Volumetric Properties, Viscosities, and Isobaric Heat Capacities of Imidazolium Octanoate Protic Ionic Liquid in Molecular Solvents

Densities (F), viscosities (?), and isobaric heat molar capacities (Cp) of binary mixtures containing imidazolium octanoate, [Im][C7CO2], a protic ionic liquid (PIL), with four molecular solvents, water, acetonitrile, ethanol, and 1-octanol, are determined as a function of temperature from (298.15 to 323.15) K and within the whole composition range at atmospheric pressure. Excess molar volumes, VE, excess molar heat capacities, Cp E, and the deviation from additivity rules of viscosities, ??, of imidazolium octanoate solutions were then deduced from the experimental results, as well as apparent molar volumes, Vfi, and partial molar volumes, V j m,i. Results are discussed according to the nature of the interaction between the PIL and the molecules and the effect of temperature. The excess Gibbs energies of activation of viscous flow (?G*E) for these systems were then calculated at 298.15 K. The excess isobaric heat capacities, Cp E, of binary ([Im][C7CO2] + solvent) systems, depend also of the nature of the molecular solvent in mixture. The excess properties were then correlated, at each temperature, as a function of composition by a Redlich-Kister-type equation. Finally results have been discussed in terms of molecular interactions and molecular structures in these binary mixtures, and thermodynamic properties of investigated binary mixtures were then compared to literature values together to investigate the impact of the nature of the solvent on these reported properties.

Interhemispheric gradient of atmospheric radiocarbon reveals natural variability of Southern Ocean winds

Tree ring Delta C-14 data (Reimer et al., 2004; McCormac et al., 2004) indicate that atmospheric Delta C-14 varied on multi-decadal to centennial timescales, in both hemispheres, over the period between AD 950 and 1830. The Northern and Southern Hemispheric Delta C-14 records display similar variability, but from the data alone is it not clear whether these variations are driven by the production of C-14 in the stratosphere (Stuiver and Quay, 1980) or by perturbations to exchanges between carbon reservoirs (Siegenthaler et al., 1980). As the sea-air flux of (CO2)-C-14 has a clear maximum in the open ocean regions of the Southern Ocean, relatively modest perturbations to the winds over this region drive significant perturbations to the interhemispheric gradient. In this study, model simulations are used to show that Southern Ocean winds are likely a main driver of the observed variability in the interhemispheric gradient over AD 950-1830, and further, that this variability may be larger than the Southern Ocean wind trends that have been reported for recent decades (notably 1980-2004). This interpretation also implies that there may have been a significant weakening of the winds over the Southern Ocean within a few decades of AD 1375, associated with the transition between the Medieval Climate Anomaly and the Little Ice Age. The driving forces that could have produced such a shift in the winds at the Medieval Climate Anomaly to Little Ice Age transition remain unknown. Our process-focused suite of perturbation experiments with models raises the possibility that the current generation of coupled climate and earth system models may underestimate the natural background multi-decadal- to centennial-timescale variations in the winds over the Southern Ocean.

The synthesis, characterisation and reactivity of 2-phosphanylethylcyclopentadienyl complexes of cobalt, rhodium and iridium

2-Phosphanylethylcyclopentadienyl lithium compounds, Li[C5R'(4)(CH2)(2)PR2] (R = Et, R' = H or Me, R = Ph, R' = Me), have been prepared from the reaction of spirohydrocarbons C5R'(4)(C2H4) with LiPR2. C5Et4HSiMe2CH2PMe2, was prepared from reaction of Li[C5Et4] with Me2SiCl2 followed by Me2PCH2Li. The lithium salts were reacted with [RhCl(CO)2]2,[IrCl(CO)3] or [Co-2(CO)(8)] to give [M(C5R'(4)(CH2) 2PR2)(CO)] (M = Rh, R = Et, R' = H or Me, R= Ph, R' = Me; M = Ir or Co, R = Et, R' = Me), which have been fully characterised, in many cases crystallographically as monomers with coordination of the phosphorus atom and the cyclopentadienyl ring. The values of nu(CO) for these complexes are usually lower than those for the analogous complexes without the bridge between the cyclopentadienyl ring and the phosphine, the exception being [Rh(Cp'(CH2)(2)PEt2)(CO)] (Cp' = C5Me4), the most electron rich of the complexes. [Rh(C5Et4SiMe2CH2PMe2)(CO)] may be a dimer. [Co-2(CO)(8)] reacts with C5H5(CH2)(2)PEt2 or C5Et4HSiMe2CH2PMe2 (L) to give binuclear complexes of the form [Co-2(CO)(6)L-2] with almost linear PCoCoP skeletons. [Rh(Cp'(CH2)(2)PEt2)(CO)] and [Rh(Cp'(CH2)(2)PPh2)(CO)] are active for methanol carbonylation at 150 degrees C and 27 bar CO, with the rate using [Rh(Cp'(CH2)(2)PPh2)(CO)] (0.81 mol dm(-3) h(-1)) being higher than that for [RhI2(CO)(2)](-) (0.64 mol dm(-3) h(-1)). The most electron rich complex, [Rh(Cp'(CH2)(2)PEt2)(CO)] (0.38 mol dm(-3) h(-1)) gave a comparable rate to [Cp*Rh(PEt3)(CO)] (0.30 mol dm(-3) h(-1)), which was unstable towards oxidation of the phosphine. [Rh(Cp'(CH2)(2)PEt2)I-2], which is inactive for methanol carbonylation, was isolated after the methanol carbonylation reaction using [Rh(Cp'(CH2)(2)PEt2)(CO)].

Amination and dehydration of 1,3-propanediol by hydrogen transfer: reactions of a bio-renewable platform chemical

1,3-propanediol was subjected to a range of amination conditions. The N-heterocyclic carbene piano stool complex [Cp*IrCl2(bmim)] was found to be a good catalyst for amination and dehydration in toluene or ionic liquid; product compositions could be tuned by altering the ratio of diol to amine.

Dependence of the kinetics of liquid-phase photocatalyzed reactions on oxygen concentration and light intensity

The initial kinetics of the oxidation of 4-chlorophenol, 4-CP, photocatalyzed by titania films and aqueous dispersions were studied as a function of oxygen partial pressure, P-O2, and incident light intensity, I. The reaction conditions were such that the kinetics were independent of [4-CP] but strongly dependent on PO2-a situation that allowed investigation of the less-often studied kinetics of oxygen reduction. The observed kinetics fit a pseudo-steady-state model in which the oxygen is Langmuir-adsorbed on the titania photocatalyst particles before being reduced by photogenerated electrons. The maximum rate of photocatalysis depends directly on I-beta, where, beta = 1 for films and 0.7 for dispersions of titania, indicating that the kinetics are dominated by the surface reactions of the photogenerated electrons and holes for the films and by direct recombination for the powder dispersions. Using the pseudo-first-order model, for both titania films and dispersions, the apparent Langmuir adsorption constant, K-LH, derived from a Langmuir-Hinshelwood analysis of the kinetics, appears to be largely independent of incident light intensity, unlike KLH for 4-CP Consequently, similar values are obtained for the Langmuir adsorption constant, K-ads, extracted from a pseudosteady-state analysis of the kinetics for oxygen on TiO2 dispersions and films in aqueous solution (i.e., ca. 0.0265 +/- 0.005 kPa(-1)), and for both films and dispersions, oxygen appears to be weakly adsorbed on TiO2 compared with 4-CP, at a rate that would take many minutes to reach equilibrium. The value of Kads for oxygen on titania particles dispersed in solution is ca. 4.7 times lower than that reported for the dark Langmuir adsorption isotherm; possible causes for this difference are discussed. (c) 2006 Elsevier Inc. All rights reserved.

Kinetics of liquid phase semiconductor photoassisted reactions: Supporting observations for a pseudo-steady-state model

The kinetics of liquid phase semiconductor photocatalytic and photoassisted reactions are an area of some debate, reignited recently by an article by Ollis(1) in which he proposed a simple pseudo- steady- state model to interpret the Langmuir- Hinshelwood type kinetics, commonly observed in such systems. In the current article, support for this model, over other models, is provided by a reinterpretation of the results of a study, reported initially in 1999,2 of the photoassisted mineralization of 4- chlorophenol, 4-CP, by titania films and dispersions as a function of incident light intensity, I. On the basis of this model, these results indicate that 4- CP is adsorbed more strongly on P25 TiO2 when it is in a dispersed, rather than a film form, due to a higher rate constant for adsorption, k(1). In addition, the kinetics of 4- CP removal appear to depend on I-beta where, beta = 1 or 0.6 for when the TiO2 is in a film or a dispersed form, respectively. These findings are discussed both in terms of the pseudo- steady- state model and other popular kinetic models.

The kinetics of semiconductor photocatalysis: Light intensity effects

The kinetics of the photomineralisation of 4-chlorophenol, 4-CP, by oxygen, sensitized by TiO2 as a function of incident light intensity are described. Degussa P25 TiO2 in the form of either a thin film or a dispersion is used as the photocatalyst. With a TiO2 dispersion the initial rate of photomineralisation, R-i, depends upon I-0.64, implying that electron-hole recombination is the dominant process with respect to photogenerated holes (where R-i is expected proportional to I-0.5), but that the light intensities used spanned both the high (R-i expected proportional to I-0.5) and low (R-i expected proportional to I) intensity regimes. With a TiO2 film R-i is proportional to I indicating that the photocatalytically active particles of the TiO2 film are shielded in some way and so operate under low intensity conditions. Most significantly, it was also found that the apparent value of the Langmuir adsorption coefficient, K4-CP, as determined from the kinetic data, was not independent of I for either a TiO2, film or dispersion photocatalyst. Rather K4-CP increased with decreasing light intensity. A possible mechanism is suggested as a rationale for the observed light intensity effects reported.

Photomineralisation of 4-chlorophenol sensitised by TiO2 thin films

The results of a study of the oxidative mineralisation of 4-CP by oxygen, sensitised by thin films of Degussa P25 TiO2, are reported. The films are used under conditions in which the kinetics of photomineralisation are independent of mass transfer effects and stable towards repeated irradiation. Using a TiO2 film, the process goes through the same mechanism as a TiO2 dispersion, generating the same intermediates, namely: 4-chlorocatechol and hydroquinone. The kinetics of photomineralisation show clear differences between a TiO2 film and a dispersion. With TiO2 films the initial rate of photomineralisation is strongly dependent upon photocatalyst loading, (units; g dm(-3)) reaching a distinct maximum, which appears to be associated with the formation of a monolayer of aggregated particles - the diameter of the aggregated particles is estimated as 0.44 mu m. A simple 2D model is presented to help illustrate the features of such a system. With TiO2 dispersions the rate usually reaches a plateau at ca. 0.5 g dm(-3) of TiO2. For TiO2 films the initial rate depends directly upon the incident light intensity, implying that the photocatalytically active particles are under low illumination conditions, partially shielded by the other particles making up each aggregated particle. In contrast, with TiO2 dispersions R-i depends upon I-0.64, implying that the different light intensities used spanned both the high (R(i)proportional to I-1/2) and low (R(i)proportional to I) intensity kinetic regions. The kinetics of photomineralisation of 4-CP, sensitised by TiO2 films obey the same Langmuir-Hinshelwood expressions as found in most semiconductor photocatalyst work conducted with TiO2 dispersions. However, in a study of the variation R-i as a function of [4-CP] and [O-2] the values for the maximum rates were larger, and those for the apparent Langmuir adsorption coefficients were smaller, than those found for TiO2 dispersions. (C) 1998 Elsevier Science S.A. All rights reserved.

ACTIVATION-ENERGIES IN SEMICONDUCTOR PHOTOCATALYSIS FOR WATER-PURIFICATION - THE 4-CHLOROPHENOL TIO2 O-2 PHOTOSYSTEM

The variation in the activation energy for the initial stage of photomineralization of 4-chlorophenol (4-CP), sensitized by Degussa P25 TiO2 was investigated as a function of P-O2 and [4-CP]. A model was developed based on the incorporation of Arrhenius-type functions in a general rate equation for the initial stage of photomineralization. Values of the essential constants in the model were derived from a few simple experiments. Positive, negative and zero apparent activation energies were predicted using the model, and verified experimentally, under moderate reaction conditions. The general applicability of the model is briefly discussed.

PHOTOCATALYTIC DEGRADATION OF 4-CHLOROPHENOL MEDIATED BY TIO2 - A COMPARATIVE-STUDY OF THE ACTIVITY OF LABORATORY MADE AND COMMERCIAL TIO2 SAMPLES

The photocatalytic efficiencies of laboratory made and commercial TiO2 samples were compared using a standard test reaction: the photomineralization of 4-chlorophenol (4-CP) to CO2, H2O and HCl mediated by Degussa P25 TiO2 in a batch reactor. The results show that the rate of photodegradation of 4-CP, sensitized by a sample of TiO2, shows no clear simple dependence on physical characteristics such as the degree of crystallinity, the surface area and the percentage of H2O.

PHOTOMINERALIZATION OF 4-CHLOROPHENOL SENSITIZED BY TITANIUM-DIOXIDE - A STUDY OF THE INITIAL KINETICS OF CARBON-DIOXIDE PHOTOGENERATION

The kinetics of photomineralization of 4-chlorophenol (4-CP) sensitized by Degussa P25 TiO2 in O2-saturated solution is studied as a function of the following different experimental parameters: pH, [TiO2], percentage O2 [O2], [4-CP], T, I, lambda and [KNO3]. At pH 2 and T=30-degrees-C the initial relative rate of CO2 photogeneration R(CO2) conforms to a Langmuir-Hinshelwood-type kinetic scheme and the relationship between R(CO2) and the various experimental parameters may be summarized as follows: R(CO2) = gammaK(O2)[O2](I(a))(theta)K(4-CP]0/(1 + K(O2])(1 + K(4-CP)[4-CP]0) where gamma is a proportionality constant, K(O2) = 0.044 +/- 0.005[O2]-1, theta = 0.74 +/- 0.05 and K(4-CP) = (29 +/- 3) x 10(3) dm3 mol-1. The overall activation energy for this photosystem was determined as 16 +/- 2 kJ mol-1. This work forms part of an overall characterization study in which it is proposed that the 4-CP-TiO2-O2 photosystem is adopted as a standard test system for incorporation into all future semiconductor-sensitized photomineralization studies in order to facilitate comparisons between the results of the different studies.

PHOTOMINERALISATION OF 4-CHLOROPHENOL SENSITIZED BY TITANIUM-DIOXIDE - A STUDY OF THE INTERMEDIATES

The photomineralisation of 4-chlorophenol (4-CP) sensitised by Degussa P25 TiO2 in O2-saturated solution represents a possible standard test system in semiconductor-sensitised photomineralisation studies. As part of a detailed examination of this photosystem, the results of the temporal variations in the concentrations of 4-CP, CO2, Cl- and the major organic intermediates, namely, 4-chlorocatechol (4-CC), hydroquinone (HQ), benzoquinone and 4-chlororesorcinol, are reported. The observed variations in [4-CP], [4-CC], [HQ] and [CO2] fit those predicted by a kinetic model which utilises kinetic equations with a Langmuir-Hinshelwood form and assumes that there are three major possible routes in which the photogenerated hydroxyl radicals can react with 4-CP, ie. 4-CP --> 4-CC, 4-CP --> HQ and 4-CP --> (unstable intermediate) --> CO2 and that these routes have the following probabilities of occurring: 48%, 10% and 42%.

Effect of a biofilm on the adsorption of 4-chlorophenol on activated carbon

The adsorption of 4-chlorophenol (4-CP) on activated carbon was studied experimentally both in the presence and in the absence of an inactivated anaerobic biofilm on the surface of carbon pellets. The presence of the biofilm markedly decreased the rate of 4-CP adsorption. However, the final near-equilibrium state (at 27 h) was not affected, and the incremental amount of material adsorbed on the pellets was similar both in the presence and in the absence of the biofilm. The biosorption of 4-CP by a biofilm coating non-adsorbing pellets was also determined. It appears that the biofilm also has some adsorption capability. Freundlich-type equations were used to correlate all data, and transient and near-equilibrium isotherms were obtained for 4-CP adsorption on different adsorbing materials at different times.