Aqueous NH Research Articles

Geophysical Investigations of Habitability in Ice‐Covered Ocean Worlds

AbstractGeophysical measurements can reveal the structures and thermal states of icy ocean worlds. The interior density, temperature, sound speed, and electrical conductivity thus characterize their habitability. We explore the variability and correlation of these parameters using 1‐D internal structure models. We invoke thermodynamic consistency using available thermodynamics of aqueous MgSO4, NaCl (as seawater), and NH3; pure water ice phases I, II, III, V, and VI; silicates; and any metallic core that may be present. Model results suggest, for Europa, that combinations of geophysical parameters might be used to distinguish an oxidized ocean dominated by MgSO4 from a more reduced ocean dominated by NaCl. In contrast with Jupiter's icy ocean moons, Titan and Enceladus have low‐density rocky interiors, with minimal or no metallic core. The low‐density rocky core of Enceladus may comprise hydrated minerals or anhydrous minerals with high porosity. Cassini gravity data for Titan indicate a high tidal potential Love number (k2>0.6), which requires a dense internal ocean (ρocean>1,200 kg m−3) and icy lithosphere thinner than 100 km. In that case, Titan may have little or no high‐pressure ice, or a surprisingly deep water‐rock interface more than 500 km below the surface, covered only by ice VI. Ganymede's water‐rock interface is the deepest among known ocean worlds, at around 800 km. Its ocean may contain multiple phases of high‐pressure ice, which will become buoyant if the ocean is sufficiently salty. Callisto's interior structure may be intermediate to those of Titan and Europa, with a water‐rock interface 250 km below the surface covered by ice V but not ice VI.

Upper-Bound Efficiency of Spray Towers To Capture CO2 Using Polydispersed NH3 Droplets

Chemical absorption of CO2 with aqueous NH3 was numerically analyzed in an Eulerian manner for steady 1D spray towers in which gas velocity and liquid flow were uniform, and the results were formulated into a universal correlation. The capture efficiency η predicted by the proposed correlation is a sort of upper bound, and can be used as a base to evaluate the optimality of each design. Drop-size poly dispersity was considered; a spray of poly dispersed droplets was found to be equivalent in η to a spray of monodispersed droplets of an equivalent diameter, and a general formula for the equivalent size was attained in terms of mean size and geometric standard deviation. Total mass transfer coefficient was linearly proportional to the gas–liquid flow rate ratio, and the efficiency correlation agreed well with published results.

Experimental study and rate-based modeling on combined CO2 and SO2 absorption using aqueous NH3 in packed column

Combined CO2 and SO2 absorption performance in a new combined capture process was evaluated in this work by experimental study using a lab-scale packed column system and a developed rate-based model in Aspen Plus. The combined absorption experiments were carried out to identify the impact of several key operating parameters, including flue gas SO2 and CO2 concentrations, CO2 and SO2 loadings, the absorption temperature, and the L/G ratio, on CO2 absorption and NH3 volatilization. Experimental results indicated that ≥85% CO2 absorption efficiency was achieved in 5wt% aqueous NH3 solvent containing lean CO2 loading at 0.2mol CO2/mol NH3 (C/N) and SO2 loading at 0.1mol SO2/mol NH3 (S/N). The rate-based model was developed using the electrolyte-NRTL method and the RateFrac module in Aspen Plus, and validated as compared to the present experimental results. The modeling results showed that the SO2 loading provided the similar effect on the CO2 mass transfer, the absorption efficiency and the heat of CO2 absorption as compared to the CO2 loading, however, the SO2 loading resulted in lower NH3 volatilization compared to CO2 loading. The lean CO2 loading and the solvent flow rate dynamic adjustment approaches in association with the lean NH3 solvent splitting process were studied to analyze the potential coordination of the combined absorption process and the sulfite treatment system. Maintaining 85% CO2 capture efficiency was possible when SO2 loading was increased from 0.1 to 0.2S/N by reducing the lean CO2 loading from 0.2 to 0.088C/N or increasing the solvent flow rate from 8 to 14.1L/h. The time window for the SO2 treatment by the precipitation process was increased with the increasing split ratio of the lean NH3 solvent splitting process that was associated with the dynamic adjustment approaches. In the present study, the discussion of the combined absorption experiments using the CO2 and SO2 loaded NH3 solvent, the developed rate-based model, and the operation strategies provided valuable contributions to the advancement of the combined CO2 and SO2 capture process.

Process development for selective precipitation of valuable metals and simultaneous synthesis of single-phase spinel ferrites from saprolite-limonite laterite leach liquors

To comprehensively utilize the laterite resources, the present study focused on the selective recovery of valuable metals Ni, Co or Al, Cr, and concurrent synthesis of spinel ferrites from saprolite-limonite laterite leach liquors by a one-step selective precipitation method. The precipitation behaviors were investigated in detail, as were factors such as precipitant reagent, pH value, precipitation method, and initial metal ion concentration. In optimal conditions, about 93.0% Ni and 92.0% Co could be enriched in the filtrate by using ammonia (aqueous NH3) solution as precipitant reagent while the recoveries of Al and Cr were 92.0% and 90.0% by using sodium hydroxide (NaOH) solution. After the separation and selective precipitation processes, the precipitates were utilized to synthesize spinel ferrites and the effects of saprolite to limonite laterite mass ratio (MS/L) and calcination temperature on the product purity are discussed. Single phase multi-metal doped magnesium ferrites with high purity could be synthesized when the precipitates were obtained using MS/L ratio of 9:1 and 7:3 by using aqueous NH3 and NaOH solutions as precipitant reagents, and then calcined at 1000°C for 2h, respectively. The overall metal recoveries from laterite blends using aqueous NH3 and NaOH precipitant reagents were 89.2% and 85.4%, respectively.

Activation and Utilization of CO2 Using Ionic Liquid or Amine-Functionalized Basic Nanocrystalline Zeolites for the Synthesis of Cyclic Carbonates and Quinazoline-2,4(1H,3H)-dione

CO2 was activated and used as a reactant for the preparation of cyclic carbonates and quinazoline-2,4(1H,3H)-dione using functionalized basic nanocrystalline zeolite Nano-ZSM-5 as catalysts. Nano-ZSM-5 was treated with aqueous NH3 solution to prepare basic Nano-ZSM-5. The surface basicity of the basic Nano-ZSM-5 was systematically varied by the surface modification with various amines and basic ionic liquids. Powder X-ray diffraction, N2 adsorption–desorption, scanning/transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, 29Si and 13C cross polarized-magic angle spin NMR, elemental analysis, and temperature-programmed desorption techniques were used to characterize the materials. Kinetic (rate constant, activation energy) and thermodynamic parameters (change in enthalpy, free energy, and entropy) were calculated for the cycloaddition reaction of CO2 to epichlorohydrin and 2-aminobenzonitrile by varying the reaction parameters. Basic Nano-ZSM-5 functionalize...

Modeling Solid-liquid Equilibrium of the NH3-CO2-SO2-K2SO4-H2O System and Its Application to Combined Capture of CO2 and SO2 Using Aqueous Ammonia

It is of significance to intensively investigate the solid-liquid equilibrium of the NH3-CO2-SO2-K2SO4-H2O system to assess the novel aqueous NH3 based CO2 and SO2 combined capture process proposed in our previous work. In this work, the solubility of K2SO4 in aqueous NH3 at various temperatures, CO2 and SO2 loadings, and NH3 concentrations was predicted using Aspen Plus with a developed thermodynamic model package, which can accurately simulate the vapor-liquid equilibrium and the solid-liquid equilibrium of the combined CO2 and SO2 capture system. The results indicate that the solubility of K2SO4 increases with temperature and CO2 loading, but decreases with NH3 concentration. The precipitation starting point of K2SO4 shift to higher temperature with the increasing of SO2 loading and NH3 concentration. It is favorable to collect K2SO4 precipitates at lower CO2 loading and temperature, and higher SO2 loading and NH3 concentration.

In Ukrainian

Novel neutron capture agents for the boron and gadolinium neutron capture therapy magnetic nanostructures have been created. The magnetic nanocomposites obtained could be applied as carriers for targeted delivery of 157 Gd and 10 В in order to their retention in tissues. Such materials can find an application in neutron capture therapy of cancer and multimodal Т 1 /Т 2 MRI. The aim of research is the synthesis of B- and Gd-containing nanomaterials perspective for application in neutron capture therapy of cancer and MRI. All reagents were of analytical grade and used without further purification. Demineralized water was used for preparation of all sample solutions. Starch, sodium thiosulfate, 0.1 N iodine solution in water, Phosphate buffer (рН 7.2), DMSO, ethanol, FeCl 3 ×6H 2 O, FeSO 4 ×7H 2 O, Gd(NO 3 ) 3 ×6H 2 O, and aqueous NH 4 OH (25 %) were purchased from local supplier (Himlaborreaktiv, Ltd). Meso-2,3-dimercaptosuccinic acid (DMSA) was purchased from Sigma-Aldrich. Orto-thiocarborane was purchased from Merck Schuchardtohg. 2,2'-dipyridyldisulfide was purchased from Sigma. 2-Mercaptonicotinic acid ≥99.0 % (HPLC) was purchased from Sigma-Aldrich. UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray powder difraction (XRD) were used for analysis. In order to obtain novel neutron capture agents magnetic nanostructures have been developed for the boron and Gd neutron capture therapy based on Fe 3 O 4 with optional Gd content and molecules containing 10-boron atoms. Molecular formula of the composite is Fe 3 O 4 /Gd 2 O 3 -S-S-Н 11 В 10 С 2 . Ortho-thiocarborane immobilization was carried out by thiol-disulphide exchanging reaction. The surface of Fe 3 O 4 /Gd 2 O 3 composite was modified by meso-2,3 dimercaptosuccinic acid in order to create free SH groups on the surface. Dipyridildisulphide was used as @leaving@ molecule from the surface of DMSA-Fe 3 O 4 /Gd 2 O 3 composite. The XPS spectroscopy studies confirmed presence of boron about and S-S bonds on the surface. According to our estimations, 0.07 mmol/g of carborane was immobilized.

Copper(II) Dihalotetracyanoplatinate(IV) Coordination Polymers and Their Vapochromic Behavior

The coordination polymers [Cu(H2O)2(μ2-NC)4PtX2] (X = Cl, Br) form networks of square grid sheets that align in a staggered manner with one another via weak X···X interactions. Upon stepwise dehydration, the layers fuse, forming a 3-D network of distorted cubes. The materials were tested for visible vapochromic, Raman, and IR response to dimethyl sulfoxide, N,N-dimethylformamide, and pyridine. Analyte-bound coordination polymers of the form Cu(analyte)2[PtX2(CN)4] were structurally characterized by PXRD and found to form layers of square grids that align through X···X interactions. The reaction of [Cu(H2O)2(μ2-NC)4PtX2] with concentrated aqueous NH3 generated [PtBr(CN)4(NH3)]- and [PtCl(CN)4(OH)]2- anions that were incorporated into 1-D chain structures. UV-visible reflectance data show that a combination of shifting d-d transitions and the visible Br-Pt LMCT absorption band in [Cu(H2O)2(μ2-NC)4PtBr2] results in a greater vapochromic effect in comparison to that in chlorine-containing analogues.

Direct synthesis of Pd incorporated in mesoporous silica for solvent-free selective hydrogenation of chloronitrobenzenes

Pd incorporated in mesoporous silica (Pd-MS) catalysts were prepared by a direct synthesis method in the presence of 1, 3, 5-trimethylbenzene (TMB) and their formation mechanism was proposed. TMB not only acted as an effective expanding agent to enlarge pore size and pore volume of MS but also acted as a structure-directing agent to induce the formation of worm-like morphology. For solvent-free hydrogenation of p-chloronitrobenzene (p-CNB), a complete conversion of p-CNB with a selectivity towards p-chloroaniline of 99.9% over the Pd-MS catalyst with addition of TMB (Pd-MS-50-TMB, where 50 represented the addition of 5mL of aqueous NH3) was obtained at 85°C and 3.45MPa of H2 in 2h, while only 48.4% p-CNB conversion over Pd-MS-50 synthesized without TMB was obtained. The enhanced activity of the Pd-MS-50-TMB was not only attributed to the smaller size of Pd particles, but also to the worm-like morphology of the support with larger pore size and pore volume that could enhance mass transfer and allow the reactants more facile access to Pd for reaction.

Catalytic Amidation of 5‐Hydroxymethylfurfural to 2,5‐Furandicarboxamide over Alkali Manganese Oxides

Abstract2,5‐Furandicarboxamide was firstly synthesized in yield of 85% via catalytic oxidative amidation of 5‐hydroxymethylfurfural with aqueous NH3 over alkali manganese oxides of α‐MnO2/NaxMnO2. The intermediates of 5‐hydroxymethyl‐furonitrile, 2,5‐dicyanofuran, and 5‐cyano‐2‐furancarboxamide were verified and their reactivities were further examined. The kinetic analysis results showed that the transformation of intermediate product of 5‐cyano‐2‐furancarboxamide to 2,5‐furan‐dicarboxamide is a slower step, which is closely relative to the reaction temperature and basicity of catalyst.

Surfactant free synthesis of gold nanoparticles within meso-channels of non-functionalized SBA-15 for its promising catalytic activity

This work reports surfactant free synthesis of monodisperse gold (~2.3nm) particles confined within the pore channels of ordered hexagonal mesoporous silica SBA-15 (Au/SBA-15) by a modified wetness impregnation method. The synthesized Au/SBA-15 composite showed excellent catalytic activity towards the reduction of different wastewater organic pollutants as well as their mixtures under ambient conditions. The composite was also investigated for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). XRD, UV-DR visible spectroscopy, N2 adsorption-desorption analysis, ICP-AES, FT-IR spectroscopy, and TEM were employed to characterize the catalyst samples. The wetness impregnation method followed by a washing step with dilute aqueous NH3 was found to be an effective route to synthesize stable and highly dispersed small gold nanoparticles (Au NPs) within the mesopore channels of SBA-15. All the catalytic reactions followed pseudo-first-order kinetics and catalytic efficiency of the composite was found almost constant up to five cycles.

Chromatographic determination of nitrophenols in aqueous media after two-stage preconcentration using an N-vinylpyrrolidone-based polymer

Two-stage procedures for the preconcentration of nitrophenols (4-nitrophenol, 2,4- and 2,5-dinitrophenol, and 2,4,6-trinitrophenol) from aqueous solutions are proposed. At the first stage, the preconcentration and desorption of nitrophenols under dynamic conditions is carried out. At the second stage, depending on the nature of the desorption solution, the eluate is evaporated (acetonitrile) or saturated with ammonium sulfate and extracted with acetone (aqueous NH3 solution). The concentration factors are 4000 and 910, respectively. Nitrophenols are determined in concentrates by thin layer chromatography and HPLC, the limits of detection are 1.0–1.8 and 0.25–0.45 μg/L, respectively. The duration of analysis is 200 min.

Enhanced plasmon-mediated photo-assisted hydrogen evolution on silicon by interfacial modification

The superior catalytic activity of Pt towards proton reduction suggests application of Pt also in device architectures where hydrogen is produced by light-generated charge carriers. Large optical absorption cross sections of Pt nanoparticles, however, turn the attention to potential substitutes for Pt such as Au with more advantageous optical properties. In order to approach a functional Si/Au photocathode for hydrogen evolution, we report here on modifications of the Si–Au interface which result in improvements of charge transfer kinetics and optical properties of the device. After current-less deposition of Au nanoparticles onto silicon, these improvements are realized by chemical oxide exchange reactions at the Si/SiO_2/Au interface, i.e., dynamic etching of SiO_2 and re-oxidation of Si in NH_4F (40%). A chemical reaction route for the reformation of the SiO_2 layer in the presence of Au and the aqueous NH_4F solution is discussed. Simultaneous to the modification of the Si/SiO_2 interface, small Au nanoparticles form larger clusters with enhanced effective scattering cross sections. Thereby, improved electronic interface properties and enhanced forward scattering of light increase the saturation photocurrent density by about 9% from 32 to 35 mA cm^(−2). Improved stability of the device in acidic electrolytes, near the thermodynamic potential for evolution of hydrogen, is furthermore discussed.

Thermodynamic modeling of NH3-CO2-SO2-K2SO4-H2O system for combined CO2 and SO2 capture using aqueous NH3

A new application of aqueous NH3 based post-combustion CO2 and SO2 combined capture process was proposed to simultaneously capture CO2 and SO2, and remove sulfite by solid (K2SO4) precipitation method. The thermodynamic model of the NH3-CO2-SO2-K2SO4-H2O system for the combined CO2 and SO2 capture process was developed and validated in this work to analyze the heat of CO2 and SO2 absorption in the NH3-CO2-SO2-H2O system, and the K2SO4 precipitation characteristics in the NH3-CO2-SO2-K2SO4-H2O system. The average heat of CO2 absorption in the NH3-CO2-H2O system at 40°C is around −73kJ/mol CO2 in 2.5wt% NH3 with CO2 loading between 0.2 and 0.5 C/N. The average heat of SO2 absorption in the NH3-SO2-H2O system at 40°C is around −120kJ/mol SO2 in 2.5wt% NH3 with SO2 loading between 0 and 0.5S/N. The average heat of CO2 absorption in the NH3-CO2-SO2-H2O system at 40°C is 77, 68, and 58kJ/mol CO2 in 2.5wt% NH3 with CO2 loading between 0.2 and 0.5 C/N, when SO2 loading is 0, 0.1, 0.2S/N, respectively. The solubility of K2SO4 increases with temperature, CO2 and SO2 loadings, but decreases with NH3 concentration in the CO2 and SO2 loaded aqueous NH3. The thermodynamic evaluation indicates that the combined CO2 and SO2 capture process could employ the typical absorption/regeneration process to simultaneously capture CO2 and SO2 in an absorber, thermally desorb CO2 in a stripper, and feasibly remove sulfite (oxidized to sulfate) content by precipitating K2SO4 from the lean NH3 solvent after the lean/rich heat exchanger.

An Efficient, Visible Light Driven, Selective Oxidation of Aromatic Alcohols and Amines with O2 Using BiVO4/g-C3N4 Nanocomposite: A Systematic and Comprehensive Study toward the Development of a Photocatalytic Process

In this study, BiVO4 was prepared by a hydrothermal synthesis route in the presence of sodium dodecyl sulfate using aqueous NH3 as precipitant. g-C3N4 was prepared by a combustion method using melamine. In order to develop highly efficient photocatalyst, a heterojunction catalyst based on g-C3N4 and BiVO4 was prepared. Different amounts of BiVO4 and g-C3N4 were mixed and annealed to obtain heterojunction photocatalysts. FeVO4 and LaVO4 were also prepared for the comparative catalytic investigation. Catalysts were characterized by a series of complementary combinations of powder X-ray diffraction, thermogravimetric analysis, elemental analysis, N2 adsorption–desorption, scanning electron microscopy, transmission electron microscopy, temperature-programmed desorption of NH3 and CO2, diffuse reflectance ultraviolet visible spectroscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, and photoelectrochemical studies. Catalysts were investigated in the visible light driven oxidation of benzy...

Mechanistic study of reaction mechanism on ammonia photodecomposition over Ni/TiO2 photocatalysts

Photodecomposition of NH3 to H2 and N2 was carried out using metal-supported TiO2 (M/TiO2) photocatalysts in an aqueous NH3 solution under UV irradiation at room temperature. Ni/TiO2 photocatalysts indicated the highest yield of H2. The NH2 radical was formed as a dominant intermediate during NH3 decomposition, as confirmed by electron spin resonance measurements. Reaction pathways via NH2 radical formation were also investigated in detail by density functional theory. The results showed that H2 and the H2N-NH2 as intermediate were formed by the coupling of an NH2 radical and an NH3 molecule in the gas phase during the photodecomposition of NH3. We believe that our findings would be useful for further developing efficient catalytic systems.

The Logic behind a Physical–Organic Chemist’s Research Topics

Although my research has no common theme or defining area, a coherence connects the diverse topics insofar as one project leads logically to another. Thus, studies on mechanisms of hydrogen exchange in amides and amidines led to the influence of hydrogen bonding and to NMR methods for chemical kinetics, including 2D-EXSY spectroscopy. Another connection was the OH--catalyzed NH exchange in amines that had supported the hypothesis of stereoelectronic control. We therefore analyzed that hypothesis critically, tested it, found counterexamples, and proposed an alternative hypothesis. We next addressed one-bond NMR coupling constants in ethers and the reverse anomeric effect. The latter studies required a highly accurate NMR titration method that we developed to measure the additional steric bulk resulting from protonation of a substituent. This method is also applicable to measuring secondary isotope effects on acidity, and we could demonstrate that they arise from n-σ* delocalization, not from an inductive effect. Other studies included kinetic isotope effects for both dissociation and H exchange of aqueous NH4+, for C-N rotation in amides, and for a hydride transfer. The role of hydrogen bonding led us to the rotation of NH4+ within its solvent cage and then to the symmetry of hydrogen bonds.

Synthesis of ZrO2–SiO2 and ZrO2–SiO2–Cu(II) xerogels by joint hydrolysis in an aqueous ammonia atmosphere

ZrO2–SiO2 xerogels have been synthesized through hydrolysis of a mixture of tetrabutoxyzirconium and tetraethoxysilane in a desiccator in a vapor of a 15% aqueous NH3 atmosphere. ZrO2–SiO2–Cu(II) xerogels were synthethized analogously through joint hydrolysis of a mixture of the organometallic precursors and copper(II) chloride. The effect of synthesis conditions on the physical and chemical properties of the resulting material has been studied.

Use of halloysite nanotubes to reduce ammonium concentration in water and wastewaters

Halloysite nanotubes (HNTs) were used for the reduction of ammonium concentration in aqueous solutions under various experimental conditions. The results indicated that HNTs exhibit fast adsorption rates and high removal capacity for the NH4+ ions at neutral pH. The removal efficiency of the treated halloysite depends on the mass/volume ratio and the initial concentration of NH4+ ions. The adsorption capacity of the material was examined for different mass/volume ratios at initial concentration <40 mg/L and it was found that in some cases the material exhibit up to 30% removal efficiency. Halloysite clay removal efficiency was also examined in a 4–10 pH range and it was found that it is increasing continually upon increasing pH values. Additionally the adsorption efficiency is strongly and negatively related to temperature. Langmuir adsorption models were applied to describe the equilibrium isotherms. Estimation of thermodynamic parameters such as enthalpy (ΔH°), entropy (ΔS°) and change in free energy (ΔG°) confirms that the process is spontaneous and exothermic. Adsorption experiments were also performed in aqueous NH4+ solutions in the presence of other cations and it was found that the removal efficiency for NH4+ follows the order Na > K > Zn > Cu > Mn > Ca > Fe > Mg. The above results indicate that halloysite clay mineral can be considered as a new material for use in large and/or industrial-scale applications for water and wastewater purification purposes.

Kinetic modeling and dynamic simulation for the catalytic wet air oxidation of aqueous ammonia to molecular nitrogen

A kinetic model for the catalytic wet air oxidation of aqueous ammonia over Ru/TiO2 catalyst was developed considering the consecutive reaction steps as follows: (i) formation of active oxygen sites O* by the dissociative adsorption of aqueous O2 on the catalyst, (ii) oxidation of aqueous NH3 by the reaction with three O* sites to produce HNO2, (iii) aqueous phase dissociation of HNO2 into H+ and NO 2 − , (iv) formation of NH 4 + by the association of NH3 with the HNO2-dissociated H+, (v) formation of N2 by the aqueous phase reaction between NO 2 − and NH 4 + , (vi) formation of NO3 by the reaction of NO 2 − with an O* site. For each reaction step, a rate equation was derived and its kinetic parameters were optimized by experimental data fitting. Activation energies for the reactions (ii), (v), and (vi) were 123.1, 76.7, and 54.5 kJ/mol, respectively, suggesting that the oxidation reaction of aqueous NH3 to HNO2 was a ratedetermining step. From the simulation using the kinetic parameters determined, the initial pH adjustment of the ammonia solution proved to be critical for determining the oxidation product selectivity between desirable N2 and undesirable NO 3 − as well as the degree of oxidation conversion of ammonia.