Synthesis, heat capacity and enthalpy of formation of [Ho2(l-Glu)2(H2O)8](ClO4)4·H2O

A complex of holmium perchlorate coordinated with l-glutamic acid, [Ho₂(l-Glu)₂(H₂O)₈](ClO₄)₄·H₂O, was prepared with a purity of 98.96%. The compound was characterized by chemical, elemental and thermal analysis. Heat capacities of the compound were determined by automated adiabatic calorimetry from 78 to 370 K. The dehydration temperature is 350 K. The dehydration enthalpy and entropy are 16.34 kJ mol⁻¹ and 16.67 J K⁻¹ mol⁻¹, respectively. The standard enthalpy of formation is −6474.6 kJ mol⁻¹ from reaction calorimetry at 298.15 K.     

PAMAM dendrimer composite membrane for CO2 separation: Formation of a chitosan gutter layer

A poly(amidoamine) (PAMAM) dendrimer composite membrane with an excellent CO₂/N₂ separation factor was developed in-situ. The In-situ Modification (IM) method was used to modify the surface of commercial porous membranes, such as ultrafiltration membranes, to produce a gas selective layer by controlling the interface precipitation of the membrane materials in the state of a received membrane module. Using the IM method, a chitosan layer was prepared on the inner surface of a commercially available ultrafiltration membrane as a gutter layer, in order to affix PAMAM dendrimer molecules on the porous substrate. After chitosan treatment, the PAMAM dendrimer was impregnated into the gutter layer to form a PAMAM/chitosan hybrid layer. The CO₂ separation performance of the resulting composite membrane was tested at a pressure difference of 100 kPa and a temperature of 40 °C, using a mixed CO₂ (5 vol%)/N₂ (95 vol%) feed gas. The PAMAM dendrimer composite membrane, with a gutter layer prepared from ethylene glycol diglycidyl ether and a 0.5 wt% chitosan solution of two different molecular weight chitosans, revealed an excellent CO₂/N₂ separation factor and a CO₂ permeance of 400 and 1.6 × 10⁻⁷ m³ (STP) m⁻² s⁻¹ kPa⁻¹, respectively. SEM observations revealed a defect-free chitosan layer (thickness 200 nm) positioned directly beneath the top surface of the UF membrane substrate. After PAMAM dendrimer treatment, the hybrid chitosan/PAMAM dendrimer layer was observed with a thickness of 300 nm. XPS analysis indicated that the hybrid layer contained about 20–40% PAMAM dendrimer.     

Solid products and rate-limiting step in the thermal half decomposition of natural dolomite in a CO2 (g) atmosphere

Natural dolomite powders obtained from caves which give unusual high resistance building materials, have been decomposed in a Knudsen cell at high CO₂ pressures in the temperature range of 913-973 K. XRD traces for the final solid products, after the first half thermal decomposition, have shown, that beside the XRD patterns for the calcite and MgO, the existence of a new structure with major peaks at 2θ equal to 38.5 and 65°. This finding has been ascribed to a solid solution of MgO in calcite. The kinetic analysis of the TG curves yield a total apparent enthalpy (ΔH^∗) for the decomposition equal to 440±10 kJ mol⁻¹ for a range of fraction decomposed (α) varying between 0.2 and 0.7. This value is much closer to the theoretical expected at 950 K value ΔH=486 kJ mol⁻¹ for the dolomite decomposition in CO₂ environment, where CaO, MgO and oxides of solid solution can be the solid reaction products. The rate determining step is the transport of CO₂ across the reacting interface through an high activated thermal process due to solid state diffusion of CO₃²⁻ in the bulk and/or the grain boundaries phases of CaCO₃ and/or of the solid solution. The microstructure evolution of the solid products follows a shear-transformation mechanism. At temperatures below 943 K, porous product particles are characterized by a monomodal narrow pore size distribution around 0.05 μm. At higher temperatures, a critical level of tensions inside the particles is reached and a bimodal pore size distribution around 1 and 0.05 μm is formed.     

Anodic alumina supported dual-layer microporous silica membranes

We present a new processing scheme for the deposition of microporous, sol–gel derived silica membranes on inexpensive, commercially available anodic alumina (Anodisk™) supports. In a first step, a surfactant-templated mesoporous silica sublayer (pore size 2–6 nm) is deposited on the Anodisk support by dip-coating, in order to provide a smooth transition from the pore size of the support (20 or 100 nm) to that of the membrane (3–4 Å). Subsequently, the microporous gas separation membrane layer is deposited by spin-coating, resulting in a defect-free dual-layer micro-/mesoporous silica membrane exhibiting high permeance and high selectivity for size selective gas separations. For example, in the case of CO₂:N₂ separation, the CO₂ permeance reached 3.0 MPU (1 MPU = 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹) coupled with a CO₂:N₂ separation factor in excess of 80 at 25 °C. This processing scheme can be utilized for laboratory-scale development of other types of microporous or dense inorganic membranes, taking advantage of the availability, low cost and low permeation resistance of anodic alumina (or other metal oxide) meso- and macroporous supports.     

Facile fabrication of a novel high performance CO2 separation membrane: Immobilization of poly(amidoamine) dendrimers in poly(ethylene glycol) networks

Poly(amidoamine) (PAMAM) dendrimers showed high CO₂ separation properties and were successfully immobilized in a poly(ethylene glycol) (PEG) network upon photopolymerization of PEG dimethacrylate. The PAMAM dendrimer incorporation ratio was readily controlled, and a stable self-standing membrane containing up to 75 wt.% PAMAM dendrimer was obtained. The CO₂ separation properties over smaller H₂ were investigated by changing the PAMAM dendrimer content or generation and CO₂ partial pressure (ΔPCO₂$\mathrm{\Delta }{P}_{\text{C}{\text{O}}_2}$) under atmospheric conditions. Especially, a polymeric membrane containing 50 wt.% PAMAM dendrimer (0th generation) exhibited an excellent CO₂/H₂ selectivity of 500 with CO₂ permeability of 2.74 × 10⁻¹⁴ m³(STP)m/(m² s Pa) or 3.65 × 10³ barrer (1 barrer = 7.5 × 10⁻¹⁸ m³(STP)m/(m² s Pa)) when a mixture gas (CO₂/H₂: 5/95 by vol.) was fed at 25 °C and 100 kPa with 80% relative humidity. This polymeric materials are promising for a novel CO₂ separation membrane.     

Calorimetric study and thermal analysis of [Gd4/3Y2/3(Gly)6(H2O)4](ClO4)6·5H2O and [ErY(Gly)6(H2O)4](ClO4)6·5H2O (Gly: glycin)

Two solid-state coordination compounds of rare earth metals with glycin, [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O and [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O were synthesized. The low-temperature heat capacities of the two coordination compounds were measured with an adiabatic calorimeter over the temperature range from 78 to 376 K. [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O melted at 342.90 K, while [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O melted at 328.79 K. The molar enthalpy and entropy of fusion for the two coordination compounds were determined to be 18.48 kJ mol⁻¹ and 53.9 J K⁻¹ mol⁻¹ for [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O, 1.82 kJ mol⁻¹ and 5.5 J K⁻¹ mol⁻¹ for [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O, respectively. Thermal decompositions of the two coordination compounds were studied through the thermogravimetry (TG). Possible mechanisms of the decompositions are discussed.     

Change in mechanistic pathway of hydroboration: A detailed kinetic study of H2BBr·SMe2 and HBBr2·SMe2

Hydroboration reactions of 1-octene and 1-hexyne with H₂BBr·SMe₂ in CH₂Cl₂ were studied as a function of concentration and temperature, using ¹¹B NMR spectroscopy. The reactions exhibited saturation kinetics. The rate of dissociation of dimethyl sulfide from boron at 25 °C was found to be (7.36 ± 0.59 and 7.32 ± 0.90) × 10⁻³ s⁻¹ for 1-octene and 1-hexyne, respectively. The second order rate constants, k₂, for hydroboration worked out to be 7.00 ± 0.81 M s⁻¹ and 7.03 ± 0.70 M s⁻¹, while the overall composite second order rate constants, k K, were (3.30 ± 0.43 and 3.10 ± 0.37) × 10⁻² M s⁻¹, respectively at 25 °C. The entropy and enthalpy values were found to be large and positive for k₁, whilst for k₂ these were large and negative, with small values for enthalpies. This is indicative of a limiting dissociative (D) for the dissociation of Me₂S and associative mechanism (A) for the hydroboration process. The overall activation parameters, ΔH^≠ and ΔS^≠, were found to be 98 ± 2 kJ mol⁻¹ and +56 ± 7 J K⁻¹ mol⁻¹ for 1-octene whilst, in the case of 1-hexyne these were found out to be 117 ± 7 kJ mol⁻¹ and +119 ± 24 J K⁻¹ mol⁻¹, respectively. When comparing the kinetic data between H₂BBr·SMe₂ and HBBr₂·SMe₂, the results showed that the rate of dissociation of Me₂S from H₂BBr·SMe₂ is on average 34 times faster than it is in the case of HBBr₂·SMe₂. Similarly, the rate of hydroboration with H₂BBr·SMe₂ was found to be on average 11 times faster than it is with HBBr₂·SMe₂. It is also clear that by replacing a hydrogen substituent with a bromine atom in the case of H₂BBr·SMe₂ the mechanism for the overall process changes from limiting dissociative (D) to interchange associative (I_a).     

Systematic investigation on new SrCo1−yNbyO3−δ ceramic membranes with high oxygen semi-permeability

SrCo_1−yNb_yO_3−δ (y = 0.025–0.4) were synthesized for oxygen separation application. The crystal structure, phase stability, oxygen nonstoichiometry, electrical conductivity, and oxygen permeability of the oxides were systematically investigated. Cubic perovskite, with enhanced phase stability at higher Nb concentration, was obtained at y = 0.025–0.2. However, the further increase in niobium concentration led to the formation of impurity phase. The niobium doping concentration also had a significant effect on electrical conductivity and oxygen permeability of the membranes. SrCo_0.9Nb_0.1O_3−δ exhibited the highest electrical conductivity and oxygen permeability among the others. It reached a permeation flux of ∼2.80 × 10⁻⁶ mol cm⁻² s⁻¹ at 900 °C for a 1.0-mm membrane under an air/helium oxygen gradient. The further investigation demonstrated the oxygen permeation process was mainly rate-limited by the oxygen bulk diffusion process.     

Theoretical study of the triplet excited state of PtPOP and the exciplexes M-PtPOP (M = Tl, Ag) in solution and comparison with ultrafast X-ray scattering results

The [Pt₂(H₂P₂O₅)₄]⁴⁻ ions in the ground and excited states and the excited-state complexes M-[Pt₂(H₂P₂O₅)₄]³⁻ and M₂-[Pt₂(H₂P₂O₅)₄]²⁻ (M = Ag, Tl) were studied in solution with various density functional theory (DFT) functionals from Gaussian 09 and Amsterdam Density Functional (ADF) programs. Calculated results were compared with ultrafast X-ray solution scattering data. Time dependent DFT (TD-DFT) calculations with the B3PW91 functional and unrestricted open shell calculations with the mPBE functional produce good agreement with the experimental results. Compared to gas phase calculations, the surrounding solvent is found to play an important role to shorten the Pt-Pt and M-Pt (M = Ag, Tl) bond lengths, lowering the molecular orbital energies and influences the molecular orbital transitions upon excitation, which stabilizes the excited transient molecules in solution.     

Direct electrocatalytic oxidation of nitric oxide and reduction of hydrogen peroxide based on α-Fe2O3 nanoparticles-chitosan composite

α-Fe₂O₃ nanoparticles prepared using a simple solution-combusting method have been dispersed in chitosan (CH) solution to fabricate nanocomposite film on glass carbon electrode (GCE). The as-prepared α-Fe₂O₃ nanoparticles were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM). The nanocomposite film exhibits high electrocatalytic oxidation for nitric oxide (NO) and reduction for hydrogen peroxide (H₂O₂). The electrocatalytic oxidation peak is observed at +0.82 V (vs. Ag/AgCl) and controlled by diffusion process. The electrocatalytic reduction peak is observed at −0.45 V (vs. Ag/AgCl) and controlled by diffusion process. This α-Fe₂O₃-CH/GCE nanocomposite bioelectrode has response time of 5 s, linearity as 5.0 × 10⁻⁷ to 15.0 × 10⁻⁶ M of NO with a detection limit of 8.0 × 10⁻⁸ M and a sensitivity of −283.6 μA/mM. This α-Fe₂O₃-CH/GCE nanocomposite bioelectrode was further utilized in detection of H₂O₂ with a detection limit of 4.0 × 10⁻⁷ M, linearity as 1.0 × 10⁻⁶ to 44.0 × 10⁻⁶ M and with a sensitivity of 21.62 μA/mM. The shelf life of this bioelectrode is about 6 weeks under room temperature conditions.     

Prussian Blue electrodeposited on MWNTs-PANI hybrid composites for H2O2 detection

A Prussian Blue (PB)/polyaniline (PANI)/multi-walled carbon nanotubes (MWNTs) composite film was fabricated by step-by-step electrodeposition on glassy carbon electrode (GCE). The electrode prepared exhibits enhanced electrocatalytic behavior and good stability for detection of H₂O₂ at an applied potential of 0.0 V. The effects of MWNTs thickness, electrodeposition time of PANI and rotating rate on the current response of the composite modified electrode toward H₂O₂ were optimized to obtain the maximal sensitivity. A linear range from 8 × 10⁻⁹ to 5 × 10⁻⁶ M for H₂O₂ detection has been observed at the PB/PANI/MWNTs modified GCE with a correlation coefficient of 0.997. The detection limit is 5 × 10⁻⁹ M on signal-to-noise ratio of 3. To the best of our knowledge, this is the lowest detection limit for H₂O₂ detection. The electrode also shows high sensitivity (526.43 μA μM⁻¹ cm⁻²) for H₂O₂ detection which is more than three orders of magnitude higher than the reported.     

Thermochemistry of dicesium calcium tetraborate octahydrate

The enthalpies of solution of Cs₂Ca[B₄O₅(OH)₄]₂·8H₂O(s) in approximately 1 mol dm⁻³ aqueous hydrochloric acid and of CsCl(s) in aqueous (hydrochloric acid + boric acid + calcium oxide) were determined. From these results and the enthalpies of solution of H₃BO₃(s) in approximately 1 mol dm⁻³ HCl(aq) and of CaO(s) in aqueous (hydrochloric acid + boric acid), the standard molar enthalpy of formation of −(10328 ± 6) kJ mol⁻¹ for Cs₂Ca[B₄O₅(OH)₄]₂·8H₂O(s) was obtained from the standard molar enthalpy of formation of CaO(s), CsCl(s), H₃BO₃(s) and H₂O(l). The standard molar entropy of formation of Cs₂Ca[B₄O₅(OH)₄]₂·8H₂O(s) was calculated from the thermodynamic relation with the standard molar Gibbs free energy of formation of Cs₂Ca[B₄O₅(OH)₄]₂·8H₂O(s) computed from a group contribution method.     

Enzyme mimics of spinel-type CoxNi1−xFe2O4 magnetic nanomaterial for eletroctrocatalytic oxidation of hydrogen peroxide

A series of spinel-type Co_xNi_1−xFe₂O₄ (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) magnetic nanomaterials were solvothermally synthesized as enzyme mimics for the eletroctrocatalytic oxidation of H₂O₂. X-ray diffraction and scanning electron microscope were employed to characterize the composition, structure and morphology of the material. The electrochemical properties of spinel-type Co_xNi_1−xFe₂O₄ with different (Co/Ni) molar ratio toward H₂O₂ oxidation were investigated, and the results demonstrated that Co_0.5Ni_0.5Fe₂O₄ modified carbon paste electrode (Co_0.5Ni_0.5Fe₂O₄/CPE) possessed the best electrocatalytic activity for H₂O₂ oxidation. Under optimum conditions, the calibration curve for H₂O₂ determination on Co_0.5Ni_0.5Fe₂O₄/CPE was linear in a wide range of 1.0 × 10⁻⁸–1.0 × 10⁻³ M with low detection limit of 3.0 × 10⁻⁹ M (S/N = 3). The proposed Co_0.5Ni_0.5Fe₂O₄/CPE was also applied to the determination of H₂O₂ in commercial toothpastes with satisfactory results, indicating that Co_xNi_1−xFe₂O₄ is a promising hydrogen peroxidase mimics for the detection of H₂O₂.     

Amperometric biosensor based on a nanoporous ZrO2 matrix

A biosensor was investigated based on the use of ZrO₂ sol-gel matrix for enzyme immobilization in the mild condition. This bioceramic zirconia alcogel has been prepared by the novel alcohothermal route with a cheap inorganic salt Zr(NO₃)₄·5H₂O with several desirable features including a large surface area (about 460 m² g⁻¹) as well as pore volume and a well-developed textural mesoporosity, and horseradish peroxidase was selected as a model enzyme. The results of transmission electron microscopy (TEM) and BET measurement of the substrate showed that the as-prepared zirconia matrix has an advantageous microenvironment and large surface area available for high enzyme loading. The parameters affecting both the entrapment of enzyme and the biosensor response were optimized. The resulting biosensor exhibited high sensitivity of 111 μA mM⁻¹ for hydrogen peroxide over a wide range of concentrations from 2.5×10⁻⁷ to 1.5×10⁻⁴ mol l⁻¹, quick response of less than 10 s and good stability over 3 months.     

New solid-state synthesis routine and mechanism for LiFePO4 using LiF as lithium precursor

Li₂CO₃ and LiOH·H₂O are widely used as Li-precursors to prepare LiFePO₄ in solid-phase reactions. However, impurities are often found in the final product unless the sintering temperature is increased to 800 °C. Here, we report that lithium fluoride (LiF) can also be used as Li-precursor for solid-phase synthesis of LiFePO₄ and very pure olivine phase was obtained even with sintering at a relatively low temperature (600 °C). Consequently, the product has smaller particle size (about 500 nm), which is beneficial for Li-extraction/insertion in view of kinetics. As for cathode material for Li-ion batteries, LiFePO₄ obtained from LiF shows high Li-storage capacity of 151 mAh g⁻¹ at small current density of 10 mA g⁻¹ (1/15 C) and maintains capacity of 54.8 mAh g⁻¹ at 1500 mA g⁻¹ (10 C). The solid-state reaction mechanisms using LiF and Li₂CO₃ precursors are compared based on XRD and TG-DSC.     

Flow system to gas capture from a nebulized solution

The use of aerosol produced in a nebulization chamber is proposed as an alternative to gas sample capture in flow systems. This paper describes the coupling of a sampling interface with a flow system, for in situ gas monitoring. Aspects related with the behavior of aerosol formation and gas solubilization in liquid drops are discussed. The method is applied to the determination of residual lime in acidic soils. Aliquots of 5.0 ml of 1.0 mol l⁻¹ HCl were mixed with soil samples (1 g). The CO₂ released from these samples was captured by a nebulized aerosol and determined conductivity. The analytical curve from 1.0×10⁻² to 5.0×10⁻² mol kg⁻¹ CaCO₃ was ploted applying the matrix matching approach. This proposition, allowed an increase in the sensibility with detection limit of 6.0×10⁻³ mol kg⁻¹. The precision was good (R.S.D. <3%) for an analytical frequency of 22 determinations per hour. A fair agreement, at 95% confidence level, was found between the results from the proposed method and certified values of the investigated samples.     

Cobalt-doped silica membranes for gas separation

Cobalt-doped silica membranes were synthesized using tetraethyl orthosilicate-derived sol mixed with cobalt nitrate hexahydrate. The cobalt-doped silica structural characterization showed the formation of crystalline Co₃O₄ and silanol groups upon calcination. The metal oxide phase was sequentially reduced at high temperature in rich hydrogen atmosphere resulting in the production of high quality membranes. The cobalt concentration was almost constant throughout the film depth, though the silica to cobalt ratio changed from 33:1 at the surface to 7:1 at the interface with the alumina layer. It is possible that cobalt has more affinity to alumina, thus forming CoOAl₂O₃. The He/N₂ selectivities reached 350 and 570 at 160 °C for dry and 100 °C wet gas testing, respectively. Subsequent exposure to water vapour, the membranes was regenerated under dry gas condition and He/N₂ selectivities significantly improved to 1100. The permeation of gases generally followed a temperature dependency flux or activated transport, with best helium permeation and activation energy results of 9.5 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ and 15 kJ mol⁻¹. Exposure of the membranes to water vapour led to a reduction in the permeation of nitrogen, attributed to water adsorption and structural changes of the silica matrix. However, the overall integrity of the cobalt-doped silica membrane was retained, given an indication that cobalt was able to counteract to some extent the effect of water on the silica matrix. These results show the potential for metal doping to create membranes suited for industrial gas separation.     

Preparation and hydrogen permeation of SrCe0.95Y0.05O3−δ asymmetrical membranes

Asymmetrical thin membranes of SrCe_0.95Y_0.05O_3−δ (SCY) were prepared by a conventional and cost-effective dry pressing method. The substrate consisted of SCY, NiO and soluble starch (SS), and the top layer was the SCY. NiO was used as a pore former and soluble starch was used to control the shrinkage of the substrate to match that of the top layer. Crack-free asymmetrical thin membranes with thicknesses of about 50 μm and grain sizes of 5–10 μm were successfully pressed on to the substrates. Hydrogen permeation fluxes (J_H2) of these thin membranes were measured under different operating conditions. At 950 °C, J_H2 of the 50 μm SCY asymmetrical membrane towards a mixture of 80% H₂/He was as high as 7.6 × 10⁻⁸ mol/cm² s, which was about 7 times higher than that of the symmetrical membranes with a thickness of about 620 μm. The hydrogen permeation properties of SCY asymmetrical membranes were investigated and activation energies for hydrogen permeation fluxes were calculated. The slope of the relationship between the hydrogen permeation fluxes and the thickness of the membranes was −0.72, indicating that permeation in SCY asymmetric membranes was controlled by both bulk diffusion and surface reaction in the range investigated.     

Thermodynamic properties of hydrated sodium l-threonate Na(C4H7O5)·H2O(s)

Low-temperature heat capacities of the compound Na(C₄H₇O₅)·H₂O(s) have been measured with an automated adiabatic calorimeter. A solid-solid phase transition and dehydration occur at 290-318 K and 367-373 K, respectively. The enthalpy and entropy of the solid-solid transition are Δ_transH_m = (5.75 ± 0.01) kJ mol⁻¹ and Δ_transS_m = (18.47 ± 0.02) J K⁻¹ mol⁻¹. The enthalpy and entropy of the dehydration are Δ_dH_m = (15.35 ± 0.03) kJ mol⁻¹ and Δ_dS_m = (41.35 ± 0.08) J K⁻¹ mol⁻¹. Experimental values of heat capacities for the solids (I and II) and the solid-liquid mixture (III) have been fitted to polynomial equations.     

Hydrogen purification using a SAPO-34 membrane

A SAPO-34 membrane separated CO₂/H₂ and H₂/CH₄ mixtures at feed pressures up to 1.7 MPa. Strong CO₂ adsorption inhibited H₂ adsorption and decreased H₂ permeances significantly, especially at low temperatures, so that CO₂ preferentially permeated and CO₂/H₂ selectivities were higher at low temperatures. At 253 K, CO₂/H₂ separation selectivities were greater than 100 with CO₂ permeances of 3 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹. The CO₂/H₂ separation exceeded the upper bounds (selectivity–permeability plot) for polymer membranes. The SAPO-34 membrane separated H₂ from CH₄ because CH₄ is close to the SAPO-34 pore size and has a lower diffusivity than H₂. The H₂/CH₄ separation selectivity had a small maximum with temperature, and decreased slightly with feed pressure and CH₄ feed concentration.