Showing papers on "Ammonium hydroxide published in 2016"

Solubility of Nanocrystalline Cerium Dioxide: Experimental Data and Thermodynamic Modeling

Abstract: Ultrafine 5 nm ceria isotropic nanoparticles were prepared using the rapid chemical precipitation approach from cerium(III) nitrate and ammonium hydroxide aqueous solutions. The as-prepared nanoparticles were shown to contain predominantly Ce(IV) species. The solubility of nanocrystalline CeO2 at several pH values was determined using ICP-MS and radioactive tracer methods. Phase composition of the ceria samples remained unchanged upon partial dissolution, while the shape of the particles changed dramatically, yielding nanorods under neutral pH conditions. According to X-ray absorption spectroscopy investigation of the supernatant, Ce(III) was the main cerium species in solution at pH < 4. Based on the results obtained, a reductive dissolution model was used for data interpretation. According to this model, the solubility product for ceria nanoparticles was determined to be log Ksp = −59.3 ± 0.3 in 0.01 M NaClO4. Taken together, our results show that the pH dependence of ceria anti- and pro-oxidant activit...

Improving the performance of TFC membranes via chelation and surface reaction: applications in water desalination

Abstract: Here we report modification of thin film composite (TFC) membranes via a series of chemical and surface reactions. Initially, the nascent polyamide (PA) active layer was prepared by interfacial polymerization and composited with graphene oxide (GO) nanosheets and then reacted with cupric chloride dihydrate (CuCl2·2H2O). Finally, the composited membrane was treated by a reaction with ammonium hydroxide (NH4OH) solution. The chemical modifications of the PA active layer included the formation of a polyamide–copper–graphene oxide complex (PA–Cu2+–GO), whereas, the surface modifications, mineralization, include the formation of copper hydroxide [Cu(OH)2] on the membrane surface through a reaction between the residual CuCl2·2H2O and NH4OH solution. The results of the compositional analysis of mineralized membranes showed that the active layer is fully cross-linked, with Cu2+ chelated with amide nitrogen and coordinated with the carbonyl groups. The membrane performance was evaluated using a cross-flow apparatus at 2000 mg L−1 NaCl solution, 25 °C and a pressure of 15 bar. The mineralized membrane with optimum concentrations of copper chloride and ammonium hydroxide of 0.125 molar and 0.1%, respectively, and a reaction time of 1 minute showed a higher pure water permeability and solute water flux (44.25, 33.77 L m−2 h−1) compared to the pristine TFC membrane (21.36, 20.2 L m−2 h−1) with an excellent salt rejection (≥98.5%). Moreover, the mineralized membranes were found to resist chlorine attack and fouling adsorption more than the non-treated TFC membrane.

Hierarchical TS-1 synthesized effectively by post-modification with TPAOH and ammonium hydroxide

Abstract: Hierarchical TS-1 with intracrystalline voids could be synthesized by post-modification with tetrapropyl ammonium hydroxide (TPAOH), however the process was supposed to be restrained by the charge balance effect. In order to release the constraint, NH3·H2O was introduced in the post-modification. The influences of the TPAOH/NH3·H2O modification, the TPAOH concentration and the modification time on the physiochemical properties were studied. The dissolution process and recrystallization process were observed in the combined modification, and both of them were intensified by the NH3·H2O introduced, indicating that the constraint on the OH− diffusion was released. Owing to the intensified processes, the TPAOH concentration and post-modification time could be reduced, and hierarchical TS-1 with relative high crystallinity, less defect sites and a larger secondary pore volume (about 0.18 cm3 g−1) was achieved in 4 h. However, the combined-modification exerted little influence on the chemical composition and acidity, and the microporous properties were almost the same with that of TS-1 modified with TPAOH only. The secondary porosity in the combined-modified samples were mainly intracrystalline voids, and grooves on the surface were also found. Although extra-framework titanium species were created by the post-modification, part of the titanium was still in the framework position. The catalytic activity was evaluated by phenol hydroxylation and 1-octene epoxidation, and better catalytic activity was achieved for the improved accessibility of the active sites.

A Simple Way to Produce γ-Alumina From Aluminum Cans by Precipitation Reactions

Abstract: In this paper, a new way for γ-alumina synthesis was proposed, the raw material being aluminum powders obtained by high-energy milling of aluminum cans. This seems a good option for this metal recycling and energy saving, as well as hydrogen production. The materials were prepared by precipitation techniques, in which aluminum powders reacted with hydrochloric acid, giving aluminum chloride, which was subsequently transformed into aluminum hydroxide by reaction with ammonium hydroxide or sodium hydroxide as precipitant agents, and finally into γ-alumina by calcination. Results showed that the used preparation methods gave a γ-alumina structure, confirmed by XRD, with surface areas values (174 and 204 m2 g-1) close to those of a commercial γ-alumina Cyanamid Ketjen (180 m2 g-1) or an alumina prepared by a typical precipitation route (203 m2 g-1). Using sodium hydroxide as precipitant agent turned out to be more ecologically compatible since it did not release harmful environmental compounds.

Carbocatalysis: N-doped reduced graphene oxide catalyzed esterification of fatty acids with long chain alcohols

Abstract: Nitrogen doped reduced graphene oxide (N-rGO), 5.8% N readily synthesized from the thermal annealing of graphene oxide (GO) in ammonium hydroxide at 453 K, was demonstrated to be a superior metal-free non-acidic carbo-catalyst for the esterification of fatty acids with different alcohols. The effect of various reaction parameters such as reaction temperature, reaction time, catalyst amount etc. has been studied. The developed catalyst was found to be highly stable and exhibited consistent reusability for seven cycles without any significant decrease in the product yields.

A gold electrode modified with silver oxide nanoparticle decorated carbon nanotubes for electrochemical sensing of dissolved ammonia

Abstract: We have prepared silver oxide nanoparticles with a diameter of ~ 15 nm and decorated with carbon nanotube nanocomposites (Ag2O/CNT NCs) by a facile wet chemical method using reducing agents in alkaline medium. These NCs were characterized by UV/vis, FTIR and energy dispersive X-ray spectroscopy, by X-ray powder diffraction and field emission scanning electron microscopy. The NCs were then deposited on a flat gold electrode with the help of a conducting binder to result in an electrochemical sensor for aqueous ammonia using the I-V technique. Response is based on surface oxidation of ammonium hydroxide with electrode-adsorbed oxygen to form nitrogen oxide, these simultaneously liberating free electrons in the conduction band. Sensor features include a sensitivity of 32.856 μA.μM‾1.cm‾2, a low detection limit (1.3 pM at a signal to noise ratio of 3), reliability, reproducibility, ease of integration, and long term stability. The response to dissolved ammonia is linear (r2: 0.9778) over the 0.01 nM to 0.1 mM concentration range.

Heterogeneous Catalytic Reductive Amination of Carbonyl Compounds with Ni-Al Alloy in Water as Solvent and Hydrogen Source

Abstract: The heterogeneous catalytic reductive amination of carbonyl compounds has been achieved by reactions of ammonium hydroxide and various amines with ketones and aldehydes. The process is based on the application of Raney type Ni-Al alloy in an aqueous medium. The reaction of the carbonyl compounds with the amine provided the corresponding Schiff bases that immediately underwent a reduction to provide primary and secondary amines as products. The controlled reaction of the Al content of the alloy with the solvent water generates hydrogen, and the in situ formed Raney Ni® serves as a hydrogenation catalyst. The method is a simple and efficient way of preparing a broad variety of primary and secondary amines.

Synthesis and application of magnetite polyacrylamide amino-amidoxime nano-composites as adsorbents for water pollutants

Abstract: In this work, we aimed to develop a feasible method for in situ preparation of a magnetite ionic polymer nanocomposite at room temperature. For this purpose, acrylonitrile (AN) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) monomers were copolymerized and crosslinked using different monomer mol ratios in the presence of N,N-methylenebisacrylamide (MBA) as crosslinker to produce ionic crosslinked polymers P(AN-co-AMPS. The nitrile groups were converted to amine amidoxime by reacting with hydroxylamine to increase the adsorption characteristics of the ionic polymers. The produced polymers were swelled in iron cations produced from the reaction of ferric chloride and potassium iodide, followed by reaction with an ammonium hydroxide solution to produce magnetite nano-polymer composites. We performed FT-IR and XRD analysis to determine the chemical and crystalline structures, and assessed the morphologies and magnetite content using SEM, TEM and TGA analyses. We investigated the adsorption capacity and mechanism of the prepared magnetite nano-composites as adsorbents for methylene blue, Co2+ and Ni2+ cations from water.

Synthesis of Yttria Nanopowders by Two Precipitation Methods and Investigation of Synthesis Conditions

Abstract: Yttrium oxide nanopowder was successfully synthesized by two precipitation methods, through which Y2O3 nanopowder was prepared by ammonium hydroxide and ammonium hydrogen carbonate as precipitants. Hydroxide and carbonate precursors of Y2O3 with approximate composition of Y(OH)3 and Y2(CO3)3, respectively, were synthesized using yttrium nitrate as the starting salt. XRD results show cubic yttrium oxide phase for annealed samples. SEM and TEM images show that samples are composed of agglomerated and nonagglomerated nanoparticles with different shapes and sizes. Optimal conditions for synthesis of nanoparticles were defined as 3-h aging time, ammonium hydrogen carbonate as precipitant, and calcination temperature of 1000°C.

Preparation and evaluation of 3 m open tubular capillary columns with a zwitterionic polymeric porous layer for liquid chromatography.

Abstract: A 3 m zwitterionic polymeric porous layer open tubular column (3 m × 25 μm id × 375 μm od) with a polymeric porous layer thickness of 4 μm was fabricated by the copolymerization of [2-(methacryloyloxy)ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide and N,N'-methylenebis(acrylamide). The effects of the diameter of the capillary, reaction temperature, and polymerization time on the preparation of the open tubular column were investigated. Characterized by scanning electron microscopy, the zwitterionic layer was observed to be rough and throughout the fused-silica capillary homogenously, which increased the phase ratio. The separation of neutral, basic, and acidic compounds demonstrates the strong hydrophilicity of the poly[2-(methacryloyloxy)ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide coating. In addition, the poly[2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide porous layer open tubular column was applied for the analysis of flavonoids from the rootstalk of licorice, revealing the potential in separating complex samples. The relative standard deviation of retention time for run-to-run (n = 5), day-to-day (n = 3), and column-to-column (n = 3) of toluene, N,N-dimethylformamide, formamide, and thiourea were below 1.2%, exhibiting good repeatability.

Sodium hydroxide catalyzed monodispersed high surface area silica nanoparticles.

Abstract: Understanding of the synthesis kinetics and our ability to modulate medium conditions allowed us to generate nanoparticles via an ultra-fast process. The synthesis medium is kept quite simple with tetraethyl orthosilicate (TEOS) as precursor and 50% ethanol and sodium hydroxide catalyst. Synthesis is performed under gentle conditions at 20 °C for 20 min Long synthesis time and catalyst-associated drawbacks are most crucial in silica nanoparticle synthesis. We have addressed both these bottlenecks by replacing the conventional Stober catalyst, ammonium hydroxide, with sodium hydroxide. We have reduced the overall synthesis time from 20 to 1/3 h, ~60-fold decrease, and obtained highly monodispersed nanoparticles with 5-fold higher surface area than Stober particles. We have demonstrated that the developed NPs with ~3-fold higher silane can be used as efficient probes for biosensor applications.

Synthesis and characterization of hematite nanopowders

Abstract: A facile solution approach was employed to synthesize hematite (α-Fe2O3) nanoparticles by using starting precursor iron (III) chloride (FeCl3) and sodium hydroxide (NaOH) as reducing agent without templates at low temperature. The growth and solubility of iron oxide particle was controlled by adjusting the pH of the solution using ammonium hydroxide. As-prepared powders were subsequently calcined in air for 3 h at three different temperatures ranging from 400 to 800 °C. The precursor and the synthesized particles were characterized using TGA-DTA thermal analysis to study the decomposition pattern. X-ray diffraction (XRD) technique confirmed the nanocrystal formation of α-Fe2O3 and Fourier transform infra-red (FTIR) spectral information identified the metal-oxide phase formation. Scanning electron microscope (SEM) was engaged to study the morphology and the purity of the sample was evaluated from the energy dispersive spectrum (EDS). The optical band gap of the particles and its variations with calcination temperature (2.32–2.49 eV) was obtained from the constructed Tauc plot using the optical absorption data. The electrical parameters of the samples were obtained from two probe measuring technique and the effect of temperature on the electrical properties of α-Fe2O3 was discussed.

Removal of NO from flue gas using heat-activated ammonium persulfate aqueous solution in a bubbling reactor

Abstract: Ammonium persulfate aqueous solution was used for the first time for NO removal from flue gas in a bubbling bed due to its low cost compared with other persulfate salts (sodium persulfate, potassium persulfate and ammonium persulfate). The effects of ammonium persulfate concentration, solution temperature, initial pH value, additive concentration, NO concentration, O2 concentration and SO2 concentration on NO removal were investigated systematically. The increased pH had a significant and negative effect on NO removal. The optimal solution temperature was 50 °C and increased ammonium persulfate concentration greatly promoted the NO removal efficiency. Urea showed a better performance on NO removal efficiency than ammonium hydroxide. The NO concentration and O2 concentration affected NO removal slightly while the increased SO2 concentration weakened NO removal efficiency. NO generation in alkaline ammonium persulfate aqueous solution was detected. The detection of free radicals in ammonium persulfate solution using the HPLC method and the effect of O2 concentration on NO generation was carried out with the initial pH value increased. Due to the reducibility of ammonia, the solution pH and O2 concentration in the flue gas were proven to play a major role in NO generation using ammonium persulfate. The NO generation mechanism and the possible reactions in the aqueous solution were elucidated and speculated. The experimental results indicated that the proposed technology using heat-activated ammonia persulfate in acidic aqueous solution might be a feasible method for the NO removal from flue gas.

Non-aqueous organo liquid delivery systems containing dispersed poly (organic acids) that improve availability of macro & micro-nutrients to plants

Abstract: The present invention relates to improving the efficiency of man-made and/or natural organic-based animal manure fertilizers by administration of formulations containing poly(organic acids), [P(OA)]s, and/or their salts dispersed in a Non-aqueous Organic Solvent Delivery System (NOSDS). Utilizing a NOSDS allows for coating all components in a fertilizer formulation including but not limited to Urea, Manure, mono-ammonium phosphate (MAP), di-ammonium phosphate (DAP), solid micronutrients such as lime, zinc chloride, etc.) with a layer of [P(OA)]s and/or their salts that liberates, in a plant available form, the micronutrient metals and macronutrients, that are bound as insoluble salts and complexes in the soil. The carboxylic groups of a [P(OA)] that can exist within the [P(OA)] as carboxylic acids, carboxylic anhydrides and/or carboxylic imides, dispersed within the NOSDS, can be neutralized with one or more metals in the form of elemental metals, metal oxides, metal hydroxides, metal alkylates and metal carbonates and/or nitrogen containing compounds such as ammonia, ammonium hydroxide or organoamines to form a stable dispersion that can contain completely complexed micronutrients and provide the vehicle for the delivery of these nutrients to soils and/or as a coating to the surfaces fertilizer granules and seeds.

Optimizing Both Catalyst Preparation and Catalytic Behaviour for the Oxidative Dehydrogenation of Ethane of Ni–Sn–O Catalysts

Abstract: Bulk Ni–Sn–O catalysts have been synthesized, tested in the oxidative dehydrogenation of ethane and characterized by several physicochemical techniques. The catalysts have been prepared by evaporation of the corresponding salts using several additives in the synthesis gel, i.e. ammonium hydroxide, nitric acid, glyoxylic acid or oxalic acid, in the synthesis gel. The catalysts were finally calcined at 500 °C in air. Important changes in the catalytic behaviour have been observed depending on the additive. In fact, an important improvement in the catalytic performance is observed especially when some additives, such as glyoxylic or oxalic acid, are used. Thus the productivity to ethylene multiplies by 6 compared to the reference Ni–Sn–O catalyst if appropriate templates are used, and this is the result of an improvement in both the catalytic activity and the selectivity to ethylene. This improved performance has been explained in terms of the decrease of the crystallite size (and the increase in the surface area of catalyst) as well as the modification of the lattice parameter of nickel oxide.

Influence of the pH of the synthesis using sol-gel method on the structural and optical properties of TiO2

Abstract: The photocatalysis process using semiconductor materials, in particular TiO2, is one of the most attractive treatment for polluted waters decontamination because of its advantages over other oxidation processes [1-6]. In this study the effect on the physical properties of TiO2 due to the pH used during the manufacturing of the semiconductor is studied. Different samples were synthesized using ammonium hydroxide (NH4OH) and nitric acid (HNO3) as catalysts to provide basic and acid pH environments, respectively. Changes in composition, structure and morphology of the samples were studied and its dependence with the pH of the synthesis is discussed. Results indicate that the base catalysis favours the formation of anatase TiO2 crystalline phase with crystallite size ~ 26nm obtained by Rietveld refinement; the spherical particles formed agglomerates of ~100nm; the average pore size is in the range of mesopores and the surface area increases with the amount of NH4OH added in the process. On the other hand, with acid catalysis, a mixture of two crystalline phases, anatase and rutile, was obtained with crystallite sizes around 26 and 49nm, respectively. The grain size is several orders of magnitude higher than those obtained by basic catalysis. The photocatalytic activity was measured using methylene blue solutions to determine their degradation with radiation. Greater efficiency was observed in the photocatalysts synthesized with NH4OH.

Role of Ammonium Ions in the Formation of Ammonium Uranyl Peroxides and Uranyl Peroxo-oxalates

Abstract: The flexibility of the ammonium ion environment is suitable for inducing the formation of several uranyl peroxides and peroxo-oxalates. For a given concentration of uranium and various oxalate/uranium ratios, by varying the pH with ammonium hydroxide, crystals of eight compounds have been isolated and characterized by X-ray diffraction, in addition to the studtite (UO2)(O2)·4H2O. All the compounds contain anionic uranyl polyhedra clusters with charge compensated by ammonium ions. Three are uranyl peroxides built from uranyl hexagonal bipyramids [(UO2)(O2)3]4– or [(UO2)(O2)2(OH)2]4– sharing peroxide or dihydroxyl equatorial edges to form cage clusters [(UO2)28(O2)42]28– (U28) and [(UO2)44(O2)66]44– (U44) in 7 and 3 respectively, or crown-shaped cluster [(UO2)32(O2(OH)2)52]40– (U32R) in 2. In these uranyl peroxides the pentagonal and hexagonal uranyl polyhedra rings are stabilized by ammonium ions. The other five compounds are uranyl peroxo-oxalates with various condensations of uranyl hexagonal bipyramids:...

Synthesis of Iron Oxide Nanoparticles Using Isobutanol

Abstract: Iron oxide nanoparticles were synthesized by precipitation in isobutanol with sodium hydroxide and ammonium hydroxide. The isobutanol played a role of a surfactant in the synthesis. The nanoparticles were calcined for 100 min to 5 hours in the range of 300 to 600°C. The characterization of the samples by FTIR (Fourier-transform infrared) and XRD (X-ray diffraction) confirmed the formation of ź-Fe2O3 (maghemite) from Fe3O4 (magnetite) at calcination at 300°C. The morphology and particle size were studied by SEM (scanning electron microscope). Nanoparticles in the range of 11ź22 nm prepared at 0.09 M of ferrous chloride exhibited superparamagnetic properties. Nanoparticles synthesized with ferrous chloride and ammonium hydroxide at 75°C and calcined at 530°C for 2 h were ź-Fe2O3 (hematite).