Viscometric Properties of Carboxymethylchitosan Solutions

The viscosity of carboxymethylchitosan solutions was measured via an Ubbelohde viscometer. The effect of carboxymethylchitosan concentration, pH of the carboxymethylchitosan solution, and concentration of added NaCl and CaCl₂ on the reduced viscosity of the carboxymethylchitosan solutions were comparatively investigated. The results showed that the reduced viscosity of the carboxymethylchitosan solution decreased with the increase of carboxymethylchitosan concentration. The reduced viscosity of carboxymethylchitosan decreased with the addition of NaCl and CaCl₂, and CaCl₂ affected the viscosity more significantly than NaCl. With the increase of pH, the reduced viscosity first decreased and then increased. The interaction between Ca²⁺ ions and carboxymethylchitosan was studied by means of dynamic light scattering and scanning electron microscopy.     

Calcium precipitation in NaCl monitored by the Eu2+ -fluorescence

Taking into account that the optical spectroscopy of the Eu²⁺ ion is quite sensitive to the crystalline environment in which this ion is located, in the present investigation the fluorescence of a small concentration (8 ppmm) of divalent europium incorporated into a NaCl crystal which was also doped with ≈4500 ppmm of Ca²⁺ has been systematically investigated as a function of different thermal treatments in order to study the calcium-precipitation processes in the host NaCl. The data presented in this paper strongly suggest that the annealing of quenched samples at 200°C produces the incorporation of Eu²⁺ into the stable dihalide phase CaCl₂, as well as into the metastable precipitated CaCl₂-like plate zones parallel to the {111} planes of the NaCl matrix. This fact is associated with the increase in intensity of two overlapping emission bands peaking at 430 and 432 nm. On the other hand, the aging of quenched samples at room temperature produces the growth of three emission bands peaking at 400, 414, and 447 nm. The former two emission bands have been associated with Eu²⁺ embedded into calcium precipitates, the structures of these precipitates being different from that of CaCl₂, while the band at 447 nm has been ascribed to europium ions incorporated into the metastable precipitated CaCl₂-like plate zones parallel to the {310} planes of the NaCl matrix. Some of the characteristics of the different calcium second phase precipitates have been obtained by measuring the crystal field splitting (10 Dq) of the 4f⁶5d configuration of the divalent europium ions when they were located inside them. Values for the 10 Dq splitting were determined from the excitation spectrum of each of the emission bands associated with the different calcium-precipitated phases.     

Removal of heavy metals from aqueous solutions using Fe3O4, ZnO, and CuO nanoparticles

This study investigated the removal of Cd²⁺, Cu²⁺, Ni²⁺, and Pb²⁺ from aqueous solutions with novel nanoparticle sorbents (Fe₃O₄, ZnO, and CuO) using a range of experimental approaches, including, pH, competing ions, sorbent masses, contact time, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The images showed that Fe₃O₄, ZnO, and CuO particles had mean diameters of about 50?nm (spheroid), 25?nm (rod shape), and 75?nm (spheroid), respectively. Tests were performed under batch conditions to determine the adsorption rate and uptake at equilibrium from single and multiple component solutions. The maximum uptake values (sum of four metals) in multiple component solutions were 360.6, 114.5, and 73.0?mg?g^?1, for ZnO, CuO, and Fe₃O₄, respectively. Based on the average metal removal by the three nanoparticles, the following order was determined for single component solutions: Cd²⁺?>?Pb²⁺?>?Cu²⁺?>?Ni²⁺, while the following order was determined in multiple component solutions: Pb²⁺?>?Cu²⁺?>?Cd²⁺?>?Ni²⁺. Sorption equilibrium isotherms could be described using the Freundlich model in some cases, whereas other isotherms did not follow this model. Furthermore, a pseudo-second order kinetic model was found to correctly describe the experimental data for all nanoparticles. Scanning electron microscopy, energy dispersive X-ray before and after metal sorption, and soil solution saturation indices showed that the main mechanism of sorption for Cd²⁺ and Pb²⁺ was adsorption, whereas both Cu²⁺ and Ni²⁺ sorption were due to adsorption and precipitation. These nanoparticles have potential for use as efficient sorbents for the removal of heavy metals from aqueous solutions and ZnO nanoparticles were identified as the most promising sorbent due to their high metal uptake.     

Uptake and Sequestration of Naphthalene and 1,2-Dichlorobenzene by C60

The interactions of common environmental contaminants with C₆₀ have been studied to evaluate the environmental impact of carbon nanomaterials. The adsorption and desorption interaction of the hydrophobic contaminants naphthalene and 1,2-dichlorobenzene with C₆₀ was characterized. Processes that cause the wetting and disaggregating of C₆₀ particles also affect the extent of organic contaminant sorption to C₆₀ aggregates by orders of magnitude. C₆₀ dissolved in organic solvents such as toluene can form stable nanoscale aggregates upon vigorous mixing in water. These nanoscale C₆₀ particles form stable suspensions in water and are referred to as ‘nano-C₆₀’. Desorption of contaminants from stable suspensions of nano-C₆₀ exhibits hysteresis. The experimentally observed adsorption/desorption hysteresis is described by a two-compartment desorption model: first, adsorption to the external surfaces that are in contact with water, and second, adsorption to the internal surfaces within the aggregates.     

Density functional investigation of metal encapsulated X@C12Si8 heterofullerene (X=Li, Na, K, Be, Mg, Ca, Al, Ga)

The stability and the possible application of our recently reported SiC heterofullerenes inspire the investigation of their further stabilization through ion encapsulation. The endohedral complexes X@C₁₂Si₈, where X=Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, Ca²⁺, Al³⁺, and Ga³⁺, are probed at the MPWB1K/6-311G? and B3LYP/6-311G* levels of theory. The optimized geometries show the expanding or contracting capability of C₁₂Si₈ in order to accommodate metal ion guests. The inclusion energies indicate the stability of the complexes compared to the components. Meanwhile, the calculated binding energies show the stabilization of C₁₂Si₈ through the inclusion of Be²⁺, Mg²⁺, Al³⁺, and Ga³⁺. The host-guest interaction that is probed through NBO atomic charges supports the obtained results. This study refers to “metal ion encapsulation” as a strategy for stabilization of SiC heterofullerenes.     

Microscopic structure of liquid dimethyl sulphoxide and its electrolyte solutions: molecular dynamics simulations

Molecular dynamics (MD) simulations of pure dimethyl sulphoxide (DMSO) and solutions of Na⁺, Ca²⁺, Cl^?, NaCl and CaCl₂ in DMSO have been performed at 298.15 K and 398.15 K in NVT ensembles by using a four-interaction-site model of DMSO and reaction field method for Coulombic interactions. The structure of solvent, ion-solvation shells and ion-pairs have been analysed by employing a concept of coordination centres and characteristic vectors of the solvent molecule. Results are given for atom-atom (corresponding to DMSO), ion-atom and ion-ion radial distribution functions (RDFs), orientation of the DMSO molecules and their geometrical arrangements in the first solvation shells of the ions (Na⁺, Ca²⁺, Cl^?). A preferential formation of cyclic dimers with antiparallel alignment between dipole moments of nearest-neighbour molecules in the pure solvent is found. Geometrical models of the first coordination shells of the ions in ‘infinitely dilute solutions’ are proposed. Ion-ion RDFs in NaCl-DMSO and CaCl₂-DMSO solutions reveal the presence of both solvent separated (SSIP) and contact (CIP) ion pairs. The structures of the solvation shells of such ion pairs are also discussed.     

Effects of metal ion on the water structure studied by the Raman O?H stretching spectrum

Raman spectra in the O H stretching region of aqueous salt solutions were measured and compared, and the effects of metal ions on water structure deduced. The effects of alkali ions, alkaline ions or the first‐row transition metals on water structure were found to be similar. Differences of metal ionic effects on water structure exist among Na⁺, Mg²⁺ and Al³⁺, and between Ca²⁺ and Mn²⁺ and Al³⁺ and Fe³⁺. The factors that influence the metal ionic effects on the water structure are the ionic charge, the outmost electronic structure and ionic size, the ionic charge being the most important. With a five‐component Gaussian deconvolution of the Raman spectra of the aqueous solutions of NaCl, MgCl₂, AlCl₃ and FeCl₃ with concentrations of 0 to ∼1mol/l, the ionic effects were found to be similar on the bands at 3233, 3393, 3511 and 3628 cm⁻¹, but different on the band at 3051 cm⁻¹. With increasing polarization of the metal ion, the band at 3051 cm⁻¹, due to strong hydrogen bonding, increases. Copyright © 2009 John Wiley & Sons, Ltd.     

Repulsion parameters of ions and radicals—Application to perovskite structures

The compressible ion approach to repulsion which has been shown to work well for the alkali halides (J. Phys. Chem. Solids37, 395 (1976) ; Curr. Sci. 46, 359 (1977)) has been extended to other cubic ionic crystals. Repulsion parameters have been refined for a number of ions and radicals viz., Cu⁺, Ag⁺, Tl⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Sm²⁺, Eu²⁺, Yb²⁺, Pb²⁺, H^?, O^2?, S^2?, Se^2?, Te^2?, NH₄⁺, SH^?, SeH^?, BrO₃^?, ClO₃^?, ClO₄^?, CN^?, NH₂^?, NO₃^?, BH₄^?, BF₄^?, SO₄^2?, NH^2?. Using these parameters, calculations have been made on the lattice spacings and compressibilities of a number of perovskite-like crystals of the form A⁺B²⁺C₃^?. The predicted values agree well with experiment. In the case of four crystals viz., LiBaF₃, LiBaH₃, LiEuH₃ and LiSrH₃, there were large discrepancies between the calculated and observed lattice spacings. When these crystals were assumed to be of the inverse perovskite structure, calculations showed good agreement with the experimental data.     

Absolute cross sections and kinetic energy release distributions for electron-impact ionization and dissociation of CD<Superscript>+</Superscript><Subscript>4</Subscript>

Absolute cross sections for electron-impact dissociative excitation and ionization of CD⁺ ₄ leading to formation of ionic products (CD²⁺ ₄, CD⁺ ₃, CD⁺ ₂, CD⁺, C⁺, D⁺ ₃, D⁺ ₂, and D⁺) have been measured. The animated crossed-beams method is applied in the energy range from the reaction threshold up to 2.5 keV. Around 100 eV, the maximum cross sections are found to be (3.8±0.2) ×10^-19 cm²,  cm², (7.1±0.8) ×10^-17 cm², (9.0±0.8) × 10^-17 cm² and (3.7±0.4) ×10^-17 cm² for the heavy carbonaceous ions CD²⁺ ₄, CD⁺ ₃, CD⁺ ₂, CD⁺ and C⁺ respectively. For the light fragments, D⁺ ₃, D⁺ ₂, and D⁺, the cross sections around the maximum are found to be (5.0±0.6) ×10^-19 cm², (1.7± 0.2) ×10^-17 cm² and (10.6±1.0) ×10^-17 cm², respectively. The cross sections are presented in closed analytic forms convenient for implementation in plasma simulation codes. The analysis of ionic product velocity distributions allows determination of the kinetic energy release distributions which are seen to extend from 0 to 9 eV for heavy fragments, and up to 14 eV for light ones. The comparison of present energy thresholds and kinetic energy release with available published data gives information about states contributing to the observed processes. Individual contributions for dissociative excitation and dissociative ionization are determined for each detected product. A complete database including cross sections and energies is compiled for use in fusion application.     

Fluorescence Quenching of 4-tert-Octylphenol by Room Temperature Ionic Liquids and its Application

The interactions between room temperature ionic liquids (RTILs) and weak fluorescent chemicals still remain unclear, which hinders the complete and efficient utilization of these “green” solvents in fluorescent analyses of organic chemicals. Herein, we reported the effects of four RTILs, [C₈MIM]BF_4, [C₁₄MIM]BF_4, [C₈MIM]PF₆ and [C₁₄MIM]PF₆, on fluorescence behavior of 4-tert-octylphenol (4-t-OP). In the fortified concentration range of 0.2–1.0 mM, the quenching effects were increased with increasing concentrations of RTILs. However, no obvious variation of peak shape of 4-t-OP was observed in the quenching process, suggesting no formation of ground-state complex between fluorophores in 4-t-OP and quencher (ionic liquids). As for anion effect, the fluorescence quenching efficiency of 4-t-OP by BF₄ ^- was greater than PF₆ ^-, but the carbon chain length on the imidazolium ring had no significant relationship with fluorescence intensity of 4-t-OP. Both Ksv values (>1.0?×?10³?L/mol.s) and the different temperature effects demonstrated that the quenching of 4-t-OP by four RTILs was the presence of dynamic and static quenching mechanism. The FI of dansyl chloride within [C₈MIM]BF₄ increased nearly 5-fold as compared to the control, showing a sensitizing effect on the strong fluorescent chemicals, while a quenching effect on 4-t-OP belonging to weak fluorescent chemicals. The fluorescence-enhanced amplitude of dansyl chloride in [C₈MIM]PF₆ was greater than [C₈MIM]BF_4. The fluorescence quenching of 4-t-OP by [C₈MIM]PF₆ did not belong to FRET phenomenon because of no overlap of emission spectrum of 4-t-OP and absorption spectrum of [C₈MIM]PF₆. When 0.6 mM [C₈MIM]PF₆ in acetonitrile was used as the solvent, the detection limit of 4-t-OP was 3.7 μg/L, and the linearity range was 0.01–0.8 mg/L (R²?=?0.9990). In summary, these results provide a theoretical foundation for the application of RTILs in weak fluorescent chemicals.     

Influence of oxalate anions on manganese electrodeposition in sulfate solution

The influences of oxalate anions on manganese electrodeposition in sulfate solution were investigated on the basis of cathode current efficiency, characterization of SEM-EDX and XRD, solution chemistry calculation, thermodynamics and electrochemical test. The experimental results show that the range of (NH₄)₂C₂O₄ was adjusted from 0 mol/L to 4.8?×?10^?3 mol/L. And 1.5?×?10^?3 mol/L (NH₄) ₂C₂O₄ was suitably used with initial pH 7.0. The characterization of SEM indicates that oxalate anions can improve the morphology of electrodeposited films. The electrodeposited films containing manganese were characterized and determined by EDX and XRD. The solution chemistry calculation of catholyte and oxalate anions shows that the main active species are MnSO₄, Mn(SO₄)2? 2, Mn²⁺, Mn(SO₄)C₂O2? 4, MnC₂O 4, Mn(NH₃)²⁺, and C₂O2? 4. The reaction trend between C₂O2? 4 and Mn²⁺ ions is confirmed by computation of reaction energy. Electrochemical test analysis indicates oxalate anions increase the overpotentials of hydrogen evolution reaction and manganese electrodeposition.     

Effect of the ionic radius on jump frequencies of alkaline earth cations in NaCl crystals

By comparing diffusion coefficientsD of bivalent cations Ba²⁺, Ca²⁺, Sr²⁺ in NaCl crystals it was shown that in the temperature range above 550 °CD (Ba²⁺)>D (Sr²⁺)>D (Ca²⁺) is valid. Temperature dependences of jump frequenciesw ₂ of these cations are described byw ₂ (Ba²⁺)=(2·15±0·55) × 10¹² × exp {?(0·817±0.007)/kT};w ₂ (Sr²⁺)=(2·9±1·1) × 10¹² × exp {?(0·84±0.02)/kT} andw ₂ (Ca²⁺)=(5·5±6·5) × 10¹⁰ × exp {?(0·51±0·07)/kT}. It was demonstrated that in NaCl crystals the activation enthalpy and the preexponential factor of the jump frequencyw ₂ increase with increasing ionic radius and mass of the bivalent alkaline earth cation.     

Optical absorption spectra of s2 impurity ions in aqueous halide ion glasses

The optical absorption bands of aqueous 0·05 M Sn²⁺ in 7 M LiI at 77°K appear at 361, 352, 325, 310, 300, 292 and 262 nm. They are considered to be the A₁, A₂, B, C₁, C₂, C₃ and D′ bands since the positions and relative intensities lie within the range of those bands for Sn²⁺-doped alkali iodide crystals. Upon warming the glass there is an uncorrelated increase in the B band and a decrease in the A₁ band. In 3·6, 4·1, 4·6 and 5·1 M CaCl₂ glasses with 5×10^?3 M Sn²⁺ the A₁ and A₂ bands show uncorrelated increases with increasing concentration of Cl^?. Comparable observations are reported for Pb²⁺-doped glasses of lithium halides and CaI₂. In general the spectra of the Sn²⁺- and Pb²⁺-doped glasses correlate well with those of the corresponding crystal systems. The effect of temperature and halide-ion concentration are attributed to shifts in chemical equilibria among the well-known halo complexes, MX_n^2?n MX_n?1^1?n+X^?, each having a characteristic, absorption and emission. Absorptions may be attributed to M²⁺(³P₁ ← ¹S₀) and M²⁺(¹P₁ ← ¹S₀) in the complex, shifted by partially covalent bonding of n halide ions.     

Condensation Product of 1-Naphthaldehyde and 3-Aminophenol: Fluorescent “on” Probe for Ce3+and “off” Probe for Dichromate (Cr2O72−)

A new probe (Z)-3-((naphthalen-1-ylmethylene)amino)phenol has been synthesized by condensation reaction between 1-naphthaldehyde and 3-aminophenol for the fluorescent sensing of Ce³⁺ by “on” mode and dichromate (Cr₂O₇^2?) by “off” mode. Metal ions—Ag⁺, Al³⁺, As³⁺, Ba²⁺, Ca²⁺, Cd²⁺, Ce⁴⁺, Co²⁺, Cr³⁺, Cr⁶⁺, Cu²⁺, Fe²⁺, Fe³⁺, Hg²⁺, K⁺, La⁺, Li⁺, Mg²⁺, Mn²⁺, Na⁺, Ni²⁺, Pb²⁺, Zn²⁺and anions Br^?, C₂O₄^2?, CH₃COO^?, Cl^?, CO₃^2?, F^?, H₂PO₄^?, HCO₃^?, HF₂^?, HPO₄^2?, I^?, MnO₄^?, NO₃^?, OH^?, S^2?, S₂O₃^2?, SCN^?, SO₄^2? do not interfere. The limit of detection (LOD) for sensing Ce³⁺ and Cr₂O₇^2? ions are 1.286?×?10^–7 M and 6.425?×?10^–6 M, respectively.

     

From quantum chemistry to dissociation kinetics: what we need to know †

The relationship between rate constants for dissociation and the reverse association reactions and their potential energy surfaces is illustrated. The reaction systems e^? + SF₆ ? SF₆ ^? →SF₅ ^? + F, H + CH₃ ?CH₄, 2 CF₂ ? C₂F₄, H + O₂ →HO₂, HO + O ?HO₂ ? H + O₂, and C + HO →CHO are chosen as representative examples. The necessity to know precise thermochemical data is emphasised. The interplay between attractive and anisotropic components of the potentials influences the rate constants. Spin–orbit and electronic–rotational coupling in reactions between electronic open-shell radicals so far generally has been neglected, but is shown to have a marked influence on low temperature rate constants.     

X-ray study of some spinels containing gallium and manganese

The ternary oxides CrMnGaO₄, NiMnGaO₄, CuMnGaO₄ and ZnMnGaO₄, crystallize in the cubic spinel structure with lattice parametera=8.41±0.02 Å, 8.34±0.02 Å, 8.36±0.02 Å and 8.32±0.02 Å, respectively. The oxidation state of manganese in these spinels was determined x-ray spectroscopically. The site distribution was determined from the structural properties and calculated site preference energies of cations in the lattice. The ionic structures were found to be Ga³⁺ [Mn²⁺ Cr³⁺] O ₄ ^2? . Ga³⁺ [Cu²⁺ Mn³⁺] O ₄ ^2? , Mn²⁺ [Ga³⁺ Ni³⁺] O ₄ ^2? and Zn²⁺ [Mn³⁺ Ga³⁺] O ₄ ^2? .     

Search for the stannous ion in a chloride/fluoride matrix: cases of Ba1−x Sn x Cl1+y F1−y and of Ba2SnCl6

With the exception of anhydrous SnCl₂, in divalent tin fluorides and chlorides, tin(II) is always covalent bonded, i.e. its valence orbitals are hybridized and the tin lone pair is located in one of the hybrid orbitals. This lone pair is highly stereoactive and generates a large efg, resulting in a large quadrupole splitting. A doubly disordered Ba_1?x Sn _x Cl_1+y F_1?y solid solution has been prepared and found to contain either ionic tin(II) (Sn²⁺ ions) or a mixture of ionic and covalent tin(II), depending on x, y and the method of preparation. The ionic tin(II) spectrum in Ba_1?x Sn _x Cl_1+y F_1?y gives a Mössbauer single line that is broadened by the lattice efg, like in SnCl₂. Now, Sn²⁺ has been found to be present in an undistorted octahedral coordination in a newly isolated compound, Ba₂SnCl₆. It should be the first example of Sn²⁺ that is fully ionic and has a perfectly spherical lone pair.     

Stability of aqueous silica nanoparticle dispersions

In this study, we present quantification methods for nanoparticle stability analysis using non-intrusive analytical techniques: attenuated total reflectance, Fourier transform infrared (ATR-FTIR) spectroscopy, ultraviolet–visible (UV–vis) spectrophotometer, zeta potential analyses, and dynamic light scattering (DLS). We use these techniques to study the stability of silica nanoparticle dispersions and the effects of pH, temperature, and electrolytes that would be encountered in oil field brines in a reservoir. Spectral analysis of the Si–O bond at wavenumber of 1110 cm⁻¹ with the ATR-FTIR indicates a structural change on the surface of silica particles as the dispersion pH changes, which agrees with zeta potential measurements. We define a critical salt concentration (CSC) for different salts, NaCl, CaCl₂, BaCl₂, and MgCl₂, above which the silica dispersion becomes unstable. Three distinct stages of aggregation occur in the presence of salt: clear dispersed, turbid, and separated phases. Divalent cations Mg²⁺, Ca²⁺, and Ba²⁺ are more effective in destabilizing silica nanoparticle dispersion than the monovalent cation Na⁺. The CSC for Na⁺ is about 100 times more than for Ca²⁺, Ba²⁺, and Mg²⁺. Among the divalent cations studied, Mg²⁺ is the most effective in destabilizing the silica particles. The CSC is independent of silica concentration, and lowers at high temperature.     

C42+的几何构型和Jahn Teller效应

用从头计算法QCISD/6-311G得到了C₄²⁺分子的10种不同的几何构型,其中包括C_s,C_∞v,C_2v,D_2h,D_∞h,D_4h,D_2d,C_3v等不同的构型.计算表明C₄²⁺的T_d构型不能稳定存在,详细讨论了T_{d 关键词： 几何构型 4}²⁺')" href="#">C₄²⁺ Jahn Teller效应