Showing papers in "Journal of the Chemical Society, Faraday Transactions in 1981"
TL;DR: In this article, a theory of self-assembly of surfactant molecules into micelles and bilayers is critically examined and extended to include vesicles and microemulsions.
Abstract: A theory of self-assembly of surfactant molecules into micelles and bilayers is critically examined and extended to include vesicles and microemulsions. The notion of hydrophilic–lipophilic balance is quantified. The theory gives a unified account of type, size and shape of the aggregates which form under various conditions. Observed trends due to change in salt concentration, temperature and oil type, and due to the addition of cosurfactants, are correlated and emerge from a simple global framework.
755 citations
TL;DR: In this paper, the phase behavior of aqueous solutions of poly(ethylene oxide), PEO, is analyzed by means of a structural model of the system and a simple statistical-mechanical model based thereupon.
Abstract: The phase behaviour of aqueous solutions of poly(ethylene oxide), PEO, is analysed by means of a structural model of the system and a simple statistical-mechanical model based thereupon. The intention is to elucidate the structural questions involved in the water–PEO coupling and to gain some insight in possible consequences of this coupling. The experimental partial molar enthalpy and entropy of water can be reproduced, at least in fairly dilute solutions, if a zone with increased structuring of the water is assumed to exist around the PEO chain. The phase separation that takes place at high temperatures is traced back to the increase in total extension of the zones of enhanced water structure that occurs when the water content is increased. The chain-length dependence of the location of the solubility gap is mainly determined by the combinatorial entropy of the chains. The water solubility of PEO, which is unique in this respect among the polyethers, can be explained in terms of a good strutural fit between the water and the polymer.
689 citations
TL;DR: In this article, the polarization energies of 44 organic solids were determined by ultraviolet photoelectron spectroscopy in the gaseous and solid states, and the results indicate that the polarization energy of an organic solid is mainly determined by two factors: the molecular polarizability and the molecular packing in the solid.
Abstract: The polarization energies of 44 organic solids were determined by ultraviolet photoelectron spectroscopy in the gaseous and solid states. Condensed polycyclic aromatic hydrocarbons with planar molecular structures were found to have a common value, 1.7 eV, independent of their molecular sizes and also their crystal structures. The common value is approximately interpreted by the first-order expression for the polarization energy. A large variation of values in the range 0.9–3.0 eV was obtained for several compounds. Among them, molecules with intricate structures have smaller values and those with large molecular polarizabilities have larger values than the common value. These results indicate that the polarization energy of an organic solid is mainly determined by two factors: the molecular polarizability and the molecular packing in the solid. Intermolecular interactions in the solid, other than the van der Waals force, also contribute to the value.
334 citations
TL;DR: In this article, the authors have performed static and dynamic neutron small-angle scattering experiments on sodium dodecyl sulphate solutions, in the concentration range 0.04-0.8 mol dm-3, with up to 0.2 moldm−3 of added NaCl.
Abstract: We have performed static and dynamic neutron small-angle scattering experiments on sodium dodecyl sulphate solutions, in the concentration range 0.04–0.8 mol dm–3, with up to 0.2 mol dm–3 of added NaCl. We have analysed the data taking intermicellar correlations specifically into account by calculating an analytic structure factor for the fluid of interacting charged micelles. We have thus been able, for the first time, to derive micellar charge and aggregation numbers from the small-angle scattering patterns of concentrated micelle solutions. Our results largely reconcile the two opposed current views of ‘wet’ or ‘dry’ micelle structure. We effectively retain the basic micelle geometry proposed by Hartley, but take dynamic thermal fluctuations into account by allowing a rough outer layer from which monomers may penetrate into the solvent. We find the micelles are generally less than 25% ionised.Dynamic small-angle neutron spin-echo measurements of the effective micellar diffusion coefficients have also been performed, to provide independent self-consistent verfication of the calculated structure factors. The techniques used are directly applicable to the interpretation of light-scattering and small-angle X-ray studies, as well as neutron data. They form a basis for extending the study of solutions and suspensions of charged spherical particles to the concentrated regime.
248 citations
TL;DR: In this article, a numerical scheme for solving the equations which govern the behaviour of dilute suspensions of colloidal particles in an oscillating electric field is developed for the conductivity and the complex dielectric response of a dilute suspension.
Abstract: A numerical scheme is developed for solving the equations which govern the behaviour of dilute suspensions of colloidal particles in an oscillating electric field. Appropriate expressions for the conductivity and the complex dielectric response of a dilute suspension are also derived. The behaviour of these properties as functions of frequency, zeta potential, particle radius, electrolyte concentration and valency is displayed. The effect of slipping-surface boundary conditions for the electric potential is briefly discussed.
246 citations
TL;DR: In this article, the catalytic decomposition of NO has been investigated over copper-exchanged Y-type zeolites (CuNaY) at 573-823 K in a flow reactor.
Abstract: The catalytic decomposition of NO has been investigated over copper(II)-exchanged Y-type zeolites (CuNaY) at 573–823 K in a flow reactor. CuNaY exhibited an appreciable activity above 723 K and was not poisoned by either oxygen or water vapour. In the presence of the CuNaY catalyst (69% exchanged) using a contact time of 11 g(catalyst) s cm–3(gas), the extent of elimination of NO (4 vol%) in diluent helium was found to attain ca. 100% at 773 K. Below 673 K, the catalytic activity slowly declined with increasing reaction time and was restored to its original state upon heating the catalyst above 723 K. This phenomenon results from the accumulation and desorption of oxygen released from the decomposed NO. The influence of the CuII ion-exchange level on the catalytic activity has been examined and it was concluded that the active sites for the reaction are the CuII ions located at sites SII and SIII. Upon adsorption of NO at 273 K on CuNaY substantial amounts of N2O, N2 and O2, as well as NO, appear in the temperature-programmed desorption chromatogram. Based on the results of thermal desorption of various adsorbates and the temperature-dependence of N2O decomposition, two reaction paths of NO are proposed, including direct decomposition to N2 and O2 and consecutive decomposition through N2O as an intermediate.
227 citations
TL;DR: In this paper, a gas-recirculation system was used to convert methanol into hydrocarbons over ZSM-5 zeolites, and the conversion proceeds autocatalytically.
Abstract: The conversion of methanol into hydrocarbons over ZSM-5 zeolites has been investigated using a gas-recirculation system. The conversion proceeds autocatalytically. The reaction rate is greatly enhanced by the addition of ethylene or cis-but-2-ene, indicating that the autocatalysis is caused by the reaction of olefin and methanol. Infrared studies have revealed that methoxyl groups (—OCD3) are formed by the reaction of surface hydroxyl groups and methanol molecules (CD3OH), and they decompose to reproduce hydroxyl groups (—OD), giving hydrocarbons. The reaction mechanism in which methyl carbonium ions attack the C—H bond of methanol or dimethyl ether molecules is proposed. Methyl carbonium ions are supposed to be released from extensively polarised methoxyl groups formed by the reaction of methanol molecules and strong Bronsted-acid sites. In fact, strongly acidic materials, Nafion H and heteropolyacids, were found effective for methanol conversion. A semiquantitative analysis of the autocatalytic phenomenon in methanol conversion is also presented.
224 citations
TL;DR: In this paper, the manner in which ions such as Cd2+, Zn2+, Ni2+, Mg2+ and Ba2+ in aqueous solution are removed by synthetic hydroxyapatites has been probed by using both batch and column methods.
Abstract: The manner in which ions such as Cd2+, Zn2+, Ni2+, Mg2+ and Ba2+ in aqueous solution are removed by synthetic hydroxyapatites has been probed by using both batch and column methods. The behaviour is not merely an adsorption effect but a type of ion-exchange reaction between the ions in solution and the Ca2+ ions of the apatites. The ranking of the ions according to amount exchanged was as follows: Cd2+, Zn2+ > Ni2+ > Ba2+, Mg2+. These results suggest that the apatites have a selectivity for metallic cations and can be employed as a new inorganic cation-exchanger for recovering valuable ions in waste water.
215 citations
TL;DR: In this article, the same formate intermediate is formed by co-adsorption of carbon dioxide and hydrogen while hydrogen/carbon monoxide dosing does not result in its formation; indeed carbon monoxide itself did not adsorb on the defected zinc oxide.
Abstract: The kinetics of the adsorption and surface reactions of hydrogen, water, carbon dioxide, carbon monoxide, formaldehyde and methanol on what is mainly the prism face of zinc oxide have been studied using temperature programmed desorption and reaction. Both hydrogen and carbon dioxide show a multiplicity of desorption energies, adsorption into those states showing the highest binding energies being activated. Temperature programming after the room-temperature adsorption of formaldehyde or methanol shows evidence of surface reaction, with the formation of a formate intermediate. The surface reaction mechanisms of this formate intermediate and their kinetics are identical regardless of whether it was formed from methanol adsorption or formaldehyde adsorption. The formate appears to be the pivotal intermediate in zinc oxide catalysed synthesis gas chemistry, decomposing (a) to carbon monoxide and hydrogen or (b)(depending on the hydrogen coverage) to methanol. The same formate intermediate is formed by co-adsorption of carbon dioxide and hydrogen while hydrogen/carbon monoxide dosing does not result in its formation; indeed carbon monoxide itself did not adsorb on the defected zinc oxide.
206 citations
TL;DR: In this article, the fluorescence quantum yields and lifetimes for a series of metal tetraphenylporphyrins were found to decrease with increasing spin-orbital coupling constant of the central metal ion.
Abstract: The fluorescence quantum yields and lifetimes for a series of metal tetraphenylporphyrins were found to decrease with increasing spin–orbital coupling constant of the central metal ion. The triplet states gave similar effects at both 77 and 293 K, as shown by luminescence and flash photolysis studies. In particular, the triplet-state lifetimes decreased in the order Mg > Zn > Pd ≈ Cd > Hg and it was possible to relate the rate constants for non-radiative decay processes to the spin–orbital coupling constant of the metal ion although different metal ions interacted with the porphyrin π-system to a different extent.
175 citations
TL;DR: In this article, a study of the changes occurring in carbon-supported metalloporphyrins and metallo-phthalocyanines during heat treatment was made, which improved both the stability and the activity of these materials in the electrochemical reduction of oxygen in acid electrolyte.
Abstract: A study has been made of the changes occurring in carbon-supported metalloporphyrins and metallo-phthalocyanines during heat treatment, which improves both the stability and the activity of these materials in the electrochemical reduction of oxygen in acid electrolyte. A variety of physical techniques was applied, including X-ray photoelectron spectroscopy (X.p.s.), Fourier-transform infrared spectroscopy, electron spin resonance and Mossbauer spectrometry.During the heat treatment a bond can be formed between the carbon surface and both the central metal ion and the macrocyclic ligand, which thereby loses all its peripheral substituents while retaining its inner part. In some cases some of the chelate molecules are destroyed. The active sites formed in the more active catalysts consist of an isolated metal ion surrounded by the thermally modified ligand. A relation between redox potential and O2-reduction activity of the same form as that for untreated catalysts can be used to explain the observed enhancements in activity.
TL;DR: A series of materials containing nickel and aluminium ions has been prepared by coprecipitation with alkaline solutions, under various conditions, from solutions of the nitrates as discussed by the authors, and the composition and structure of the precipitates has been examined using a number of techniques including chemical analysis, X-ray diffraction, thermogravimetry and infrared spectroscopy.
Abstract: A series of materials containing nickel and aluminium ions has been prepared by coprecipitation with alkaline solutions, under various conditions, from solutions of the nitrates. The composition and structure of the precipitates has been examined using a number of techniques including chemical analysis, X-ray diffraction, thermogravimetry and infrared spectroscopy. The precipitates have structures typical of minerals of the hydrotalcite group and particularly of the nickel-aluminium compound, takovite. They consist of brucite-like layers of composition [NixAl1–x(OH)2](1–x)+ and interlayers containing CO2–3, NO–3 or OH– ions, or combinations of these, depending on the preparation conditions, together with molecular water; the anions balance the excess charge of the brucite layers. It is concluded that the aluminium ions are randomly substituted for nickel ions in the brucite layers and that the structure of these layers is independent of the anions in the interlayer. For freshly precipitated samples, 0.5 ⩽x≲ 0.85, but for hydrothermally aged materials, 0.66 ⩽x⩽ 0.75; outside these ranges, boehmite or Ni(OH)2 from as separate phases. The results are compared with those for precipitates prepared from ammoniacal solutions and it is concluded that the two types of material are indistinguishable.
TL;DR: In this paper, the state of the platinum and catalytic activity of the Pt sites in benzene hydrogenation and n-hexane dehydrocyclisation were investigated using X-ray diffraction, electron micrography and infrared studies of CO adsorption.
Abstract: Alkaline platinum L zeolites have been studied with regard to the state of the platinum and the catalytic activity of the platinum sites in benzene hydrogenation and n-hexane dehydrocyclisation. X-ray diffraction, electron micrography and infrared studies of CO adsorption led to the conclusion that there are four types of Pt particles: large 100–600 A particles outside the channels, crystals 10–25 A in diameter and small metallic cylinders inside and outside the channels and very small particles in cavities, the latter giving reversible Pt carbonyl clusters upon CO adsorption. The Pt active sites in benzene hydrogenation and n-hexane dehydrocyclization (10–25 A crystals and small cylinders) are strongly dependent upon their environment. In the absence of any acidity their activity increases with the zeolite basicity, while no electron deficiency is observed. The infrared band at 2060–2065 cm–1 of adsorbed CO suggests that Pt particles have an excess of electrons and/or typical faces, corners or edges. It is suggested that the L zeolite structure and field induced these unusual Pt state and catalytic properties.
TL;DR: A detailed vibrational analysis for CH3CCo3(CO)9 and for its deuterated analogue, and assignments have been confirmed by means of an approximate normal-coordinate analysis as discussed by the authors.
Abstract: A detailed vibrational analysis is reported for CH3CCo3(CO)9 and for its deuterated analogue, and assignments have been confirmed by means of an approximate normal-coordinate analysis. Some significant revisions of an earlier assignment have been made. Comparison of these spectra with those obtained by electron energy-loss spectroscopy of a species resulting from the chemisorption of acetylene and ethylene on Pt (111) above 300 K supports the identification of the latter as containing a C·CH3 group. The two most probable alternatives are a CH3CHPt2 species or CH3CPt3+adsorbed hydrogen atoms.
TL;DR: In this paper, a positively charged, water-soluble zinc porphyrin photosensitises the reduction of water to H2 with high efficiency, using MV2+ as electron relay and EDTA as sacrificial electron donor.
Abstract: We have confirmed an earlier report by Kalanasundaram and Gratzel that a positively charged, water-soluble zinc porphyrin photosensitises the reduction of water to H2 with high efficiency. Using MV2+ as electron relay and EDTA as sacrificial electron donor, the quantum yield for production of ½H2 is ca. 0.6. The reaction mechanism involves reduction of MV2+ by triplet porphyrin and the porphyrin π-radical cation so produced is reduced by EDTA. The concentrations of reactants have been optimised for production of H2 and to limit destruction of the porphyrin. Under optimised conditions the turnover with respect to the porphyrin can reach 6000.In addition, some consideration has been given to ways of improving oH2 and of increasing the fraction of sunlight that can be harvested. In this respect, Cd porphyrins may possess suitable properties.Finally, we note that the porphyrin π-radical cation may possess the thermodynamic capacity to oxidise water to O2, but this is very much borderline.
TL;DR: In this article, the transformation of C in the form of CO2 into hydrocarbons was investigated on supported Ru catalysts and the surface processes occurring during the removal of the O atoms of CO 2 by H2 and on the identification of surface species formed during the reaction.
Abstract: The transformation of C in the form of CO2 into hydrocarbons was investigated on supported Ru catalysts. Special attention was paid to the surface processes occurring during the removal of the O atoms of CO2 by H2 and on the identification of surface species formed during the reaction. Infrared spectroscopic measurements revealed that chemisorbed CO and formate ion are formed during the coadsorption of H2+ CO2 at 373 K and also during the methanation of CO2 at higher temperatures. The CO formed produced a weak absorption band at lower frequencies (1990–2000 cm–1) than did the CO alone (2030–2040 cm–1). This shift was attributed to the effect of hydrogen adsorbed on the same Ru atoms and to that of surface C formed during the reaction. Evidence is presented to show that formate ion forms on the Ru but migrates rapidly onto the supports. It is considered as an inactive species in the methanation of CO2.The hydrogenation of CO2 on Ru/Al2O3 occurred at a measurable rate above 443 K yielding almost exclusively CH4. The formation of surface carbon was detected during the reaction at a level ca. 1.5 orders of magnitude less than in the H2+ CO reaction. The rate of CH4 formation is described by the expression NCH4= 2.7 × 106 exp (–16.1/RT)×PH2× 0.47 PCO2. It is proposed that the synthesis of CH4 from H2+ CO2 occurs via the formation of surface C and its subsequent hydrogenation.
TL;DR: In this article, the effect of varying the ratio of SiO2/Al2O3 and alkalinity in the starting gels and the reaction temperature were studied, and it was found that the alkality was found to affect the rate of nucleation more than the speed of crystal growth.
Abstract: Zeolite ZSM-5 was synthesized from sodium tetrapropylammonium aluminosilicate gels and tetrapropylammonium silicate gel. Effects of varying the ratio SiO2/Al2O3 and alkalinity in the starting gels and the reaction temperature were studied. The alkalinity was found to affect the rate of nucleation more than the rate of crystal growth. An optimum alkalinity exists in the synthesis of ZSM-5; the optimum value is closely related to the value of SiO2/Al2O3 ratio in the batch composition. The apparent activation energies for nucleation and crystal growth are 38 and 46 kJ mol–1, respectively, for the aluminium-free silicate system and 25 and 29 kJ mol–1, respectively, for the aluminosilicate system with SiO2/Al2O3= 70. The results are consistent with a complicated solution mechanism of crystallization.
TL;DR: In this article, the problem of obtaining information about the variation of particle size with volume fraction from scattering techniques in strongly interacting systems is discussed in some detail and a possible theoretical approach suggested based on the use of a hard-sphere interaction model.
Abstract: Microemulsions formed from water, xylene, sodium dodecyl benzene sulphonate and hexanol have been investigated by three different scattering techniques, namely, time-average light scattering (l.s.), small-angle neutron scattering (SANS) and photon correlation spectroscopy (p.c.s.). The water volume fraction in this water-in-oil system, which was investigated at a constant molar ratio (hexanol: sodium dodecyl benzene sulphonate) of 3.28, was varied from zero to 0.533. Over most of the volume-fraction range the droplets were strongly interacting. The problem of obtaining information about the variation of particle size with volume fraction from scattering techniques in strongly interacting systems is discussed in some detail and a possible theoretical approach suggested based on the use of a hard-sphere interaction model. The combination of l.s., SANS and p.c.s. is shown to be an excellent one for problems of this type, in that l.s. and SANS can provide time-average structural information and p.c.s. dynamic information about the motion of the particles in strongly interacting systems. With the model proposed the information from the three experimental techniques was found to be self-consistent. For the system investigated the radius of the water core of the droplet was found to increase with increase in the water volume fraction whilst apparently maintaining a constant water–oil interfacial area.
TL;DR: In this article, the aqueous radiolytic products OH radical, HO2 radical, H2 and H2O2 molecules were measured for a variety of radiation types and scavenger concentrations.
Abstract: G values (molecules per 100 eV) of the aqueous radiolytic products OH radical, HO2 radical, H2 and H2O2 molecules were measured for a variety of radiation types and scavenger concentrations. The radiations included 60Co gamma, protons, 4He, 14N and 20Ne ions.As expected G(OH) increased with increasing scavenger concentration and decreased with increasing LET (linear energy transfer, –dE/dx) of the radiation. G(H2) increased monotonically with increasing LET, as did G(HO2). G(H2O2) at first increased and then decreased with increasing LET. The results are compared with those of other workers and with computed G values from the modified prescribed diffusion model.
TL;DR: In this article, a re-appraisal of some of the earlier sorption data suggests that the dramatic differences previously noted between nmr and sarsption data are due primarily to failure to take proper account of the effects of external heat and mass-transfer resistance in the analysis of uptake curves.
Abstract: Corrected sorption diffusivities, calculated from uptake rate experiments, are compared with self diffusivities measured by the nmr pulsed-field-gradient method For butane and propane in 5A zeolite and for triethylamine in 13X zeolite there is good agreement, both in the magnitude of the diffusivities and the trends with concentration and temperature A re-appraisal of some of the earlier sorption data suggests that the dramatic differences previously noted between nmr and sorption data are due primarily to two causes: (i) failure to take proper account of the effects of external heat- and mass-transfer resistance in the analysis of uptake curves; (ii) the use of different zeolite crystals, subjected in some cases to quite different dehydration procedures, for the sorption and nmr experimentsHowever, for benzene in 13X there is a large difference between nmr and sorption diffusivities even though the measurements were performed under apparently similar conditions on samples from the same original batch of zeolite Uptake rates measured with different sizes of crystal are consistent with the simple diffusion model and on this basis the intrusion of external heat- or mass-transfer resistance seems improbable The reason for the discrepancy for this system remains uncertain
TL;DR: In this article, the total and metallic nickel areas of a series of coprecipitated nickel-alumina catalysts prepared and pretreated in different ways were analyzed. And the high stability of the catalysts was attributed to the presence in the unreduced catalyst of nickel oxide rich phases containing dissolved aluminium ions.
Abstract: Results are presented for the total and metallic nickel areas of a series of coprecipitated nickel–alumina catalysts prepared and pretreated in different ways. The total areas of the samples decrease on reduction and with increasing reduction temperature, while the nickel area increases with reduction temperature. Increasing calcination temperature causes a decrease in total and nickel areas, this being particularly marked at high temperatures of calcination. A model for the catalyst system is proposed, based on these results and on complementary structural investigations. The high stability of the catalysts is attributed to the presence in the unreduced catalyst of nickel oxide rich phases containing dissolved aluminium ions; on reduction, alumina crystallises on the surface of the growing nickel crystallites, preventing sintering of the catalysts except under extreme conditions.
TL;DR: In this article, the potential energy of the intermolecular interaction of non-polar monoatomic molecules of noble gases on NaX zeolite has been calculated using the point moment approximation.
Abstract: Molecular statistical calculations of the thermodynamic characteristics of adsorption of Ar, Kr, Xe, O2, N2, CO, CO2 and NH3 at low (zero) filling have been carried out for X and Y zeolites. The atom–atom (atom–ion) approximation has been used to calculate the potential energy of the intermolecular interaction of non-polar monoatomic molecules of noble gases. The parameters of the potential function for the atom–ion intermolecular interaction have been improved by comparing the theoretically calculated Henry's constant for adsorption of one of the noble gases on NaX zeolite with the experimental data, as has been done previously for adsorption on graphitized thermal carbon black. The correction thus introduced into the parameters of the atom–ion potentials makes it possible to calculate not only the thermodynamic characteristics for the adsorption of different noble gas molecules on NaX zeolite, but also on other cationized zeolites of the same type, X. For polar molecules, an allowance is also made for the contribution due to the electrostatic interaction of the rigid molecular multipoles (quadrupole, dipole) with zeolite ions to the total potential energy for the intermolecular interaction with the zeolite. This contribution is calculated via the point moment approximation.
TL;DR: In this article, the rate coefficients for the reactions N + OH → NO + H (1) and O + O → O2+ H (2) have been determined, in direct experiments, from 250 to 515 K.
Abstract: Rate coefficients for the reactions N + OH → NO + H (1) and O + OH → O2+ H (2) have been determined, in direct experiments, from 250 to 515 K. A discharge-flow system is used to generate measured concentrations of N or O; then OH radicals are formed by flash photolysis of H2O and monitored by resonance fluoresence as they are removed by reaction (1) or (2) under pseudo-first-order conditions. The results are fitted to the rate expressions: k1=(2.21 ± 0.18)×10–10T–0.25 ± 0.17 cm3 molecule–1 s–1, k2=(6.65 ± 0.23)×10–10T–0.50 ± 0.12 cm3 molecule–1 s–1 where the errors represent 95% confidence intervals within the range of temperature covered in the experiments. The rate coefficient k2 is compared with a calculation assuming that the reaction proceeds via a bound state HO2 collision complex.
TL;DR: In this article, electron spin resonance studies of MgO smoke powders show that etching of the smoke cubes by water vapour leads to an increase in the number of reactive sites of low coordination on the surface without a parallel increase in surface area.
Abstract: Photoluminescent and electron spin resonance studies of MgO smoke powders show that etching of the smoke cubes by water vapour leads to an increase in the number of reactive sites of low coordination on the surface without a parallel increase in the surface area. The formation of anion radicals after adsorption of oxygen and nitrobenzene was used as a monitor of the number of sites of low coordination and it is suggested that 3-coordinated surface O2– ions are involved in the formation of radical ions from both adsorbates.
TL;DR: In this article, the formation constant and absorption spectrum of the dimer and trimer of fluorescein dianion in aqueous solution were evaluated and the geometric structures of both aggregates were determined using the exciton theory.
Abstract: The formation constant and absorption spectrum of the dimer and trimer of fluorescein dianion in aqueous solution are evaluated. The geometric structures of both aggregates are determined using the exciton theory. The nature of the association forces is also studied.
TL;DR: In this article, the authors reported absolute measurement of the thermal conductivity of the monatomic gases helium, neon, argon, krypton and xenon and of binary mixtures of helium and neon.
Abstract: The paper reports absolute measurement of the thermal conductivity of the monatomic gases helium, neon, argon, krypton and xenon and of binary mixtures of helium and neon and argon and krypton. The measurements have been carried out in a transient hot-wire apparatus at 35 °C and in the pressure range 0.5–10 MPa. The overall uncetainty in the reported thermal conductivity data is estimated to be ±0.2%, an estimate which is confirmed by a comparison with low density viscosities for the same gases.The experimental thermal conductivity for each system studied conforms to a polynomial expansion in density. It is found that the data for the binary mixtures in the limit of zero density can only be adequately represented if third-order kinetic theory expressions are employed. A recently proposed scheme for the evaluation of the thermal conductivity of dense gas mixtures is found to represent the data for argon + krypton adequately. However, for helium + neon mixtures the proposed scheme required modifications in order to provide a satisfactory description of the experimental data.
TL;DR: In this article, a simple expression for the Donnan equilibrium between a solution of charged colloid plus electrolyte and an electrolyte alone is derived, and expressions for the solute chemical potentials and the osmotic pressure are obtained.
Abstract: Thermodynamic arguments are used to derive a simple expression for the Donnan equilibrium between a solution of charged colloid plus electrolyte and a solution of electrolyte alone. From it, expressions for the solute chemical potentials and the osmotic pressure are obtained. Polydispersity, excluded volume effects and interactions between the various solute species are allowed for. The treatment has features in common with approaches based on the Poisson–Boltzmann equation but is simpler and is not restricted by considerations of particle geometry. It predicts successfully the characteristic behaviour of dilute solutions of polyelectrolyte plus salt and agrees with experimentally obtained activity coefficients of supporting electrolyte better than a prominent existing model. When the theory is applied to solutions of ionic surfactants the dubious assumptions inherent in some previous approaches are avoided, yet similar equations emerge which allow better for solution non-ideality and give good agreement with experiment. The treatment also permits the application to charged micelles of the methods successfully applied previously to non-ionic micelles. The application to colloid stability is discussed. Finally, the application to polyacid titration behaviour is outlined. This exposes some limitations of the theory and suggests appropriate modifications.
TL;DR: In this paper, a simple geometrical interpretation of the anodic transients at 0.95 and 1.30 V is provided, and the Tafel slope observed at anodic potentials is shown to be consistent with an electrochemical process having charge transfer as a rate-determining step.
Abstract: The electrochemistry and photoelectrochemistry of a (110) face of single-crystal lithiated NiO has been studied. The Mott–Schottky and photocurrent appearance potential suggest a flat-band potential of +0.8 V (NHE), and earlier capacitance data are used to fix a second acceptor level at +0.4 eV above the Li acceptor states. A simple geometrical interpretation of the anodic transients at 0.95 and 1.30 V (NHE) is provided, and the Tafel slope observed at anodic potentials is shown to be consistent with an electrochemical process having charge transfer as a rate-determining step. The optical data are interpreted with an energy-level scheme using a value of ca. 3 eV for the Hubbard parameter U defining the correlation splitting of the Ni 3d8 and Ni 3d9 configurations, and the data are consistent with a direct allowed transition at the band edge that is assigned to O 2p6→ Ni 3d9. Comparison with the X.p.e.s. spectrum and the known position of the O 2p6 band edge in other transition-metal oxides leads to a suggested Ni 3d8–O 2p6 band-edge separation of ca. 1.4 eV. The very low efficiencies found for NiO can be understood only if the minority-carrier diffusion length becomes comparable with the semiconductor Debye length. The very low ratio of free carriers to trapped holes in NiO is shown to make this material impractical for solar-energy devices.
TL;DR: In this article, an apparatus for diffuse reflectance flash photolysis measurements is described, and the potential of this method for investigating photocatalytic reactions and excited states properties on surfaces is demonstrated.
Abstract: An apparatus developed to enable diffuse reflectance flash photolysis measurements to be made is described. Transient spectra observed from five aromatic hydrocarbons adsorbed at less than monolayer levels on activated γ-alumina powder are shown to be due to triplet–triplet absorption. These spectra are strikingly different from the triplet–triplet spectra of these same hydrocarbons in homogeneous media and these differences are interpreted as arising mainly from transitions to charge-transfer states of the surface–adsorbate systems. The potential of this method for investigating photocatalytic reactions and excited states properties on surfaces is demonstrated.
TL;DR: In this article, the tripmultiplet states result from interaction between the metal d-orbitals and the porphyrin (ππ*) excited triplet states, and the rate constants for deactivation of the tri-parameter states depend markedly upon the nature of the central metal ion and are much faster for MnIII and FeIII than for CuII and CrIII.
Abstract: The absorption spectra of paramagnetic transition metal porphyrins consist of (ππ*), charge-transfer and tripmultiplet transitions. The tripmultiplet states result from interaction between the metal d-orbitals and the porphyrin (ππ*) excited triplet states. For CuIITPP, luminescence occurs from the lowest energy tripquartet state whilst CrIIITPP shows luminescence from tripquartet and tripsextet states. Luminescence from MnIIITPP and FeIIITPP is much less efficient and originates from the second tripmultiplet state. The rate constants for deactivation of the tripmultiplet states depend markedly upon the nature of the central metal ion and are much faster for MnIII and FeIII than for CuII and CrIII. Luminescence was not observed for FeIITPP, possibly due to the presence of a low-lying c.t. state.