Showing papers in "Journal of the Chemical Society, Faraday Transactions in 1979"
TL;DR: In this paper, a new resonance Raman phenomenon is proposed which is the Raman component of resonant Mie scattering, and in which the polarizability of the metal particles is modulated by the vibrations of the adsorbed molecules.
Abstract: Intense Raman scattering by pyridine molecules adsorbed on silver or gold aqueous sol particles of dimensions comparable to the wavelength is reported. The degree of intensity enhancement is strongly dependent on the excitation wavelength, with a sharp resonance Raman maximum for excitation at the wavelength of the Mie extinction maximum of the metal particles, and for the silver sols the Raman maximum is shown to follow the extinction maximum to longer wavelengths with increase in particle size. A new resonance Raman phenomenon is thus proposed which is the Raman component of resonant Mie scattering, and in which the polarizability of the metal particles is modulated by the vibrations of the adsorbed molecules. These observations confirm that surface plasma oscillations are involved in the intense Raman scattering already reported for molecules adsorbed at roughened silver surfaces. The metal dielectric function requirements for resonant Mie scattering enable the optimum excitation wavelength for plasma resonance-enhanced Raman studies at the surface of other metals to be estimated.
1,450 citations
TL;DR: In this paper, the constitutive equation for polymer melts and concentrated solutions derived in the previous papers is applied to two typical rheometrical flows: steady and transient shear flow, oscillatory shear flows superposed on steady flow, and uniaxial elongational flow.
Abstract: The constitutive equation for polymer melts and concentrated solutions derived in the previous papers is applied to two typical rheometrical flows: steady and transient shear flow, oscillatory shear flow superposed on steady flow, steady and transient uniaxial elongational flow. The stress responses predicted are qualitatively in good agreement with experiments except for one case (the first normal stress in the transient shear flow). A particularly interesting result is that the constitutive equation suggests instability in steady shear flow and uniaxial elongational flow.
430 citations
TL;DR: Experiments on suppressing convection near the membrane with the aid of microporous filters have shown that such convection cannot be responsible for the inflexion of the voltage against current curves, and for the passage through the membrane of current much greater than the “limiting” value.
Abstract: The voltage against current curves of cation exchange membranes have been studied. They have a characteristic shape with a region of slow current variation (the plateau) followed by a region of accelerated current growth as the voltage is increased (the inflexion).For currents much greater than the “limiting” one determined by the value at the “plateau” of the (V, C) curve, the current is transferred across the membrane mainly by the cations of the salt; the contribution of “water splitting” is minor.Experiments on suppressing convection near the membrane with the aid of microporous filters have shown that such convection cannot be responsible for the inflexion of the voltage against current curves, and for the passage through the membrane of current much greater than the “limiting” value.It was shown on the basis of a simple theoretical model that formation near the membrane of a region of the volume charge, reflected in replacing the electroneutrality condition by the full Poisson equation, may lead to passage through the membrane of currents greater than the “limiting” one; the voltage against current curves of the general form described above with an inflexion, were then obtained using computation. The asymptotic behaviour of these voltage against current curves at large voltages was studied.
357 citations
TL;DR: In this paper, the size and aggregation number of reversed micelles formed by the system aerosol-OT + H2O + organic solvent have been determined by viscosity and dynamic light scattering methods.
Abstract: The size and aggregation number of reversed micelles formed by the system aerosol-OT + H2O + organic solvent have been determined by viscosity and dynamic light scattering methods. For the viscosity method, a procedure for deriving values of the aggregation number from particles of variable density is described. Measurements were made in cyclohexane, toluene and chlorobenzene. The dynamic light scattering method, based on photon correlation spectroscopy, yields single exponential correlation functions from which values of the translational diffusion coefficient and the micelle radius can be derived. The droplet size was found to depend primarily on the ratio of surfactant to water concentrations, but was essentially independent of solvent and concentration at a fixed surfactant to water concentration ratio. Satisfactory agreement was obtained among the two methods discussed in this paper and one (sedimentation ultracentrifugation) described previously.
183 citations
TL;DR: The photo-activity of TiO2 (anatase P. 25) samples with a "fully hydroxylated surface" was studied in the presence of oxygen as discussed by the authors, where photo-adsorption of oxygen was observed in the early stages of u.v. illumination reducing the pressure to < 0.1 N m −2.
Abstract: The photo-activity of TiO2(anatase P. 25) samples with a “fully hydroxylated surface” was studied in the presence of oxygen. Photo-adsorption of oxygen was observed in the early stages of u.v. illumination reducing the pressure to < 0.1 N m–2. After this fast adsorption, slow photo-desorption of oxygen was detected continuing for several hours. Thermal removal of water and hydroxyl groups reduced photo-adsorption and the process became diffusion controlled. Rehydration restored fast photo-adsorption and first order kinetics. Photo-desorption of water accompanied photo-adsorption of oxygen on these “fully hydrated surfaces”. A mechanism involving the formation of OH· radicals and their reaction to give H2O2, which decomposes leading to oxygen photo-desorption, is proposed to explain these facts.
178 citations
TL;DR: In this paper, the surface characterisation of NiB and NiP catalysts with X.p.s. was carried out, and the surface concentrations of boron and phosphorus bonded to the nickel metal, surface areas and specific hydrogenation activities of the catalysts were investigated.
Abstract: The surface characterisation of nickel boride (NiB) and nickel phosphide (NiP) catalysts has been undertaken with X.p.s. Boron combined with nickel metal in NiB catalysts was found to donate electrons to the nickel metal, resulting in electron rich metal, whereas phosphorus bonded to nickel metal in NiP catalysts accepted electrons from the nickel metal, causing electron deficient metal. Preparation methods (different solvent, precursor salt and temperature) affected the surface concentrations of boron and phosphorus bonded to the nickel metal, surface areas and specific hydrogenation activities of the catalysts. The specific activities for hydrogenation reactions increased with increasing surface boron content in NiB catalysts, whereas they decreased with increasing surface phosphorus content in NiP catalysts. These positive and negative promoting effects of boron and phosphorus are explained in terms of the electron density of the nickel metal. Co-, Fe-, Pd- and PtB catalysts were also investigated for comparison.
174 citations
TL;DR: In this paper, microcalorimetry and i.r. spectroscopy were used to characterize the acid centres in ZSM-5 zeolite and showed that strongly acid sites are more heterogeneous in H-ZSM-4 than in Z-ZZM-5.
Abstract: Microcalorimetry and i.r. spectroscopy were used to characterize the acid centres in ZSM-5 zeolite. Differential heats of adsorption of ammonia at 416 K showed that there exists a strong acidity in H–ZSM-5 zeolite and also in H–Z zeolite, which exceeds that present in H–Y zeolite. The energy distribution of strongly acid sites is more heterogeneous in H–ZSM-5 than in H–Z zeolite. A comparison of calorimetric and i.r. spectroscopic data for samples with different degrees of dehydroxylation has, moreover, shown that a fraction of Bronsted sites are weakly acidic whereas all Lewis sites are strongly acid. The spatial distribution of acidity in acid-treated ZSM-5 zeolite is not uniform; the most acidic sites, and particularly Lewis sites, are located within the channel structure of the material where they are not readily accessible to ammonia molecules at 416 K or mainly to pyridine molecules at room temperature.
131 citations
TL;DR: In this paper, the effect of pretreatment temperature on the u.p.v. photo-adsorption of O2 on TiO2 has been studied by e.g., O2H· and V-centres are found for the hydrated samples and O 2, O 3 O 3 −3 for the dehydroxylated samples.
Abstract: The effect of pretreatment temperature on the u.v. photo-adsorption of O2 on TiO2 has been studied by e.p.r. Different oxygen species are found if the sample is completely hydroxylated or strongly dehydroxylated, this being related to two different photo-adsorption mechanisms. O2H· and V-centres are found for the hydrated samples and O–2, O–3 O3–3 for the dehydroxylated samples. The origin of all these species is discussed.
130 citations
TL;DR: In this article, a series of acid/base transitions in alkaline solution due to axially coordinated water molecules were identified for manganese(III) porphyrins, and electrophoresis has identified the total electronic charge of each of the acid or base forms.
Abstract: Manganese(III) forms many high spin d4 porphyrins, for which pyridyl, N-methylpyridyl, sulphonic acid and carboxylic acid and carboxylic acid functions act as water solubilising groups. Reduction with dithionite yields the corresponding manganese(II) porphyrin. Both oxidation states have been clearly identified by e.p.r. and magnetic susceptibility measurements. On the other hand, oxidation with persulphate gives an unstable manganese(III) porphyrin π-radical cation which appears to form a dimer in aqueous solution at pH ≈ 10. All the porphyrins undergo a series of acid/base transitions in alkaline solution due to axially coordinated water molecules. For manganese(III) porphyrins, there are two pK transitions, around 8.0 and 10.5, and electrophoresis has identified the total electronic charge of each of the acid/base forms.
125 citations
TL;DR: In this paper, it was found that linear Ag+3 clusters are formed upon activation, the ends of which constitute chemisorption sites for hydrogen and oxygen, while one molecule of carbon monoxide was chemisorcised per Ag ion available in the supercage.
Abstract: Carbon monoxide, oxygen and hydrogen were found to be chemisorbed on dehydrated AgA zeolites. This was investigated in detail using volumetric sorption and temperature programmed desorption techniques. Also i.r. and mass spectrometry were used to characterize the solid and the desorbed molecules.It was found that as a result of an auto-reductive process, colour centres are created upon degassing of the zeolite. These centres sorb hydrogen and oxygen dissociatively, while one molecule of carbon monoxide was chemisorbed per Ag ion available in the supercage. It is proposed that linear Ag+3 clusters are formed upon activation, the ends of which constitute chemisorption sites for hydrogen and oxygen.
122 citations
TL;DR: In this paper, the photoluminescent and reflectance spectra of MgO smoke have been compared with the spectra for ex-hydroxide and ex-carbonate, and a strong correlation exists between the optical spectra and the different morphology of the particles obtained by the different routes.
Abstract: The photoluminescent and reflectance spectra of MgO smoke have been compared with the spectra of MgO ex-hydroxide and ex-carbonate. Parallel studies by electron microscopy have shown that a strong correlation exists between the optical spectra and the different morphology of the particles obtained by the different routes. The spectra observed are associated with the surface of the oxide particles and the excitation and absorption bands are associated with oxygen ions in 3- and 4-fold coordination. The same kinds of sites are present on all samples but the ions of lowest coordination are much less abundant on the nearly perfect cubes of MgO smoke. The number of 3-fold coordinated sites on the smoke particles is considerably increased after exposure to water vapour for several h. This picture is consistent with the electron micrographs which show erosion of the edges and corners of the MgO smoke after treatment with water vapour. A model involving the removal of ion pairs from the corners and edges of the cube by water is shown to give the observed increase in the sites of lowest coordination.
TL;DR: In this paper, gold has been supported upon SiO2 and γ-Al2O3 using an impregnation technique and HAuCl4 solutions and the severity of the conditions required to effect the reduction/decomposition of the acid to metallic Au upon the support decreased and the activity per unit weight of metal in the hydrogenation of pent-1-ene at 373 K increased.
Abstract: Gold has been supported upon SiO2 and γ-Al2O3 using an impregnation technique and HAuCl4 solutions. The severity of the conditions required to effect the reduction/decomposition of the acid to metallic Au upon the support decreased and the activity per unit weight of metal in the hydrogenation of pent-1-ene at 373 K increased, as the concentration of Au decreased from 5.0 to 0.01%. Au supported upon SiO2 at these concentrations could be atomically dispersed, but in lower dispersions when upon γ-Al2O3. An increase in Au dispersion as its concentration decreased, which would provide an explanation for the unusual activity of these catalysts, may have been detected only by electron spin resonance and not by more traditional methods of characterisation. Preliminary results for SiO2-supported Ag and Pt are compared with Au.
TL;DR: In this paper, it was shown that the fundamental potential determining ion system for Ca3(PO4)2 and CaCO3 particles is the Ca2+/anion pair rather than H+/OH−.
Abstract: It is shown that the fundamental potential determining ion system for Ca3(PO4)2 and CaCO3 particles is the Ca2+/anion pair rather than H+/OH–. In addition, the electrical capacity of the inner region of the electric double layer at the aqueous solution interface with both salts near their isoelectric points is ∼40 µF cm–2, with electrokinetic potentials equal to inner diffuse layer potentials.
TL;DR: In this article, the room temperature adsorption of pyridine on η-Al2O3 dehydrated at several temperatures in the 25-700°C range has been studied by i.r. spectroscopy, u.v.-vis reflectance spectrograph and microgravimetry.
Abstract: The room temperature adsorption of pyridine on η-Al2O3 dehydrated at several temperatures in the 25–700°C range has been studied by i.r. spectroscopy, u.v.-vis reflectance spectroscopy and microgravimetry.Several species are formed that can be identified on the basis of the spectroscopic features of the 8a ring mode, whereas the 8b mode, which is common to all species, yields the total amount adsorbed. Quantitative interpretation of the spectral data is carried out using a computer program.The adsorbed species are interpreted as follows: a liquid-like physisorbed species, a species H bonded to surface OH groups through the nitrogen lone pair and three Lewis coordinated species. The latter are assigned to purely octahedral, tetrahedral–octahedral and purely tetrahedral cationic sites, respectively.The reactions occurring upon Py desorption above 400°C are discussed and a different interpretation is given to that in the literature.
TL;DR: In this paper, the simultaneous differential heat and mass balance equations describing sorption under non-isothermal conditions are solved, subject to certain simplifying assumptions, and the solution provides a theoretical model which can be used to determine the significance of thermal effects in a transient sorption rate measurement and to analyse the uptake curves obtained when diffusion is too fast for the isothermal approximation to be valid.
Abstract: The simultaneous differential heat and mass balance equations describing sorption under non-isothermal conditions are solved, subject to certain simplifying assumptions. The solution provides a theoretical model which can be used to determine the significance of thermal effects in a transient sorption rate measurement and to analyse the uptake curves obtained when diffusion is too fast for the isothermal approximation to be valid. Experimental uptake curves for selected systems are analysed. The rapid uptake of butane in small commercial Linde 13X crystals is essentially controlled by heat transfer whereas in the A zeolite thermal effects are of only minor significance. The diffusion of 2,2,4-trimethylpentane in large (24–39 µm) crystals of 13X is an intermediate case in which both heat transfer and intracrystalline diffusion control the rate. The extent to which the intrusion of thermal effects can explain the anomalous dependence of apparent diffusivity on crystal size and the discrepancy between sorption and n.m.r. diffusivities is briefly considered.
TL;DR: In this paper, the rate constants for the H2+O2 reaction were revised to take into account self-heating of the reaction mixtures, reaction of O atoms with H2O2, and other refinements in the mechanism.
Abstract: Rate constants at 500°C for the elementary steps in the H2+ O2 reaction have been revised to take into account self-heating of the reaction mixtures, reaction of O atoms with H2O2, and other refinements in the mechanism. By combination with independent data at lower temperatures, Arrhenius parameters for the reactions have been obtained.Rate constants for OH + RH [reaction (21)] and H + RH [reaction (22)] for C2–C5 alkanes have been revised to allow for self-heating, and for reaction of O atoms and HO2 radicals with the additive. Combination with data at lower temperatures has given Arrhenius parameters for the reactions. The results indicate that, to a first approximation, rate constants for an unknown alkane can be obtained by the relationships k21/k1= 0.214np exp (1070/T)+0.173ns exp (1820/T)+0.273nt exp (2060/T)k22 = 2.2 × 1010np exp (–4715/T)+4.9 × 1010ns exp (–4005/T)+5.1 × 1010nt exp (–3030/T), where np, nsnt are the number of primary, secondary and tertiary C—H bonds, and k1 is the rate constant for the reaction OH + H2= H2O + H(1).
TL;DR: In this article, a conductance equation based on a new model for ions in solution was derived, which described charge transport in solutions containing any number of ionic species of any valency type.
Abstract: In the first two papers of this series a conductance equation, based on a new model for ions in solution, was derived. The equation described charge transport in solutions containing any number of ionic species of any valency type.In this paper the model upon which the new equation is based is discussed in greater detail and the equation is used to analyse conductance data for a number of symmetrical electrolyte solutions. Excellent agreement is found between experimental results and theoretical predictions and the distance parameter values obtained show clearly the existence of solvent-separated ion-pairs (SSIP's) in many systems.
TL;DR: In this article, it was shown that on exposure of goethite to deuterium oxide vapour, the latter underwent rapid isotopic exchange to give the corresponding surface deuteroxyl groups.
Abstract: Infrared spectra of goethite (α-FeOOH) exhibited bands which have been assigned to OH stretching vibrations of bulk or surface hydroxyl groups. On exposure of goethite to deuterium oxide vapour the latter underwent rapid isotopic exchange to give the corresponding surface deuteroxyl groups. The conversion of bulk hydroxyl groups to bulk deuteroxyl groups by contact between deuterium oxide vapour and goethite was comparatively slow. Analogous conclusions were drawn from spectra of deuterated goethite (α-FeOOD) before and after treatment with water vapour. The decomposition of geothite to haematite (α-Fe2O3) by heat treatment in vacuo or in an oxygen atmosphere has been briefly investigated.
TL;DR: In this article, the canonical ensemble Monte Carlo method has been used to determine the structure of dense Lennard-Jones fluids in the vicinity of a rigid solid, and from these results the adsorption excesses and solvation forces have been calculated.
Abstract: The canonical ensemble Monte Carlo method has been used to determine the structure of dense Lennard-Jones fluids in the vicinity of a rigid solid. From these results the adsorption excesses and solvation forces have been calculated. The solvation force is very significant when compared with the van der Waals force between the solid bodies at short surface to surface separations.
TL;DR: Several of the iron-group metals such as Ni and Co were supported as catalyst substrate on spherical porous supports and the synergistic effects of the composite catalysts on the methanation rate were interpreted on the basis of the increase in adsorption capabilities of the reactants and from the viewpoint of a hydrogen spillover mechanism.
Abstract: Several of the iron-group metals such as Ni and Co were supported as catalyst substrate on spherical porous supports. Lanthanide oxides such as La2O3 and Ce2O3, and platinum-group metals such as Ru and Rh were combined with the substrate in atomic ratios of 0.2 and 98 % in methane-formation selectivity and gave an apparent activation energy of 19.6 kcal mol–1, which is less than for CO hydrogenation. The synergistic effects of the composite catalysts on the methanation rate were interpreted on the basis of the increase in adsorption capabilities of the reactants and from the viewpoint of a hydrogen spillover mechanism.
TL;DR: In this paper, a kinetic study of a metal-ligand substitution process taking place in Aerosol-OT stabilised water pools in n-heptane was made, and the system was characterized by ultracentrifugation methods over the range R= 0.26-16.9.
Abstract: A stopped-flow kinetic study has been made of a metal–ligand substitution process taking place in Aerosol–OT stabilised water pools in n-heptane. In a typical stopped-flow experiment, reversed micelles containing solubilised metal ion are mixed with micelles containing ligand such that the total concentration of micelles is unchanged on mixing. Micelle sizes are dependent on the water: surfactant mole ratio “R”(where R=[H2O]/AOT]) and the system has been characterised by ultracentrifugation methods over the range R= 0.26–16.9. The kinetic results for complexation in the reversed micellar system support a mechanism involving rapid exchange of reactants between aqueous pools followed by rate-limiting loss of a solvated water molecule from the metal-ion in a water pool. Rate constants for ligand release and water-exchange in the water pools are close to the bulk water values and are not very dependent on pool size.
TL;DR: In this article, the probability distribution of the end-to-end distance R of a polymer of N segments, length Nl=L, and self repulsion ω was studied, using the idea of an effective step length.
Abstract: A study is made of the probability distribution of the end to end distance R of a polymer of N segments, length Nl=L, and of self repulsion ω. A simple method, capable of adoption in more complicated problems, is developed, using the idea of an effective step length.The mean square value of R2 is developed as a series which for large L is R2=ω2/5L6/5l2/5(1.12 + 1.05 + 1.03 +…).The probability distribution is developed in terms of the dimensionless parameter x=R2/l2/5ω2/5L6/5, and for small x, logp(x)–x([graphic omitted]+[graphic omitted]+[graphic omitted]+…) but for large x a definite asymptotic form is derived log p(x)=–(⅗)π1/2/3 x[graphic omitted].
TL;DR: In this article, the binding isotherms of a homologous series of n-alkyl sulphates to lysozyme have been measured by equilibrium dialysis at 25°C.
Abstract: The binding of a homologous series of n-alkyl sulphates to lysozyme has been measured by equilibrium dialysis at 25°C. The binding isotherms show a concentration dependence attributable to aggregation of the protein–surfactant complexes. Both sodium n-dodecyl and n-decyl sulphates give binding isotherms characteristic of specific high energy interactions at low free surfactant concentrations. These are followed by non-specific cooperative binding. Sodium n-octyl sulphate interacts only cooperatively with lysozyme. The binding isotherms are discussed in terms of the binding potential concept of Wyman and are used to calculate an apparent Gibbs energy of binding per surfactant anion as a function of the number of surfactant anions bound.
TL;DR: In this paper, the active centres for CO chemisorption consist of groups of ions (both positive and negative) in strongly uncoordinated situations, and a mechanism leading both to oxidized (carbonate-like) and to reduced (negative CO polymers) species is proposed.
Abstract: The adsorption of CO at room temperature on well outgassed specimens of MgO gives rise to a large number of bands in the 2200–1000 cm–1 range, which can be divided into two main groups. The bands of the former group are destroyed by oxygen at room temperature: some react instantaneously and are associated with a marked pink colour of the sample; the others are less reactive as they require prolonged contact time in order to be completely oxidized at room temperature (r.t.). The bands of the latter group, far from being destroyed by oxygen, grow when the oxygen-sensitive species are depleted. The oxygen-sensitive species are thought to be negatively charged polymeric CO structures (CO clusters) of the type (CO)x–n, where x= 2 or 4 and n is > 2. The simplest Co clusters (dimers) can be transformed into larger polymers by further CO addition. Under the correct conditions the reverse process can also be carried out. The oxygen-insensitive species have a carbonate-like structure and are present on the surface in fairly constant ratios with respect to the former group species. A chemisorption mechanism leading both to oxidized (carbonate-like) and to reduced (negative CO polymers) species is proposed. The active centres for CO chemisorption consist of groups of ions (both positive and negative) in strongly uncoordinated situations.
TL;DR: In this article, the attachment of small glass spheres to the air-water interface is studied by micro-photography on a pendant drop in the presence of a cationic surfactant.
Abstract: The attachment of small glass spheres (<50 µm diameter) to the air–water interface is studied by micro-photography on a pendant drop in the presence of a cationic surfactant. The angle of wetting on the attached particles can be estimated from the photographs. Increasing the surfactant concentration increases this angle as well as the ratio of attached to unattached particles in the surface. There is a distribution of wetting angle for the attached particles which is independent of particle size. Under conditions where the number of attached particles is roughly equal to the number of unattached particles the size distributions for both sets of particles are estimated and the average limiting size for attachment calculated. The formation of a three phase contact is opposed by a line tension associated with the wetting perimeter and a force balance on the particle gives an expression for the limiting size of attached particle from which a value of the line tension can be derived. A value of 10–5 dyn (10–11 N) compares very favourably with values obtained from related experiments on foam-flotation.
TL;DR: In this paper, relativistic and non-relativistic Hartree-Fock one-centre expansion calculations are reported for the linear systems MH+ and MH2(M = Be, Mg, Ca, Sr, Ba, Ra, Zn, Cd, Hg, Yb, No).
Abstract: Relativistic and non-relativistic Hartree–Fock one-centre expansion calculations are reported for the linear systems MH+ and MH2(M = Be, Mg, Ca, Sr, Ba, Ra, Zn, Cd, Hg, Yb, No). Previous results for CuH, AgH and AuH are refined. Strong d orbital contributions and consequently very small relativistic bond length contractions, C, are found for the heavier alkaline earths. The d character increases monotonically along the series Be, Mg, Ca, Sr, Ba but drops back, due to relativistic effects, for Ra. For Zn, Cd and Hg larger C values of ≈ 1, 2 and 7% are found. “Molecular” covalent radii, consistent with Pauling's halogen radii, are deduced for all the elements considered. The corresponding radii for hydrogen and carbon, bound to them, are discussed. Bond lengths of the unknown species CaH+, SrH+, BaH+, RaH+ and YbH+ are predicted to be 193, 210, 227, 240 and 202 pm, respectively. The radii of No and Yb are found to be comparable, in agreement with experiment. The lanthanoid and actinoid contractions are discussed. Nyholm's explanation of the linear coordination of Hg as being due to a large s–p separation is ascribed to relativistic effects.
TL;DR: In this paper, two distinct CuII to CuI reduction processes are discernible in both X and Y zeolites, which are attributed to the reduction of CuII ions occupying sodalite and supercage sites; a small fraction of the CuII ion, assumed to occupy hexagonal prism sites, remain unreduced.
Abstract: Temperature programmed reduction (t.p.r.) has been used to study the redox behaviour of copper ions in X and Y zeolites. Two distinct CuII to CuI reduction processes are discernible in both X and Y zeolites. These two processes have been attributed to the reduction of CuII ions occupying sodalite and supercage sites; a small fraction of the CuII ions, assumed to occupy hexagonal prism sites, remain unreduced. At 773 K in nitrogen, autoreduction of both sodalite and supercage CuII occurs in X zeolite, while only supercage CuII ions are autoreduced in Y zeolite. The reductions are reversible in Y zeolite, but some CuO is formed in X which is subsequently reduced by a third process. Activation energies (kJ mol–1) were obtained as follows: CuII to CuI(sodalite cages) 84 ± 13, CuII to CuI(supercages) 64 ± 10 and CuO to Cu0(X-type zeolite) 49 ± 7.
TL;DR: In this paper, it was shown from the infrared spectra that, even near saturation, water sorbed in the membranes has a low degree of association and that bonds between water and cellulose acetate are considerably weaker than those in liquid water.
Abstract: Sorption of water in cellulose acetate membranes of two acetyl contents has been studied by infrared spectroscopy. A striking resemblance between the spectra of water in these membranes and those of water dissolved in ethyl acetate has been noted. It is concluded from the infrared spectra that, even near saturation, water sorbed in the membranes has a low degree of association and that bonds between water and cellulose acetate are considerably weaker than those in liquid water. Similar conclusions can be derived from the form of the sorption isotherms of water by cellulose acetate. The weak bonding of water to the membrane is consistent with its high mobility, while its low degree of association explains the low solubility of ions and hence the low permeability of the membrane to salts.
TL;DR: Benzo-1,4-quinone quenches the singlet and triplet excited states of ZnTPP and the quenching probability increases with increased polarity of the solvent.
Abstract: Zinc tetraphenylporphine shows fairly weak fluorescence and phosphorescence but intense, long-lived triplet absorption. Benzo-1,4-quinone quenches the singlet and triplet excited states of ZnTPP and the quenching probability increases with increased polarity of the solvent. Quenching leads to formation of a complex which, for the triplet reaction in toluene, is sufficiently long-lived to be observed by flash spectroscopy. In polar solvents, quenching leads to production of separated ions, the yield being a function of the solvent dielectric constant.
TL;DR: In this article, the adhesion of uniform spherical colloidal particles of chromium hydroxide (modal diameter 0.28 µm) on stainless steel surface and their subsequent removal by rinse solutions of various pH and Ca(NO3)2 concentrations were studied using the packed column technique.
Abstract: The adhesion of uniform spherical colloidal particles of chromium hydroxide (modal diameter 0.28 µm) on stainless steel surface and their subsequent removal by rinse solutions of various pH and Ca(NO3)2 concentrations were studied using the packed column technique. The particles were deposited on steel at pH 5. The pH of the rinse solution had to be adjusted to ≈ 11 before appreciable particle desorption occurred, although the isoelectric point of the steel used was ≈ 5 and that of the chromium hydroxide particles was ≈ 8. Desorption increased at still higher pH, reached a maximum at pH ≈ 12, and then decreased again with increasing rinse solution pH. An addition of Ca(NO3)2 in concentration as low as 10–3 mol dm–3 completely inhibited the removal of chromium hydroxide from the steel surface at pH 11.7. The results obtained are analysed in terms of the existing theory of the electrical double layer and the diffusional escape of the particles across the interaction energy barrier. No chemical bonding between the particles and the substrate could be detected.