous System with N1923

Perrhenate anion was extracted by extractant N1923 in sulfuric acid solution at ionic strength from (0.2 to 2.0) mol·kg–1. Molalities of perrhenate after extraction were measured in sulfuric acid aqueous system from (278.15 to 303.15) K. Standard extraction constants K0 were obtained by polynomial approximation method at various temperatures. Thermodynamic properties were investigated in the extraction process.

Investigation of amino acid-polymer aqueous biphasic systems.

Aiming at gathering further information to evaluate the recently proposed1,2 mechanism of the salt effect in aqueous polymer solutions, experimental vapor-liquid equilibria (VLE), liquid-liquid equilibria (LLE), and volumetric-compressibility measurements were carried out for several polymer-amino acid aqueous systems. The constant water activity lines (obtained through the isopiestic method at 298.15 K) of aqueous polypropylene glycol 400 (PPG400) + alanine or glycine systems, which form aqueous biphasic systems (salting-out effect), have a concave and convex slope, respectively, in the one-phase and two-phase regions. However, all the investigated polyethylene glycols (PEG400, PEG2000, PEG6000, and PEG10000) do not form aqueous biphasic systems with alanine or glycine (salting-in effect) and their constant water activity lines have a convex slope. In the second part of this work, the apparent molar volume and isentropic compressibility of transfer of alanine and glycine from water to aqueous solutions of PEG200, PEG2000, PEG10000, and PPG400 were studied at different temperatures. The third part of this work is concerned with the determination of LLE phase diagrams for several ternary polymer-amino acid aqueous systems containing polymers PPG400 and PPG725 and amino acids alanine, glycine, serine, and proline at different temperatures. On the basis of the obtained cloud point values of aqueous solutions of PPG725 in the absence and presence of various amino acids, it was found that all the investigated amino acids have a salting-out effect on PPG725 in aqueous solutions and entropy is the driving force for biphasic formation.

Rapid patterning of 1-D collagenous topography as an ECM protein fibril platform for image cytometry.

Cellular behavior is strongly influenced by the architecture and pattern of its interfacing extracellular matrix (ECM). For an artificial culture system which could eventually benefit the translation of scientific findings into therapeutic development, the system should capture the key characteristics of a physiological microenvironment. At the same time, it should also enable standardized, high throughput data acquisition. Since an ECM is composed of different fibrous proteins, studying cellular interaction with individual fibrils will be of physiological relevance. In this study, we employ near-field electrospinning to create ordered patterns of collagenous fibrils of gelatin, based on an acetic acid and ethyl acetate aqueous co-solvent system. Tunable conformations of micro-fibrils were directly deposited onto soft polymeric substrates in a single step. We observe that global topographical features of straight lines, beads-on-strings, and curls are dictated by solution conductivity; whereas the finer details such as the fiber cross-sectional profile are tuned by solution viscosity. Using these fibril constructs as cellular assays, we study EA.hy926 endothelial cells' response to ROCK inhibition, because of ROCK's key role in the regulation of cell shape. The fibril array was shown to modulate the cellular morphology towards a pre-capillary cord-like phenotype, which was otherwise not observed on a flat 2-D substrate. Further facilitated by quantitative analysis of morphological parameters, the fibril platform also provides better dissection in the cells' response to a H1152 ROCK inhibitor. In conclusion, the near-field electrospun fibril constructs provide a more physiologically-relevant platform compared to a featureless 2-D surface, and simultaneously permit statistical single-cell image cytometry using conventional microscopy systems. The patterning approach described here is also expected to form the basics for depositing other protein fibrils, seen among potential applications as culture platforms for drug screening.