Numerical simulation of voltammetry focusing on the effect of initial concentration of products in reversible systems with complex stoichiometry

The effect of initial concentration of products in a general reaction of reversible process with complex stoichiometry expressed as mO + ne^? ai qR was evaluated using numerical simulations with various complex stoichiometric coefficients m and q of oxidized (O) and reduced (R) species, respectively, and with various initial concentrations. In the simulations, the transform of voltammograms according to changes in the initial concentrations were characterized by the parameter ??? (= c ₀*(D _O)^1/2/c _R* (D _R)^1/2) for any stoichiometric system. Based on the simulation results, empirical relations were obtained for (1) peak potential involving parameters for stoichiometry (m and q) and for the initial conditions (???), and (2) peak current.     

Scattering experiments with hydrogen atoms: Velocity dependence of the integral total cross section with simple molecules in the energy range 0.01–1.00 eV (c.m.)

Integral total cross sections for hydrogen atoms scattered by H₂, D₂, N₂, CO, NO, O₂, CO₂, C₂H₂ have been measured for H atom velocities in the range 1.2 to 13.4 × 10⁵ cm s^?1 (0.007 ? E_c.m. ? 0.94 eV). The data have been fitted to a Lennard-Jones (12,6) model potential for which the product of the potential well parameters, ?R_m, was determined (? is the well depth and R_m the location of the potential minimum). Separate values for ? and R_m are estimated using a combination rule procedure tested in earlier work on fi— rare gas scattering.     

Neutron diffraction study of uranyl oxalate [UO2(C2O4)(D2O)] · 2D2O

A powdered sample of uranyl oxalate [UO₂(C₂O₄)(D₂O)] · 2D₂O (compound I) is studied using neutron diffraction. The crystals are monoclinic, space group P2₁/c, with a = 5.608(1) Å, b = 17.016(3) Å, c = 9.410(2) Å, β = 98.9369(2)°, Z = 4, R _f = 0.042, R _I = 0.054, x ² = 1.5. The main structural units of the crystals are [UO₂(C₂O₄)(D₂O)] chains. These chains, which belong to the AK⁰²M¹ (A = UO ₂ ²⁺ ) crystal-chemical group of the uranyl complexes, lie parallel to [101]. The water molecules in the crystals of I are hydrogen-bonded into zigzag chains running along [100]. Since each third oxygen atom of the chain formed of water molecules is coordinated to the uranium atom, the uranyl oxalate chains are linked into {[UO₂(C₂O₄)(D₂O)] · 2D₂O} layers that lie normal to [010]. The layers are linked into the framework through interlayer hydrogen bonds (D₂O)O-D···O (oxalate).     

The crystal and molecular structure of ortho-terphenylenemercury dimer, (C18H12Hg)2

C₃₆H₂₄Hg₂, hexabenzo[b,d,f,i,k,m][1,8] dimercuracyclotetradecene, M_r = 857.768, monoclinic, P2₁/n, a 17.315(3), b 16.576(2), c 10.545(6) Å, β 114.60(4)°, U 2751.65 ų, Z = 4, D_m 2.055, D_x 2.071 g cm⁻³, λ(Mo-K_α) 0.71069 Å, μ 107.51 cm⁻¹, F(000) = 1600, T 293 K; Final R = 0.041 for 4290 observed reflections with I > 3σ(I). The two CHgC angles are 175.5(3) and 175.6(4)°; average CHg distance, 2.088(13) Å.     

Analysis and physical significancy of the kinetic parameters associated with albumin adsorption onto glassy carbon obtained by electrochemical impedance measurements

The kinetics of albumin adsorption onto a glassy carbon rotating disk electrode in a phosphate buffer, is reported from the time variations of the double-layer capacitance C_d, of the charge transfer resistance R_t and of the Tafel coefficient of the electrochemical reaction b; these three electrical quantities are determined by electrochemical impedance and faradaic current I measurements. The variations of C_d, 1/R_t, b  (R_tI)⁻¹ and I can be written under the form: α₀ + α₁ e^−t/τ1 + α₂ e^−t/τ2, where α₀, α₁, α₂, τ₁, τ₂ characterize a given electrical quantity. We demonstrate that this type of variation validates a two-step adsorption mechanism already proposed, starting from simply taking into account C_d(t). We analyze and discuss comprehensively various possibilities of interpreting the shifts between the time-constants associated with thevarious quantities as well as the correlations between these constants and those associated with physical adsorption phenomena.     

Optimizing Adsorption of 17α-Ethinylestradiol from Water by Magnetic MXene Using Response Surface Methodology and Adsorption Kinetics,Isotherm, and Thermodynamics Studies

Magnetic MXene composite Fe₃O₄@Ti₃C₂ was successfully prepared and employed as 17α-ethinylestradiol (EE2) adsorbent from water solution. The response surface methodology was employed to investigate the interactive effects of adsorption parameters (adsorption time, pH of the solution, initial concentration, and the adsorbent dose) and optimize these parameters for obtaining maximum adsorption efficiency of EE2. The significance of independent variables and their interactions were tested by the analysis of variance (ANOVA) and t-test statistics. Optimization of the process variables for maximum adsorption of EE2 by Fe₃O₄@Ti₃C₂ was performed using the quadratic model. The model predicted maximum adsorption of 97.08% under the optimum conditions of the independent variables (adsorption time 6.7 h, pH of the solution 6.4, initial EE2 concentration 0.98 mg L⁻¹, and the adsorbent dose 88.9 mg L⁻¹) was very close to the experimental value (95.34%). pH showed the highest level of significance with the percent contribution (63.86%) as compared to other factors. The interactive influences of pH and initial concentration on EE2 adsorption efficiency were significant (p < 0.05). The goodness of fit of the model was checked by the coefficient of determination (R²) between the experimental and predicted values of the response variable. The response surface methodology successfully reflects the impact of various factors and optimized the process variables for EE2 adsorption. The kinetic adsorption data for EE2 fitted well with a pseudo-second-order model, while the equilibrium data followed Langmuir isotherms. Thermodynamic analysis indicated that the adsorption was a spontaneous and endothermic process. Therefore, Fe₃O₄@Ti₃C₂ composite present the outstanding capacity to be employed in the remediation of EE2 contaminated wastewaters.     

Identification of a new family of phosphate compounds,AIBII6(P2O7)2P3O10: structures of KMn6(P2O7)2P3O10 and AgMn6(P2O7)2P3O10

Two members of a new family of inorganic phosphates of general formula A^IB^II₆(P₂O₇)₂P₃O₁₀; KMn₆(P₂O₇)₂P₃O₁₀ (a=5.405(2), b=26.918(11), c=6.660(5), β=107.31(3)°, V=925.1(9) Å³, space group P2₁/m, Z=2, D_calc=3.481 Mg m⁻³, R=0.0377 for 2235 observed reflections) and AgMn₆(P₂O₇)₂P₃O₁₀ (a=5.424(7), b=26.97(4), c=6.627(9), β=106.81(7)°, V=928(2) Å³, space group P2₁/m, Z=2, D_calc=3.716 Mg m⁻³, R=0.0594 for 1577 observed reflections) have been synthesized and identified by single crystal X-ray diffraction. The isostructural complexes present an interesting comparison of silver and potassium bonding.     

The impact of higher polarization basis sets on molecular ab initio results.: III. The ground state of Cl2 in comparison with other diatomics

The ground state potential curve of Cl₂ has been computed near R_c by means of the SCF, MC SCF, CI(SD), and the recently proposed CPF methods. The convergence of the total energy, of D_c and R_c is studied with the aid of computations for various basis sets which include up to three d, two f and one g set. Higher polarization functions have a larger effect than for F₂ for all methods, the g set still affects D_c by 0.15 eV and R_c by 0.02 a₀ on the CPF level. The most elaborate calculation, on the CPF [7,4,3,2,1] level, yields D_c and R_c with an accuracy of 0.08 eV and 0.02 a₀. The same accuracy is obtained for the MC-178 CAS SCF treatment employing a 2d1f polarization basis set. The present results allow us to order the polarization functions according to their relative importance as: d⁽¹⁾ > f⁽¹⁾ > d⁽²⁾ > f⁽²⁾ = d⁽³⁾ > g⁽¹⁾ for the SCF and d⁽¹⁾ > f⁽¹⁾ > d⁽²⁾ > g⁽¹⁾ > f⁽²⁾ = d⁽³⁾ for methods including external correlation. CI(SD) or CPF. A comparison of the results for N₂, F₂, P₂, and Cl₂ shows the higher polarization functions d⁽³⁾, f⁽²⁾, g⁽¹⁾ to contribute 0.1 (F₂) to 0.3 eV (F₂, Cl₂) to D_c and affect R_c by 0.005 a₀ (N₂) to 0.01 7 a₀ (P₂).We have focused our attention mainly on the impact of the atomic basis set incompleteness on the accuracy of results obtained from various methods of computation. Cl₂ turns out to be more demanding than the first-row counterpart F₂ on all levels of theory, which is mainly due to the slower angular convergence rate for E, D_c and R_c (for Cl₂), tables 2 and 3. The more pronounced influence of higher polarization functions is already noticed on the SCF and MC SCF level: f⁽¹⁾ increases D_c by 0.18 eV and reduces R_c by 0.052 a₀ on the MC-178 level for Cl₂, table 6, typical corresponding results for F₂ are only 0.04 eV and 0.013 a₀ [1]. CAS SCF calculations furthermore appear to require larger active spaces for Cl₂, as discussed in section 3.3.On the CI(SD) or CPF level — which aim to account for the entire external correlation — one even finds a pronounced influence of the first g set which contributes ≈ 0.15 eV to D_c and reduces R_c by ≈ 0.02 a₀ (on the CPF level, table 3), the corresponding effects for F₂ were only ≈ 0.04 eV and 0.01 a₀ [1]. The 2d1f polarization basis, which will remain the “standard” large basis for treatments of tri- and tetraatomic molecules, appears to underestimate D_c by still 0.5 eV and to overestimate R_c by ≈ 0.02 a₀ for P₂ and Cl₂, table 7, and probably all molecules in-between. This conclusion emerges from the cumulative effect of adding d⁽³⁾, f⁽²⁾ and g⁽¹⁾ which amounts already to 0.3 eV and 0.015 a₀, table 7.     

Coalescence in quiescent polymer blends with a high content of the dispersed phase

Coalescence in molten quiescent polymer blends induced by van der Waals forces is studied theoretically. Interaction between a droplet and its nearest neighbor keeping spherical shape during drainage of the matrix trapped between them is considered. It is assumed that droplets with time dependent radius R or effective droplets with radius R + h_c/2, where h_c is the critical inter-droplet distance for breakup of the matrix trapped between them, are randomly distributed in the blend through the whole course of the coalescence. Various approaches to calculation of the average time of coalescence, t_c (calculation with preaveraged distance between a droplet and its nearest neighbor at the start of coalescence, h₀, direct averaging of t_c and averaging coalescence frequency, 1/t_c) are compared. Calculated dependence of R on the time of coalescence, t, is compared with experimental results for polypropylene/ethylene–propylene rubber (PP/EPR) blends with EPR content from 15 to 30 wt.%. Calculations using average h₀ and direct averaging of t_c lead to more-less linear dependence of R³ on t. Bare averaging of 1/t_c leads to a steeper than linear dependence of R³ on t and to unreasonably high rate of the coalescence; averaging of 1/t_c with exclusion of pairs with elapsed coalescence time leads to decreasing rate of R³ growth but unreasonably low rate of coalescence. Theories based on the concept of effective droplet radius give smaller differences among various methods of calculations of t_c than the theories assuming random distribution of the droplets. Experimental results show decreasing slope of R³ vs. t dependence, especially for a higher content of dispersed EPR. Theories using average h₀ or direct averaging of t_c predict somewhat smaller rate of coalescence than that experimentally determined for PP/EPR blends. Reasons of these differences are discussed.     

Single ion activity coefficients in concentrated aqueous hydrogen chloride solutions

The adsorption behaviour of the steroids: ouabagenin, ouabain, proscillaridin, digoxin, and k-strophanthine was studied by a.c. polarography and capacitance—time curves at the dropping mercury electrode. The steroids behave like strongly surface-active substances: the relative capacitance decrease ΔC/C₀ depends linearly both on the concentration of the solution and on the root of the drop age. The surface area determined for ouabagenin to be 125 Ų on the basis of adsorption kinetics corresponds roughly to the maximum crosssection of the molecule. With glycosides, the surface area increases with the number of monosaccharide molecules being attached in position 3 of the steroid. It was inferred, therefore, that the adsorbed molecule rests with its steroid and sugar moiety flat on the electrode. A capacitance minimum with sharply defined edges (pit) occurs in the a.c. polarograms of ouabain. In this potential area, the dependences Δ/₀=f(c) and ΔC/C₀=f(t) show a step-like course with two plateaus, which is discussed to be due to association of the adsorbed molecules.     

Adsorptive recovery of geniposidic acid from gardenia yellow pigment extraction wastewater by anion exchange: equilibrium,thermodynamics and mechanism modeling and simulation

For many years, the traditional process of gardenia yellow pigment extraction has produced wastewater containing significant quantities of Geniposidic acid (GSA), a substance that could be put to pharmacological uses if it could be effectively recovered. This study aimed to provide an efficient adsorption material, D08, for recycling GSA. Batch experiments showed that adsorption capacity depends on initial concentration and temperature. The maximal adsorption capacity of GSA onto an anionic exchanger reached 310 mg/g. The pK _a value of GSA was determined to be 4.21. Pore diffusion coefficients (D _p) of GSA for 283, 298 and 313 K were 3.274 × 10^?10, 5.069 × 10^?10 and 7.356 × 10^?10 m²/s, respectively. Recovery efficiency of GSA was achieved to 99.81 %. In comparison with pseudo first-order and pseudo second-order equations, the PDM model demonstrated the best fit to the kinetics data of GSA adsorption. Adsorption/desorption experiments proved that D08 offers great adsorption capacity, high adsorption rate and good repeatability. In order to help us to accurately comprehend the mass transfer process, numerical simulation and post-processing to variables c(r, t) and q(r, t) were performed to clarify the adsorption process.     

ESR Study of Nitroxide Radicals Generated from Triaz-2-en-1-ols

The triazenols 4-R¹? C₆H₄? N?N? N(OH)? R² ( 1 ), oxidized with t-BuO radicals, produced nitroxide radicals R¹? C₆H₄? N(O^?)? N?N(R²) ⁺O^? ( 5 ). The suggested radical structure was confirmed by ¹⁵N-labeling. The reaction of triazenols 1 with PbO₂ proceeded under N₂ elimination, in which case nitroxides R¹? C₆H₄? N(R₂)? O^?( 2 ) were observed as the final radical products. The intermediate R¹? C₆H radicals were identified by spin-trapping.     

Kinetics of water sorption on a CaCl2-in-silica-gel-pores sorbent: The effects of the pellet size and temperature

Kinetics of water vapor sorption on the CaCl₂-in-KSK-pores composite (SWS-1L) have been studied at T = 33–69°C and vapor pressures of 8–70 mbar for pellet sizes of 2R _pel = 0.355–0.425, 0.71–0.85, and 1.2–1.4 mm. Sorption has been measured under isothermal conditions on a thermobalance by abruptly raising the vapor pressure in the measurement cell by a small value and then maintaining the new pressure. In the initial portion of the kinetic curves, the amount of sorbed water (Δm) increases in proportion to the sorption time (t) to the power 1/2. From the slope of the Δm versus t ^1/2 curve, it is possible to derive the sorption rate constant k _D = D _eff/R ² _pel and the effective diffusivity D _eff. The latter is independent of R _pel for 2R _pel ≥ 0.71 mm. The rate of water sorption on smaller (0.355-to 0.425-mm) pellets grows less rapidly, apparently because of the effect of the heat of sorption. The effective diffusivity is determined by the local slope of the water vapor sorption isotherm for SWS-1L. Applying an appropriate correction enables one to calculate the effective diffusivity for water vapor in the sorbent pores, which appears to be D _e = (0.35 ± 0.17) × 10^?6 m²/s. This value is approximately 10 times smaller than the Knudsen water diffusion coefficient calculated for a single cylindrical pore with a size equal to the average pore size of the composite. Two possible causes of this discrepancy are discussed, specifically, an increase in the pore tortuosity because of the presence of the salt and the interaction between water and the salt.     

Electronic properties and crystal structure of aqua (mepirizole-oxalato)copper(II)monohydrate: [Cu(C11H14N4O2)C2O4·H2O]H2O

A Cu(ll) complex with mepirizole: 4-methoxy-2-(5-methoxy-3-methyl-pyrazoll-yl)-6-methylpyrimidine (L) and oxalate as ligands with the formula [CuL(C₂O₄)(H₂O)]·H₂O has been synthesized. The crystal structure has been determined by X-ray diffraction analysis: monoclinic, space group P2₁/n, Z = 4, a = 7.707(1), b = 14.951(3), c = 14.986(2) Å,β = 92.40(2)°, V = 1725.2(8) ų, D_m = 1.61(1) g cm⁻³, D_c = 1.62 g cm⁻³, R = 0.032 and R_w = 0.035 for 2016 observed reflections. The CuN₂O₂O′chromophore can be described as square pyramidal strongly distorted towards trigonal bipyramidal. The basal coordination positions are occupied by the two oxygen atoms of the bidentate oxalate group, the coordinated water molecule and one nitrogen atom of the bidentate mepirizole group; the other coordinated nitrogen atom occupies the apical position. Magnetic moment, IR, electronic reflectance and ESR spectra are interpreted in accordance with the proposed stereochemistry.     

Theoretical study of the energetics of the O3(X̃ 1A1) → O2(X 3Σ−g) + O(3P) dissociation process

The dissociation energy (D_e) for the O₃(X̃ ¹A₁) → O₂(X ³Σ⁻_g) + O(³P) process is computed using MC SCF, CI, MBPT, and CCD methods. A full-valence MC SCF calculation utilizing a [9s5p3d1f/5s3p2d1f] basis set yields a D_e value of 0.43 eV, far below the experimental value of 1.13 eV, demonstrating the importance of correlation effects involving non-valence orbitals. A CI calculation in the same basis set allowing for all single and double excitations from three-reference configuration yields a D_e value of 0.72 eV. This value is increased to 1.06 eV when the Davidson correction is included. When the number of reference configurations is increased to eight, the resulting CI calculation gives a D_e value of 0.82 eV prior to the Davidson correction and 1.10 eV after this correction.     

Refinements of the six-layer structures of the R-type hexagonal ferrites BaTi2Fe4O11 and BaSn2Fe4O11

The structures of BaTi₂Fe₄O₁₁ and BaSn₂Fe₄O₁₁ have been determined from neutron powder diffraction data collected at 300 K using the Rietveld profile refinement. The compounds were found to be isostructural, space group $\text{P6}{}_3\text{mmc}$. BaTi₂Fe₄O₁₁: a = 5.8470(2) Å, c = 13.6116(9) Å, V = 403.01(5) ų, M = 632.6, Z = 2, D_calc. = 3.09 Mg m^?3, final R-factor = 3.77. BaSn₂Fe₄O₁₁: a = 5.9624(5) Å, c = 13.7468(14) Å, V = 423.23(10) ų, M = 774.2, Z = 2. D_calc. = 3.66 Mg m^?3, final R-factor = 2.41. The structure consists of h-stacked BaO₃ and O₄ layers in the ratio 1:2. The BaO₃ layers contain a mirror plane. Between the O₄ layers three octahedral sites are occupied, and between the BaO₃ and O₄ layers an octahedral site and a tetrahedral site are occupied. Because of the mirror plane in the BaO₃ plane the latter sites both share faces in the BaO₃ plane. The octahedral sites are occupied by Fe and Ti or Sn, the pair of tetrahedral sites is occupied by one Fe atom. This Fe atom may hop between these two tetrahedral sites. The structure is considered to be constructed by two R-blocks of the BaFe₁₂O₁₉ (M) structure. Unit-cell dimensions are given of a number of isostructural compounds of general formula A^IIB^IV₂C^III₃O₁₁. Mössbauer experiments on some of these compounds were focused on the tetrahedral positions that show an unusual quadrupole splitting. A brief review is given of the observed magnetic properties of some compounds with the R-structure.     

Neutron diffraction study of Na2UO2(C2O4)2 · 5D2O

A sample of Na₂UO₂(C₂O₄)₂ · 5D₂O (I) was studied by powder neutron diffraction. The compound crystallizes in the triclinic system, space group P1, unit cell parameters: a = 6.934(1) ?, b = 7.566(1) ?, c = 15.409(2) ?, ?? = 94.720(6)°, ?? = 96.281(6)°, ?? = 111.765(5)°, Z = 2, R _F = 5.35, R _I = 6.73 and ??² = 2.89. The hydrogen bonds and non-valence contacts involved in the formation and binding of the {Na₂[UO₂(C₂O₄)₂(D₂O)](D₂O)₄} layers in I were analyzed using the Voronoi-Dirichlet polyhedra.     

Diffusion-controlled adsorption kinetics at the interface between air and aqueous micellar solution of heptaethylene glycol monododecyl ether

The diffusion-controlled adsorption kinetics of micellar surfactant C₁₂E₇ (heptaethylene glycol monododecyl ether) solutions was studied theoretically and experimentally. The corrected diffusion equation, which was used to describe the diffusion of the monomers in the micellar solutions, was solved under the initial and boundary conditions by means of Laplace transformation. The dynamic surface adsorption γ(t) as a function of surface lifetime t, monomer diffusion coefficient D and the demicellization constant was derived. The dynamic surface tensions γ(t) of aqueous submicellar and micellar solutions were measured via maximal bubble pressure method. By analyzing the experimental data, the determined demicellization constant of C₁₂E₇ at 25°C was between 100–116 s^?1.     

Highly efficient ethylene/norbornene copolymerization by o‐Di(phenyl)phosphanylphenolate‐based half‐titanocene complexes

A series of o‐di(phenyl)phosphanylphenolate‐based half‐titanocene complexes CpTiCl₂[O‐2‐R¹‐4‐R²‐6‐(Ph₂P)C₆H₂] (Cp = C₅H₅, 2a : R¹ = R² = H; 2b : R¹ = F, R² = H; 2c : R¹ = Ph, R² = H; 2d : R¹ = SiMe₃, R² = H; 2e : R¹ = ^tBu, R² = H; 2f : R¹ = R² = ^tBu) have been synthesized in high yields (65–87%) by treating CpTiCl₃ with 1.0 equiv of the deprotonated ligands in THF. The ¹H and ³¹P NMR spectra indicated that the phosphorus is not coordinated to titanium in complexes 2a – c , but is coordinated to titanium in complexes 2d – f . Structures for 2c – f were further confirmed by X‐ray crystallography. Complex 2c is essentially a four‐coordinate tetrahedral geometry, whereas complexes 2d ‐ f adopt five‐coordinate distorted square–pyramid geometry around the titanium center. All complexes exhibited low to moderate activities toward homopolymerization of ethylene. Excitingly, they displayed excellent ability to copolymerize ethylene with norbornene, and catalytic activity was more than 100 times larger than that of ethylene homopolymerization in the case of Ph₃CB(C₆F₅)₄/ⁱBu₃Al as cocatalyst, affording the copolymers with high comonomer incorporations. Moreover, DFT calculations study had been performed to shed light on the active species and the fundamental role of NBE in improving the catalytic activity. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013     

The synthesis and molecular structure of π-cyclopentadienyl-π-tetraphenylcyclobutadienerhodium(I)

The reaction of π-cyclopentadienyl-π-1,5-cyclooctadienerhodium(I) and diphenylacetylene gives hexaphenylbenzene as the principal product with a low yield of π-cyclopentadienyl-π-tetraphenylcyclobutadienerhodium(I). The crystal structure of π-cyclopentadienyl-π-tetraphenylcyclobutadienerhodium(I) was determined by X-ray diffraction techniques using diffractometer data. The crystals are monoclinic with unit cell dimensions of a=13.416(3), b=19.534(6), c=13.411(2) Å and β=135.01 (1)°. The space group is P2₁/c and, with four molecules per unit cell, no molecular symmetry is required (D_m=1.40 g/cm³ and D_c=1.411 g/cm³). The structure was solved by the heavy atom method and refined by least-squares methods to a final R of 0.043 for the 3675 observed reflections used in the analysis. The rhodium atom is coordinated to both the cyclopentadienyl group (Rh-ring distance is 1.868 Å) and the tetraphenylcyclobutadiene group (Rh-ring distance is 1.828 Å). The phenyl groups are twisted relative to the C₄ ring and bent away from the rhodium atom.