Thermochemistry on dodecylamine hydrochloride and <Emphasis Type="Italic">bis</Emphasis>-dodecylammonium tetrachlorozincate

Dodecylamine hydrochloride C₁₂H₂₅NH₃·Cl(s) and bis-dodecylammonium tetrachlorozincate (C₁₂H₂₅NH₃)₂ZnCl₄(s) were synthesized by the method of liquid phase reaction. The constant-volume energy of combustion of dodecylamine hydrochloride was measured by means of a RBC-II precision rotating-bomb combustion calorimeter at T = (298.15 ± 0.001) K. The standard molar enthalpy of formation of C₁₂H₂₅NH₃·Cl(s) was calculated to be \Updelta_f H_m^o \Updelta_{\rm{f}} H_{\rm{m}}^{\rm{o}} (C₁₂H₂₅NH₃·Cl, s) = −(706.79 ± 3.97) kJ mol⁻¹ from the constant-volume energy of combustion. In accordance with Hess’ law, a reasonable thermochemical cycle was designed and the enthalpy change of the synthesis reaction of the complex (C₁₂H₂₅NH₃)₂ZnCl₄(s) was determined by use of an isoperibol solution-reaction calorimeter. The standard molar enthalpy of formation of (C₁₂H₂₅NH₃)₂ZnCl₄(s) was calculated as \Updelta_f H_m^o \Updelta_{\rm{f}} H_{\rm{m}}^{\rm{o}} [(C₁₂H₂₅NH₃)₂ZnCl₄, s] = −(1862.14 ± 7.95) kJ mol⁻¹ from the standard molar enthalpy of formation of C₁₂H₂₅NH₃·Cl(s) and other auxiliary thermodynamic data.     

Hydrothermal synthesis of (Fe,N) co-doped TiO<Subscript>2</Subscript> powders and their photocatalytic properties under visible light irradiation

(Fe, N) co-doped titanium dioxide powders have been prepared by a quick, low-temperature hydrothermal method using TiOSO₄, CO(NH₂)₂, Fe(NO₃)₃, and CN₃H₅ · HCl as starting materials. The synthesized powders were characterized by XRD, TEM, BET, XPS, and UV–Vis spectroscopy. Experimental results show that the as-synthesized TiO₂ powders are present as the anatase phase and that the N and Fe ions have been doped into the TiO₂ lattice. The specific surface area of the powders is 167.8 m²/g by the BET method and the mean grain size is about 11 nm, calculated by Scherrer’s formula. UV–Vis absorption spectra show that the edge of the photon absorption has been red-shifted up to 605 nm. The doped titanium dioxide powders had excellent photocatalytic activity during the process of photo-degradation of formaldehyde and some TVOC gases under visible light irradiation.     

Thermochemical study on ternary complex of dysprosium <Emphasis Type="Italic">m</Emphasis>-nitrobenzoic acid with <Emphasis Type="Italic">o</Emphasis>-phenanthroline

A ternary binuclear complex of dysprosium chloride hexahydrate with m-nitrobenzoic acid and 1,10-phenanthroline, [Dy(m-NBA)₃phen]₂·4H₂O (m-NBA: m-nitrobenzoate; phen: 1,10-phenanthroline) was synthesized. The dissolution enthalpies of [2phen·H₂O(s)], [6m-HNBA(s)], [2DyCl₃·6H₂O(s)], and [Dy(m-NBA)₃phen]₂·4H₂O(s) in the calorimetric solvent (V_DMSO:V_MeOH = 3:2) were determined by the solution–reaction isoperibol calorimeter at 298.15 K to be \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [2phen·H₂O(s), 298.15 K] = 21.7367 ± 0.3150 kJ·mol⁻¹, \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [6m-HNBA(s), 298.15 K] = 15.3635 ± 0.2235 kJ·mol⁻¹, \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [2DyCl₃·6H₂O(s), 298.15 K] = −203.5331 ± 0.2200 kJ·mol⁻¹, and \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [[Dy(m-NBA)₃phen]₂·4H₂O(s), 298.15 K] = 53.5965 ± 0.2367 kJ·mol⁻¹, respectively. The enthalpy change of the reaction was determined to be \Updelta_\textr H_\textm^q = 3 6 9. 4 9 ±0. 5 6   \textkJ·\textmol ^{- 1} . \Updelta_{\text{r}} H_{\text{m}}^{\theta } = 3 6 9. 4 9 \pm 0. 5 6 \;{\text{kJ}}\cdot {\text{mol}}^{ - 1} . According to the above results and the relevant data in the literature, through Hess’ law, the standard molar enthalpy of formation of [Dy(m-NBA)₃phen]₂·4H₂O(s) was estimated to be \Updelta_\textf H_\textm^q \Updelta_{\text{f}} H_{\text{m}}^{\theta } [[Dy(m-NBA)₃phen]₂·4H₂O(s), 298.15 K] = −5525 ± 6 kJ·mol⁻¹.     

Temperature programmed desorption of F-doped SnO<Subscript>2</Subscript> films deposited by inverted pyrosol technique

Fluorine-doped tin dioxide (FTO) films were deposited on silicon wafers by inverted pyrosol technique using solutions with different doping concentration (F/Sn=0.00, 0.12, 0.75 and 2.50). The physical and electrical properties of the deposited films were analyzed by SEM, XRF, resistivity measurement by four-point-probe method and Hall coefficient measurement by van der Pauw method. The electrical properties showed that the FTO film deposited using the solution with F/Sn=0.75 gave a lowest resistivity of 3.2·10^–4 ohm cm. The FTO films were analyzed by temperature programmed desorption (TPD). Evolved gases from the heated specimens were detected using a quadruple mass analyzer for mass fragments m/z, 1(H⁺), 2(H₂ ⁺), 12(C⁺), 14(N⁺), 15(CH₃ ⁺), 16(O⁺), 17(OH⁺ or NH₃ ⁺), 18(H₂O⁺ or NH₄ ⁺), 19(F⁺), 20(HF⁺), 28(CO⁺ or N₂ ⁺), 32(O₂ ⁺), 37(NH₄F⁺), 44(CO₂ ⁺), 120(Sn⁺), 136(SnO⁺) and 152(SnO₂ ⁺). The majority of evolved gases from all FTO films were water vapor, carbon monoxide and carbon dioxide. Fluorine (m/z 19) was detected only in doped films and its intensity was very strong for highly-doped films at temperature above 400°C.     

Synthesis and properties of LiMIIPO4 (MII = Mg,Mn0.5Mg0.5, Co0.5Mg0.5) affected by isodivalent doping and Li-sources

NH₄M^IIPO₄·H₂O (M^II = Mg, Mn_0.5Mg_0.5, Co_0.5Mg_0.5) were synthesized by direct-precipitating method. The olivine-like LiM^IIPO₄ were successfully generated through the solid state reaction between the synthesized NH₄M^IIPO₄·H₂O precursors and two different Li-sources (Li₂CO₃ or LiOH·H₂O). The NH₄M^IIPO₄·H₂O and LiM^IIPO₄ compounds were confirmed by TG/DTG/DTA, AAS/AES, FTIR and XRD methods. The structural and morphological properties of LiM^IIPO₄ compounds were studied by XRD and SEM, respectively. The XRD reflection shifts of olivine-like LiM^IIPO₄ from the Li-source of Li₂CO₃ revealed changing toward higher diffraction angles than that of LiM^IIPO₄ from the Li-source of LiOH·H₂O. The XRD shifts of LiM_0.5Mg_0.5PO₄ (M = Mn or Co) compounds confirmed the formation of the single phase of isodivalent doping of Mn²⁺ and Co²⁺ ions according to the change in the lattice parameters and cell volumes. The morphological investigations of the LiM^IIPO₄ obtained from Li₂CO₃ system illustrated the grain-like shape particles having smaller size of about 150–400 nm on account of the sequential transformations of types: deammoniation, dehydration, polycondensation and decarbonization. Conversely, the larger size particles (300–700 nm) of the LiM^IIPO₄ obtained from LiOH·H₂O were observed due to the shorter transformation path through the reactions of types: deammoniation and dehydration without polycondensation and decarbonization.     

High photosynthetic productivity of green microalga Chlorella sorokiniana

The batch culture of a newly isolated strain of a green microalga, Chlorella sorokiniana, was carried out using a conical helical tubular photobioreactor. The isolate was capable of good growth at 40°C under an airstream enriched with 10% CO₂. The maximum photosynthetic productivity was 34.4g of dry biomass/(m² of installation area · d) (12-h light/12-h dark cycle) when the cells were illuminated with an average photosynthetic photon flux density (photosynthetically active radiation ([PAR] 400–700 nm) simulating the outdoors in central Japan (0.980 mmol photons/[m²·s]). This corresponded to a photosynthetic efficiency of 8.67% (PAR), which was defined as the percentage of the light energy recovered as biomass (394 kJ/[reactor·d]) to the total light energy received (4545 kJ/[reactor·d]). A similarly high photosynthetic efficiency (8.12% [PAR]) was also attained in the combined presence of 10% CO₂, 100 ppm of NO, and 25 ppm of SO₂. Moreover, good photosynthetic productivity was also obtained under high temperature and high light intensity conditions (maximum temperature, 46.5°C; 1.737 mmol photons/[m²·s]), when simulating the strong irradiance of the midday summer sun. This strain thus appears well suited for practical application for converting CO₂ present in the stack gases emitted by thermal power plants and should be feasible even during the hot summer weather.     

Thermodynamics of sodium 5-methylisophthalic acid monohydrate and sodium isophthalic acid hemihydrate

Two crystal samples, sodium 5-methylisophthalic acid monohydrate (C₉H₆O₄Na₂·H₂O, s) and sodium isophthalic acid hemihydrate (C₈H₄O₄Na₂·1/2H₂O, s), were prepared from water solution. Low-temperature heat capacities of the solid samples for sodium 5-methylisophthalic acid monohydrate (C₉H₆O₄Na₂·H₂O, s) and sodium isophthalic acid hemihydrate (C₈H₄O₄Na₂·1/2H₂O, s) were measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 379 K. The experimental values of the molar heat capacities in the measured temperature region were fitted to a polynomial equation on molar heat capacities (C _p,m) with the reduced temperatures (X), [X = f(T)], by a least-squares method. Thermodynamic functions of the compounds (C₉H₆O₄Na₂·H₂O, s) and (C₈H₄O₄Na₂·1/2H₂O, s) were calculated based on the fitted polynomial equation. The constant-volume energies of combustion of the compounds at T = 298.15 K were measured by a precise rotating-bomb combustion calorimeter to be Δ_c U(C₉H₆O₄Na₂·H₂O, s) = −15428.49 ± 4.86 J g⁻¹ and Δ_c U(C₈H₄O₄Na₂·1/2H₂O, s) = −13484.25 ± 5.56 J g⁻¹. The standard molar enthalpies of formation of the compounds were calculated to be Δ _f H _m ^θ (C₉H₆O₄Na₂·H₂O, s) = −1458.740 ± 1.668 kJ mol⁻¹ and Δ _f H _m ^θ (C₈H₄O₄Na₂·1/2H₂O, s) = −2078.392 ± 1.605 kJ mol⁻¹ in accordance with Hess’ law. The standard molar enthalpies of solution of the compounds, Δ _sol H _m ^θ (C₉H₆O₄Na₂·H₂O, s) and Δ _sol H _m ^θ (C₈H₄O₄Na₂·1/2H₂O, s), have been determined as being −11.917 ± 0.055 and −29.078 ± 0.069 kJ mol⁻¹ by an RD496-2000 type microcalorimeter. In addition, the standard molar enthalpies of hydrated anion of the compounds were determined as being Δ _f H _m ^θ (C₉H₆O₄ ²⁻, aq) = −704.227 ± 1.674 kJ mol⁻¹ and Δ _f H _m ^θ (C₈H₄O₄Na₂ ²⁻, aq) = −1483.955 ± 1.612 kJ mol⁻¹, from the standard molar enthalpies of solution and other auxiliary thermodynamic data through a thermochemical cycle.     

The effect of solid adsorbents in Triethanolamine (TEA) solution for enhanced CO2 absorption rate

This study aimed to investigate CO₂ absorption using chemical solvent of amine H₂O-TEA-CO₂ in presence of activated carbon (AC) particles. The studied experimental range includes the temperature in range of 293–333 K, pressure in range of 3.5–9.5 bar, the concentration of solvents in range of 2.5–8.5 wt%, and amount of activated carbon in range of 0.3–0.9 kg/m³. The central composite design (CCD) with four parameters of temperature, pressure, amine concentration, and active carbon was applied in 5 levels. The physical solubility CO₂ in amine solutions decreases with the increasing temperature that indicates the process is exothermic. The optimal values of temperature, pressure, concentration, and active carbon are 303.0 K, 8.00 bar, 7.00 M, 0.75 g, respectively, and 25.99% for the input variables and desirability index of 0.732. The CO₂ loading, absorption capacity, and absorption percentage are obtained in the range of 0.572–1.180 mol_CO2/mol_TEA, 0.208–0.506 wt%, and 12.73–32.61% in Triethanolamine (TEA) solutions in activated carbon, respectively. All dependent variables had a p value of less than 0.05, indicating that models were significant and substantial. The result showed that the addition of solid particles to chemical solvents effectively enhances CO₂ absorption.

     

Gas sensing selectivity of hexagonal and monoclinic WO3 to H2S

Hexagonal and monoclinic tungsten oxide (h- and m-WO₃) samples were produced by annealing hexagonal ammonium tungsten bronze, (NH₄)_0.07(NH₃)_0.04(H₂O)_0.09WO_2.95 at 470 and at 600 °C, respectively. Their structure, composition and morphology were analyzed by XRD, Raman, XPS, ¹H-MAS NMR and SEM. In order to study the effect of crystal structure on the gas sensitivity of tungsten oxides, h- and m-WO₃ were tested as gas sensors to CH₄, CO, H₂, NO and H₂S (1000 and 10 ppm) at 200 °C. Monoclinic WO₃ responded to all gases, but its gas sensing signal was two magnitudes greater to 10 ppm H₂S than to other gases, and it also detected H₂S even at 25 °C. Hexagonal WO₃ responded only to 10 ppm H₂S. Its sensitivity was smaller compared to m-WO₃, however, the response time of h-WO₃ was significantly faster. The gas sensing tests showed that while m-WO₃ had relative selectivity to H₂S in the presence CH₄, CO, H₂, NO; h-WO₃ had absolute selectivity to H₂S in the presence these gases.     

Study on Adsorption Properties of Ammonium Exchanged Chabazite for CO2

Ammonium type chabazite (NH₄CHA) and magnesium type chabazite (MgCHA) was prepared by hydrothermal synthesis and hydrothermal ion exchange. The structure and morphology of ion‐exchanged chabazite was characterized with various experimental techniques such as XRD, SEM, and ICP. The gas adsorption amount of chabazite decreases gradually with increase in temperature or decrease in pressure. The adsorption capacity of NH₄CHA to CO₂ was 3.33 mmol · g^–1 at 273 K, and the saturated adsorption capacity of NH₄CHA reached 3.88 mmol · g^–1 under extreme pressure. The CO₂ molecule was more likely to be adsorbed by all chabazite samples than the N₂ molecule due to its linear molecular structure and greater molecular polarity. NH₄CHA exhibited larger CO₂/N₂ selectivity, which first increased and then declined with the temperature decreasing, and reached the maximum value between 400 K to 450 K.     

Thermodynamic properties of Na2Ti6O13 and Na2Ti3O7: electrochemical and calorimetric determination

Standard values of Gibbs free energy, entropy, and enthalpy of Na₂Ti₆O₁₃ and Na₂Ti₃O₇ were determined by evaluating emf-measurements of thermodynamically defined solid state electrochemical cells based on a Na–β″-alumina electrolyte. The central part of the anodic half cell consisted of Na₂CO₃, while two appropriate coexisting phases of the ternary system Na–Ti–O are used as cathodic materials. The cell was placed in an atmosphere containing CO₂ and O₂. By combining the results of emf-measurements in the temperature range of 573⩽T/K⩽1023 and of adiabatic calorimetric measurements of the heat capacities in the low-temperature region 15⩽T/K⩽300, the thermodynamic data were determined for a wide temperature range of 15⩽T/K⩽1100. The standard molar enthalpy of formation and standard molar entropy at T=298.15 K as determined by emf-measurements are Δ_fH_m⁰=(−6277.9±6.5) kJ · mol⁻¹ and S_m⁰=(404.6±5.3) J · mol⁻¹ · K⁻¹ for Na₂Ti₆O₁₃ and Δ_fH_m⁰=(−3459.2±3.8) kJ · mol⁻¹ and S_m⁰=(227.8±3.7) J · mol⁻¹ · K⁻¹ for Na₂Ti₃O₇. The standard molar entropy at T=298.15 K obtained from low-temperature calorimetry is S_m⁰=399.7 J · mol⁻¹ · K⁻¹ and S_m⁰=229.4 J · mol⁻¹ · K⁻¹ for Na₂Ti₆O₁₃ and Na₂Ti₃O₇, respectively. The phase widths with respect to Na₂O content were studied by using a Na₂O-titration technique.     

A synthesis of porous activated carbon materials derived from vitamin B9 base for CO2 capture and conversion

CO₂ capture and conversion are still a favorable way to reduce CO₂ in the atmosphere. Herein, we have developed an environmentally friendly, low energy consumption porous activated carbon from vitamin B9 carbonaceous material for CO₂ capture and conversion materials. It is demonstrated that the KOH/vitamin B9 carbonaceous material impregnation ratio of 2 is the optimum condition for obtaining porous activated carbons with high specific surface area of 1903 m²g^-1, micropore surface area of 710 m²g^-1, total pore volume of 1.05 cm³g^-1 and micropore volume of 0.38 cm³g^-1. Among all the porous activated carbons prepared, the porous activated carbon synthesized with the KOH/vitamin B9 carbonaceous material impregnation ratio of 2 registers the most excellent CO₂ capture for 5.41 mmolg^?1 at 0 °C/1 bar and 3.66 mmolg^?1 at 25 °C/1 bar. They can also effectively catalyze the cycloaddition of CO₂ and epoxides under mild conditions (1 bar, 100 °C and 8 h) with a yield of 89–94%. The synthesized porous carbon materials from vitamin B9 is a promising candidate material for CO₂ capture and fixation.     

Thermochemical Study on [La(Hsal)2•(tch)]•2H2O [Hsal＝salicylate ( ), tch＝thioprolinate (C4H6NO2S-)]

The product from reaction of lanthanum chloride heptahydrate with salicylic acid and thioproline, [La(Hsal)2•(tch)]•2H2O, was synthesized and characterized by IR, elemental analysis, molar conductance, thermogravimatric analysis and chemistry analysis. The standard molar enthalpies of solution of LaCl3•7H2O (s), [2C7H6O3 (s)], C4H7NO2S (s) and [La(Hsal)2•(tch)]•2H2O (s) in a mixed solvent of absolute ethyl alcohol, dimethyl sulfoxide (DMSO) and 3 mol•L－1 HCl were determined by calorimetry to be [LaCl3•7H2O (s), 298.15 K]＝(－102.36±0.66) kJ•mol－1, [2C7H6O3 (s), 298.15 K]＝(26.65±0.22) kJ•mol－1, [C4H7NO2S (s), 298.15 K]＝(－21.79±0.35) kJ•mol－1 and {[La(Hsal)2•(tch)]•2H2O (s), 298.15 K}＝(－41.10±0.32) kJ•mol－1. The enthalpy change of the reaction LaCl3•7H2O (s)＋2C7H6O3 (s)＋C4H7NO2S (s)＝[La(Hsal)2•(tch)]•2H2O (s)＋3HCl (g)＋5H2O (l) (Eq. 1) was determined to be ＝(41.02±0.85) kJ•mol－1. From date in the literature, through Hess’ law, the standard molar enthalpy of formation of [La(Hsal)2•(tch)]•2H2O (s) was estimated to be {[La(Hsal)2•(tch)]•2H2O (s), 298.15 K}＝(－3017.0±3.7) kJ•mol－1.     

Measuring the solubility of CO2 and H2S in sulfolane and the density and viscosity of saturated liquid binary mixtures of (sulfolane + CO2) and (sulfolane + H2S)

The density and viscosity of liquid sulfolane saturated (loaded) with single CO₂ and H₂S gases were measured simultaneously with the solubility of the single CO₂ and H₂S gases in sulfolane at temperatures ranging from (303.15 to 363.15) K and pressures of up to about 2.4 MPa using a new experimental set-up developed in our laboratory. The experimental density and viscosity values were correlated using a modified Setchenow-type equation. It was observed that the density and viscosity of mixtures decrease by increasing temperature and acid gas solubility (loading) in sulfolane. Acid gas loading has a much profounder effect on the viscosity of solutions than on their density, i.e. at a concentration of 1 mol CO₂/H₂S per kg of sulfolane the density decreases by less than 3%, but viscosity decreases by more than 30%. Results show that at fixed temperature and pressure H₂S is more than four times as soluble as CO₂ in sulfolane. The measured solubility and density values were respectively used to obtain Henry’s law constants and partial molar volumes at infinite dilution for dissolution of CO₂ and H₂S gases in the liquid sulfolane at the temperatures studied. The Henry’s law constants obtained at different temperatures were used to determine infinite dilution partial molar thermodynamic functions (Gibbs free energy, enthalpy and entropy) of solution. The measured solubility data were correlated by using a model comprised of the extended Henry’s law and the Pitzer’s virial expansion for the excess Gibbs free energy.     

Study of the solubility of CO2, H2S and their mixture in the ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate: Experimental and modelling

New experimental results are presented for the solubility of carbon dioxide, hydrogen sulfide in the ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate ([C₈mim][PF₆]) at temperatures range from (303.15 to 353.15) K and pressures up to about 2 MPa. The solubility of the mixture of CO₂/H₂S in [C₈mim][PF₆] under various feed compositions were also measured at temperatures of (303.15, 323.15 and 343.15) K and the pressure up to 1 MPa. The solubility of carbon dioxide and hydrogen sulfide increased with increasing pressure and decreased with increasing temperature and the solubility of H₂S is about three times that of CO₂ in the particular ionic liquid studied. The measured data were correlated using extended Henry’s law included Pitzer’s virial expansion for the excess Gibbs energy, and the generic Redlich–Kwong cubic equation of state proposed for gas/ionic liquid systems. The correlations from the two models show quite good consistency with the experimental data for CO₂/IL and H₂S/IL binary mixtures within experimental uncertainties. For CO₂/H₂S/IL ternary mixtures, the RK model shows better correlation with the experimental values. We also studied the effect of cation alkyl chain length on the CO₂ and H₂S solubility by comparison of the experimental data of this study with those of previous reports. As the cation alkyl chain length became longer, the solubility of CO₂ and H₂S increased in the ionic liquid. Additionally, the influence of the anion on the solubility is studied by comparing the solubility of CO₂ and H₂S in [C₈mim][PF₆] with those in [C₈mim][Tf₂N]. As a result, CO₂ and H₂S have higher solubility in the IL with [Tf₂N]⁻ as the anion.     

Equilibrium solubility of carbon dioxide in the amine solvent system of (triethanolamine + piperazine + water)

In this study, a new set of data for the equilibrium solubility of carbon dioxide in the amine solvent system that consists of triethanolamine (TEA), piperazine (PZ), and water is presented. Equilibrium solubility values were obtained at T = (313.2, 333.2, and 353.2) K and pressures up to 153 kPa using the vapour-recirculation equilibrium cell. The TEA concentrations in the considered ternary (solvent) mixture were (2 and 3) kmol · m^?3 and those of PZ’s were (0.5, 1.0, and 1.5) kmol · m^?3. The solubility data (CO₂ loading in the amine solution) obtained were correlated as a function of CO₂ partial pressure, system temperature, and amine composition via the modified Kent–Eisenberg model. Results showed that the model applied is generally satisfactory in representing the CO₂ absorption into mixed aqueous solutions of TEA and PZ.     

Phase behaviour of mixed-gas hydrate systems containing carbon dioxide

We describe a new apparatus suitable for measurements of the phase behaviour and phase properties of fluid mixtures under conditions of high-pressure. We propose a synthetic method for the determination of gas solubility, and present results for the system (CO₂ + H₂O). In addition, we report new measurements of the hydrate equilibrium curves in aqueous systems containing either pure carbon dioxide or mixed gases including CO₂. For hydrates formed in the (CO₂ + H₂O) system, we find an enthalpy of dissociation of 77 kJ · mol^?1. This value was unchanged by the addition of mass fraction 0.043 of NaCl to the water. Compared with pure CO₂, mixtures of CO₂ with air exhibited markedly different dissociation pressures at given temperature, but were characterised by the same enthalpy of dissociation. However, two mixtures containing either nitrogen or methane and hydrogen both exhibited a higher enthalpy of dissociation, 106 kJ · mol^?1, consistent with these systems forming structure II hydrates.     

Syntheses,characterization and nonlinear optical properties of sodium–scandium carbonate Na5Sc(CO3)4·2H2O

A novel nonlinear optical (NLO) material Na₅Sc(CO₃)₄·2H₂O has been synthesized under a subcritical hydrothermal condition. The structure is determined by single-crystal X-ray diffraction and further characterized by TG analyses and UV–vis–NIR diffuse reflectance spectrum. It crystallizes in the tetragonal space group P-421c, with a = b = 7.4622(6) Å, C = 11.5928(15) Å. The Second-harmonic generation (SHG) on polycrystalline samples was measured using the Kurtz and Perry technique, which indicated that Na₅Sc(CO₃)₄·2H₂O was a phase-matchable material, and its measured SHG coefficient was about 1.8 times as large as that of d₃₆ (KDP). The results from the UV–vis diffuse reflectance spectroscopy study of the powder samples indicated that the short-wavelength absorption edges of Na₅Sc(CO₃)₄·2H₂O is about 220 nm, suggesting that this crystal is a promising UV nonlinear optical (NLO) materials.     

Synthesis and polymerization of 2-alkylanilines

2-Alkylanilines with alkyl groups in the range of 4–15 carbon atoms were synthesized via a known method as well as via a more general path which should allow the introduction of a larger variety of substituted alkyl groups into the ortho position of aniline, e.g., alkenyl or OH, NH₂, COOH, and phenyl functionality. Polymerization was found to be achievable according to a method previously described for unsubstituted aniline, i.e., chemically with Cu(ClO₄)₂ · 6H₂O in acetonitrile. Intrinsic viscosities of the obtained poly(2-alkylaniline)s lay between 0.10 and 0.26 dL/g (97% H₂SO₄ at 30°C). The dc conductivity of the HCl salts decreased with increasing length of the alkyl side chains from 1 S/cm (polyaniline) over 3 X 10^?4 S/cm [poly(2-butylaniline)] to 1 X 10^?6 S/cm poly(tridecylaniline). Further characterization of the polymers were performed by means of UV/VIS/NIR-and-IR spectroscopy, in dilute solutions or as KBr pellets, respectively, and by solubility tests. © 1993 John Wiley & Sons, Inc.     

Rare Earth Chalcogels NaLnSnS4 (Ln = Y,Gd, Tb) for Selective Adsorption of Volatile Hydrocarbons and Gases

The synthesis and characterization of the rare earth chalcogenide aerogels NaYSnS₄, NaGdSnS₄, and NaTbSnS₄ is reported. Rare earth metal ions like Y³⁺, Gd³⁺, and Tb³⁺ react with the chalcogenide clusters [SnS₄]^4– in aqueous formamide solution forming extended polymeric networks by gelation. Aerogels obtained after supercritical drying have BET surface areas of 649 m² · g^–1 (NaYSnS₄), 479 m² · g^–1 (NaGdSnS₄), and 354 m² · g^–1 (NaTbSnS₄). Electron microscopy and physisorption studies reveal that the new materials have pores in the macro (above 50 nm) and meso (2–50 nm) regions. These aerogels show higher adsorption of toluene vapor over cyclohexane vapor and CO₂ over CH₄ or H₂. The notable adsorption capacity for toluene (NaYSnS₄: 1108 mg · g^–1; NaGdSnS₄: 921 mg · g^–1; and NaTbSnS4: 645 mg · g^–1) and high selectivity for gases (CO₂/H₂: 172 and CO₂/CH₄: 50 for NaYSnS₄, CO₂/H₂: 155 and CO₂/CH₄: 37 for NaGdSnS₄, and CO₂/H₂: 75 and CO₂/CH₄: 28 for NaTbSnS₄) indicate potential future use of chalcogels in adsorption‐based gas or hydrocarbon separation processes.