Uranyl ion-selective optical test strip

A novel, optical sensor, test strip has been developed for the spectrophotometric determination of trace amounts of uranyl ions, UO₂²⁺, based on immobilization of C.I. Mordant Blue 29 (Chromazurol S)/cetyl N,N,N-trimethyl ammonium bromide ion pair on a triacetyl cellulose membrane. Optimization of the sensor for the detection of low levels of uranyl ion is described. The test strip responded linearly to uranyl ions between 3.0 × 10^?7 and 6.0 × 10^?5 mol L^?1; the reproducibility of the sensor at a medium level of UO₂²⁺ activity was ±0.55%. The optical sensor can be regenerated using 0.01 mol L^?1 HCl or 0.01 mol L^?1 NaF solution after 10 min. The developed test strip was used in the determination of UO₂²⁺ in ground water samples.     

Preparation of sulfur-doped microporous carbons for the storage of hydrogen and carbon dioxide

Structurally well ordered, sulfur-doped microporous carbon materials have been successfully prepared by a nanocasting method using zeolite EMC-2 as a hard template. The carbon materials exhibited well-resolved diffraction peaks in powder XRD patterns and ordered micropore channels in TEM images. Adjusting the synthesis conditions, carbons possess a tunable sulfur content in the range of 1.3–6.6 wt.%, a surface area of 729–1627 m² g^?1 and a pore volume of 0.60–0.90 cm³ g^?1. A significant proportion of the porosity in the carbons (up to 82% and 63% for surface area and pore volume, respectively) is contributed by micropores. The sulfur-doped microporous carbons exhibit isosteric heat of hydrogen adsorption up to 9.2 kJ mol^?1 and a high hydrogen uptake density of 14.3 × 10^?3 mmol m^?2 at ?196 °C and 20 bar, one of the highest ever observed for nanoporous carbons. They also show a high CO₂ adsorption energy up to 59 kJ mol^?1 at lower coverages (with 22 kJ mol^?1 at higher CO₂ coverages), the highest ever reported for any porous carbon materials and one of the highest amongst all the porous materials. These findings suggest that S-doped microporous carbons are potential promising adsorbents for hydrogen and CO₂.     

Diffusion coefficients and electrical conductivities for calcium chloride aqueous solutions at 298.15 K and 310.15 K

Experimental values for mutual diffusion coefficients (interdiffusion coefficients) for CaCl₂ aqueous solutions at 298.15 K and 310.15 K, not available in the literature, were experimentally determined between 0.005 mol dm^?3 and 0.1 mol dm^?3. The measurements were performed by using a conductimetric open-ended capillary cell. Values at infinitesimal concentration, D⁰, were also obtained. These data were analysed using the Onsager–Fuoss and Gordon models. In addition, molar conductance data were measured at 310.15 K for CaCl₂ aqueous solutions at the same concentration range and the value at infinitesimal concentration determined. Afterwards, it was split into the ionic limiting values. By replacing them into the Nernst equation, diffusion coefficients at infinitesimal concentration were derived (1.335 × 10^?9 m² s^?1 and 1.659 × 10^?9 m² s^?1) at both temperatures (298.15 K and 310.15 K, respectively). They agree well with the extrapolated experimental ones (1.312 × 10^?9 m² s^?1 and 1.613 × 10^?9 m² s^?1).     

The electrocatalytic properties of an IrO2/SnO2 catalyst using SnO2 as a support and an assisting reagent for the oxygen evolution reaction

Electrocatalysts made of IrO₂/SnO₂ were prepared using the Adams method for solid polymer electrolyte (SPE) water electrolysis. The physicochemical properties of the catalyst were characterized via X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical properties of the catalyst were investigated using cyclic voltammetry (CV), electrochemical impendence spectroscopy (EIS), chronopotentiometry and Tafel curve measurements in 0.1 mol L^?1 H₂SO₄ at room temperature. The test results showed that the catalytic properties of IrO₂/SnO₂ depended on the mass ratio of iridium to tin, and that the optimal mass ratio was 2:1. The optimized catalyst was applied to a membrane electrode assembly (MEA), and the stationary current–potential relationships were determined. With an IrO₂/SnO₂ (2:1) anode, a 40% Pt/C cathode and a total noble metal (Ir, Pt) loading of 1.2 mg cm^?2, the terminal applied potential difference of the water electrolysis was 1.70 V at 2 A cm^?2 and 80 °C.     

Synthesis of a graphene–carbon nanotube composite and its electrochemical sensing of hydrogen peroxide

Graphene, whose structure consists of a single layer of sp²-hybridized carbon atoms, provides an excellent platform for designing composite nanomaterials. In this study, we have demonstrated a facile process to synthesize graphene–multiwalled carbon nanotube (MWCNT) composite. The graphene–MWCNT composite material is endowed with a large electrochemical surface area and fast electron transfer properties in Fe(CN)₆^3?/4? redox species. A graphene–MWCNT composite modified electrode exhibits good performance in terms of the electrocatalytic reduction of H₂O₂; a sensor constructed from such an electrode shows a good linear dependence on H₂O₂ concentration in the range of 2 × 10^?5 to 2.1 × 10^?3 mol L^?1. The detection limit is estimated to be 9.4 × 10^?6 mol L^?1. This study provides a new kind of composite modified electrode for electrochemical sensors.     

Carbons with narrow pore size distribution prepared by simultaneous carbonization and self-activation of tobacco stems and their application to supercapacitors

Highly microporous carbons with narrow pore size distribution have been prepared by simultaneous carbonization and self-activation of tobacco wastes at temperatures ranging from 600 to 1000 °C. The efficiency of porosity development, without pores broadening, is attributed to well-distributed alkalis at the molecular level in the tobacco precursor. With Burley tobacco, the BET specific surface area and average micropore size L₀ increased up to 800 °C (Burley 800), where the values reached maxima of 1749 m² g⁻¹ and 1.2 nm, respectively. At temperatures higher than 800 °C, annealing of the materials dominates and provokes a decrease of S_BET and L₀. Burley carbons were implemented in supercapacitors using 1 mol L⁻¹ aqueous Li₂SO₄ or 1 mol L⁻¹ TEABF₄ in acetonitrile. In both electrolytes, the capacitance of Burley carbons followed the same trend as S_BET and L₀. Burley 800 demonstrated outstanding capacitance values of 167 F g⁻¹ (at 0.8 V limit) and 141 F g⁻¹ (at 2.3 V limit) in 1 mol L⁻¹ aqueous Li₂SO₄ and 1 mol L⁻¹ TEABF₄, respectively. Such values, about 50% higher as compared to commercially available carbons, are attributed to the narrow pore size distribution of this carbon with a maximum of pores around 1.2 nm close to the size of solvated ions in these electrolytes.     

Preparation,characterisation and catalytic evaluation of MgF2 supported V2O5 catalysts for ammoxidation of 3-picoline

Non-conventional MgF₂ supported V₂O₅ catalysts with different vanadia contents (2–15 wt.%) were prepared by impregnation (using NH₄VO₃), characterised and catalytically evaluated for selective ammoxidation of 3-picoline to nicotinonitrile. Oxygen and ammonia chemisorption uptakes increased continuously from 60 to over 600 μmol g^?1 and 275 to >750 μmol g^?1, respectively, with rise in V₂O₅ proportion indicating that the redox as well as acidic sites are increasing with increase in V₂O₅ content. Thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) analysis revealed endothermic as well as exothermic thermal effects mainly due to liberation of water and ammonia, and also due to structural changes. XRD patterns showed the formation of crystalline V₂O₅ in the fresh solids having 8 wt.% V₂O₅ and above and NH₄VO₃ phase in the spent samples. The conversion of 3-picoline is observed to increase continuously with increase in V₂O₅ loading. However, the selectivity of nicotinonitrile is found to be independent on conversion of 3-picoline. The catalyst with the highest V₂O₅ loading (15.7 wt.%) displayed the best activity (X > 90%) and selectivity (S > 95%) compared to all other catalysts of this series. The 3-picoline conversion of 10% at 548 K is increased to almost 100% with rise in temperature to 663 K. Increase in 3-picoline feed rate and NH₃: 3-picoline ratio exhibited an inhibiting effect on the conversion, while an increase in air: 3-picoline ratio has no significant influence on the performance.     

Synthesis and cytotoxicity of a ruthenium nitrosyl nitric oxide donor with isonicotinic acid and a cell penetrating peptide

The syntheses and properties of trans-[Ru(NH₃)₄(L)(NO)](BF₄)₃ (L = isonicotinic acid (inaH) (I) or ina-Tat48–60 (II)) are described. Tat48–60, a cell penetrating peptide fragment of the Tat regulatory protein of the HIV virus, was linked to the ruthenium nitrosyl through inaH. I and II release NO after reduction forming trans-[Ru(NH₃)₄(L)(H₂O)]^3 +. The IC₅₀ values against B16-F10 melanoma cells of I and II (21 μmol L^− 1 and 23 μmol L^− 1, respectively) are close to that of the commercially available cisplatin (33 μmol L^− 1) and smaller than similar complexes. The cytotoxicity is assigned to the NO released from I and II.     

Phase equilibria of (CO2 + H2O + NaCl) and (CO2 + H2O + KCl): Measurements and modeling

We report experimental measurements of the phase behavior of (CO₂ + H₂O + NaCl) and (CO₂ + H₂O + KCl) at temperatures from 323.15 K to 423.15 K, pressure up to 18.0 MPa, and molalities of 2.5 and 4.0 mol kg⁻¹. The present study was made using an analytical apparatus and is the first in which coexisting vapor- and liquid-phase composition data are provided. The new measurements are compared with the available literature data for the solubility of CO₂ in brines, many of which were measured with the synthetic method. Some literature data show large deviations from our results.The asymmetric (γ–φ) approach is used to model the phase behavior of the two systems, with the Peng–Robinson equation of state to describe the vapor phase, and the electrolyte NRTL solution model to describe the liquid phase. The model describes the mixtures in a way that preserves from our previous work on (CO₂ + H₂O) the values of the Henry's law constant and the partial molar volume of CO₂ at infinite dilution Hou et al. [22]. The activity coefficients of CO₂ in the aqueous phase are provided. Additionally, the correlation of Duan et al. [14] for the solubility of CO₂ in brines is tested against our liquid-phase data.     

Microporous carbons finely-tuned by cyclic high-pressure low-temperature oxidation and their use in electrochemical capacitors

Microporous carbons with a finely controlled porosity have been prepared from non-porous chars by cyclic oxidation/thermal desorption and further used in supercapacitor electrodes working in organic medium. The described activation method is shown to be effective for at least two types of non-porous carbons derived from sucrose and cellulose. The low temperature oxidation is realized by H₂O₂ at 200 °C and followed by thermal desorption of the surface functional groups at 900 °C under nitrogen flow. The porosity-forming procedure involves 4–5 oxidation/decomposition cycles, thus allowing a gradual adjustment of average pore size to that of ions making up the standard organic electrolyte ?1 mol L^?1 TEA⁺ BF₄^? in acetonitrile. The build-up of pore volume during the initial cycles proceeds essentially through the opening/formation and deepening of narrow micropores (L₀ ≈ 0.8 nm), whereas a slight pore widening appears to be the main outcome of further cycles. Due to the low burn-off of the overall process, the carbons are shown to form much denser coatings (0.71 g cm^?3) than a steam-activated carbon used in industrial supercapacitors (0.52 g cm^?3).     

Characterization of catalysts in their active state by adsorption microcalorimetry: Experimental design and application to sulfated zirconia

A method to characterize the surface sites of catalysts in their active state by adsorption microcalorimetry was developed. A calorimeter cell was used as a flow-type reactor, and the skeletal isomerization of n-butane (1 kPa) at 378 K and atmospheric pressure proceeded at comparable rates and with the same states of induction period, maximum and deactivation phase as in a tubular reactor. The reaction was run for selected times on stream and after the removal of weakly adsorbed species, n-butane or isobutane were adsorbed at 313 K. The surface of activated sulfated zirconia was characterized by at least two different sites for n-butane adsorption, a small group of sites (about 20 μmol g^?1) that yielded heats of 50–60 kJ mol^?1 and sites that were populated at higher pressures (above about 5 hPa n-butane) and yielded heats of about 40 kJ mol^?1. The strongly interacting sites disappear during the induction period and are proposed to be the sites where the isomerization reaction is initiated.     

Synthesis and adsorption studies of novel hybrid mesoporous copolymer functionalized with protoporphyrin for batch and on-line solid-phase extraction of Cd2+ ions

A hybrid copolymer [poly(ethylene glycol dimethacrylate-co-protoporphyrin)-silica], synthesized by free radical copolymerization and sol–gel process was evaluated as novel adsorbent for solid-phase extraction of Cd²⁺ ions. Characterization of hybrid polymer was performed by FTIR, SEM and surface area analyzes. Adsorption isotherms built at pH 8.9 were very well adjusted (R² = 0.9982) to hybrid non-linear Langmuir–Freundlich model for two sites, indicating the existence of different affinity constants for binding sites, which was confirmed by Scatchard plot. The estimated maximum adsorption capacity was found to be 8.28 mg g^?1. The adsorption kinetics data also corroborated to the isotherm, where the Cd²⁺ ions adsorption followed the pseudo-second-order kinetic (R² = 0.998). The on-line preconcentration procedure, optimized by means of factorial designs, was based on sample preconcentration (16 mL) at pH 8.9 through 50.0 mg of hybrid copolymer packed in mini-column at 8.0 mL min^?1 flow rate. The on-line desorption of Cd²⁺ ions towards the FAAS detector was carried out in countercurrent at 5.0 mL min^?1 flow rate using 0.8 mol L^?1 HNO₃. Using the on-line preconcentration procedure, the maximum adsorption capacity determined from breakthrough curve was found to be 2.25 mg g^?1. Analytical curve ranged from 0.0 up to 50.0 μg L^?1 (r = 0.997), limit of detection of 0.27 μg L^?1, preconcentration factor of 38.4, sample throughput of 30 h^?1 and consumptive index of 0.41 mL, were achieved. The preconcentration method, very tolerable to several foreign ions, was successfully applied to the Cd²⁺ ions determination in water samples and cigarette sample. The accuracy was checked from analysis of certified reference materials.     

Voltammetric investigation of iron(III) complexes with siderophore chrysobactin in aqueous solution

Voltammetric investigations of iron(III)–chrysobactin complexes in aqueous solution at static mercury electrode, were performed. With c_Fe = (0.5–30) × 10^?7 mol dm^?3 and c_Cb = (0.5–100) × 10^?7 mol dm^?3 in pH range 6.7–10, reduction peaks with E_p ?0.64 to ?0.74 V (1) and E_p ?0.50 to ?0.62 V (2) vs. Ag/AgCl, were registered. These reduction processes were time dependent as well as solution composition (c_Fe, c_Cb and pH). Complexes are adsorbed at the mercury drop surface. Presumed stoichiometry of the detected complexes was Fe^IIICb₃ (1) and Fe^IIICb₂(OH)_x (2). Their formation/dissociation processes were described. These investigations are of biological importance as well, since provide an insight into possible reduction mechanism in the bacterial cells that use chrysobactin to acquire the iron.     

Adsorption characteristics of a fully exchanged potassium chabazite zeolite prepared from decomposition of zeolite Y

In this work a comprehensive study was undertaken to characterize the porous nature of a fully exchanged potassium chabazite zeolite (KCHA) and evaluate its adsorption properties under different conditions. A synthetic chabazite was prepared from the decomposition of zeolite Y and ion-exchanged to produce a fully exchanged potassium chabazite with Si/Al ratio of 2.4. In addition, sodium chabazite (NaCHA) and lithium chabazite (LiCHA) were synthesized for comparison purposes. Equilibrium isotherms for N₂ and CO₂ were measured at 273 K for further characterization. Our results show that the porous structure characterization by N₂ at 77 K and Ar at 87 K following the standard methods of BET for surface area, t-plot, DR and DFT for pore size distribution and volume reveal pore blockage phenomenon with substantially diminished adsorption capacities. However, CO₂ adsorption capacity on KCHA at 273 K reveals magnitudes of 70.1% and 78.7% of those on LiCHA and NaCHA, and a DFT pore volume of 0.214 cm³ g^?1. The surface area of KCHA calculated from the CO₂ isotherm using the Tóth model in its revised form demonstrates a surface area of 584.4 m² g^?1. This is in contrast to 17.82 and 13.48 m² g^?1 obtained from the BET model using N₂ and Ar at 77 and 87 K, respectively. It was concluded that the reliability of standard methods (viz. BET using N₂ at 77 K) for characterizing these particular porous solids is questionable under certain circumstances leading to misevaluation of adsorbent properties.     

Chemically modified carbon nanotubes as efficient and selective sorbent for enrichment of trace amount of some metal ions

Multi-walled carbon nanotubes (MWCNT) was oxidized and chemically functionalized by 3-hydroxy-4-((3-silylpropylimino) methyl) phenol (HSPIMP) and characterized with FT-IR technique. This new sorbent was used for enrichment and preconcentration of Cu²⁺, Ni²⁺, Zn²⁺, Pb²⁺, Co²⁺, Fe³⁺ ions. Variables such as pH, amount of solid phase, eluting solution conditions (type, volume and concentrations) have significant effect on sorption and recoveries of analytes and the influence was optimized. At optimum value of conditions, the interference of other ions on understudy ions recoveries was investigated. The metal ions loaded on the solid phase via chelation with the new sorbent and subsequently efficiently eluted using 6 mL of 4 mol L^?1 HNO₃ solution. At each run, metal ions content was determined by flame atomic absorption spectrometry (FAAS). Relative standard deviation (N = 3) for determination of 0.2 μg mL^?1 of analytes was between 1.6 and 3.0%, while their detection limit was between 1.0 and 2.6 ng mL^?1 (3Sb, n = 10). The sorption capacity of HSPIMP–MWCNT for understudy ions was above 30 mg g^?1. The proposed method successfully applied for the extraction and determination of the understudy metal ions in different samples.     

A highly thermal stable microporous lanthanide–organic framework for CO2 sorption and separation

A new lanthanide–organic framework formulated as TbL 1 (H₃L = 9-(4-carboxy-phenyl)-9H-carbazole-3,6-dicarboxylic acid), was synthesized under hydrothermal reaction condition. Single-crystal X-ray diffraction analysis shows that 1 crystallizes in a hexagonal P6₅ space group with three-dimensional network and microporous structure. The desolventized framework of 1 shows much higher uptake of CO₂ (43.7 cm³ g^− 1) than that of CH₄ (15.1 cm³ g^− 1) at 1 atm and 273 K, which makes it a potential candidate for CO₂/CH₄ separation.     

Isosynthesis via CO hydrogenation over SO4–ZrO2 catalysts

Catalytic performances of sulfated zirconia catalysts with various contents of sulfur (from 0.1 to 0.75%) on isosynthesis were studied. It was firstly found that undoped-zirconia synthesized from zirconyl nitrate provided higher activity towards isosynthesis reaction (106 μmol kg-cat^?1 s^?1) compared to that synthesized from zirconyl chloride (84.9 μmol kg-cat^?1 s^?1). Nevertheless, the selectivity of isobutene in hydrocarbons was relatively lower. It was then observed that the catalytic reactivity and selectivity significantly improved by sulfur loading. The most suitable sulfur loading content seems to be at 0.1%, which gave the highest reaction rate and selectivity of isobutene. By applying several characterization techniques, i.e. BET, XRD, NH₃- and CO₂-TPD and SEM, it was revealed that the high reaction rate and selectivity towards isosynthesis reaction of sulfated zirconia catalysts are related to the acid–base properties, Zr³⁺ quantity and phase composition.     

High-temperature conductivity,stability and redox properties of Fe3−xAlxO4 spinel-type materials

Iron-based oxides are considered as promising consumable anode materials for high temperature pyroelectrolysis. Phase relationships, redox stability and electrical conductivity of Fe_3?xAl_xO₄ spinels were studied at 300–1773 K and p(O₂) from 10^?5 to 0.21 atm. Thermogravimetry/XRD analysis revealed metastability of the sintered ceramics at 300–1300 K. Low tolerance against oxidation leads to dimensional changes of ceramics upon thermal cycling. Activation energies of the total conductivity corresponded to the range of 16–26 kJ/mol at 1450–1773 K in Ar atmosphere. At 1573–1773 K and p(O₂) ranging from 10^?5 to 0.03 atm, the total conductivity of Fe_3?xAl_xO₄ is nearly independent of the oxygen partial pressure. The conductivity values of Fe_3?xAl_xO₄ (0.1 ≤ x ≤ 0.4) at 1773 K and p(O₂) ～10^?5 to 10^?4 atm were found to be only 1.1–1.5 times lower than for Fe₃O₄, showing high potential of moderate aluminium additions as a strategy for improvement of refractoriness for magnetite without significant deterioration of electronic transport.     

A self-healing polymer network based on reversible covalent bonding

A self-healing polymer network for potential coating applications was designed based on the concept of the reversible Diels–Alder (DA) reaction between a furan functionalized compound and a bismaleimide. The network allows local mobility in a temperature window from ca. 80 °C to 120 °C by shifting the DA equilibrium towards the initial building blocks. Changing the spacer length in the furan functionalized compound leads to tailor-made properties. Elastomeric model systems were chosen to evaluate the kinetic parameters by Fourier transform infrared spectroscopy. For the DA reaction a pre-exponential factor ln(A_DA in kg mol^?1 s^?1) equal to 13.1 ± 0.8 and an activation energy (E_DA) of 55.7 ± 2.3 kJ mol^?1 are found. For the retro-DA reaction, ln(A_rDA) and E_rDA are 25.8 ± 1.8 s^?1 and 94.2 ± 4.8 kJ mol^?1, respectively. The enthalpy and entropy of reaction are calculated as ?38.6 kJ mol^?1 and ?105.3 J mol^?1 K^?1. The kinetic results are validated by micro-calorimetry. Non-isothermal dynamic rheometry provides the gel-point temperature of the reversible network. The sealing capacity is evaluated by atomic force microscopy for micro-meter sized defects. Repeatability of the non-autonomous healing is checked by micro-calorimetry, ruling out side-reactions below 120 °C.     

Supercritical CO2 and highly selective aromatase inhibitors: Experimental solubility and empirical data correlation

The solubility of highly selective and potent third-generation aromatase inhibitors includes the non-steroidal agents letrozole and anastrozole and the steroid exemestane in supercritical carbon dioxide (SC-CO₂) has been investigated. The experiments were carried out using the simple and static method at pressures in the range of 12.1–35.5 MPa and temperatures ranging from 308 to 348 K. The mole fraction solubilities ranged from 0.22 × 10⁻⁵ to 1.88 × 10⁻⁴. Solubility data were correlated using six empirical models (Chrastil model, dV–A model, K–J model, Bartle model, Yu model and Gordillo model). The results showed that these models can be applied to satisfactory solubility predictions at different pressures and temperatures. A comparison among the six models revealed that the K–J, and Gordillo models gave much better correlations of the solubility data with an average absolute relative deviation (AARD%) ranging from 0.2 to 2.3 and from 1.6 to 2.5%, respectively. Using the correlation results, the heat of drug–CO₂ solvation and that of drug vaporization was separately approximated in the range of −17.3 to −17.5 and 93.0–112.1 kJ mol⁻¹.