Showing papers on "Ammonium hydroxide published in 2019"

Chaotropic Effects in Sub/Supercritical Fluid Chromatography via Ammonium Hydroxide in Water-Rich Modifiers: Enabling Separation of Peptides and Highly Polar Pharmaceuticals at the Preparative Scale

Abstract: Chromatographic separation, analysis and characterization of complex highly polar analyte mixtures can often be very challenging using conventional separation approaches. Analysis and purification of hydrophilic compounds have been dominated by liquid chromatography (LC) and ion-exchange chromatography (IC), with sub/supercritical fluid chromatography (SFC) moving toward these new applications beyond traditional chiral separations. However, the low polarity of supercritical carbon dioxide (CO2) has limited the use of SFC for separation and purification in the bioanalytical space, especially at the preparative scale. Reaction mixtures of highly polar species are strongly retained even using polar additives in alcohol modifier/CO2 based eluents. Herein, we overcome these problems by introducing chaotropic effects in SFC separations using a nontraditional mobile phase mixture consisting of ammonium hydroxide combined with high water concentration in the alcohol modifier and carbon dioxide. The separation mechanism was here elucidated based on extensive IC-CD (IC couple to conductivity detection) analysis of cyclic peptides subjected to the SFC conditions, indicating the in situ formation of a bicarbonate counterion (HCO3-). In contrast to other salts, HCO3- was found to play a crucial role acting as a chaotropic agent that disrupts undesired H-bonding interactions, which was demonstrated by size-exclusion chromatography coupled with differential hydrogen-deuterium exchange-mass spectrometry experiments (SEC-HDX-MS). In addition, the use of NH4OH in water-rich MeOH modifiers was compared to other commonly used basic additives (diethylamine, triethylamine, and isobutylamine) showing unmatched chromatographic and MS detection performance in terms of peak shape, retention, selectivity, and ionization as well as a completely different selectivity and retention behavior. Moreover, relative to ammonium formate and ammonium acetate in water-rich methanol modifier, the ammonium hydroxide in water additive showed better chromatographic performance with enhanced sensitivity. Further optimization of NH4OH and H2O levels in conjunction with MeOH/CO2 served to furnish a generic modifier (0.2% NH4OH, 5% H2O in MeOH) that enables the widespread transition of SFC to domains that were previously considered out of its scope. This approach is extensively applied to the separation, analysis, and purification of multicomponent reaction mixtures of closely related polar pharmaceuticals using readily available SFC instrumentation. The examples described here cover a broad spectrum of bioanalytical and pharmaceutical applications including analytical and preparative chromatography of organohalogenated species, nucleobases, nucleosides, nucleotides, sulfonamides, and cyclic peptides among other highly polar species.

Nano-architecture of highly sensitive SnO2–based gas sensors for acetone and ammonia using molecular imprinting technique

Abstract: This article presents the nano-architecturing of highly sensitive SnO2–based gas sensors prepared by molecular imprinting technique with the presence of acetone and/or ammonia solvents to develop a sensor that has the ability to detect both gases which is being developed for the first time. Nanoparticles are prepared via hydrothermal method and then they have been characterized by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and N2 adsorption-desorption analyzer (BET) to determine their morphology, crystal structure, optical properties and surface area properties respectively. Four SnO2 films are fabricated using spin coating under different conditions of introducing ammonium hydroxide or acetone during the hydrothermal synthesis. Regular microsheets of about 5 μm in length and 500 nm thickness have been built up from nanoparticles of sizes ranged from 20 to 50 nm depending on the preparation conditions. The sensing properties of the fabricated sensors are tested against (ammonium hydroxide, acetone, LPG, oxygen and benzene), where the results showed that when the participation of the solvent during the synthesis process, it increases the response for these gaseous. The performance of the gas sensor devices is demonstrated and got higher values (about 90%) for Ammonia gas when the device is template with ammonium hydroxide and water and washed with water (SD) and limit of detection (600 ppb). Also, high sensitivity (about 77%) for Acetone is recorded for the device is template with ammonium hydroxide and acetone and washed with acetone (SA) and limit of detection (280 ppb).

Optimization of magnesium recovery from reject brine for reuse in desalination post-treatment

Abstract: In this work, the recovery of magnesium from desalination reject brine through reaction with ammonia has been evaluated and statistically optimized using response surface methodology. The process is based on precipitation of magnesium hydroxide by the reaction of MgCO3 in the brine with ammonium hydroxide. A software, which is designed for studying chemical reaction and equilibrium, was employed to perform the thermodynamic analysis of the reaction of magnesium carbonate with ammonia, which was found to be exothermic and spontaneous in the temperature range of 0–22 °C. Central composite design (5-level, 3-factor) was used to optimize the process to obtain the maximum response of magnesium recovery as a function of reaction temperature, brine salinity, and ammonia to magnesium molar ratio. Maximum recovery of 99% was obtained at a temperature of 15 °C, brine salinity of 85 g/L, and a molar ratio of 4.4NH3: 1 Mg. The predicted response was in excellent agreement with the experimental results. The collected solid product at optimum conditions was characterized using X-ray Diffraction, Energy Dispersive Spectra analysis and thermogravimetric analysis. The analysis indicated the high purity of the recovered product in the form of Brucite (Mg(OH)2).

The effects of precipitants on co-precipitation synthesis of yttria-stabilized zirconia nanocrystalline powders

Abstract: Yttrium-stabilized zirconia (Y0.08Zr0.92O1.96, YSZ) nanocrystalline powders were prepared by co-precipitation methods. Different precipitants (ammonium hydroxide, ammonium bicarbonate, oxalic acid, and urea) were used to study the effects of precipitants on co-precipitation synthesis of YSZ nanocrystalline powders. Thermogravimetric analysis-differential scanning calorimetry, powder X-ray diffraction, Fourier-transform infrared, scanning electron microscope, energy-dispersive spectrometer, Brunauer–Emmett–Teller, Barrett–Joyner–Halenda, and X-ray photoelectron spectroscopy analysis methods were employed to investigate the thermal decompositions, phase evolutions, micro-morphologies, surface areas, and elements analysis of the synthesized YSZ precursor powders or nanoparticles. Although different precipitants were used, the calcined products at 600 °C have nearly identical chemical compositions. The crystallization temperature of the precursor powders to evolve to cubic phase is the lowest (about 400 °C) when ammonium hydroxide is used as a precipitant, while it is about 500 °C in the case of other three types of precipitants (ammonium bicarbonate, oxalic acid, and urea) that were used. Ammonium bicarbonate cannot precipitate ZrO2+ effectively in the solution, resulting in the formation of cubic Y0.18Zr0.82O1.91 at 1000 °C. Despite the time-consuming co-precipitation process, urea was proved to be the optimal precipitant in terms of the fabrication of nanocrystalline YSZ powders with designed Y/Zr/O molar ratio, large surface area, small crystallite size, and well dispersion.

Structural, optical, electrical and morphological properties of CdS films deposited by CBD varying the complexing agent concentration

Abstract: CdS thin films were deposited on commercial glass substrates by CBD technique at constant temperature and deposition time of 90 °C and 50 min, respectively. The reaction was performed by mixing cadmium acetate, ammonium acetate, ammonium hydroxide, thiourea, and deionized water as an aqueous medium. The S/Cd ratio in the solution was kept constant at 4.46 to make sure that the films were as stoichiometric as possible. Optical, electrical, structural properties and the presence of organic compounds in the films were studied modifying the concentration of ammonium hydroxide (complexing agent) in the bath solution. X-ray diffraction patterns show that all films have the cubic phase with a preferential orientation in the plane (1 1 1). An increase of the film’s resistivity from 102 to 107 Ω-cm is observed by increasing the ammonium hydroxide concentration in the solution in the narrow interval of 0.18–0.36 M. Transmittance values up to 70% are obtained at the lowest concentrations of this reagent, obtaining from these spectra the highest value of the direct bandgap, 2.37 eV. Results about the presence of organic compounds and their influence on the photoluminescence properties are shown, which have not been reported to date. The main organic compound identified by FTIR is cyanamide, whose concentration is higher at the lowest ammonium hydroxide concentrations. Photoluminescence spectra of the films show green, red and orange bands, located at 2.27 eV, 1.78 eV, and 2.02 eV, respectively. An additional band was observed with low intensity at 2.99 eV associated with the presence of nanoparticles in some films. The films with the lower presence of defects, higher uniformity and best optical, electrical and structural properties for their use as window material in solar cells are those deposited from a bath solution with a 0.24 M concentration of the complexing agent.

Co-precipitation synthesis of magnetic nanoparticles for efficient removal of heavy metal from synthetic wastewater

Abstract: The emergence of magnetic nanoparticles (MNP) has proven to be useful as a tool or catalyst in many industrial usages such as in biomedical, drug delivery, catalysis, and the environment. Due to its size, MNP has a greater surface area compared to larger particles that makes it more reactive to some other molecules. The highlight of this study is to focus on the usage of MNP on the environmental issue, which related to the discharging of the heavy metal from industrial effluents. Conventionally, the removal of heavy metals from the wastewater stream is by using chemical reactions, electrodialysis, and membrane separation. However, the drawback is expensive due to energy consumption and membrane fouling as well as resulting in the generation of toxic byproducts. Therefore, the aim of this study is to synthesis MNP with a smaller size to entrap heavy metal ions to a complex, thus easily removed by a magnetic drive. The MNP was synthesized using different factors such as temperature (25°C, 50°C, 70°C) and bases (sodium hydroxide; NaOH, potassium hydroxide; KOH, ammonium hydroxide; NH4OH), added into a solution containing iron(II) and iron(III) to obtain different size and morphology. The efficiency of MNP removal was tested on solution containing Cr, Ni and Cu then analyzed using Atomic Adsorption Spectroscopy (AAS). The characterization of the MNP was done using transmission electron microscopy (TEM), Fourier Transform Infrared spectroscopy (FTIR) and X-ray Diffraction (XRD). From the result, 90% of the Cr removal is found to be with the MNP that been synthesized with NH4OH at 70°C. Due to the smallest size (9nm) of the MNP, thus adsorbing more Cr ions. As a conclusion the strong base gives the MNP of lowest dispersion and addition of surfactant provide less adsorption of heavy metal, however stronger resistance to oxidation. This work has provided an insight into the feasibility of the MNP as an alternative method to heavy metal ion removal.

Effect of Carbonate Anions on Quaternary Ammonium-Hydroxide Interaction

Abstract: Currently, there are two main challenges in state-of-the-art anion-exchange membrane fuel cells (AEMFCs)—first, cation degradation in the presence of hydroxide anions; second, carbonation process d...

Valorization of Carbohydrates of Agricultural Residues and Food Wastes: A Key Strategy for Carbon Conservation

Abstract: The complete conservation of the carbon, hydrogen, and oxygen atoms of cellulose and starch can theoretically be achieved by their conversion to levulinic and formic acids. Similarly, hemicellulose can be converted to furfural and water with 100% atom economy. The valorization of carbohydrates of agricultural residues (banana-, orange-, and potato-peels, corn leaf and root, and rice husk), potential components of raw food wastes (corn, rice, potato, lettuce, onion, leek, vegetable, bean, and tomato), and cooked food wastes (rice noodle, spaghetti, risotto, noodle, bread, and biscuit) was demonstrated in the presence of sulfuric acid at 130 °C in γ-valerolactone as the green solvent to yield levulinic and formic acids as the two main products. Levulinic acid was also produced from furfural by its transfer hydrogenation with formic acid to furfuryl alcohol in the presence of Shvo’s catalyst followed by its acid catalyzed conversion to levulinic acid. Neutralization of the sulfuric acid in the reaction mixture with ammonium hydroxide resulted in an aqueous ammonium sulfate phase and a γ-valerolactone rich organic phase. Due to the salting out effect of the ammonium sulfate in the aqueous phase, levulinic acid and formic acid partitioned to the γ-valerolactone rich organic phase at >99.8% and >97.1%, respectively. The transfer hydrogenation of levulinic acid with formic acid in the presence of the Shvo’s catalyst resulted in the formation of 4-hydroxyvaleric acid, which readily underwent dehydration to yield γ-valerolactone, a green and sustainable liquid. The possibility of converting C₅- and C₆-carbohydrates to levulinic acid or γ-valerolactone is a great opportunity for carbon conservation with a carbon-economy higher than that for butanol or ethanol.

Synthesis of Zwitterionic Copolymers via Copper-Mediated Aqueous Living Radical Grafting Polymerization on Starch

Abstract: [2-(Methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA) is a well-studied sulfobetaine-methacrylate as its zwitterionic structure allows the synthesis of polymers with attractive properties like antifouling and anti-polyelectrolyte behavior. In the present work, we report the Cu0-mediated living radical polymerization (Cu0-mediated LRP) of SBMA in sodium nitrate aqueous solution instead of previously reported solvents like trifluoroethanol and sodium chloride aqueous/alcoholic solution. Based on this, starch-g-polySBMA (St-g-PSBMA) was also synthesized homogeneously by using a water-soluble waxy potato starch-based macroinitiator and CuBr/hexamethylated tris(2-aminoethyl)amine (Me6TREN) as the catalyst. The structure of the macroinitiator was characterized by 1H-NMR, 13C-NMR, gHSQC, and FT-IR, while samples of PSBMA and St-g-PSBMA were characterized by 1H-NMR and FT-IR. Monomer conversion was monitored by 1H-NMR, on the basis of which the reaction kinetics were determined. Both kinetic study and GPC results indicate reasonable controlled polymerization. Furthermore, a preliminary study of the thermal response behavior was also carried through rheological tests performed on aqueous solutions of the prepared materials. Results show that branched zwitterionic polymers are more thermal-sensitive than linear ones.

Formation Features of Hybrid Nanocomposites Based on Polydiphenylamine-2-Carboxylic Acid and Single-Walled Carbon Nanotubes.

Abstract: Hybrid nanocomposites based on electroactive polydiphenylamine-2-carboxylic acid (PDPAC) and single-walled carbon nanotubes (SWCNTs) were obtained for the first time. Polymer-carbon nanomaterials were synthesized via in situ oxidative polymerization of diphenylamine-2-carboxylic acid (DPAC) in the presence of SWCNTs by two different ways. Hybrid SWCNT/PDPAC nanocomposites were prepared both in an acidic medium and in the heterophase system in an alkaline medium. In the heterophase system, the monomer and the SWCNTs are in the organic phase (chloroform) and the oxidant (ammonium persulfate) is in an aqueous solution of ammonium hydroxide. The chemical structure, as well as the electrical and thermal properties of the developed SWCNT/PDPAC nanocomposite materials were investigated.

Elucidation of the Relationship between Intrinsic Viscosity and Molecular Weight of Cellulose Dissolved in Tetra-N-Butyl Ammonium Hydroxide/Dimethyl Sulfoxide.

Abstract: The determination of molecular weight of natural cellulose remains a challenge nowadays, due to the difficulty in dissolving cellulose. In this work, tetra-n-butylammonium hydroxide (TBAH) and dimethyl sulfoxide (DMSO) aqueous solution (THDS) were used to dissolve cellulose in a few minutes under room temperature into true molecular solutions. That is to say, the cellulose was dissolved in the solution in molecular level, and the viscosity of the solution is linearly dependent on the concentration of cellulose. The relationship between the molecular weight of cellulose and the intrinsic viscosity tested in such dilute solutions has been established in the form of the Mark-Houwink equation, η=0.24×DP1.21. The value of 1.21 indicates that the cellulose molecules dissolve in THDS quite well. The cellulose dispersion in the THDS was proved to be in molecular level by atomic force microscope (AFM) and dynamic light scattering (DLS). The reliability of the established Mark-Houwink equation was cross-checked by the gel permeation chromatography (GPC) and traditional copper (II) ethylenediamine (CED) method. No considerate degradation was observed by comparing the intrinsic viscosity and the degree of polymerization (DP) values of the original with and the regenerated cellulose samples. The natural cellulose can be molecularly dispersed in the multiple-component solvent (THDS), and kept stable for a certain period. A time efficient and reliable method has been supplied for determination of the degree of polymerization and the molecular weight of cellulose.

Improved catalytic performance of mesoporous ZSM-5 nanocrystalline zeolite prepared by the cationic surfactant-ammonium salt mixed agent method in the methanol to gasoline reaction

Abstract: A mixed organic agent system was employed to achieve mesoporous highly crystalline ZSM-5 zeolite. Decyltrimethylammonium bromide (DeTAB) and tetramethyl ammonium hydroxide (TMAOH) were used as the mesogenous and molecular templates respectively in the synthesis gel with a composition of 60SiO2: 1Al2O3:12Na2O:3150H2O:xDeTAB:8TMAOH. The sole presence of DeTAB as the mesogenous template in the synthesis gel led to the high degrees of mesoporosity in the ZSM-5/xD samples but negatively affected the intrinsic properties of zeolites. At the high concentration of DeTAB (x = 0.7), the mesopore volume dramatically increased while the relative crystallinity and the total acid sites critically decreased. By adding the TMA+ ions as a microporous template to the ZSM-5/0.7D synthesis gel, not only a zeolite with well-developed mesoporosity was obtained but also its crystal structure and the intrinsic acidity were preserved. The catalyst samples were characterized by FESEM, TEM, XRD, FT-IR, nitrogen adsorption–desorption isotherms, NH3-TPD and TGA techniques. The ZSM-5/0.7D/T exhibited higher surface area, higher mesopore volume, higher crystallinity and more acid sites than the ZSM-5/0.7D. The catalytic conversion of methanol to gasoline was conducted in a fixed bed reactor at T = 390 °C and WHSV = 4.74 h−1. In ZSM-5/0.7D/T catalyst the mesoporosity formation without severely damaging the crystal structure and the acidity of the zeolite led to the best catalytic performance including the highest liquid hydrocarbon yield, most stable catalytic performance and longest catalytic lifetime.

Separation of Ce, La and Nd in Rare Earth Hydroxide (REOH) by Oxidation with Potassium Permanganate and Precipitation

Abstract: The present work describes the development of an efficient and relatively simple process to obtain high grade Ce(OH)4 from REOH (Rare earth hydroxide). The Rare earth hydroxide was obtained through base digestion of monazite. The steps investigated in the process for obtaining Ce(OH)4 were: (i) i) dissolution RE hydroxide (REOH) with HNO3 and oxidation of ce+3 to ce-4 , (ii) selective precipitation of Ce(OH)4 with Na2CO3, (i i i) selective precipitation of Nd(OH)3 with ammonium hydroxide (iv} precipitation of La with oxalic acid. The main variables affecting the cerium oxidation were: the ratio of the K MnO4 /REOH, temperature and oxidation time. A ratio of 1 .25110 of KMnO4 I R EOH was necessary for full cerium recovery. The recovery of cerium increases as temperature and oxidation time rises, the purity of the product Ce(OH)4 at the pH above 4. The process conditions were achieved in the use of 1.25/ I 0, KMnO4/REOH ratio, at the 1 20°C and the oxidation time of 75 minutes. The composition of the final product Ce(OH)4 was 97.98 wt.% Ce(OH)4, i n a process yielding a recovery of Ce greater than 93%, were obtained. The composition of the final product Nd(OH)3 was 37 wt.% Nd(OH)3, in a process yielding a recovery of Nd greater than 98%, were obtained. The composit ion of the final prod uct La2(C2O4)3 was 90 wt.% La2(C2O4)3, in a process yielding a recovery of La greater than 93%. were obtained. The oxidation of Ce3+ to Ce4 ' using KMnO4 follows first order reaction. The value of reaction rate constant of Ce was 0.0291 minutes.

Ammonium Hydroxide Mediated Hydrothermal Crystallization of Hydroxyapatite Coatings on Titanium Substrate

Abstract: Controlled growth of hydroxyapatite (HAp) coatings on titanium substrate plays an important role in the fabrication of the composites for bone tissue engineering. We describe the synthesis of the crystalline hydroxyapatite coatings on the Ti/TiO2 substrate through a hydrothermal method by using ethylenediamine tetraacetic acid disodium salt (Na2EDTA) and varying concentrations of ammonium hydroxide (NH4OH) in calcium-phosphate precursor solution. Na2EDTA serves as a chelating agent, while NH4OH is used as an alkaline source and crystal growth modifier. We characterized the HAp coatings using x-ray diffraction, scanning electron microscopy, and Raman spectroscopy. We also performed the elemental chemical analysis by means of a particle induced x–ray emission method. Our results show that there is a pH limit for which the hydrothermal deposition of HAp on titanium occurs. Moreover, we observed that NH4OH had a measurable influence on the coating thickness as well as on the size and shape of the HAp crystals. We found that with the increase of NH4OH concentration, the thickness of the Hap layer increases and its morphology changes from irregular flakes to well-defined hexagonal rods.

Preparation, characterization, and in vitro antioxidant activity of pH-sensitive resveratrol microcapsule in simulated intestinal fluids

Abstract: Shellac resin ammonium salts (SRAS) were prepared from the natural product of shellac resin and ammonium hydroxide by amidation. Resveratrol (RES) was embedded with SRAS to improve its ther...

Optimization of selective copper extraction from chalcopyrite concentrate in presence of ammonium persulfate and ammonium hydroxide

Abstract: The dissolution of copper and iron from chalcopyrite concentrate in the presence of ammonium persulfate (APS) and ammonium hydroxide was investigated under atmospheric leaching conditions. Experiments were designed by central composite design (CCD). Under the optimum leaching conditions ((NH4)2S2O8 concentration = 328 g/L; NH4OH addition = 16vol%; leaching temperature = 321 K (48°C); leaching time = 120 min; liquid-to-solid ratio = 16; stirring speed = 400 r/min), selective leaching was achieved. 98.14% of the copper was leached, whereas iron did not pass into the solution. X-ray diffraction analysis of the leaching residue showed that iron compounds were predominant. Given the leaching results, the fact that the leaching process does not include uneconomical leaching stages such as extended milling/mechanical activation or high pressures/temperatures, and the low copper dissolution conditions, the attained selective leaching yield may be remarkable.