Aqueous Tetrabutylammonium Hydroxide Research Articles

Highly Efficient Liquid-Phase Exfoliation of Layered Perovskite-like Titanates HLnTiO4 and H2Ln2Ti3O10 (Ln = La, Nd) into Nanosheets

Nanosheets of layered perovskite-like oxides attract researchers as building blocks for the creation of a wide range of demanded nanomaterials. However, Ruddlesden–Popper phases are difficult to separate into nanosheets quantitatively via the conventional liquid-phase exfoliation procedure in aqueous solutions of bulky organic bases. The present study has considered systematically a relatively novel and efficient approach to a high-yield preparation of concentrated suspensions of perovskite nanosheets. For this, the Ruddlesden–Popper titanates HLnTiO4 and H2Ln2Ti3O10 (Ln = La, Nd) have been intercalated by n-alkylamines with various chain lengths, exposed to sonication in aqueous tetrabutylammonium hydroxide (TBAOH) and centrifuged to separate the nanosheet-containing supernatant. The experiments included variations of a wide range of conditions, which allowed for the achievement of impressive nanosheet concentrations in suspensions up to 2.1 g/L and yields up to 95%. The latter were found to strongly depend on the length of intercalated n-alkylamines. Despite the less expanded interlayer space, the titanates modified with short-chain amines demonstrated a much higher completeness of liquid-phase exfoliation as compared to those with long-chain ones. It was also shown that the exfoliation efficiency depends more on the sample stirring time in the TBAOH solution than on the sonication duration. Analysis of the titanate nanosheets obtained by means of dynamic light scattering, electron and atomic force microscopy revealed their lateral sizes of 30–250 nm and thickness of 2–4 nm. The investigated exfoliation strategy appears to be convenient for the high-yield production of perovskite nanosheet-based materials for photocatalytic hydrogen production, environmental remediation and other applications.

Probing cellulose–solvent interactions with self-diffusion NMR: Onium hydroxide concentration and co-solvent effects

The molecular self-diffusion coefficients were accessed, for the first time, in solutions of microcrystalline cellulose, dissolved in 30 wt% and 55 wt% aqueous tetrabutylammonium hydroxide, TBAH (aq), and in mixtures of 40 wt% TBAH (aq) with an organic co-solvent, dimethylsulfoxide (DMSO), through pulsed field gradient stimulated echo NMR measurements. A two-state model was applied to estimate α (i.e., average number of ions that “bind” to each anhydroglucose unit) and Pb (i.e., fraction of “bound” molecules of DMSO, TBAH or H2O to cellulose) parameters. The α values suggest that TBA+ ions can bind to cellulose within 0.5 TBA+ to 2.3 TBA+/AGU. On the other hand, the Pb parameter increases when raising cellulose concentration for TBA+, DMSO and water in all solvent systems. Data suggests that TBAH interacts with the ionized OH groups from cellulose forming a sheath of bulky TBA+ counterions which consequently leads to steric hindrance between cellulose chains.

An eco-friendly approach to preparing cellulose nanocrystals by precisely controlling the dissolution of natural cellulose in TBAH/H2O solvent

Applications of cellulose nanocrystals (CNCs) in various fields of high value have been and are being widely studied. However, research about the fundamental preparation method has come to a standstill. This work aims to introduce a concept of progressive dissolution of cellulosic fibers and an eco-friendly way of preparing CNCs. By controlling TBAH concentration, the amphiphilicity and dissolving capability of TBAH/H2O can be regulated. Through a controlled partial dissolution of cellulose in the solvent, aqueous tetra-butylammonium hydroxide (TBAH), the fiber can be dissolved to make nanoscale particles (CNC suspensions). Polarized light microscopy provides a quantitative evaluation of the progress of dissolution, by which a processing window (43% TBAH/H2O, 30 min dissolution at room temperature) for preparing CNCs from cotton pulp has been determined. The multiscale cellulose products, including micron-scale, nanoscale, and well-dissolved products of cellulose, have been separated with the assistance of the derivatization process. There are interestingly homogeneous materials of cellulose I with a needle-like shape in the nanoscale products extracted. Furthermore, the cellulose raw materials can be extended from cotton pulp to wood pulp, bamboo pulp, straw pulp, and microcrystalline cellulose, indicating it to be a universal method. Analysis of XRD patterns of the raw and CNCs indicates that amorphous and less-crystalline cellulose can be precisely and controllably dissolved by the solvent, leaving CNCs.

Silk Fibroin Dissolution in Tetrabutylammonium Hydroxide Aqueous Solution

Bombyx mori L. silk fibroin (SF) is widely used in different areas due to its ability to form durable and resilient materials with notable mechanical properties. However, in some of these applications the dissolution of SF is required, and this is not often straightforward due to its inability to be dissolved in the majority of common solvents. This work reports a novel approach to dissolve SF using 40 wt % aqueous tetrabutylammonium hydroxide, TBAOH(aq), at mild temperature. A thorough rheological study combined with small-angle X-ray scattering is presented to correlate the SF state in solution with changes in the rheological parameters. The scattering data suggest that the SF conformation in TBAOH(aq) is close to a random coil, possibly having some compact domains linked with flexible random chains. The radius of gyration (Rg) and the molecular weight (Mw) were estimated to be ca. 17.5 nm and 450 kDa, respectively, which are in good agreement with previous works. Nevertheless, a lower Mw value was deduced from rheometry (i.e., 321 kDa) demonstrating a low degree of depolymerization during dissolution in comparison to other harsh processes. The transition from a dilute to a semidilute regime coincides with the estimated critical concentration and is marked by the presence of a shear-thinning behavior in the flow curves, violation of the empirical Cox-Merz rule, and an upward increase in the activation energy. This work paves the way toward the development of advanced high-tech SF-based materials.

Pretreatment of corn stalk by low concentration tetrabutylammonium hydroxide aqueous solution at low temperature (20–80 °C)

Corn stalk was pretreated by aqueous tetrabutylammonium hydroxide to enhance enzymatic hydrolysis process. The effects of temperature (20–80 °C), concentration of tetrabutylammonium hydroxide (10–40 wt%), time (5–60 min) and ratio of solid to liquid (1:4–1:8, wt/wt) were investigated to find the optimal operational condition, which was determined as 20 °C, 30 wt%, 20 min and 1:5 respectively. This was a quite mild pretreatment condition resulting in 68.17% enzymatic hydrolysis sugar yield and the removal rate of hemicelluloses and lignin were 23.5% and 31.5% respectively. Besides, the microstructure and crystal structure changes of raw material and pretreated samples were analyzed by scanning electron microscope and X-ray diffraction respectively. Finally, a possible mechanism of pretreatment process was put forward based on the comprehensive analysis.

Functionalization of Intact Trimetaphosphate: A Triphosphorylating Reagent for C, N, and O Nucleophiles.

Trimetaphosphate (TriMP, [P3O9]3-) reacts with PyAOP ([(H8C4N)3PON4C5H3][PF6]) to yield an activated TriMP, [P3O9P(NC4H8)3]- (1), incorporating a phosphonium moiety. Anion 1 is isolated as its bis(triphenylphosphine)iminium (PPN) salt in 70% yield and phosphorylates nucleophiles with elimination of phosphoramide OP(NC4H8)3. Treatment of 1 with amines HNR1R2 generates [P3O8NR1R2]2- (2a: R1 = R2 = Et; 2b: R1 = H, R2 = tBu) in greater than 70% yield as mixed PPN and alkyl ammonium salts. Treatment of 1 with primary alcohols in the presence of a tertiary amine base results in salts of intact TriMP alkyl esters [P3O9R]2- (3a: R = Me; 3b: R = Et) in greater than 60% isolated yield. Reaction of 1 with [PPN][H2PO4] provides orthophosphoryl TriMP (4, [P4O12H2]2-) in 40% yield as the PPN salt. Treatment of 1 with Wittig reagent H2CPPh3 (4 equiv) provides phosphorus ylide [P3O8CHPPh3]2- (5) in 61% yield as a mixed salt. Ylide 5 reacts with water to provide [P3O8Me]2- (6) and with aldehydes to give olefins [P3O8CHCHR]2- (7a: R = H; 7b: R = 4-C6H4Br), products in which one TriMP oxygen is replaced by a phosphonate P-C linkage. Treatment of intact TriMP derivatives 2a, 2b, 3a, and 7a with aqueous tetrabutylammonium hydroxide results in ring opening to linear triphosphate derivatives. X-ray crystal structures are provided for salts of 1, 2a, 3a, and 4.

Performance of aqueous tetrabutylammonium hydroxide, piperazine and their blends for carbon dioxide capture

The potential of aqueous ammonium based IL, tetrabutylammonium-hydroxide (TBAOH), the aqueous tertiary amine, piperazine (PZ) and two aqueous solutions of TBAOH and PZ blend for CO2 capturing was estimated by solubility study. For this purpose, the experiments were carried at five different pressures and three temperatures by using a solubility cell. The experimentally obtained solubility data was used to determine Henry's constant which further used to estimate the enthalpy and entropy of the system. The overall results revealed that CO2 solubility in all the solutions is directly proportional to pressure but inversely proportional to temperature. The experimental solubility data was correlated with artificial neural network (ANN) modeling and predicted solubilities are reported. On comparison with literature, it was found that the TBAOH exhibited high CO2 solubility than many other solvents under same conditions of temperature, pressure and concentration. On the other side, the aqueous blends of TBAOH and PZ also showed promising results and CO2 solubility was higher in the low concentrated blends of TBAOH and PZ as compared with high concentration.

Stable, metastable and unstable cellulose solutions.

We have characterized the dissolution state of microcrystalline cellulose (MCC) in aqueous tetrabutylammonium hydroxide, TBAH(aq), at different concentrations of TBAH, by means of turbidity and small-angle X-ray scattering. The solubility of cellulose increases with increasing TBAH concentration, which is consistent with solubilization driven by neutralization. When comparing the two polymorphs, the solubility of cellulose I is higher than that of cellulose II. This has the consequence that the dissolution of MCC (cellulose I) may create a supersaturated solution with respect to cellulose II. As for the dissolution state of cellulose, we identify three different regimes. (i) In the stable regime, corresponding to concentrations below the solubility of cellulose II, cellulose is molecularly dissolved and the solutions are thermodynamically stable. (ii) In the metastable regime, corresponding to lower supersaturations with respect to cellulose II, a minor aggregation of cellulose occurs and the solutions are kinetically stable. (iii) In the unstable regime, corresponding to larger supersaturations, there is macroscopic precipitation of cellulose II from solution. Finally, we also discuss strong alkali solvents in general and compare TBAH(aq) with the classical NaOH(aq) solvent.

On the dissolution of cellulose in tetrabutylammonium acetate/dimethyl sulfoxide: a frustrated solvent

We have found that the dissolution of cellulose in the binary mixed solvent tetrabutylammonium acetate/dimethyl sulfoxide follows a previously overlooked near-stoichiometric relationship such that one dissolved acetate ion is able to dissolve an amount of cellulose corresponding to about one glucose residue. The structure and dynamics of the resulting cellulose solutions were investigated using small-angle X-ray scattering (SAXS) and nuclear magnetic resonance techniques as well as molecular dynamics simulation. This yielded a detailed picture of the dissolution mechanism in which acetate ions form hydrogen bonds to cellulose and causes a diffuse solvation sheath of bulky tetrabutylammonium counterions to form. In turn, this leads to a steric repulsion that helps to keep the cellulose chains apart. Structural similarities to previously investigated cellulose solutions in aqueous tetrabutylammonium hydroxide were revealed by SAXS measurement. To what extent this corresponds to similarities in dissolution mechanism is discussed.

From a new cellulose solvent to the cyclodextrin induced formation of hydrogels

A new efficient solvent for cellulose dissolution was developed based on the mixture of aqueous tetrabutylammonium hydroxide, TBAH(aq) and an organic co-solvent, dimethylsulfoxide (DMSO). Clear cellulose solutions were readily obtained at mild conditions in a few minutes. The viscoeleastic properties of the dopes formed are found to be dependent on the cellulose content and TBAH(aq)/DMSO ratio. Additionally, stiff hydrogels are formed when adding β-cyclodextrin (β-CD) to the cellulose dopes. The formation of a host-guest complex between the β-CD and the tetrabutylammonium cations (TBA+), which presumably destabilizes the cellulose solution state triggering the hydrogel formation, is suggested as mechanism. The robust hydrogels formed have been characterized regarding their viscoelasticity, microscopic morphology and release properties. The kinetics and released amount of the TBA+ from the cellulose gel matrixes are found to be strongly dependent on the balance between average pore diameter, surface area and “free” volume of the hydrogels.

On cellulose dissolution and aggregation in aqueous tetrabutylammonium hydroxide.

Aqueous tetrabutylammonium hydroxide, TBAH(aq), has been found to dissolve cellulose and to be a potential solvent for chemical processing or fiber spinning. In this paper, we have investigated the dissolution state of cellulose in 40 wt % TBAH(aq) solvent, and present an extensive study of rheology, combined with static light and small-angle X-ray scattering, to correlate cellulose aggregation with changes in the rheological parameters. Two cellulose molecular weights are compared. Microcrystalline cellulose (MCC), with a degree of polymerization of ca. 260, and a dissolving pulp with an approximately ten times higher molecular weight. Scattering data demonstrate that cellulose is molecularly dissolved at lower cellulose concentrations, while aggregates are present when the concentration exceeds a certain value. The onset of the aggregate formation is marked by a pronounced increase in the scattering intensity at low q, shear thinning behavior and violation of the empirical Cox-Merz rule. Additionally, the SAXS data suggest the presence of a solvation shell enriched in TBA(+) ions, compared to the bulk solvent. The results are consistent with the recent suggestion that while native cellulose I may still dissolve, solutions are, above a particular concentration, becoming supersaturated with respect to the more stable crystal form cellulose II.

Cellulose–solvent interactions from self-diffusion NMR

Molecular self-diffusion coefficients were measured in solutions of microcrystalline cellulose (MCC) and dissolving pulp, in 40 wt% aqueous tetrabutylammonium hydroxide (TBAH), using pulsed field gradient stimulated echo NMR. From the cellulose diffusion coefficients, a weight averaged radius of hydration <Rh>w = 6.1 nm for MCC and <Rh>w = 15 nm for pulp were obtained. Water and TBA+ ions show a significantly different dependence on the cellulose concentration, revealing different molecular interactions with the polymer. Water-cellulose are essentially excluded volume. TBA+ ions, on the other hand, bind to cellulose with approximately 1.2 TBA+ ions per glucose unit.

Preparation of silica-supported carbon by Kraft lignin pyrolysis, and its use in solid-phase extraction of fluoroquinolones from environmental waters

The article describes a carbon-based material for solid-phase extraction (SPE) of fluoroquinolones from waters. It was obtained by pyrolytic deposition of Kraft lignin (LG) on silica particles. Marbofloxacin (MAR) and enrofloxacin (ENR) were chosen as model contaminants. The material was prepared by first adsorbing LG onto silica microparticles, this followed by pyrolytic treatment at 1200 °C for 2 h. Silica-supported carbon was characterized by scanning electron microscopy, surface area measurement (by BET), thermogravimetric analysis, and electron paramagnetic resonance. The carbon-coated silica particles were then tested as a column packing for SPE of MAR and ENR from spiked tap and river waters. Quantitative adsorption was observed at pH values of ~7.5 for both drugs. They were eluted with a 70:30 mixture of aqueous tetrabutylammonium hydroxide and acetonitrile and then quantified by HPLC coupled to fluorescence detection. Samples spiked with MAR and ENR in the range from 10 to 1000 ng·L−1 gave recoveries ranging from 70 to 116% (for n = 3). Good inter-day precision (with RSDs between 7 and 16%) was observed for 20–1000 ng·L−1 spikes, also in natural river water. Sample volumes up to 500 mL provided enrichment factors up to 125, and this makes this material useful for determination of the two drugs at environmentally significant levels which are as low as a few ng·L−1. The batch-to-batch reproducibility was verified for 3 preparations. The sorbent was successfully applied to the determination of these drugs in environmental waters.

Wheat straw lignin fractionation and characterization as lignin-carbohydrate complexes

Alkaline extracted and untreated wheat straw were ball-milled with liquid nitrogen cooling rendering them completely soluble in the solvent system dimethylsulfoxide—aqueous tetrabutylammonium hydroxide for subsequent fractionation into two lignin-carbohydrate complex fractions termed glucan-lignin and xylan-lignin according to their preferred association with glucan or arabinoxylan, respectively. This is the first description using this fractionation protocol for wheat straw. Eventually, acidolysis lignins were prepared from both lignin-carbohydrate complexes and structurally characterized using wet chemistry and NMR spectroscopy methods. Using the novel procedure we could reveal differences regarding wheat straw lignin association with polysaccharides, p-hydroxycinnamic acids and tricin as well as in their monomer composition. In glucan-lignin the lignin moiety was found to be linked mainly to glucan but also to branched arabinoxylan. Xylan-lignin, however, was rich in structures creating cross-links between lignin and linear arabinoxylan via ether-ester bridges by bi-functional ferulic acid. Inter-molecular ether-ester-linkages by ferulic acid connecting the lignin moieties of the two LCC fractions glucan-lignin and xylan-lignin were proposed. Alkaline extraction of the straw resulted in a strikingly lower recovery of xylan-lignin in the subsequent fractionation which was attributed to cleavage of ester linkages between ferulic acid and arabinoxylan. Structural characteristics indicated glucan-lignin and xylan-lignin deriving from different morphological origins of the cell wall.

Plasmonic-heating-induced nanofabrication on glass substrates.

Fabricating nano-sized through-holes on a coverslip approximately 100 μm thick is challenging but rewarding when applied to ultrafine filters that separate proteins and DNA of various sizes and isolate viruses from cells. Toward this end, we developed an in situ etching-assisted laser processing technique exploiting gold nanoparticles. Plasmonic heating of a single gold nanoparticle through focused illumination of a continuous-wave laser beam enables structural modifications to be localized to the contact area on the glass surface. This results in the embedding of the particle forming nanocavities caused by chemical etching with aqueous tetrabutylammonium hydroxide. Depending on the shape of the nanoparticle, a highly flexible face geometry design such as a disk and triangle was achieved. The etching was monitored in situ through measurements of spectral red shifts in single-particle scattering, indicating an increasing medium refractive index consistent with embedding. The embedding process is unexpectedly fast, at 0.8 μm with 5 minutes of illumination. Besides nanoholes, we fabricated nanodomes around a single gold nanoparticle supported on a glass substrate through laser-heating-induced encapsulation. Overall, we were able to demonstrate true nano-laser processing free from diffraction-limited optics, with potential benefits of simple low-cost fabrication.

Physical-chemical Properties of Aqueous TBAOH Solution for Gas Hydrates Promotion

Gas hydrates attract the attention of many industries for various potential applications such as gas separation and storage. To industrialize the gas hydrate technology, rapid hydrate formation at mild conditions is crucial. Chemical additives such as ionic liquids were investigated for hydrate promotion. The knowledge of physical-chemical properties of ionic liquids is crucial in development of gas hydrate technology in industry as these fundamental properties determined the hydrate formation rate. This work measures the density, pH, electrical conductivity, and surface tension of aqueous tetrabutylammonium hydroxide solutions. The concentrations were chosen to cover the common hydrate promotion range of 0.001-10 wt%. The results showed high dependence of the studied properties on the concentration. pH and electrical conductivity were increased with increase of TBAOH concentration conversely to density and surface tension. The amount of CO2 consumed to form the hydrate was measured at a pressure of 35bar and a temperature 274.15. Significant increase of CO2 consumption in the presence of TBAOH solutions was observed. However, as the concentration increased, more CO2 was consumed.

On the dissolution state of cellulose in aqueous tetrabutylammonium hydroxide solutions

We have characterized the dissolution state of microcrystalline cellulose (MCC) in aqueous 40 wt% tetrabutylammonium hydroxide (TBAH) using a combination of light and small angle X-ray scattering, up to 0.1 g cm−3.

On the role of hydrophobic interactions in cellulose dissolution and regeneration: Colloidal aggregates and molecular solutions

The development of strategies for dissolution and regeneration of cellulose constitutes an increasingly active research field due to the direct relevance for many production processes and applications. A wide variety of suitable solvents for cellulose are already available. However, cellulose solvents are of highly different nature reflecting the great challenges in the understanding of the subtle balance between the different interactions. Here, we report on the effect of two different solvents on the dissolution of cellulose on multiple length scales and its consequences for the characteristics of the regenerated material. While an aqueous tetrabutylammonium hydroxide solution gives rise to what appears to be dissolution down to the molecular level, a sodium hydroxide solution does not dissolve cellulose molecularly but rather leaves aggregates of high crystallinity stable in the cellulose dope. The dramatic difference between a small inorganic cation and an amphiphilic cation indicates a critical role of hydrophobic interactions between cellulose molecules and provides support for the picture that cellulose molecules have pronounced amphiphilic properties. (C) 2015 Elsevier B.V. All rights reserved. (Less)

Novel fluorinated gemini surfactants with γ-butyrolactone segments.

In this work, novel γ-butyrolactone-type monomeric and dimeric (gemini) surfactants with a semifluoroalkyl group [Rf- (CH2)3-; Rf = C4F9, C6F13, C8F17] as the hydrophobic group were successfully synthesized. Dimethyl malonate was dimerized or connected using Br(CH2)sBr (s = 0, 1, 2, 3) to give tetraesters, and they were bis-allylated. Radical addition of fluoroalkyl using Rf-I and an initiator, i.e., 2,2'-azobisisobutyronitrile for C4F9 or di-t-butyl peroxide for C6F13 and C8F17, was perform at high temperature, with prolonged heating, to obtain bis(semifluoroalkyl)-dilactone diesters. These dilactone diesters were hydrolyzed using KOH/EtOH followed by decarboxylation in AcOH to afford γ-butyrolactonetype gemini surfactants. Common 1 + 1 semifluoroalkyl lactone surfactants were synthesized using the same method. Their surfactant properties [critical micelle concentration (CMC), γCMC, pC20, ΓCMC, and AG] were investigated by measuring the surface tension of the γ-hydroxybutyrate form prepared in aqueous tetrabutylammonium hydroxide solution. As expected, the CMC values of the gemini surfactants were more than one order of magnitude smaller than those of the corresponding 1 + 1 surfactants. Other properties also showed the excellent ability of the gemini structure to reduce the surface tension. These surfactants were easily and quantitatively recovered by acidification. The monomeric surfactant was recovered in the γ-hydroxybutyric acid form, and the gemini surfactant as a mixture of γ-butyrolactone and γ-hydroxybutyric acid forms.

Graphene-derivatized silica as an efficient solid-phase extraction sorbent for pre-concentration of fluoroquinolones from water followed by liquid-chromatography fluorescence detection

This work presents a novel analytical method based on graphene for the determination of five widely used fluoroquinolones (FQs) in aqueous matrices. The procedure entails solid-phase extraction (SPE) on graphene-derivatized silica (200mg), followed by liquid chromatography with fluorescence detection. Monolayer graphene oxide (GO) flakes were covalently bonded onto aminopropyl silica microparticles, and then treated with aqueous hydrazine to obtain the reduced GO (RGO). The final material (RGO–silica) was characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and BET analysis, and for the first time evaluated as mixed-mode sorbent for the SPE of FQs from natural waters. Accuracy was studied on tap/raw river water in the concentration range 5–10,000ngL−1, obtaining mean absolute recoveries from 72 to 118%. The inter-day precision was good, showing relative standard deviations (RSDs) in the range 5–15%. Sample volumes up to 1L provided enrichment factors up to 1000, achieving accurate quantification of concentrations as low as 5ngL−1. The analytes were simultaneously and quantitatively eluted from the RGO–silica cartridge in a single fraction by using acetonitrile combined with aqueous tetrabutyl ammonium hydroxide. The batch-to-batch reproducibility was verified on three independently prepared RGO–silica samples. RGO–silica was advantageous in terms of adsorption capacity and reusability with respect to commercial sorbents; the cartridge proved to be reusable for at least 10 consecutive extractions, with no significant loss of efficiency (recovery >70%). The analytical procedure was applied to the determination of FQs in actual environmental waters.