Showing papers in "Journal of the Chemical Society, Faraday Transactions in 1983"
TL;DR: In this paper, a model phase diagram is deduced which shows phase structure as a function of surfactant volume fraction and micelle curvature, and two separate mechanisms are proposed for the lower consolute behaviour of polyoxyethylene (CnEOm) + water solutions (the cloud point).
Abstract: From a review of the major factors responsible for surfactant mesophase structure, a model phase diagram is deduced which shows phase structure as a function of surfactant volume fraction and micelle curvature. To test this model the phase behaviour of a series of pure polyoxyethylene surfactants (CnEOm) with water has been studied using optical microscopy over the temperature range 0–100 °C. The compounds studied were C8EO3, C8EO4, C8EO8, C8EO12, C10EO3, C12EO3-C12EO6, C12EO8, C12EO12, C14EO3, C14EO6, C16EO3, C16EO4, C16EO6, C16EO8, C16EO12, C9PhEO8 and C12(2-C10)EO10. Phase diagrams were determined for C8EO4, C12EO3-C12EO6, C12EO8, C16EO4, C16EO8 and C16EO12. With the other compounds optical microscopy was used to determine the number, sequence and type of mesophases.The mesophases observed were cubic–spherical-micelles (I1), hexagonal (H1), normal-cubic–bicontinuous (V1), lamellar (Lα) and reversed-cubic–bicontinuous (V2). Large head groups and low temperatures favour I1 and H1 phases, while Lα and reversed phases occur for small head groups and higher temperatures.There is agreement between experiment and theory for low to medium temperatures if increasing temperature is assumed to lead to a decreased surface area per molecule at the micelle surface (a). At high temperatures and low water content theoretical concepts were reconciled to practical behaviour only by assuming that increased interactions between EO groups occur at a critical water concentration. Two separate mechanisms are proposed for the lower consolute behaviour of surfactant + water solutions (the cloud point). One, involving van der Waals attractions between micelle cores, operates at low temperatures, while the second, involving intermicellar EO—EO attractions occurs at high temperatures. These two mechanisms can account for the ‘double’ cloud point phenomenon observed for surfactants with short EO groups.
927 citations
TL;DR: In this paper, an extensive study of the surface and bulk properties of both single-crystal and polycrystalline Fe2O3 is reported surface pretreatment is found to have a major effect on the photoelectrochemical properties Even in properly treated samples, however, the photocurrent onset is delayed due to the small value of the faradaic rate constant for the oxidation of water.
Abstract: Iron(III) oxide has been extensively studied as a possible n-type semiconductor for use in solar photoelectrolysis cells However, its properties have remained curiously elusive; even such fundamental properties as bandgap and flat-band potential are still controversial, and this uncertainty has hindered any rational evaluation of the use of the material in solar cells In this paper, an extensive study of the surface and bulk properties of both single-crystal and polycrystalline Fe2O3 is reported Surface pretreatment is found to have a major effect on the photoelectrochemical properties Even in properly treated samples, however, the photocurrent onset is found to be delayed due to the small value of the faradaic rate constant for the oxidation of water, and a semi-quantitative treatment of this case is provided Improper surface treatment is shown to lead to a substantial conversion of the surface of Fe2O3 to Fe3O4; this introduces a large fraction of recombination sites at the surface that not only delay dc photocurrent onset to very anodic potentials but also reduce the observed efficiency to remarkably low values
458 citations
TL;DR: In this paper, an approximate analytic expression for the electrophoretic mobility of a spherical colloidal particle in a symmetric electrolyte solution was obtained, consistently to order 1/κa(where κ is the Debye-Huckel parameter and a is the particle radius), all correction terms to Smoluchowski's formula and was found to be in good agreement with the exact computer calculation.
Abstract: An approximate analytic expression is obtained for the electrophoretic mobility of a spherical colloidal particle in a symmetric electrolyte solution. This expression includes, consistently to order 1/κa(where κ is the Debye–Huckel parameter and a is the particle radius), all correction terms to Smoluchowski's formula and is found to be in good agreement with the exact computer calculation by the method of O'Brien and White (J. Chem. Soc., Faraday Trans. 2, 1978, 74, 1607). On the basis of this expression a semi-empirical formula with relative errors < 1% for κa 10 is derived. The same approximation method is employed to obtain a large κa approximate expression for the conductivity of a dilute suspension of spherical colloidal particles.
232 citations
TL;DR: In this article, a more accurate fluctuation potential problem is considered in the modified Poisson-Boltzmann theory, and numerical solutions of the resulting new equation are compared with those of the previous theory and 1 : 1, 1 : 2, 2 : 2 Monte Carlo calculations.
Abstract: A more accurate fluctuation potential problem is considered in the modified Poisson–Boltzmann theory Numerical solutions of the resulting new equation are compared with those of the previous theory and 1 : 1, 1 : 2, 2 : 2 Monte Carlo calculations The new modified Poisson–Boltzmann equation is found to be much more successful in predicting the Monte Carlo results, especially for the higher-valency electrolytes
198 citations
TL;DR: In this paper, low-temperature reduction of LaNiO3 under hydrogen leads to new compounds such as La2Ni2O5 and LaNi2 before total reduction.
Abstract: Low-temperature reduction of LaNiO3 under hydrogen leads to new compounds such as La2Ni2O5 and LaNiO2 before total reduction. Hydrogen consumption, X-ray diffraction and XANES demonstrate the presence of these new phases. Ni3+ in LaNiO3 becomes Ni2+ in La2Ni2O5, and a pure monovalent nickel phase is obtained in LaNiO2. After this stage nickel leaves the structure as nickel metal. Before total reduction, reversible reoxidation of La2Ni2O5 and LaNiO2 leads to the original structure of the LaNiO3 perovskite.
194 citations
TL;DR: In this article, a generalized theory of the double-layer free energy of aqueous solutions is proposed, which explicitly takes into account the microscopic structure of the solvent, and the interaction of two double layers which include specific surface polarization.
Abstract: The formalism derived in the preceding paper is used to model the response of aqueous solutions to a spatially-varying applied electric field. It leads to a generalized theory of the electric double layer which explicitly takes into account the microscopic structure of the solvent. As the solvent polarization is allowed to vary depending on both the macroscopic electric field and the specific interactions at the surface, the result is more freedom in the structure of the electric double layer. We consider generalized expressions for the double-layer free energy, as well as the interaction of two double layers which include specific surface polarization. Such interaction consists of both classical double-layer repulsion and the strong, short-range ‘hydration force’.
144 citations
TL;DR: In this paper, the second-order rate constants and acid dissociation constants of primary amines were found to be overall second order, first order in CO2 and amine at temperatures between 5 and 30 °C.
Abstract: The kinetics of the reactions between carbon dioxide and a series of primary amines, both in aqueous solution, have been studied at temperatures between 5 and 30 °C. In all cases the reactions were found to be overall second order, first order in CO2 and amine. A Bronsted relationship was found to exist between the second-order rate constants and the acid dissociation constants of the amines. At 20 °C. log10k= 0.34 pKa+ 0.45. The mechanism of reactions between carbon dioxide and amines is discussed.
135 citations
TL;DR: In this paper, the use of 29Si-{29Si} homonuclear decoupling for very high-field 29Si n.m. spectra was described, and structures for ten species which yield second-order splitting patterns were proposed and two further singlet peaks were assigned.
Abstract: As with the preceding paper, this article describes the use of 29Si—{29Si} homonuclear decoupling for very-high-field 29Si n.m.r. spectra of isotopically enriched silicate solutions in order to derive structural information. Structures for ten species which yield second-order splitting patterns are proposed and two further singlet peaks are assigned. Computer simulations are shown to support some of the assignments. Chemical shifts, coupling constants and relative concentrations are given for all structures.
130 citations
TL;DR: Extended-Rydberg potentials have been derived for the ground states of all diatomic molecules obtained from atoms in the periodic list Li to Cl for which accurate spectroscopic data are available as mentioned in this paper.
Abstract: Extended-Rydberg potentials have been derived for the ground states of all diatomic molecules obtained from atoms in the periodic list Li to Cl for which accurate spectroscopic data are available. From a comparison with RKR data where these are known we conclude that this simple function is an excellent representation of the potential in the valence region.
125 citations
TL;DR: In this paper, the forces between two molecularly smooth curved mica surfaces a distance D apart immersed in a liquid have been measured, both in the absence and in the presence of macromolecules adsorbed from the liquid.
Abstract: The forces between two molecularly smooth curved mica surfaces a distance D apart immersed in a liquid have been measured, both in the absence and in the presence of macromolecules adsorbed from the liquid.The forces between bare mica surfaces in 0.2 mol dm–3 KNO3 aqueous solution are repulsive for D≲ 5 nm and correspond reasonably well to electrostatic double-layer (DLVO) theory. Following adsorption of soluble monomeric collagen onto the surfaces from the solution, repulsion commences at D≲ 600–700 nm and increases monotonically with decreasing D, suggesting that the collagen monomers are adsorbed in an upright configuration normal to each surface.The forces between bare mica surfaces in cyclohexane are monotonically attractive for D≲ 10 nm, and appear to obey a van der Waals-like potential acting across the non-polar medium. Following adsorption of polystyrene (of two molecular weights) onto the mica from the cyclohexane, interactions between the surfaces are found to commence at D≲ 2.5 Rg(unperturbed radius of gyration of the respective polymers) and are initially attractive. For D≲Rg the attraction decreases, and on further reducing D strong repulsion between the surfaces is observed. These results may be understood in terms of the phase equilibrium of the polystyrene–cyclohexane system (which under the experimental conditions is below its critical temperature), and are in good accord with the predictions of a recent theory for interaction between adsorbed polymer layers in a poor solvent.
121 citations
TL;DR: In this paper, a series of powder Pt/TiO2 catalysts containing from 0.05 to 10 wt% Pt as well homodispersed particles (mean diameter ca. 2 nm).
Abstract: Photoconductivity measurements have been carried out for a series of powder Pt/TiO2 catalysts containing from 0.05 to 10 wt% Pt as well homodispersed particles (mean diameter ca. 2 nm). The presence of platinum, at least for contents ca. 1 wt%, caused a decrease in the anatase photoconductance σeq at equilibrium under vacuum and this decrease was more pronounced for the highest loadings (5 and 10 wt%). In addition, differences in the times required to reach the steady state were observed, and an attenuation of the u.v. light flux lowered σeq of the Pt-loaded samples, whereas it did not affect that of TiO2 alone. These phenomena can be rationalized in terms of electron transfer from the titania to the platinum. Accordingly, the existence of such a withdrawal by small metal crystallites is substantiated. Conversely, in H2 the Pt deposits decreased the resistance of TiO2, illuminated or not, and this is tentatively attributed to a migration of adsorbed hydrogen atoms from Pt to TiO2 where they form OH– ions and release electrons.
TL;DR: In this article, the effects of metal particle size on reaction selectivity were explained in terms of the fraction of metal atoms located at the corners and edges in the metal crystallites, and the mean particle size of nickel increases with an increase in the concentration of metal in the catalyst, varying from 2.2 to 25.8%.
Abstract: Techniques to control metal particle size in a supported catalyst have been investigated. The mean particle size of nickel increases with an increase in the concentration of metal in the catalyst, varying from 2.2 to 25.8% in weight. The effects of metal particle size on reaction selectivity are explained in terms of the fraction of metal atoms located at the corners and edges in the metal crystallites. During the reaction of propionaldehyde with hydrogen on the catalyst, hydrogenation may occur on the metal atoms located at the corners or edges of the crystallites, while the decomposition of the aldehyde may take place on the metal atoms located on the plane surface of the crystallites.
TL;DR: In this paper, it is shown that empty gaps are responsible for nonadiabatic behavior and that saturated and aromatic parts of the protein permit electron transfer over larger distances than so far recognized.
Abstract: Thermal electron transfer in protein structures is discussed on the basis of a model first proposed by R. A. Marcus. The electronic matrix element H12 is obtained in a many-electron theory for a number of typical structures of interest in proteins. Repetitive structures often permit resonance transfer over long distances provided the absolute value of the coupling matrix element between neighbouring atomic orbitals is larger than a critical value. The crucial energy separation Δ is obtained as a product of the transfer ‘pathway’ multiplied by coupling matrix elements at the gaps. It is shown that empty gaps are responsible for non-adiabatic behaviour and that saturated as well as aromatic parts of the protein permit electron transfer over larger distances than so far recognized. The Salemme model of the cytochrome c–cytochrome b5 interaction may permit electron transfer if the 8.4 A gap between the haem edges is filled by matter, for instance one of the propionate groups at the haem edge. Finally, the cytochrome c–cytochrome c peroxidase model of Poulos and Kraut is discussed and some alternative pathways suggested.
TL;DR: In this paper, the effect of phosphate on the anatase → rutile transformation has been studied and the conclusion has been reached that the polymorphic transformation takes place through the nucleation of rutiles on the surface of TiO2 when the oxide undergoes either thermal or mechanical treatment.
Abstract: The effect of phosphate on the anatase → rutile transformation has been studied. The conclusion has been reached that the polymorphic transformation takes place through the nucleation of rutile on the surface of TiO2 when the oxide undergoes either thermal or mechanical treatment. The phosphate strongly inhibits the anatase → rutile conversion through a mechanism that implies its chemisorption on TiO2 as a bidentate ligand which hinders the surface ionic mobility.
TL;DR: In this article, the image-charge forces between zwitterionic phospholipid bilayers are analyzed in a dielectric model for both the bilayer and the aqueous region.
Abstract: The image-charge forces between zwitterionic phospholipid bilayers are analysed in a dielectric model for both the bilayer and the aqueous region. When a second bilayer approaches surface charges are induced by the ionic groups and a repulsive force is generated. The molecular origin of the repulsion is the long-range character of the polar headgroup solvation and the second bilayer excludes some of the solvating water molecules. The effect is analysed quantitatively in a combined statistical-mechanical–electrostatic formulation. It is found that the range and the strength of the force depend in a crucial way on the zwitterionic correlations within a bilayer. For strong correlations as in a lattice the force decays exponentially with short decay lengths ( < 1 A), while in the completely uncorrelated case the leading term follows a power law. The calculated magnitude of the repulsion is of the same order of magnitude as those found experimentally. We conclude that the image-charge mechanism should be considered as a possible source of the hydration force found in these systems. The explanation is appealing since its source is simply the hydrophilicity of the polar groups.
TL;DR: In this article, a general method based on the phenomenon of the non-solvation of large tetraalkyl(aril)onium ions is proposed for the separation of Λ0 values into ionic components in organic solvents.
Abstract: All existing indirect methods for the separation of Λ0 values into ionic components in organic solvents are analysed. A general method, based on the phenomenon of the non-solvation of large tetraalkyl(aril)onium ions, is proposed. The method is shown to be independent of the chemical nature of organic solvents and temperature. This permits us to examine the relationship between ionic limiting equivalent conductances and values calculated on their basis, and the intrinsic structure of organic solvents. By using this method, the ionic limiting equivalent conductances are calculated for 50 organic solvents at 25 °C and for 9 solvents over a wide temperature interval. The use of the method for obtaining ionic limiting equivalent conductances in organic mixtures is demonstrated. The values calculated by the suggested method under various conditions are in good agreement with the experimental literature values.
TL;DR: In this article, the combined use of high-resolution electron microscopic imaging, electron diffraction, optical diffraction and computer graphics for characterizing intergrowth structures of ZSM-5 and ZSM11 is described.
Abstract: The combined use of high-resolution electron microscopic imaging, electron diffraction, optical diffraction and computer graphics for characterizing intergrowth structures of ZSM-5 and ZSM-11 is described. In particular, a specific preparation is shown to consist mainly of the ZSM-5 framework structure but with single insertions of strips of ZSM-11 at an average spacing of ca. 66 A along [100]. Evidence is also presented for the occurrence of an intergrowth in which one slab of ZSM-5 is related to an adjoining slab such that one of these is rotated through 90° around a [001] axis. An idealized atomic model for this intergrowth is proposed.
TL;DR: In this paper, the electrical current caused by mass transport to a growing hemispherical nucleus is derived for the case where the electrolyte solution is initially quiescent and contains a large excess of inert electrolyte.
Abstract: The electrical current caused by mass transport to a growing hemispherical nucleus is derived for the case where the electrolyte solution is initially quiescent and contains a large excess of inert electrolyte. Both diffusion and radial convection are included. It is demonstrated that the convective term can be neglected in most cases of nucleus growth and that for these cases a simplified solution will suffice.In the second half of the paper the result for the growth of a single, isolated nucleus is generalized to the case of a statistically large sample of continuously increasing numbers of nuclei, N(t). A simple method of analysing experimental data is suggested which can yield N(t) directly.
TL;DR: In this paper, the structural and catalytic properties of oxides in the Bi-V-Sb-O system, which are propene oxidation catalysts, have been studied by X-ray photoelectron spectroscopy (X.p.s.).
Abstract: The structural and catalytic properties of oxides in the Bi–V–Sb–O system, which are propene oxidation catalysts, have been studied. Two domains of solid solutions exist for the compounds BiV1–xSbxO4, with the scheelite structure for 0 ⩽x < 0.04 and a monoclinic structure for 0.876 ⩽x⩽ 1. Characterization by X-ray photoelectron spectroscopy (X.p.s.) shows that for a given MO (M = Bi, V or Sb) environment, the higher the average interatomic distance, the higher the cation binding energy, corresponding to an effective decrease in electronic density. From a semi-quantitative X.p.s. analysis of the surface composition of the BiV1–xSbxO4 system it is shown that for low values of x(x⩽ 0.10) the surface concentrations of vanadium and oxygen decrease sharply compared with those of the other elements. Activities and selectivities for acrolein, determined in a stirred gas–solid reactor, are measured as a function of x. Oxides having the scheelite structure exhibit a sharp increase in activity with increasing x. The larger performance found for x= 0.035 is connected with a high oxygen mobility.
TL;DR: In this article, the rate constants for proton transfer between H2O and H3O+ and between H 2O and OH+ were derived from the pH dependence of the oxygen-17 scalar relaxation.
Abstract: Oxygen-17 scalar relaxation data from light and heavy water and from KCl solutions are reported. From the pH dependence of the relaxation, we extract the rate constants for proton transfer between H2O and H3O+(k+) and between H2O and OH–(k–). In H2O at 28 °C, we find k+=(7.1 ± 0.4)× 109 dm3 mol–1 s–1 and k–=(3.4 ± 0.2)× 10–9 dm3 mol–1 s–1. The kinetic H/D isotope effect is 1.6 ± 0.2 for k+ and 2.7 ± 0.4 for k–. The 1H—17O spin–spin coupling constant (JOH) in H2O, which is needed for the calculation of the rate constants, was redetermined, and we obtained JOH= 81.1 Hz, in good agreement with previous direct measurements but differing from the commonly adopted value.
TL;DR: The thermal decomposition of both βNiO(OH) and Ni(2p) has been studied by combining X-ray photoelectron spectroscopic (X.p.s.) studies of the solid with mass-spectrometric analysis of the gas phase as mentioned in this paper.
Abstract: The thermal decomposition of both βNiO(OH) and ‘nickel peroxide’ have been studied by combining X-ray photoelectron spectroscopic (X.p.s.) studies of the solid with mass-spectrometric analysis of the gas phase. Through monitoring the O(1s) and Ni(2p) spectra of the as-prepared solids during decomposition, with simultaneous analysis of the gas phase, it has been established that ‘nickel peroxide’ behaves in an identical fashion to βNiO(OH). We conclude that the two solids are chemically identical; on the other hand previous studies of ‘nickel peroxide’ have suggested it to be a hydrated defective oxide Ni2O3. Central to our argument is the observation that both solids exhibit initially a single O(1s) peak at 530.5 eV, but during decomposition this peak splits into two components, one at 529.7 eV and the other at 531.4 eV. It is suggested that intercalated water within the βNiO(OH) structure results in the equivalence (by X.p.s.) of the ‘oxygen species’ through the stabilisation of ‘OHO’ groups. Water and molecular oxygen are the predominant gaseous decomposition products, the solid, at 773 K, being converted into defective NiO.
TL;DR: In this article, the reduction of dioxygen to water has been investigated on ternary ruthenium(IV) oxides having the pyrochlore structure; in particular, compounds of the general form Bi2-2xPb2xRu2O7-y have been studied.
Abstract: The reduction of dioxygen to water has been investigated on ternary ruthenium(IV) oxides having the pyrochlore structure; in particular, compounds of the general form Bi2–2xPb2xRu2O7-y have been studied. Oxygen reduction on these materials appears to proceed by a rate-determining outer-sphere electron transfer, followed by displacement of OH– groups coordinated to RuIV by the much stronger nucleophile O2H˙. The cyclic voltammetry of these oxides is interpreted in the light of the X-ray and ultraviolet photoelectron spectra, and a connection between the bandwidth in these oxides and the potential of the main redox processes observed on the voltammagrams is suggested.
TL;DR: In this paper, it was shown that the increase in the number of cations associated with each disaccharide unit was estimated from measurements of the salt dependence of the midpoint of the thermally induced order-disorder transition.
Abstract: Cation binding to iota and kappa carrageenan has been investigated by i.r. spectroscopy, differential scanning calorimetry, optical rotation, intrinsic viscosity and light scattering. From measurements of the salt dependence of the midpoint of the thermally induced order–disorder transition the increase in the number of cations associated with each disaccharide unit was estimated. I.r. studies of sulphate stretching frequencies for the ordered conformation indicate that association of tetramethylammonium ions to carrageenan is by simple atmospheric binding. With K+, by contrast, there is evidence of ion-pair formation, with stronger binding to kappa carrageenan than to iota. Enthalpy changes for the order–disorder transition support these conclusions. Comparison of intrinsic viscosity at high temperature in sodium or potassium chloride solution with values obtained in tetramethylammonium chloride solution indicate a less expanded conformation, consistent with a reduction in charge density by site binding of Na+ and K+, but not Me4N+. Binding constants were estimated from the variation in optical rotation of the disordered form with [Na+] and [K+]. Light-scattering studies for segmented iota carrageenan in the high-temperature (disordered) conformation give radii of gyration for the Na+ and K+ salt forms which are close to the value calculated for an unperturbed random coil, while in tetramethylammonium chloride the radius of gyration is appreciably higher.
TL;DR: In this article, a simulation of the soft-sphere, SS fluid is presented, where the LJ state points agree with the predictions of a recent equation of state for this fluid and the shear rigidity moduli are fitted to better than 1 %.
Abstract: Extensive molecular-dynamics, MD, simulations of Lennard-Jones, LJ, and soft-sphere, SS, fluids have been made. The LJ state points agree excellently with the predictions of a recent equation of state for this fluid. Self-diffusion coefficients obtained from the LJ mean-square displacements at equilibrium are fitted to a simple analytic expression, involving temperature and density, which has a density and temperature range of wider applicability than that of Levesque and Verlet. The corresponding shear viscosities in the limit of zero shear rate have been obtained by a new non-equilibrium MD technique, which involves orthogonal longitudinal distortions (eliminating pure expansion or compression terms). The LJ shear rigidity moduli are fitted to better than 1 % by a simple analytic expression. A similar relationship for the shear viscosities is less satisfactory but this merely reflects the greater uncertainty in this collective transport property. The Stokes–Einstein relationship using slip boundary conditions gives an effective ‘flow unit’ diameter which decreases from several molecular diameters to one as the density increases. This suggests that the motion between a molecule and those in its first coordination shell is more cooperative at moderate densities resulting in greater coupling between molecular trajectories. Support for this comes from the direct evaluation of the friction coefficient by non-equilibrium MD, pair radial and pair fluctuation correlation functions.The Verlet algorithm was used in these calculations. The more accurate Toxvaerd algorithm is shown not to improve noticeably the accuracy of the systematic component of single (and hence possibly collective) particle motion, as measured by velocity and force autocorrelation functions.
TL;DR: In this article, the photochemical reaction of Ar-purged aqueous solutions containing various silver salts and TiO2 powder in suspension has been studied at room temperature, and the reaction rate depended on the anions of the silver salt and increased in the order ClO−4 < NO−3≈ SO2-4 < F−(≈ PO3−4).
Abstract: The photochemical reaction of Ar-purged aqueous solutions containing various silver salts and TiO2 powder in suspension has been studied at room temperature. Photoirradiation (λex < 300 nm) resulted in O2 formation and deposition of Ag metal on the TiO2 particles. The apparent reaction rate depended on the anions of the silver salt and increased in the order ClO–4 < NO–3≈ SO2–4 < F–(≈ PO3–4). The sensitizing activity of the rutile [TiO2(R)] was comparable to that of the anatase [TiO2(A)]. The molar ratio of deposited Ag metal to liberated O2, which was independent of the reaction rate, was equal to ca. 5 except for the case of TiO2(A)/AgClO4. The pH of the reaction mixture decreased with irradiation time, resulting in deactivation of the TiO2. Although O2 formation and Ag-metal deposition did not occur at pH < 2, the photosensitizing activity of the TiO2 powder was recovered by the addition of NaOH. The addition of propan-2-ol to the deactivated acidic suspension of TiO2 was also effective for Ag-metal deposition but not for O2 formation.
TL;DR: Water-soluble diamagnetic metalloporphyrins have been prepared which contain either zinc(II), palladium(II) or tin(IV) ions as the central metals and their photophysical properties have been measured in dilute aqueous solution as mentioned in this paper.
Abstract: Water-soluble, diamagnetic metalloporphyrins have been prepared which contain either zinc(II), palladium(II) or tin(IV) ions as the central metals and their photophysical properties have been measured in dilute aqueous solution. All the compounds undergo efficient intersystem crossing to form long-lived excited triplet states that can participate in electron-transfer reactions. Thus excitation of the metalloporphyrin in dilute aqueous solution containing an appropriate electron acceptor, such as iron(III), may result in formation of the metalloporphyrin π-radical cation in quite high yield. These π-radical cations are powerful oxidants, in some cases E° > 1 V vs NHE, but they undergo secondary reactions that lead to formation of π-dications and isoporphyrins. Despite the high redox potentials, it has not been possible to couple the one-electron reduction of the π-radical cations to the four-electron oxidation of water to molecular oxygen, even in the presence of a redox catalyst such as RuO2. Therefore these compounds appear to possess little promise as water oxidants in homogeneous photosystems.
TL;DR: The solid-film-resistance linear-driving-force model (l.d.f) as mentioned in this paper provides a mathematically simple but adequate description of non-isothermal gas sorption kinetics in a differential test.
Abstract: The solid-film-resistance linear-driving-force model (l.d.f.) for mass transfer provides a mathematically simple but adequate description of non-isothermal gas sorption kinetics in a differential test. Analytical equations for mass uptake and adsorbent-temperature–time profiles are derived. The model allows direct calculation of a mass-transfer coefficient from the experimental uptake data to be used in the design of adsorbers. Interactions between the equilibrium and transport properties of the adsorption system predicted by the l.d.f. model are equivalent to those given by other mathematically more complicated non-isothermal models.Experimental uptake curves for adsorption of n-butane and n-pentane on 5 A zeolite and i-octane on 13X zeolite were quantitatively described by the l.d.f. model. The analysis shows that a ‘surface barrier’ may be the principal resistance to mass transfer for these systems.
TL;DR: The mesophase structures formed in sodium dodecanoate + water mixtures have been investigated using n.m. spectroscopy and polarising microscopy as discussed by the authors, and it was concluded that the two mesophases with highest surfactant concentrations both consist of bilayers.
Abstract: The mesophase structures formed in sodium dodecanoate + water mixtures have been investigated using n.m.r. spectroscopy and polarising microscopy. Four different regions were indicated by optical microscopy, while 2H and 23Na n.m.r. measurements detected only three mesophases separated by first-order phase boundaries. From the n.m.r. data we conclude that the two mesophases with highest surfactant concentrations both consist of bilayers. One is the normal lamellar (Lα) phase whilst the second, containing less surfactant and occurring over limited temperature and composition ranges, has very thin bilayers. We suggest that within this phase there is a hydrogen-bonded water network linking the bilayers. The phase formed at lowest surfactant concentration is hexagonal (H1). To account for the optical microscope and n.m.r. data, we propose that as concentration is increased the H1 phase gradually changes to a deformed hexagonal lattice (H1d). The H1d structure and the second lamellar phase are termed ‘intermediate’ phases.Optical microscopy has been used to investigated the occurrence of intermediate phases in other C8-C18 sodium and potassium alkanoates with even chain numbers. These phases are found with the C12 to C18 sodium soaps whilst the C8 and C10 sodium soaps form a cubic phase (V1). The C10 derivative also forms one intermediate phase (probably H1d). Broadly similar phase behaviour was found for the potassium soaps except that two intermediate phases and a V1 phase occur with the C10 compound, while with the C12 derivative the intermediate phases are transformed to V1 at higher temperatures. The same technique has been used to investigate mesophases of sodium n-alkyl sulphates. A single intermediate phase only forms with C10 to C14 sodium alkyl sulphates. For the hexyl derivative a V1 phase occurs, while the intermediate phase of the C8 homologue changes to V1 on heating. Only H1 and Lα occur for sodium oleyl sulphate.Intermediate phases only appear to form with longer-chain ionic surfactants. Literature data indicate that only V1 phases occur with non-ionic and zwitterionic surfactants. There is a brief discussion of possible explanations for this.
TL;DR: Sorption uptake measurements have been used to measure the intracrystalline diffusivities of benzene in NaX zeolite within wide ranges of sorbate concentration at different temperatures as mentioned in this paper.
Abstract: Sorption uptake measurements have been used to measure the intracrystalline diffusivities of benzene in NaX zeolite within wide ranges of sorbate concentration at different temperatures. Their success is due to a significant decrease in the response time of the uptake equipment (< ca. 0.1 s) compared with current methods, this being obtained by application of a recently developed method of data evaluation that accounts for external effects (via a theory of statistical moments) and by using relatively large zeolite crystals (ca. 120 µm). The coincidence of corrected sorption diffusion data with n.m.r. self-diffusivities indicates that the sorption technique gives reliable information on intracrystalline molecular mobility, even for hydro-carbons in large-port microporous sorbents.
TL;DR: In this article, the effect of mixing on the different phases in the bulk or at the outer layers of bismuth molybdate was investigated by using diffraction, X-ray photoelectron spectroscopy and infrared spectroscopic analysis.
Abstract: Different phases (α, β and γ) and intimate equimolar mixtures of the α and γ phases of bismuth molybdate have been investigated for the mild oxidation of propene into acrolein. The mixtures were prepared either as a coprecipitate or as intimately compressed and ground mixtures. A synergy effect between the α and γ phases was observed with an enhancement in activity and selectivity for an intimate equimolar mixture. A study by X-ray diffraction, X-ray photoelectron spectroscopy and infrared spectroscopy allowed us to follow the effect of mixing on the different phases in the bulk or at the outer layers. Changes in elemental composition in either Mo or Bi because of mixing or preparation conditions were not detected.