Showing papers on "Ammonium hydroxide published in 2018"

Cationic hydrophobicity promotes dissolution of cellulose in aqueous basic solution by freezing-thawing.

Abstract: The physical dissolution of cellulose in aqueous solutions of tetramethyl ammonium hydroxide, triethylmethyl ammonium hydroxide, tetraethyl ammonium hydroxide, benzyltrimethyl ammonium hydroxide, benzyltriethyl ammonium hydroxide, NaOH and LiOH via freezing-thawing was investigated. Increasing the hydrophobicity of the cation greatly improved its dissolution capacity, leading to significant enhancement of cellulose solubility and stability against chain aggregation and gelation. The hydrophobic cations accumulated at the cellulose interface and decreased the surface tension, favouring dispersion of the disintegrated cellulose due to its amphiphilicity; this was consistent with molecular dynamics simulations. On the other hand, the solubility of cellulose followed the Hofmeister series, and cations with greater kosmotropicity originating from their greater hydrophobicity exhibited stronger dissolution power; this observed interaction pattern may be useful for further exploration and designation of novel solvents of cellulose. These aqueous quaternary ammonium hydroxides can be readily recycled and reused, which presents great potential in the green chemistry field.

Molecular Simulation of Quaternary Ammonium Solutions at Low Hydration Levels

Abstract: Much research has focused on the stability of substituted ammonium salts in anion-exchange membranes (AEMs). While cation chemistry dictates AEM stability, chemical degradation has been recently shown to be significantly influenced by the hydration level at which the AEM operates. At low hydration, it is now known that almost every quaternary ammonium may suffer significant decomposition. In this work, we use molecular dynamics simulations to explore the behavior of three common quaternary ammonium cations with stoichiometric hydroxide concentration and at very low hydration. We find that water preferentially solvates hydroxide anions and hence when water is present in sufficient amount (more than four water molecules per ion pair), stability of the cations is expected to significantly improve. However, lower amounts of water result in the formation of isolated molecular clusters and ammonium hydroxide pairing that lead to degradation of the cation. The composition and size of the water–hydroxide–cation c...

Kinetic Assessment of Tetramethyl Ammonium Hydroxide (Ionic Liquid) for Carbon Dioxide, Methane and Binary Mix Gas Hydrates

Abstract: This present work highlights the impact of ammonium-based ionic liquid tetramethylammonium hydroxide (TMAOH) on the formation kinetics of carbon dioxide (CO 2 ), methane (CH 4 ), and their binary mixed gas (50–50 mole%) hydrates. The TMAOH (IL) is applied in varying concentrations (0.5, 1, and 2 wt%) at different experimental temperatures, i.e., 1 and 4°C. The kinetic experiments are conducted in a high-pressure reactor equipped with two-bladed impeller, to provide sufficient agitation. The experimental pressures of CO 2 , CH 4 , and mixed 50% CO 2 + 50% CH 4 were 3.50, 8.0, and 6.50 MPa, respectively. Induction time, the initial apparent rate of formation and the total gas consumed are the kinetic parameters used to evaluate the performance of TMAOH as KHI. The results are further compared with commercial KHI (PVP), at higher subcooling condition of 1°C and 1 wt% of all the studied gaseous systems. Furthermore, the KHI performance of TMAOH is also evaluated via the relative inhibition performance (RIP) compared with other ILs for CO 2 and CH 4 hydrates. Results revealed that TMAOH delays the induction time for all the considered systems. The presence of TMAOH also reduced the total gas consumed and the initial rate of hydrate formation in most of the studied systems.

Cellulose Dissolution in a Mixed Solvent of Tetra(n-butyl)ammonium Hydroxide/Dimethyl Sulfoxide via Radical Reactions

Abstract: 9.19 wt % of microcrystalline cellulose (MCC) could be dissolved in a new mixed solvent of tetra(n-butyl)ammonium hydroxide (TBAH; 20 wt %) and dimethyl sulfoxide (DMSO; 80 wt %) within 5 min at room temperature. The ratio of TBAH in the mixed solvent (WTBAH) is found to exert great influence on the solubility of cellulose. Dissolution mechanism relative to radical reactions has been proposed according to electron spin resonance (ESR) and UV–vis results, showing positive correlation between cellulose solubility and the radical amount produced in the mixed solvent (i.e., WTBAH). Partial degradation of the reducing AGU terminals via radical attack could be observed, followed by recombination of cellulose chain radicals, resulting in amorphous structures of all regenerated cellulose with higher average degree of polymerization values. Therefore, dissolution mechanism with regard to radical reactions has been proposed in this letter, supplementing the predominant electron donor–acceptor complexation theory.

Improving negative liquid chromatography/electrospray ionization mass spectrometry lipidomic analysis of human plasma using acetic acid as a mobile-phase additive

Abstract: Rationale Mobile phase additives in LC-MS are used to improve peak shape, analyte ionization efficiency and method coverage. Both basic and acidic mobile phases have been used successfully for negative ESI, but very few systematic investigations exist to date to justify the choice of mobile phase. Acetic acid was previously shown to improve ionization in untargeted metabolomics of urine, but has not been investigated in lipidomics. The goal of this study was to systematically compare the performance of acetic acid to other commonly employed additives in negative ESI-LC-MS lipidomics. Methods The performance of acetic acid was compared to commonly utilized mobile phase additives in lipidomics: ammonium acetate, ammonium acetate with acetic acid and ammonium hydroxide using lipid standard solutions containing representatives of major mammalian lipid subclasses and isopropanol-precipitated human plasma. This design allowed comparison of the influence of additive and additive concentration on lipid signal intensity, lipid peak shape and lipid coverage in both simple and complex biological matrices using both Orbitrap and quadrupole-time-of-flight MS platforms with different ESI source designs. Results Ammonium hydroxide caused 2- to 1000-fold signal suppression of all lipid classes in comparison to acetic acid. In comparison to ammonium acetate, acetic acid increased lipid signal intensity from 2 to 19-fold for 11 lipid subclasses, and decreased ionization efficiency only for ceramide and phosphatidylcholine lipid classes which can be effectively ionized in positive ESI mode. The improved ionization efficiency using acetic acid also increased lipid coverage by 21-50% versus ammonium acetate additive. Conclusions Acetic acid at a concentration 0.02% (v/v) is the suggested choice as a mobile phase additive for lipidomics and targeted lipid profiling with negative ESI-LC-MS based on signal enhancement and improved lipid coverage compared to ammonium acetate, ammonium acetate with acetic acid, and ammonium hydroxide mobile phases.

Removal of tetramethyl ammonium hydroxide from synthetic liquid wastes of electronic industry through micellar enhanced ultrafiltration

Abstract: In this paper, the separation of tetramethyl ammonium hydroxide (TMAH) from synthetic liquid wastes of electronic industry is carried out by using a micellar enhanced ultrafiltration (MEUF) process. This treatment represents the first step of an integrated process, aimed at the recovery of TMAH and surfactant and water reuse. The laboratory tests are carried out with an ultrafiltration module using initial solutions having a concentration of pollutant equal to 2 g/L and by adding sodium dodecyl sulfate as a surfactant, at a concentration in the range 4–10 mM/L, that is, under and above its critical micellar concentration (CMC). The experiments have been carried out at a fixed temperature of 25°C. The obtained results showed that very good percentage removals of TMAH are achieved (99%), especially when the surfactant was above the CMC.

Direct non-biological CO2 mineralization for CO2 capture and utilization on the basis of amine-mediated chemistry

Abstract: Considering the perspective of sustainable development, non-biological CO2 mineralization was an important strategic significance for CO2 capture and utilization. We herein demonstrate the direct fixation of CO2 to prepare well-defined metal carbonate (MCO3, M = Ca, Sr, Ba, Mn, Cd, and Pb) crystals under mild conditions on the basis of amine-mediated chemistry. Six well-defined MCO3 crystals were successfully synthesized by regulating key influencing parameters, including the amine adding amount, CO2 pressure, reaction temperature and time, and M2+ concentration. The tested amines, including ethylenediamine (EDA), monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), N-methyldiethanolamine (MDEA), 2-amino-2-methyl-1-propanol (AMP), and ammonium hydroxide (NH3·H2O), can buffer the pH value of the reaction solution, coordinate with the metal ion through chelation, activate the incoming CO2, and direct the growth and assembly of the MCO3 crystals. This methodology was found to be generally applicable and customizable. As a result, this study provided scientific basis for the development of amine chemistry, and such an approach was facile and potential importance for direct non-biological CO2 mineralization and well-controlled MCO3 crystals.

Chemoselective Synthesis of Amines from Ammonium Hydroxide and Hydroxylamine in Continuous Flow

Abstract: The chemoselective amination of alkyl bromides and chlorides with aqueous ammonia and hydroxylamine was achieved in continuous flow to produce primary ammonium salts and hydroxylamines in high yields. An in-line workup was designed to isolate the corresponding primary amine, which was also telescoped in further reactions, such as acylation and Paal-Knorr pyrrole synthesis. Monosubstituted epoxides are also compatible with the reaction conditions.

Mass Spectrometric Analysis of Bisphenol A Desorption from Titania Nanoparticles: Ammonium Acetate, Fluoride, Formate, and Hydroxide as Chemical Desorption Agents

Abstract: Bisphenol A (BPA) is a widely used chemical in several consumer products and a well-studied environmental toxicant, and therefore, its accurate measurement is highly demanded However, the co-presence of nanoparticles as an emerging class of contaminants could result in inaccurate determination of BPA due to binding of BPA onto nanoparticle surface In this study, mass spectrometry (MS) was used to investigate desorption of BPA bound on the surface of titania (TiO2) nanoparticles in water Ammonium acetate, fluoride, formate, and hydroxide were evaluated as chemical agents for their desorption capabilities The percentages of recovery, adsorption, and desorption were determined by this new method without requiring any prior separation of nanoparticles from BPA MS analysis demonstrated the desorption of BPA by 10–20 mM of ammonium hydroxide for a mixture of 5 µg/mL BPA and 10 µg/mL TiO2 nanoparticles, with a desorption efficiency of 72 ± 1% Due to adsorption of BPA onto the nanoparticle surface that was inefficient for electrospray ionization, the resulting abundance of target ions could be reduced in the detection of BPA by mass spectrometry As such, these findings collectively promise an accurate determination of the total BPA concentration in water whether it exists in the free or bound form Efficient desorption of contaminants from the surface of nanoparticles would improve the accuracy of the contaminant analysis by mass spectrometry

Synthesis of Small-Sized SAPO-34 Crystals with Varying Template Combinations for the Conversion of Methanol to Olefins

Abstract: SAPO-34 molecular sieves were synthesized under hydrothermal conditions using different combinations of tetraethyl ammonium hydroxide (TEAOH)/morpholine (Mor)/triethylamine (TEA) as templates, with different silicon:aluminum ratios. The physicochemical properties of the synthesized SAPO-34 were characterized using XRD, SEM, N2 adsorption–desorption, XRF, TG, NH3-TPD, FT-IR, and 29Si MAS NMR analyses. According to the SEM and the N2 adsorption–desorption of the catalysts produced by the ternary template exhibited a larger surface area and a smaller crystal size than those produced by the single or binary templates. The FT-IR analysis indicated the increased acidity of the catalyst prepared by the ternary template. A high activity and selectivity to olefins (C2= + C3=) and an optimal silicon to aluminum ratio of 0.4 were obtained from the catalyst synthesized with the ternary template. At the reaction temperature of 450 °C, the methanol conversion approached 100% and the ethylene–propylene selectivity and the lifetime of the catalyst reached maximums of 89.15% and 690 min, respectively.

Microwave-Assisted Coprecipitation Synthesis of LaCoO3 Nanoparticles and Their Catalytic Activity for Syngas Production by Partial Oxidation of Methane

Abstract: LaCoO3 perovskite-type oxides were prepared by microwave-assisted coprecipitation route and investigated in the catalytic partial oxidation of methane (CPOM) to syngas. This preparation method aims to achieve higher specific surface areas than soft-chemical methods commonly used in the preparation of engineered materials. In an attempt to accomplish the creation of mesostructured porous LaCoO3, an ionic template such as cetyl trimethyl ammonium bromide has been used as endotemplate in some samples. The influence of pH and the type of precipitating agent has been studied. The materials have been characterized at different levels: morphology has been studied by scanning electron microscopy, textural properties by nitrogen adsorption-desorption at -196oC, structural analysis by X-ray diffraction, surface composition by X-ray photoelectron spectroscopy (XPS), thermal stability by Thermogravimetric Analysis (TGA) and carbon formation in spent catalysts, by Raman spectroscopy. Structure-activity correlations point out that the precipitating agent has a key role on the morphology and porosity of the resultant oxide, as well as on the average crystalline domain of lanthanum perovskite (catalyst precursor). Thus, the use of ammonium hydroxide as precipitant leads to materials with a higher surface area and a greater specific surface area of cobalt (per unit mass), improving their catalytic performance for the CPOM reaction. The best catalytic performance was found for the catalyst prepared using ammonium hydroxide as precipitant (pH 9) and without adding CTAB as endotemplate.

Investigation of Approaches to Control the Compositions of Zn(Se,OH) Buffers Prepared by Chemical Bath Deposition Process for Cu(In,Ga)Se2 (CIGS) Solar Cells

Abstract: We deposited zinc-based films with various ammonia (ammonium hydroxide; NH4OH) and selenourea concentrations, at the bath temperature of 80 °C, on soda-lime glass substrates using the chemical bath deposition (CBD) process. We analyzed the results using X-ray photoelectron spectroscopy (XPS), which showed binding energies of zinc, selenium, and oxygen. The as-deposited films, containing zinc selenide, zinc oxide, and zinc hydroxide, were also verified. The films prepared in this investigation can be referred to a zinc compound, characterized as Zn(Se,OH). A conformal coverage of the Zn(Se,OH) films, with the smooth surface morphologies, was obtained by optimizing the ammonia or selenourea concentrations in the deposition solutions. The Zn(Se,OH) films had a preferred (111) orientation, corresponding to a cubic crystal structure. The bandgap energies of the as-deposited Zn(Se,OH) films were determined from the optical absorption data, suggesting a dependence of the bandgap energies on the atomic percentages of ZnSe, Zn(OH)2 and ZnO in the films. The same variation tendency of the compositions and the bandgap energies for the films, deposited with an increment in the ammonia or selenourea concentrations was achieved, attributing to the facilitation of ZnSe formation. These results show that the compositions, and therefore the bandgap energies, can be controlled by the ammonia concentrations, or selenourea concentrations.

Li doping induced physico-chemical modulations in Cd ferrite (CdLixFe(2−x)O4−x) synthesized using aqueous ammonia assisted co-precipitation route

Abstract: Ammonium hydroxide as a co-precipitating agent has been used in nanofabrication of pure and Li doped Cd ferrites (CdLixFe(2−x)O(4−x); x = 0.0–0.5) using wet chemical route. Various spectroscopic investigations viz. simultaneous thermal analysis (STA), powder X-ray diffraction (XRD), infrared (FT-IR), elemental analysis (ICAP), electron microscopy (SEM, TEM), magnetic measurements (VSM) and Mӧssbauer technique have been employed to ascertain the modulations in structural, magnetic and other microstructural parameters of as-obtained ferrite, thus, establish the formation of single phasic, nanocrystalline, magnetically ordered alloys with novel physico-chemical properties. An increase in Li+ concentration from x = 0.0 to 0.3 inculcates a reduction in the particle size thereby improving electro-magnetic parameters of the doped ferrites. Overall, concentration of the dopant along with the chemical method employed for the synthesis control the size of as-obtained particles and site status within the ferrite lattice structure.

Effect of TS-1 Treatment by Mixed Alkaline on Propylene Epoxidation

Abstract: Titanium silicate-1 (TS-1) was treated with a mixed alkaline of tetrapropyl ammonium hydroxide (TPAOH) and NaOH. It was characterized by XRD, nitrogen physical adsorption, SEM, FT-IR, UV–Vis and ICP-OES, and studied in propylene epoxidation. The mixed alkaline treatment with TPAOH/NaOH solution did not destroy the MFI structure of TS-1. With increasing NaOH concentrations, the relative crystallinity and the framework titanium decreased to some extent while the mesopore volume, mesopore diameter, and extra-framework titanium increased appreciably. When NaOH concentration was 0.0333 mol L−1, the best catalytic performance was obtained.

Applying an activated carbon/silver catalyst to the decomposition of the aqueous solutions of tetramethyl ammonium hydroxide

Abstract: This study applied catalytic (AC/Ag) ozonation combined with hydrogen peroxide (H2O2) to investigate the feasibility of tetramethyl ammonium hydroxide (TMAH) decomposition. The synthesized catalysts were characterized using X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The pH of the isoelectric point of AC/Ag was 10.8. Subsequently, the removal efficiency of the system was examined using operational parameters such as pH condition (3, 5, 7, 9, 11, and 12), AC/Ag dosage (0.5, 1, 1.5, and 2 g/L), and H2O2 (4.4, 8.8, 17.6, and 26.4 mM). The results revealed that the optimal mineralization rate of TMAH was 72% when using the 1.5 g/L AC/Ag catalyst combined with 8.8 mM H2O2 at pH 11. The removal rate of 500 mg/L-TMAH was 81%, and the end products in nitrate and ammonium were 167 mg/L and 102 mg/L, respectively, for a 60 min reaction time. Tert‑butyl alcohol (TBA) was used as an •OH scavenger to assess the contributions of direct and indirect ozonation. The results indicated that indirect ozonation dominated in TMAH mineralization. The calculated krad value of the AC/Ag/H2O2 ozonation method was 1.91 × 10−2 min−1, which was higher than that in the AC/Ag ozonation (1.21 × 10−2 min−1) and sole ozonation (1.70 × 10−3 min−1) methods.