2O System Research Articles

Elucidating NH3 formation during NOx reduction by CO on Pt–BaO/Al2O3 in excess water

The reduction of NO was investigated with CO, H2, CO+H2O and CO+H2 as the reducing species on a Pt–BaO/Al2O3 monolith catalyst over an intermediate temperature range (200–300°C). NH3 is a major product of the NO+CO+H2O system under conditions of CO inhibition. The data are interpreted by the known NH3 formation route in which the NO is reduced by H2 formed by the water gas shift (WGS) reaction. In the absence of water, the strong adsorption of CO leads to sharp transitions between a high rate mass transport controlled regime and a lower rate kinetically controlled regime between 200 and 300°C. Differential kinetics and integral experiments are reported at 270°C. The intrinsic order with respect to CO in the latter regime is −1. When water is added with the CO feed, the regime transitions are more gradual and mitigated by the enhancement afforded by the hydrogen formed by the WGS reaction. Kinetic evidence for the effect of hydrogen is the much lower inhibition by CO during the WGS reaction (−0.23 order). When H2 is added to the NO+CO mixture (without H2O) in the CO inhibited feed regime NH3 and CO2 are the major products even for low H2/NO feed ratio (∼1). Collectively, the steady-state findings are consistent with the major NH3 formation pathway involving reaction of surface H (from WGS) and OH (from water) with adsorbed NO and N. The NH3 formation route involving the hydrolysis of a surface isocyanate species formed from the reaction of NO and CO, is only of secondary importance.

Local pH control by electrolysis for ZnO epitaxial deposition on a Pt cathode

The epitaxial deposition of an oxide semiconductor ZnO thin film was demonstrated on a Pt(1 1 1)/sapphire(0 0 0 1) cathode by local pH control in the vicinity of the cathode. The local pH near the cathode was increased by the selective reduction of NO 3 − ions, resulting in the deposition of a ZnO thin film only on the cathode surface by hydrolysis. The pH distribution near the cathode during electrolysis was calculated using a 1-dimensional discrete model, which is simple but concise and beneficial to expeditiously estimate an appropriate deposition condition in combination with the obtained potential-pH diagram of a Zn–H 2O system. An investigation undertaken using a quartz crystal microbalance revealed that ZnO started to deposit immediately after the application of electrical current at 100 μA cm −2, and that it grew linearly to ca . 350 nm over 5000 s, suggesting that the film thickness can be easily controlled by electrolysis time.

Phase transitions, ferroelectric behavior and second-order nonlinear optics of a new mixed sodium dihydrogen phosphate–arsenate

Aiming at the development of new proton conducting solids, recent studies of the NaH 2PO 4·H 2O–NaH 2AsO 4·H 2O system have lead to the synthesis of a new compound NaH 2(PO 4) 0.48(AsO 4) 0.52·H 2O (NDAP). Calorimetric studies have confirmed the presence of four reversible phase transitions (abbreviated by PhT), at 257/270 (PhT, IV), 261/290 (PhT, III), 267/301 (PhT, II) and 317/317.5 K (PhT, I) (for cooling/heating processes, respectively). It is shown that the III and IV phase transitions are of a first order type, with a “order-disorder and displacive” character, accompanied by specific dielectric anomalies. The behavior of the dielectric constant ε′ r and of tan δ shows that, at 272 K, the (PhT, IV) could be ferroelectric–paraelectric. As for the (PhT, III) at 296 K, it leads to a superionic–protonic phase; a jump in the conductivity is associated to this transition with an unusual high value of conductivity 1.07×10 −4 Ω −1 cm −1 and a low activation energy 0.39 eV (Kh. Jarraya et al .). Quandratic nonlinear (NLO) properties of NDAP powder was confirmed efficiency of the grown crystal by the Kurtz and Perry second harmonic generation (SHG) technique.

Study of bromide salts solubility in the ( m1NaBr + m2MgBr 2)(aq) system at T = 323.15 K. Thermodynamic model of solution behavior and (solid + liquid) equilibria in the (Na + K + Mg + Br + H 2O) system to high concentration and temperature

The bromide minerals solubility in the mixed system ( m 1NaBr + m 2MgBr 2)(aq) have been investigated at T = 323.15 K by the physico-chemical analysis method. The equilibrium crystallization of NaBr·2H 2O(cr), NaBr(cr), and MgBr 2·6H 2O(cr) has been established. The solubility-measurements results obtained have been combined with all other experimental equilibrium solubility data available in literature at T = (273.15 and 298.15) K to construct a chemical model that calculates (solid + liquid) equilibria in the mixed system ( m 1NaBr + m 2MgBr 2)(aq). The solubility modeling approach based on fundamental Pitzer specific interaction equations is employed. The model gives a very good agreement with bromide salts equilibrium solubility data. Temperature extrapolation of the mixed system model provides reasonable mineral solubility at high temperature (up to 100 °C). This model expands the previously published temperature variable sodium–potassium–bromide and potassium–magnesium–bromide models by evaluating sodium–magnesium mixing parameters. The resulting model for quaternary system (Na + K + Mg + Br + H 2O) is validated by comparing solubility predictions with those given in literature, and not used in the parameterization process. Limitations of the mixed solution models due to data insufficiencies at high temperature are discussed.

Leaching of low grade zinc oxide ores in Ida 2--H 2O system

Ida 2--H 2O system (iminodiacetate aqueous solution) was used to leach a low grade zinc oxide ore for Zn extraction. The effects of leaching time, liquid-solid ratio (L/S), total concentration of Ida 2- ([Ida 2-] t), leaching temperature and pH on Zn leaching recovery and the dissolution of impurities such as Ca, Mg, Cu, Ni, Fe, Pb and Cd were investigated. Results show that Ca, Mg and Fe in ores were hardly dissolved in alkalescent iminodiacetate aqueous solution, while valuable metals such as Cu, Ni, Pb and Cd were partly dissolved into leaching liquor with Zn. The recovery of Zn reaches 76.6% when the ores were leached for 4 h at 70 °C by 0.9 mol/L iminodiacetate aqueous solution with pH of 8 and L/S of 5:1.

Silver effect on the structure of SiO 2-CaO-P 2O 5 ternary system

In this study are reported results obtained from the structural, morphological and textural investigations of 56SiO 2∙(40-x)CaO·4P 2O 5·xAg 2O system, where 0 ≤ x ≤ 10 mol%. The samples obtained by sol–gel method were annealed and then characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), thermal gravimetric analysis (TGA), vibrational spectroscopy (Raman, FTIR), N 2-adsorption measurements, and transmission electron microscopy (TEM). XRD patterns of the investigated samples exhibit tricalcium phosphate (TCP) nanostructured phase and show the existence of metallic silver as dispersed phase. The presence of apatite-like phase is underlined by the recorded Raman and especially FT-IR spectra. TEM pictures indicate the presence of silver nanoparticles of almost spherical shapes and various sizes inside the matrix, depending on the Ag 2O content. Regarding the textural properties, it was observed both a decrease of the specific surface area as well as a progressive change of the mesoporous characteristics with the silver addition, the latter behavior recommending the potential use of these samples for applications, where the morphology control is required.

Oxidation pathways for formic acid under low temperature hydrothermal conditions: Implications for the chemical and isotopic evolution of organics on Mars

In order to evaluate the oxidation effect of dissolved hydrogen peroxide and the catalytic role of iron oxides on the kinetics of formic acid decarboxylation, a series of flow-through hydrothermal experiments was conducted at temperatures ranging from 80 to 150 °C and pressures of 172–241 bar. δ 13C composition of residual HCOOH (aq) was also monitored to examine kinetic isotope effects associated with oxidation processes. Our results reveal that decomposition of H 2O 2(aq) in presence of magnetite follows pseudo first order kinetics, highly enhanced relative to the homogeneous H 2O 2(aq)–HCOOOH (aq)–H 2O system, which possibly reflect synthesis of hydroxyl radicals ( OH) through Fenton processes. The kinetic rate constants of HCOOH (aq) decarboxylation to CO 2(aq) are also elevated relative to those previously measured in H 2O 2(aq) free experiments. However, reaction kinetics are slightly slower in the case of H 2O 2(aq) aqueous solutions coexisting with magnetite than in the absence of mineral phases. This behavior is attributed to the possible formation of Fe-bearing hydroxyl formate aqueous species that could serve as stable transition states leading to a decrease in the activation entropy of formic acid decomposition. δ 13C values of residual formic acid in the homogeneous H 2O 2(aq)–HCOOH (aq)–H 2O system are consistent with previous studies. However, magnetite-bearing experiments produce a negative shift in δ 13C of residual formic acid, perhaps specific to OH-imposed oxidation of organic compounds. This would indicate that isotopic fractionations by this oxidation pathway are opposite to kinetic fractionation effects expected in biologically driven oxidation processes. This could have important implications for putative H 2O 2(aq)-bearing Martian subsurface environments and the evolution of organics at low-temperature hydrothermal conditions.

Synergic effect of cyclopentane and tetra-n-butyl ammonium bromide on hydrate-based carbon dioxide separation from fuel gas mixture by measurements of gas uptake and X-ray diffraction patterns

The synergic effect of Cyclopentane (CP) and Tetra-n-butyl Ammonium Bromide (TBAB) on the hydrate-based carbon dioxide (CO 2) separation from IGCC (Integrated Gasification Combined Cycle) syngas is investigated by measuring the gas uptake and the power X-ray diffraction (PXRD) patterns in this work. The CP with CP/TBAB solution ratio of 5 vol% added into the 0.29 mol% TBAB solution can remarkably increase the gas uptake at 4.0 MPa and 274.65 K. The PXRD patterns of the semi-clathrate (sc) hydrate and structure II (sII) hydrate are obtained for the CP/TBAB/gas/H 2O system. The synergic effect of the CP and the TBAB includes two aspects: On one hand, the CP molecules housed in the hollow centers of the large cavities together with TBAB cations (TBA +) make the sc hydrate more stable. On the other hand, the TBA + displaced out of the large cavities by the CP molecules make the ionization reaction of TBAB in the solution going toward the reverse direction. Thus, the more TBAB molecules exist in the solution and form the more sc hydrate, resulting in the considerable increase of the gas uptake.

Efficient and convenient synthesis of spiroindolinone-quinazolines induced by stannous chloride

An efficient, convenient, one-pot synthesis of 1′ H-spiro[indoline-3,2′-quinazoline]-2,4′(3′ H)-dione derivatives was accomplished in good yields via the novel reductive cyclization of 2-nitrobenzamides and isatins mediated by SnCl 2·2H 2O system. A variety of substrates can participate in the process with good yields, making this methodology have broad applicability. The structure of compound 3c has been confirmed by X-ray diffraction analysis.

Control of the water fugacity at high pressures and temperatures: Applications to the incorporation mechanisms of water in olivine

A new method is developed to control water fugacity at a fixed pressure and temperature. We use two divariant phase assemblages (clinohumite–periclase–forsterite and brucite–periclase) in the MgO–SiO 2–H 2O system and the chemical reactions among co-existing phases buffer the water fugacity. In order to avoid a reaction between the water fugacity buffer and the specimen, a double-capsule assemblage was designed such that the water fugacity buffer was separated from the specimen by an inner metal jacket permeable to hydrogen and impermeable to other components. This method was applied to investigate the incorporation mechanisms of water in single crystals of San Carlos olivine as a function of water fugacity at 5 GPa and 1273 K. The chemical environment of the olivine crystal was controlled by the water fugacity buffer, the Ni–NiO oxygen fugacity buffer, and the olivine–orthopyroxene silica activity buffer. The establishment of chemical equilibrium was demonstrated by the presence of all relevant phases in the buffering reactions. The effect of water fugacity on water concentration in olivine was investigated using Fourier transform infrared (FTIR) spectroscopy with a polarized light. The total water concentration is nearly linearly dependent on water fugacity, indicating that the dominant incorporation mechanism of water in olivine involves two hydrogen atoms substituted in a Mg-site vacancy. The proposed method of the water fugacity buffer can be applicable to investigate the role of water in various important properties including water solubility and partitioning between mantle minerals, rheological properties, electrical conductivity, as well as solidus temperatures.

Pyrite–anhydrite–magnetite–pyroxene-type deposits and coexisting hydrothermal fluids in Mesozoic volcanic basins, Yangtze River Valley, China

Anhydrite–pyrite–magnetite–pyroxene–type deposits occur in the Mesozoic volcanic areas of the Middle–Lower Yangtze Valley in China. These deposits are hosted in alkaline basaltic rocks, and are generally accompanied by melanocratic and leucocratic alteration zones, both of which are characterized by a distinct vertical zonation pattern. Investigation of these zones indicates that the chemical compositions of solid solutions and polymorphs of various minerals vary spatially in the alteration profile, upwards from the lowest level, and outwards from the center. Here we report a case study on the Luohe deposit. In the melanocratic-alteration zone, the composition of magnetite (including trace elements Ti, V, Mg, Mn), pyroxene (Mg, Fe 2+, Fe 3+, Al 2O 3), plagioclase (An x Ab 1 − x ), pyrite (Co, Ni) and apatite (F, CeO 2 + Y 2O 3 + La 2O 3) changes with depth. The isotherms of hydrothermal fluids determined from fluid inclusion data, including homogenization temperature and salinity, also vary with depth. Activity diagrams were constructed from mineral and isotherm analysis to estimate the chemical constraints on the alteration-mineral assemblages and the coexisting hydrothermal solutions for the Na 2O–K 2O–CaO–MgO–FeO–Fe 2O 3–A1 2O 3–SiO 2–H 2SO 4–H 2S–HCI–H 2O system at 350 to 600 °C and 500 bars (50 MPa), assuming that the major alteration mineral assemblages along the profile reflect the nature of the coexisting hydrothermal solutions. The activity diagrams adopted the major minerals as buffers to fix the activities of the aqueous species in the system, simulating the physicochemical conditions of the magnetite–anhydrite–pyroxene equilibrium and of solid solutions of diopside–hedenbergite, grossular–andradite and anorthite–albite found in the profile. This study provides an approach to modeling the chemical constraints of coexisting fluids in ore-alteration zones based on field observations.

φ-pH diagram of V-Ti-H 2O system during pressure acid leaching of converter slag containing vanadium and titanium

To analyze the thermodynamic characteristics of leaching process of converter slag, φ-pH diagram of V-Ti-H 2O system at oxygen partial pressure of 0.5 MPa, ionic mass concentration of 0.1 mol/kg and temperatures ranging from 60 to 200 °C was obtained by recently published critically assessed standard Gibbs energies and activity coefficients of various species. When pH<2, stable regions of V 3+, VO 2+ and VO 2 + exist in the stable region of TiO 2. The pH values of stable regions of vanadium and titanium decrease and redox potentials become more positive with the temperature increasing. Vanadium and titanium could be separated by one-step leaching based on thermodynamics. The experiment results of pressure acid leaching of converter slag show that leaching rates of vanadium and titanium are 96.87% and 8.76% respectively, at 140 °C of temperature, 0.5 MPa of oxygen partial pressure, 0.055-0.075mm of particle size, 15:1 of liquid to solid ratio, 120 min of leaching time, 500 r/min of stirring speed and 200 g/L of initial acid concentration. Vanadium and titanium could be selectively separated in the pressure acid leaching process, and the experiment result is in agreement with thermodynamic calculation result.

Formation mechanism of fibrous cobalt oxalate precipitated from alkaline Co 2+–NH 3–C 2O 42−–H 2O system

The cobalt oxalate particles with fibrous morphology were obtained by precipitating CoCl 2 and mixed (NH 4) 2C 2O 4, NH 3·H 2O solutions in a double jets process. The samples were characterized by SEM, XRD, FTIR, TG/DTA and GCMS. Thermodynamic calculations and experiments revealed that the formation of Co(NH 3) n 2+ ( n = 1,2,…,6) results in species variation of cobalt oxalate precipitated in alkaline Co 2+–NH 3–C 2O 4 2−–H 2O system. It was found that there are two kinds of cobalt oxalates precipitated in Co 2+–NH 3–C 2O 4 2−–H 2O system with the change of synthetic conditions. One is β-CoC 2O 4·2H 2O with a square columnar morphology. The other is Co(NH 3) 1.5C 2O 4·2H 2O with a fibrous morphology, a species of cobalt oxalate without being recorded in newest JCPDS files. The formation mechanism of fibrous cobalt oxalate powders is that Co(NH 3) 1.5C 2O 4·2H 2O precipitates in alkaline Co 2+–NH 3–C 2O 4 2−–H 2O system.

Progress of hydration reactions in olivine–H 2O and orthopyroxenite–H 2O systems at 250 °C and vapor-saturated pressure

We conducted hydrothermal experiments in olivine (Ol; Fo 91)–H 2O and orthopyroxenite (Opx; composed of 95% of orthopyroxene, En 66)–H 2O systems under conditions of 250 °C and vapor-saturated pressure (P sat) to examine the temporal evolution of the solution chemistry and products in runs of up to 1008 h in duration. The maximal degree of hydration (i.e., H 2O content in the solid sample) in the Ol–H 2O experiments (3.6 wt.%) was much higher than that in the Opx–H 2O experiments (0.4 wt.%). In the Ol–H 2O experiments, Mg and Si in solution showed an initial increase (stage I) before decreasing (stage II) and finally attaining a steady state after 504 h (stage III). Following a drop in silica activity toward the level of brucite stability field, the products also changed from serpentine + magnetite (stages I and II) to serpentine + brucite + magnetite (stage III). Serpentine minerals also changed from lizardite (stages I and II) to lizardite + chrysotile (stage III). The zoning pattern of the products around olivine at 1008 h (brucite + serpentine at the olivine contact, and serpentine at the outermost rim) is consistent with the temporal changes in the mineralogy of the products, and is similar to the pattern observed in the mesh rims in partly serpentinized dunites. In the Opx–H 2O experiments, chlorite formed after orthopyroxene grains, which differs from the formation of talc and serpentine after orthopyroxene (bastite), as observed in natural hydrated harzburgites. The Opx–H 2O system maintained 10–10 3 times higher silica activity than Ol–H 2O system, suggesting that brucite does not form after olivine during hydration of peridotites when the Ol–H 2O system is linked to the Opx–H 2O system. The progress of hydration reactions is affected by mechanical properties of host rocks. The hydration reactions observed in this study produced hierarchical fractures in the reactants, which became filled with reaction products, similar to mesh textures after olivine in natural peridotites. This reaction-induced fracturing produced new reaction surfaces and fluid pathways that enhanced the hydration reactions. The overall reaction producing serpentine + brucite in the Ol–H 2O experiments showed the large volume expansion ( V/V 0 = 1.43 at stage III), whereas that producing only serpentine proceeded with near constant volume ( V/V 0 = 1.19 at stage I). The volume expansion is more difficult to occur in the oceanic lithosphere than in our experiments during serpentinization. Thus, in the case that volume expansion is prevented at reaction sites, one of the following outcomes occurs: (1) the hydration reaction stops until new fractures form, or (2) the reaction proceeds with low volume expansion (absence of brucite) by removing Mg from the system. These two outcomes would produce contrasting distributions or extent of hydration in oceanic lithosphere.

Hydrothermal transformation of magadiite into ferrierite in Al 2O 3–Na 2O–ethylenediamine–H 2O system

This study investigated the transformation of magadiite into ferrierite in Al 2O 3–Na 2O–ethylenediamine (EDA)–H 2O system. The influence of various parameters such as reaction temperature, time, alkalinity, the reactant Na 2O/SiO 2 ratio and EDA/SiO 2 ratio were examined. Thermal and acid stability of the synthetic ferrierite are presented. Highly crystallized and pure ferrierite could be obtained from dispersion with the molar composition: 0.01 Na 2O: 0.005 Al 2O 3: SiO 2: 30 H 2O: 20 EDA by heating at 433 K for 48 h. The structure of ferrierite was destroyed when the temperature rose above 873 K and the framework of the sample, stirred in 5 mol/L HCl for 3 h, is consistent with the untreated ferrierite.

Characterization of iron(III) oxide/hydroxide nanostructured materials produced by sol–gel technology based on the Fe(NO 3) 3·9H 2O–C 2H 5OH–CH 3CHCH 2O system

Nanostructured iron oxide/hydroxide materials were synthesized by sol–gel technology, starting from the ternary system Fe(NO 3) 3·9H 2O/ethanol/propylene oxide. Evaporative drying and supercritical fluids extraction were used as drying techniques to produce xerogels and aerogels, respectively. The materials were physically, structurally and chemically characterized, to analyze their suitability for surface-dependent applications and the influence of the drying technique on their properties. In addition, the chemistry involved in the sol–gel synthesis of iron oxides/hydroxides with the referred ternary system is reviewed. The produced materials were composed by aggregates of nanometric crystallites: ∼1 nm for xerogels and ∼5 nm for aerogels. Their high porosity and surface area (xerogels – 50% and 150 m 2 g −1; aerogels – 90% and 400 m 2 g −1) make them suitable for surface-dependent processes, being the aerogels far more adequate. The FTIR, XRD and Mössbauer spectroscopy results gave some insight on the composition of these materials, showing that the 2-line ferrihydrite is their most probable constituent phase. Finally, it was concluded that the continuous supercritical fluids extraction is the best drying procedure for these materials, since it preserves the mesoporous structure of the gels. When evaporative drying is used, the pores shrinkage leads to a predominantly microporous structure.

The formation of metastable aluminosilicates in the Al–Si–H 2O system: Results from solution chemistry and solid-state NMR spectroscopy

We present the results of a series of experiments designed to probe the interactions between Al and the amorphous silica surface as a function of thermodynamic driving forces. The results from 27Al single pulse magic angle spinning (SP/MAS) and 27Al{ 1H} rotational echo double resonance (REDOR) allow us to identify the reaction products and constrain their structure. In all cases, despite low Al and Si concentrations we observe the formation of metastable aluminosilicates. Results from low temperature experiments indicate that despite thermodynamic driving forces for the formation of gibbsite we observe the precipitation of separate octahedrally coordinated Al (Al [6]) and tetrahedrally coordinated Al (Al [4]) silicate phases. At higher temperatures the Al [4] silicate phase dominates the speciation. Structural models derived from the NMR data are also proposed, and the results are discussed as they relate to previous work on Al/Si cycling.

Synthesis and photocatalytic property of ZnSe flowerlike hierarchical structure

Spherical flowerlike hierarchical structure of ZnSe(en) 0.5 was synthesized via a solvothermal route in the NH 3·H 2O–ethylenediamine (en)–N 2H 4·H 2O system at 180 °C for 24 h. The hierarchical structure is assembled from lots of regular nanosheets. The ZnSe(en) 0.5 was further converted into pure hexagonal ZnSe by annealing in a flowing nitrogen gas at 500 °C for 1 h with morphology preserved. The formation mechanism of ZnSe was discussed. The UV–visible absorption spectrum and PL spectrum of the ZnSe spherical flowerlike hierarchical structure were measured. In addition, photocatalytic activity of the ZnSe flowerlike structure for the degradation of methyl orange under the irradiation of the simulated sunlight was investigated. The excellent catalytic activity for the degradation of methyl orange was found and the possible mechanism of the photocatalytic activity is also proposed.

Co-precipitation of radium in high ionic strength systems: 1. Thermodynamic properties of the Na–Ra–Cl–SO 4–H 2O system – Estimating Pitzer parameters for RaCl 2

The fate of divalent radium (Ra 2+) in high ionic strength systems is an important issue with relevant aspects to environmental concerns. As a consequence, the description of the thermodynamic properties of Ra 2+ in such systems is a critical matter which was not addressed yet. This can be done using the Pitzer formalism, which is regarded as the most accurate approach to describe activity coefficients of aquatic species in high ionic strength solutions. Isopiestic measurements, measurements of the electromotive force or the solubility of RaSO 4,S in NaCl solutions, which are essential for the evaluation of the Pitzer ion interaction parameters, were not experimentally tested, due to the high radioactivity concentration which involves such experiments. Therefore, the present study examined the possibility to extrapolate the RaCl 2 cation–anion interaction parameters ( β (0), β (1) and C ϕ) by linear regression of other MCl 2 cation–anion interaction parameters with their respective hydrated ionic radii (M 2+ = Mg 2+, Ca 2+, Sr 2+ and Ba 2+). γ Ra 2 + calculated with the estimated RaCl 2 parameters revealed that the ratios of activity coefficients γ Mg 2 + / γ Ba 2 + > γ Ca 2 + / γ Ba 2 + > γ Sr 2 + / γ Ba 2 + > 1 > γ Ra 2 + / γ Ba 2 + follow the opposite order of the ratios of hydrated ionic radii R Mg 2 + / R Ba 2 + < R Ca 2 + / R Ba 2 + < R Sr 2 + / R Ba 2 + < 1 < R Ra 2 + / R Ba 2 + . The activity coefficient of Ra 2+, γ Ra 2 + , calculated with these estimated values is used to test the limitation of the common assumption that the activity coefficients ratio, γ Ra 2 + / γ Ba 2 + , is close to unity. It is found that the common assumption of γ Ra 2 + / γ Ba 2 + = 1 may be considered reasonable up to high NaCl concentration. The largest deviation in the γ Ra 2 + / γ Ba 2 + ratio from this assumption was of the order of ∼25% in the range of halite solubility (6 mol kg −1 of NaCl). However, experimental results of co-precipitation of Ra 2+ in barite are described with more accuracy when the estimated RaCl 2 Pitzer parameters are used. These results are described in a consecutive paper of this journal.

Facile synthesis of gamma-MnS hierarchical nanostructures with high photoluminescence

A facile solvothermal method in the ethylene glycol–H 2O system has been proposed for controllable fabrication of well-crystallized γ-MnS hierarchical nanostructures. In this method, the addition of deionized water into the reaction solution shows a remarkable influence upon the morphology, especially on the preferential orientation growth. Typically, hollow γ-MnS nanospheres could be generated without use of deionized water. However, γ-MnS nanoflowers radially constructed by anisotropic nanorods would be readily obtained with the assistance of deionized water. Moreover, the dosage of deionized water can be used for controlling the crystallinity and particle size of γ-MnS nanoflowers. The role of deionized water played on the growth of γ-MnS nanoflowers has been discussed based on transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). The obtained γ-MnS nanorod-constructed nanoflowers exhibit improved PL property compared to hollow nanospheres, evidenced by the enhanced NBE emission centered at 364 nm.