Aqueous NH3 Solution Research Articles

Photocatalytic Ammonia Decomposition Using Dye-Encapsulated Single-Walled Carbon Nanotubes

The photocatalytic decomposition of ammonia to produce N2 and H2 was achieved using single-walled carbon nanotube (SWCNT) nanohybrids. The physical modification of ferrocene-dye-encapsulated CNTs by amphiphilic C60-dendron yielded nanohybrids with a dye/CNT/C60 coaxial heterojunction. Upon irradiation with visible light, an aqueous solution of NH3 and dye@CNT/C60-dendron nanohybrids produced both N2 and H2 in a stoichiometric ratio of 1/3. The action spectra of this reaction clearly demonstrated that the encapsulated dye acted as the photosensitizer, exhibiting an apparent quantum yield (AQY) of 0.22% at 510 nm (the λmax of the dye). This study reports the first example of dye-sensitized ammonia decomposition and provides a new avenue for developing efficient and sustainable photocatalytic hydrogen production systems.

An Effective Biochar Application for Reducing Nitrogen Emissions from Buffalo Digestate Storage Tank

Open manure storage contributes to the release of ammonia (NH3) into the atmosphere. Tank floating covers represent an effective technique to reduce NH3 emissions and biochar has been gain attention as a floating cover and as manure additive. Nevertheless, the mechanisms involved in the process still need to be elucidated since they are influenced by the biochar specific properties, application methods and dose. This work aims to study: (i) the biochar adsorption performances in an NH3 aqueous solution under conditions relevant to manure storage and (ii) the effect of different biochar application methods and dosage on NH3 emissions from buffalo digestate storage. The results show that a 43% reduction in NH3 emissions can be achieved by using biochar as a floating cover of 2 cm rather than as an additive. Moreover, the results show that the biochar produced at 550 °C acts as an adsorbent material for both NH4+ and NH3, by being adsorbed on the biochar surface in the form of NH4+ after H+ abstraction from the acid groups. A minimum cover height of 2 cm is required to give compactness and provide an additional resistance to the gas transfer, which is even more relevant than the adsorption in reducing NH3 emissions.

A new model-aided approach for the design of packed columns for CO2 absorption in aqueous NH3 solutions

A novel model-based approach to design packed beds for CO2 absorption with NH3 is proposed and experimentally validated. The two-film theory is adopted to model gas/liquid mass transfer while the thermodynamic equilibrium among ion species is considered in the liquid. Such strategy allows to simulate both CO2 absorption and NH3 evaporation, that represent the most important aspects to improve capture efficiency and process cost-effectiveness. The resulting ODEs system is a two boundary-value problem which is solved by means of the shooting method. The model is then exploited to develop a new algorithm that, based on the adopted operating conditions, evaluates the packed bed height as a function of the desired capture efficiency. The height calculated for different combinations of operating conditions is successfully compared with the real height of the experimental column, thus confirming the reliability of the developed tool which can be run with very low computational loads.

Synthesis of Polystyrene@TiO2 Core–Shell Particles and Their Photocatalytic Activity for the Decomposition of Methylene Blue

In this study, we investigated the preparation conditions of polystyrene (PS)@TiO2 core–shell particles and their photocatalytic activity during the decomposition of methylene blue (MB). TiO2 shells were formed on the surfaces of PS particles using the sol–gel method. Homogeneous PS@TiO2 core–shell particles were obtained using an aqueous NH3 solution as the promoter of the sol–gel reaction and stirred at room temperature. This investigation revealed that the temperature and amount of the sol–gel reaction promoter influenced the morphology of the PS@TiO2 core–shell particles. The TiO2 shell thickness of the PS@TiO2 core–shell particles was approximately 5 nm, as observed using transmission electron microscopy. Additionally, Ti elements were detected on the surfaces of the PS@TiO2 core–shell particles using energy-dispersive X-ray spectroscopy analysis. The PS@TiO2 core–shell particles were used in MB decomposition to evaluate their photocatalytic activities. For comparison, we utilized commercial P25 and TiO2 particles prepared using the sol–gel method. The results showed that the PS@TiO2 core–shell particles exhibited higher activity than that of the compared samples.

Speciation and Ammonia-Induced Precipitation of Neptunium and Uranium Ions.

The pH evolution and corresponding changes in the UV-Vis-NIR absorption spectra of oxygenated neptunium (NpO2+ and NpO22+) and uranyl ions (UO22+) in nitric acid are investigated during titration with an aqueous NH3 solution. The speciation and precipitation regimes between acidic (pH 1.5) and alkaline (pH 10) conditions at room temperature are discussed to assess the suitability of Np(V) or Np(VI) in sol-gel conversion processes for fuel target fabrication. Under the applied experimental conditions, Np(V) hydrolyzes and precipitates into the insoluble hydroxide NpO2OH only above pH values 7.5 and an increase up to pH 10.0 is required to precipitate quantitatively. Np(VI) displays changes in the coordination environment of NpO22+ ions in the pH interval 1.6-4.0, similar to what is observed for U(VI). Precipitation into NpO3·H2O or other hydroxide compounds takes place between pH 4.0 and 5.9, which overlaps largely with precipitation of ammonium diuranate species from the U(VI) solution. The use of concentrated NH3 aqueous solution, as commonly used in the external gelation process, will allow to quantitatively precipitate both Np(V) and Np(VI) species. Internal gelation process conditions, on the other hand, seem incompatible with the high pH required to precipitate Np(V) completely. For fabricating mixed-oxide (U,Np) targets using sol-gel conversion, a feed broth containing Np(VI) and U(VI) will be required to achieve homogeneous gelation.

Thermodynamic modeling of MDEA(aq)-NH3(aq)-K2CO3(aq)-CO2(aq) using the Extended UNIQUAC model

The development of advanced processes for carbon dioxide capture requires reliable thermodynamic models to ensure accurate process design. This work presents an optimized parameter set of the Extended UNIQUAC model for advanced mixed solvent solutions containing CO2-MDEA-NH3-K2CO3 in water. The model was parameterized using vapor–liquid equilibrium, pure component saturation pressure, excess enthalpy, heat of absorption, molar heat capacity, apparent molar heat capacity, and solid–liquid equilibrium. These thermal and equilibrium properties cover temperatures between 253.6K to 600K and pressures up to 75.6bar. The current model represents an extension of previous versions that were suitable for modeling aqueous NH3 and K2CO3 solutions. This parametrization accounts for molecular interactions between MDEA and these two components, which allows for the design of advanced capture processes. This paper demonstrates that the new model parameters are valid within the range of operational conditions typically found in CO2 capture processes.

Continuous-flow synthesis of amphiphilic rhodamine B-polymethylsilsesquioxane fluorescent microspheres for micro-PIV analysis

• Rhodamine B- polymethylsilsesquioxane fluorescent microspheres were prepared. • Synthetic process was performed in a one-step continuous-flow microreaction system. • The hydrophilic and hydrophobic RhB-PMSQ microspheres were synthesized. • Amphiphilic RhB-PMSQ particles were used as tracer particles for micro-PIV analysis. Tracer particle is a key element in the micro-PIV flow field measurements. The oil-dispersible tracer particles are mainly obtained by post modification, resulting in relatively poor uniformity and dispersibility. In this work, we developed a molecular-level amphiphilic tracer particle, i.e., rhodamine B-polymethylsilsesquioxane (RhB-PMSQ) fluorescent microspheres. The RhB-PMSQ microspheres were synthesized in a continuous-flow microreaction system with the aqueous solution of NH 4 OH and RhB as the continuous phase and methyltrimethoxysilane (MTMS) as the dispersed phase. The microreaction system consisted of a T -junction micromixer, a capillary reactor for MTMS hydrolysis, and a millimeter-scale tubular reactor for condensation reaction. By controlling the condensation degree of surface Si-OH groups, the hydrophilic and hydrophobic RhB-PMSQ microspheres could be synthesized with the same reaction system, and they could be uniformly dispersed in the aqueous phase and oil phase, respectively. The density, pore structure, and fluorescence property of the RhB-PMSQ microspheres were investigated in detail. The RhB-PMSQ microspheres were employed as the tracer particles of water and liquid paraffin, and the two-phase velocity profiles were measured via micro-PIV technique in a step T -junction microchannel. The micro-PIV results indicated that amphiphilic RhB-PMSQ microspheres could serve as the tracer particles for the flow field measurement both of aqueous phase and oil phase.

CO2 absorption in aqueous NH3 solutions: Novel dynamic modeling of experimental outcomes

It is well known that CO2 capture and re-use is one of the main challenges to be pursued in order to tackle global warming issues. Aqueous ammonia solutions are among the most promising sorbents for post-combustion CO2 capture and could represent a valid and potentially economical alternative to the use of conventional alkanolamines, due to their higher absorption capacity, lower energy requirements for sorbent regeneration and greater resistance to oxidative and thermal degradation. Despite its apparent simplicity and convenience, the dynamic evolution of CO2 − NH3 system needs to be further investigated through proper mathematical models that permit to design, optimize, and control the capture process.In this work, the chemical absorption of carbon dioxide contained in a simulated flue gas (N2+CO2; CO215%v/v) by means of aqueous NH3 solutions was investigated both experimentally and theoretically. In particular, a rigorous mathematical model, capable to quantify the CO2 capture efficiency dynamics and the sorbent chemical composition during the process, is proposed for the first time. The model is validated by comparing modeling results with experimental data obtained under different operating conditions. The effect of both operating temperature and sorbent concentration are investigated. The good agreement between model results and experimental data confirms the effectiveness and the reliability of the developed tool that turns out to be able to quantify the dynamics of capture efficiency during the variation of the operating conditions. Therefore, it may be exploited to properly design, optimize and control the capture process and the absorbent regeneration section whose energy requirements also depend on the species concentration into the absorbent solution.

Effect of precipitating agents on the magnetic and structural properties of the synthesized ferrimagnetic nanoparticles by co-precipitation method

In this work, the effect of four different precipitating agents on the structural and magnetic properties of synthesized ferromagnetic nanoparticles (FMNPs) by the co-precipitation method has been explored. In particular, different precipitating agents used in work include (I) NH3, (II) NH3 with alcohol, (III) NaOH, and (IV) aqueous NH3 solution. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), scanning electron microscope (FESEM/EDS), zeta-potential, and vibrating sample magnetometer (VSM). From the XRD pattern and Debye-equation, it appears that the obtained nanoparticles were magnetite with an average crystallite size of 8–27.6 nm. The FTIR spectrum of NH3 in an alcohol solution indicates a perfect stretching of the Fe–O, O–H, C–H functional groups compared to other cases. Moreover, superparamagnetic behavior at room temperature was also noticed from VSM analysis. NH3 in an alcohol solution as a precipitating agent showed higher magnetic properties of FMNPs than the other cases. Conversely, the response time was found to be the longest for the same set. The procedure with NaOH in an aqueous solution was the cheapest with a shorter reaction time. Nevertheless, the particle surface and magnetic characteristics were lesser than the other cases of precipitating agents.

Control of aragonite formation and its crystal shape in CaCl2-Na2CO3-H2O reaction system

Calcium carbonate (CaCO3) was synthesized in the CaCl2-Na2CO3-H2O reaction system at the reaction temperature of 40, 50, 60, and 70℃. The initial pH was changed to 2.4–11.0 at 50–70 ℃. The initial pH was adjusted by changing the pH of CaCl2 aqueous solution using HCl and NH3 aqueous solution. The CaCO3 precipitates obtained were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), and specific surface area measurement. In the case of no adding the pH adjustment solution, the product was a mixture of calcite and vaterite at 40 ℃. The formation of aragonite was observed at ≥50 ℃, and single-phase aragonite was obtained at ≥60 ℃, according to XRD measurements. Thus, Aragonite could be synthesized by changing the reaction temperature. At 70 ℃, the synthesis of CaCO3 was performed by changing the initial pH of 2.4–11.0. The formation of single-phase aragonite was detected in the initial pH range of 2.4–10.4. However, a small amount of calcite was contained in aragonite at the initial pH ≥ 10.8. The crystal shape of obtained aragonite was needle-like, and its particle size became finer as the initial pH increased. At an initial pH 2.4, the length and width of the crystals were 2–7 μm and 0.5–1.0 μm, respectively. The finest particles were samples synthesized at the initial pH 11.0, its length and width were 1–2 μm and 0.1–0.2 μm, respectively. The specific surface area of the products was 4.12–14.88 m2 g−1 at the initial pH of 2.4–11.0. The particle size of aragonite could be controlled by changing the initial pH at 70 ℃.

Ammonia Oxidation Activity Enhancement of Platinum with N-Doped Graphene and Tungsten Carbide Support

Ammonia electrooxidation reaction (AOR) involving multistep electron-proton transfer is a significant reaction for fuel cells, hydrogen production and understanding nitrogen-cycle. Platinum has been established as the best electrocatalyst for AOR in aqueous alkaline media. 1 In previous studies, it has been observed that nitrogen-doped graphene 2 (NDG) and tungsten carbide 3 (WC) as support could help in increasing activity for some other electrochemical reactions.In this study, Pt/NDG and Pt/WC/NDG were synthesized by a wet chemistry method 4 and their activities were compared to commercial Pt/C. Structure and morphology of the obtained electrocatalysts were examined by TEM, XPS and XRD. Moreover, Ir atoms were deposited on the surface of electrocatalyst Pt/WC/NDG via a modified self-deposition process. 5 LSV and chronoamperometry methods were applied to illustrate the activity and stability of electrocatalysts, respectively. LSVs of electrocatalysts in 0.1M KOH + 0.1M NH3 aqueous solution at a scan rate of 50 mV s-1 are elucidated in Figure 1.It was observed that Pt/NDG exhibited a specific activity of 0.472 mA cm-2 which was 44% higher than commercial Pt/C, thus establishing NDG as a more efficient support for AOR than carbon. Furthermore, WC as support also has an impact on AOR activity (30 % increase in activity in comparison to Pt/NDG) with Pt/WC/NDG having a specific activity of 0.61 mA cm-2. Further surface modification with Ir results in the best electrocatalytic activity for AOR with Pt-Ir/WC/NDG (specific activity 0.94 mA cm-2) having almost thrice the current density of commercial Pt/C. Pt-Ir/WC/NDG also demonstrated the lowest onset potential of 0.48 V vs RHE. It was also found that Pt/WC/NDG delineated the best stability among the catalysts, thus highlighting the role of WC in improving stability for AOR.This work adds insights regarding the role of NDG and WC as efficient supports along with significant impact of Ir surface modification on AOR activity of Pt. Figure 1. LSVs of electrocatalysts in 0.1M KOH + 0.1M NH3 aqueous solution at 50 mV s-1

Cu(I)-Catalyzed Heterogeneous Multicomponent Polymerizations of Alkynes, Sulfonyl Azides, and NH4Cl

Nitrogen-containing polymers are a group of fascinating materials, which are usually prepared from nitrogen-containing organic monomers produced from NH₃ gas or aqueous solution of ammonia. The direct utilization of safe, clean, convenient, and inexpensive inorganic NH₄Cl salt as a nitrogen source for the construction of functional polymers is highly desired but challenging. Multicomponent polymerizations, with their strong designability, structural diversity, high efficiency, simple procedure, and environmental benefit, have been proven to be powerful tools to efficiently convert simple monomers to complex polymer materials. In this work, Cu(I)-catalyzed multicomponent polymerizations of alkynes, sulfonyl azides, and NH₄Cl are developed, utilizing simple inorganic NH₄Cl salt to serve as a monomer for the preparation of functional poly(sulfonyl amidine)s. The heterogeneous polymerization goes smoothly at room temperature in CH₂Cl₂/tetrahydrofuran, which is also applicable to a range of different monomer structures, affording seven poly(sulfonyl amidine)s with high yields (up to 96%) and high molecular weights (up to 47,100 g/mol). Unique functionalities such as photophysical properties and metal ion detection can be introduced to the poly(sulfonyl amidine)s either from monomer structures or the in situ generated product structures, rendering them as selective and sensitive fluorescence sensors for Ru³⁺. This multicomponent polymerization showed high synthetic efficiency with environmental and economic benefit, which has opened up a feasible synthetic method of using inorganic NH₄Cl salt instead of organic amines, isocyanates, isocyanides, or nitriles to construct nitrogen-containing polymers, demonstrating a promising synthetic approach for the synthesis of advanced functional polymer materials.

Modelling and simulation study of CO2 capturing process in coal fired power plant using various amine solvents

In the present world, Scientists are very much concern on to reduce the concentration level of carbon dioxide in environment to save the world. In the present work, the CO2 capturing efficiencies of three different amine solvents were analyzed. The selected solvents were mono-ethanol amine (MEA), solvent containing mixture of methyl diethanol amine (MDEA) and piperazine (PZ) called activated -MDEA and aqueous ammonia (NH3) solution. Rigorous simulation method was considered in the current study. The effects of different key parameters for different solvents on the CO2 removal efficiency were analyzed. Packing height, solvent temperature and absorber height were the significant influential parameters for MEA system whereas for activated-MDEA (a-MDEA), those are the ratio of the solvent to feed quantity and the mixed solvent PZ concentration level. For aqueous NH3 solution, absorber and stripper’s temperature, CO2 loading, concentration of NH3, height of the absorber, lean and rich solvent flow rate, boil up ratio, regeneration energy, temperature of the condenser, and duty of the reboiler were considered. The comparative study showed that MEA process recovered the maximum CO2 from flue gas. But it was suffered by the maximum regeneration duty. a-MDEA with PZ recovered 91% CO2. Overall, technically, a-MDEA was the best choice as solvent. Compared to a-MDEA and MEA, aqueous ammonia was identified as more propitious and environment friendly solvent due to its satisfactory performance and easy availability.

A green and recyclable ligand-free copper (I) catalysis system for amination of halonitrobenzenes in aqueous ammonia solution

The amination of halonitrobenzenes is an important reaction to produce the corresponding nitroanilines. Direct amination of p-chloronitrobenzene (p-CNB) to p-nitroaniline (p-NAN) with aqueous NH3 solution was investigated over various transition metal salts in the absence of ligand, inorganic base and organic solvent. It was found that CuI is the most effective catalyst with respect to p-CNB conversion, p-NAN selectivity (≈ 100%) and the post-reaction separation and recycling. A high p-NAN yield of 97% could be obtained at 200 °C in 6.5 h with molar ratios of NH3/p-CNB and CuI/p-CNB of 21 and 0.1, respectively. A possible reaction mechanism was proposed, in which NH3 was not only a substrate but also a ligand to coordinate with CuI and formed a water-soluble Cu complex, and then it started the catalytic cycle. The influence of reaction variables such as NH3 concentration, CuI concentration, temperature and time on the p-CNB conversion and the p-NAN selectivity was examined. At room temperature the desired product of p-NAN is insoluble in water but the Cu complex catalyst is water-soluble and so the aqueous phase including the catalyst and NH3 can be easily separated and reused for the subsequent reaction runs. The green and sustainable system is effective for the conversion of diverse halonitrobenzenes to nitroanilines.

Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 2: Quartz and amorphous silica

Abstract. Divergent ice nucleation (IN) efficiencies of quartz, an important component of atmospheric mineral dust, have been reported in previous studies. We show here that quartz particles obtain their IN activity from milling and that quartz aged in water loses most of its IN efficiency relative to freshly milled quartz. Since most studies so far reported IN activities of commercial quartz dusts that were milled already by the manufacturer, IN active samples prevailed. Also, the quartz surface – much in contrast to that of feldspars – is not prone to ammonia-induced IN enhancement. In detail we investigate the influence of solutes on the IN efficiency of various silica (SiO2) particles (crystalline and amorphous) with special focus on quartz. We performed immersion freezing experiments and relate the observed variability in IN activity to the influence of milling, the aging time and to the exposure conditions since milling. Immersion freezing with silica particles suspended in pure water or aqueous solutions of NH3, (NH4)2SO4, NH4HSO4, Na2SO4 and NaOH, with solute concentrations corresponding to water activities aw=0.9–1.0, were investigated in emulsified droplets by means of differential scanning calorimetry (DSC) and analyzed in terms of the onset temperature of the heterogeneous freezing signal Thet and the heterogeneously frozen water volume fraction Fhet. Quartz particles, which originate from milling coarse samples, show a strong heterogeneous freezing peak in pure water with Thet equal to 247–251 K. This IN activity disappears almost completely after aging for 7 months in pure water in a glass vial. During this time quartz slowly grew by incorporating silicic acid leached from the glass vial. Conversely, the synthesized amorphous silica samples show no discernable heterogeneous freezing signal unless they were milled. This implies that defects provide IN activity to silica surfaces, whereas the IN activity of a natural quartz surface is negligible, when it grew under near-equilibrium conditions. For suspensions containing milled quartz and the solutes (NH4)2SO4, NH4HSO4 or Na2SO4, Thet approximately follows ThetΔawhet(aw), the heterogeneous freezing onset temperatures that obey Δawhet criterion, i.e., ThetΔawhet(aw)=Tmelt(aw+Δawhet) with Δawhet being a constant offset with respect to the ice melting point curve, similar to homogeneous IN. This water-activity-based description is expected to hold when the mineral surface is not altered by the presence of the solutes. On the other hand, we observe a slight enhancement in Fhet in the presence of these solutes, implying that the compliance with the Δawhet criterion does not necessarily imply constant Fhet. In contrast to the sulfates, dilute solutions of NH3 or NaOH (molality ≥5×10-4 mol kg−1) reveal Thet by 3–8 K lower than ThetΔawhet(aw), indicating a significant impact on the mineral surface. The lowering of Thet of quartz suspended in dilute NH3 solutions is opposite to the distinct increase in Thet that we found in emulsion freezing experiments with aluminosilicates, namely feldspars, kaolinite, gibbsite and micas. We ascribe this decrease in IN activity to the increased dissolution of quartz under alkaline conditions. The defects that constitute the active sites appear to be more susceptible to dissolution and therefore disappear first on a dissolving surface.

Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 3: Aluminosilicates

Abstract. Aluminosilicates and quartz constitute the majority of airborne mineral dust. Despite similarities in structures and surfaces they differ greatly in terms of their ice nucleation (IN) efficiency. Here, we show that determining factors for their IN activity include surface ion exchange, NH3 or NH4+ adsorption, and surface degradation due to the slow dissolution of the minerals. We performed immersion freezing experiments with the (Na-Ca)-feldspar andesine, the K-feldspar sanidine, the clay mineral kaolinite, the micas muscovite and biotite, and gibbsite and compare their IN efficiencies with those of the previously characterized K-feldspar microcline and quartz. Samples were suspended in pure water as well as in aqueous solutions of NH3, (NH4)2SO4, NH4Cl and Na2SO4, with solute concentrations corresponding to water activities aw equal to 0.88–1.0. Using differential scanning calorimetry (DSC) on emulsified micron-sized droplets, we derived onset temperatures of heterogeneous (Thet) and homogeneous (Thom) freezing as well as heterogeneously frozen water volume fractions (Fhet). Suspensions in pure water of andesine, sanidine and kaolinite yield Thet equal to 242.8, 241.2 and 240.3 K, respectively, while no discernable heterogeneous freezing signal is present in the case of the micas or gibbsite (i.e., Thet≈Thom≈237.0 K). The presence of NH3 and/or NH4+ salts as solutes has distinct effects on the IN efficiency of most of the investigated minerals. When feldspars and kaolinite are suspended in very dilute solutions of NH3 or NH4+ salts, Thet shifts to higher temperatures (by 2.6–7.0 K compared to the pure water suspension). Even micas and gibbsite develop weak heterogeneous freezing activities in ammonia solutions. Conversely, suspensions containing Na2SO4 cause the Thet of feldspars to clearly fall below the water-activity-based immersion freezing description (Δaw= const.) even in very dilute Na2SO4 solutions, while Thet of kaolinite follows the Δaw= constant curve. The water activity determines how the freezing temperature is affected by solute concentration alone, i.e., if the surface properties of the ice nucleating particles are not affected by the solute. Therefore, the complex behavior of the IN activities can only be explained in terms of solute-surface-specific processes. We suggest that the immediate exchange of the native cations (K+, Na+, Ca2+) with protons, when feldspars are immersed in water, is a prerequisite for their high IN efficiency. On the other hand, excess cations from dissolved alkali salts prevent surface protonation, thus explaining the decreased IN activity in such solutions. In kaolinite, the lack of exchangeable cations in the crystal lattice explains why the IN activity is insensitive to the presence of alkali salts (Δaw= const.). We hypothesize that adsorption of NH3 and NH4+ on the feldspar surface rather than ion exchange is the main reason for the anomalous increased Thet in dilute solutions of NH3 or NH4+ salts. This is supported by the response of kaolinite to NH3 or NH4+, despite lacking exchangeable ions. Finally, the dissolution of feldspars in water or solutions leads to depletion of Al and formation of an amorphous layer enriched in Si. This hampers the IN activity of andesine the most, followed by sanidine, then eventually microcline, the least soluble feldspar.

Electrochemical Oxidation of Liquid Ammonia on Pt(100) Electrode: First-Principles Study

Ammonia is a good source of hydrogen and has an advantage in comparison with molecular hydrogen for fuel cell application with respect to the storage in liquid phase.1,2,3 Moreover, the raw energy density of liquid ammonia is higher than for liquid hydrogen. Ammonia fuel cells were intensively developed using aqueous solution of ammonia while the developing direct ammonia fuel cells based on liquid ammonia has less attention. Fuel cells based on liquid ammonia NH3(l) have the significant advantages in comparison with aqueous solution of NH3(aq): liquid ammonia NH3(l) is three times energy denser than the saturated aqueous solution of ammonia;alkaline solution of NH3(aq) is corrosive to metallic containers, whereas the infrastructure for liquid NH3(l) production, storage and distribution is already well developed;there is no formation of hindering poisoning NOx species. The mechanism of electrochemical oxidation of aqueous NH3(aq) is well studied,4,5,6 whereas the detailed mechanism of oxidation of liquid NH3(l) is not known. Hanada et al.7 in experimental study of NH3(l) electrolysis in support of LiNH2, NaNH2, and KNH2 electrolytes show that the products of the reaction are hydrogen gas (on the cathode) and nitrogen gas (on the anode) and the highest activity of the reaction is taking place with KNH2 electrolyte. The authors attributed the products H2 and N2 to the reduction of NH3 and oxidation of NH2 -, respectively, however, the mechanism was not substantiated. It is known that the reaction of NH3 electrooxidation is very sensitive to the surface of Pt electrode and occurs at surface sites with (100) geometry,8 whereas the surface sites with (111) and (110) geometries will be blocked by hollow nitrogens.4 In this study we present the detailed steps of the electrochemical oxidation of liquid ammonia on the Pt(100) anode surface in support of KNH2 electrolyte. We model the electrochemical reaction by solid/liquid interface using density functional theory method developed in our previous work.4 One of the possible pathways of the electrochemical oxidation of NH3(l) is going through spontaneous adsorption of NH3(l) to the surface forming NH3(top) (1), the following oxidation of NH3(top) forming NH2(top) (2), then breaking the hydrogen bond with the just formed NH3(l) molecule and transformation to NH2(bridge) (3), and the following oxidation of NH2(bridge) forming the bridging nitrogen (reactions (4)-(5)). The final product of the NH3(l) oxidation is the atomic nitrogen in bridging position (see Fig.). (1) NH3(l) → NH3(top) (2) NH3(top) + NH2 - → NH2(top) + NH3(l) + e- (3) NH2(top) → NH2(bridge) (4) NH2(bridge) + NH2 - → NH(bridge) + NH3(l) + e- (5) NH(bridge) + NH2 - → N(bridge) + NH3(l) + e- The process of the surface accumulation of the bridging nitrogens is going until the moment when the spontaneous dimerization of N(bridge) will happen. The result of the dimerization is N2(hollow) (6). The following spontaneous desorption of N2(hollow) from the surface results the molecular nitrogen dissolved in the solution (7). (6) N(bridge) + N(bridge) → N2(hollow) (7) N2(hollow) → N2(l) References R. Lan, S. Tao "Ammonia as a suitable fuel for fuel cells", Frontiers in Energy Res., 2, 35, 2014.D.J. Little, M.R. Smith, III, T.W. Hamann "Electrolysis of liquid ammonia for hydrogen generation", Energy Environ. Sci., 8, 2775, 2015.D. Cheddie "Ammonia as a hydrogen source for fuel cells: A review", InTech DOI:10.5772/47759, 2012.D. Skachkov, V.R. Chitturi, Y. Ishikawa "Combined first-principles molecular dynamics/density functional theory study of ammonia electrooxidation on Pt(100) electrode", J. Phys. Chem. C, 117, 25451, 2013.I. Katsounaros, M.C. Figueiredo, F. Calle-Vallejo, H. Li, A.A. Gewirth, N.M. Markovic, M.T.M. Koper "On the mechanism of the electrochemical conversion of ammonia to dinitrogen on Pt(100) in alkaline environment", J. Catalysis, 359, 82, 2018.K. Siddharth, Y. Chan, L. Wang, M. Shao "Ammonia electro-oxidation reaction: Recent development in mechanistic understanding and electrocatalyst design", Curr. Opinion in Electrochem., 9, 151, 2018.N. Hanada, S. Hino, T. Ichikawa, H. Suzuki, K. Takai, Y. Kojima "Hydrogen generation by electrolysis of liquid ammonia", Chem. Comm., 46, 7775, 2010.F.J. Vidal-Iglesias, J. Solla-Gullon, V. Montiel, J.M. Feliu, A. Aldaz "Ammonia selective oxidation on Pt(100) sites in an alkaline medium", J. Phys. Chem. B, 109, 12914, 2005. Figure 1

Binary and Ternary Nanocubes As Electrocatalysts for Ammonia Electrooxidation Reaction

Ammonia electrooxidation reaction (AOR) plays a pivotal role in H2 production, direct ammonia fuel cells, electrosynthesis, electrochemical sensors as well as understanding of nitrogen cycle.1-2 AOR kinetics is slow requiring electrocatalysts among which Pt and Ir are the two best choices.2 AOR is also very sensitive to structure of electrocatalyst as (100) facets exhibit maximum activity.3-4 Among alloys, PtIr has shown the best performance but there are inconsistent reports on the amount of Ir required for enhancing the activity.5 Designing more durable electrocatalysts for AOR has also been a bottleneck. In this context, Ni could be a possible solution according to a report based on theoretical calculations.6 In this study, PtIr (several ratios), PtNi and PtIrNi cubic electrocatalysts with (100) facets were prepared by wet chemistry methods with CO as selective capping agent. Structure, morphology and composition of the obtained electrocatalysts were examined by TEM, EDX, XRD and ICP-AES. Quantitative estimation of (100) surface sites were carried out by GeO2 irreversible adsorption and analysis of H desorption peaks in KOH solution. Currents shown in Figure 1 were normalized by electrochemical surface areas obtained via the Cu UPD method. LSV and chronoamperometry methods were used to elucidate the activity and stability of electrocatalysts, respectively. It was found that only a trace amount of Ir could increase the activity of Pt cubes by more than twice. As illustrated in Figure 1, PtIr (85:1) cubes exhibited specific activity of 1.25 mA cm-2 compared to Pt cubes with 0.58 mA cm-2. Increasing the amount of Ir further decreased the activity. PtNi cubes performed better than Pt cubes with respect to stability although its specific activity of 0.51 mA cm-2 was slightly less than Pt cubes. Addition of trace amount of both Ir and Ni to Pt cubes, i.e. ternary PtIrNi cubes demonstrated the best performance in terms of stability. These PtIrNi cubes had specific activity of 0.72 mA cm-2 which was 41% more than Pt cubes. Additionally, PtIr cubes showed the least value of onset potential which was 0.429 V vs RHE as can be seen in Figure 1. This work adds new insights showing that a minute amount of Ir could improve the AOR of Pt significantly. Furthermore, Ni plays a crucial role in improving stability for AOR. Figure 1. LSVs of electrocatalysts in 0.1M KOH + 0.1M NH3 aqueous solution at 50 mV s-1 References Zhong, C., Hu ,W. B., and Cheng Y. F., Journal of Materials Chemistry A 2013, 10, 3216-3238.Siddharth, Kumar, Yattung Chan, Lu Wang, and Minhua Shao, Current Opinion in Electrochemistry 2018, Vol 9, 151-157.Liu, J., Fan, X., Liu, X., Song, Z., Deng, Y., Han, X., Hu, W. and Zhong, C., ACS applied materials & interfaces 2017, 9(22), pp.18856-18864.Zhang, C., Hwang, S.Y. and Peng, Z., Journal of Materials Chemistry A 2013, 1(45), pp.14402-14408.Li, Z.F., Wang, Y. and Botte, G.G., Electrochimica Acta 2017, 228, pp.351-360.Yang, Y., Yu, H., Cai, Y., Ferrando, R. and Cheng, D., Journal of Physics: Condensed Matter 2018, Vol 30(28). Figure 1

One-Pot Multienzymatic Transformation of NH3, CO2, and Ornithine into the Organic Nitrogen Plant Fertilizer Citrulline Using a Single Recombinant Lysate of E. coli

Biocatalytic transformation of carbamate formed readily from CO2 and NH3 provides attractive green routes for mitigation of these important environmental pollutants. Accordingly, a coupled-enzyme system was developed for the one-pot production of citrulline through carbamoylation of ornithine in aqueous solutions of CO2 and NH3. Hyperthermophilic ornithine carbamoyltransferases are produced recombinantly in E. coli with carbamate kinases known to have a propensity for carbamoyl phosphate synthesis. Importantly, in vitro biocatalysis is carried out by E. coli cell lysate prepared through coexpression of the required recombinant enzymes in a single bacterial culture, greatly reducing limitations normally associated with protein production and purification. Acetate kinase that is endogenous in the lysate also recycles the required ATP cofactor, which would otherwise have been required in costly stoichiometric amounts. Recombinant lysates catalyze the production of carbamoyl phosphate with substoichiometric A...

Effect of pH on formation of single-phase vaterite

This paper reports on the effect of pH on polymorphism of calcium carbonate (vaterite) formed in the CaCl2-Na2CO3-H2O reaction system. The initial pH of CaCl2 aqueous solution was adjusted to the initial pH 2.0–11.3 using HCl and NH3 aqueous solution. The initial pH was 6.5 without pH adjustment. When the reaction was carried out, amorphous calcium carbonate (ACC) was formed at the early stage of the reaction and crystallized to calcite and vatrite after 3 min of stirring. Formation ratio of vaterite at this time was 60％. Single-phase vaterite was formed at initial pH 2.0–2.5. Further, focusing on the pH during ACC crystallization. When HCO3− ions were 80% or more during ACC crystallization, single-phase vaterite was formed.