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In this paper, a radiation field model for a light-emitting diode-based photocatalytic reactor has been developed. The model was tested using experimental data, and good agreement between the model and experimental results was noted. The model was used to investigate the impact of irradiated distance on the homogeneity of radiation field because it is shown that a homogeneous radiation field is the most efficient. The model can be used to design an efficient photoreactor by selecting the optimal gap between adjacent light-emitting diodes, the irradiated distance and the light output of light-emitting diodes.

Conventional gas chromatography (GC) analysis of hydrocarbons displaying one broad peak provides limited information. Two GC analytical protocols using two-peak and three-peak approaches were developed to investigate transformer oil components and their degradation in soil by hydrogen peroxide. The two-peak method revealed transformer oil to be composed of 27 wt.% F2 fraction and 73 wt.% F3 fraction hydrocarbons. The three-peak method segregated the transformer oil into 40 wt.% light, 40 wt.% medium, and 20 wt.% heavy hydrocarbon fractions. In contrast to reports of success with several classes of lighter hydrocarbons, only limited degradations of transformer oil in soils by 15% and 30% hydrogen peroxide treatment was indicated by conventional one-peak analysis; two-peak analysis showed varying F2 and F3 fraction degradations with F2 fraction degradation being higher; three-peak analysis offered a richer understanding of the relative degradations of light, medium, and heavy fractions. The effect of a low pH environment on the degradation of transformer oil by hydrogen peroxide was evaluated using the three-peak method. It emerged that the degradation of the medium and heavier fractions of transformer oil was higher at pH 2·0.

A promising photolysis based technology to dechlorinate polychlorinated biphenyls (PCBs), extracted from soils, in alkaline isopropanol (IPA) as reaction medium has been proposed. To be marketable the impact of co-contaminants extracted along with the PCBs, on the photodechlorination process needs investigation. In this paper the effectiveness of the photodeclorination process on PCBs extracted from samples of a representative soil containing co-contaminants is reported. The photodechlorination of PCBs extracted from weathered soils showed promising results of more than 76% dechlorination within the first hour of UV irradiation. Nearly complete dechlorination (96%) was achieved after 2  h of UV irradiation. To provide quantitative controlled appraisal of the effect of co-contaminants and explanation of the effects, dechlorination of neat Aroclor 1254 in the presence of the common co-contaminant, transformer oil, was evaluated. Further, the effect of transformer oil on some of the individual PCB congeners in the Aroclor mixture was also studied. The difference in the maximum percentage dechlorination of PCBs with and without transformer oil is 15%.

Environmental Context.Soil uptake of xenobiotics (e.g. pesticides) can be a complex phenomenon where it is useful to distinguish readily reversible sorption from longer-term retention. A scheme for doing this using fluorescence detection is presented here, along with application to uptake of a model compound in clean and oil-contaminated soils. Both the wetting of the soil and the size of the xenobiotic seem to be important. The present data concern uptake. Desorption is expected to exhibit dependencies on similar factors. The data have implications for understanding persistence.  Abstract.Description of sorption of xenobiotics (e.g. pesticides) into soils requires identification of at least two kinetic components. In the present work, the distinction between ?labile' (readily reversible) and ?non-labile' (not reversible) uptake was extended, introducing a fluorescence-based method using 9-anthracenepropionic acid as a probe molecule. Study of clean, oil-contaminated wettable, and water-repellent oil-contaminated soils has given new perspectives into the role that water plays in xenobiotic uptake. Non-labile uptake is unimportant in the water-repellent soils; however, non-labile components are observed in both clean and wettable oil-contaminated samples, supporting earlier suggestions that water plays a role in non-labile uptake processes. A soil pre-exposed to water exhibited different labile sorption behavior from one where xenobiotic was added simultaneously with water to an air-dried soil. The comparatively rapid non-labile component of uptake (3 days) of 9-anthracenepropanoic acid by a clean soil contrasted with much longer times in earlier studies of 2,4-D and atrazine. This pointed to another factor influencing the sorption phenomenon. Literature data supports a suggestion that the non-labile component of xenobiotic sorption may be more strongly influenced by the size of the xenobiotic than by the structure (e.g. polarity) of the xenobiotic or soil composition.

The history of government-university-industry interaction in Canada shows us that the quality of intersectoral networks is crucial. An explanatory model is developed which is based on networks sufficiently connected that a ‘phase transition’ to high interactivity can occur. The assertion is that innovations are events that ‘crystallize’ out of such highly connected networks. It appears that the existence of critically complex communication networks that allowed this crystallization was as important as, or more important than, explicitly articulated government policies. The model should be useful beyond the Canadian case.

The first report of a rate of binding of a metal ion (Fe3+) by a soluble fulvic acid is derived from stopped flow measurements. The rate of complex formation is normal in Wilkins' sense and similar to that for sulfosalicylic acid. Dissociation is slow (t1/2 > 10 s). The binding of Fe3+by the fulvic acid in acid solution, pH = 1–2.5, was investigated by kinetic analysis in which the reaction of free Fe3+with sulfosalicylic acid was followed by stopped flow spectrophotometry on a time scale short compared to release of Fe3+by fulvic acid. Conditional equilibrium constants found were 1.5 ± 0.3 × 104at pH = 1.5 and 2.5, and 2.8 ± 0.3 × 103at pH = 1.0 at 25 °C (ionic strength 0.1).

The binding of Mn2+to a well characterized fulvic acid sample is reported based on the competition with K+in an ion exchange equilibration. The free energy of binding of to fulvic acid is only 1–2 kJ/equivalent more favourable than that for K+. This suggests an outer sphere electrostatic structure for the complex. The suggestion is confirmed by observation of minimal change in the presence of fulvic acid of the effect of paramagnetic Mn2+on the nmr spectra of water. The interpretation of nmr spectra is supported by comparison with nmr measurements of Mn2+complexes with simple ligands and contrast with nmr measurements on Fe3+– fulvic acid complexing. The latter is confirmed as inner sphere.

We report new measurements adding to the literature on solvent and counter ion dependence of 10F−chemical shift. These are compared to earlier results for 35Cl−, 79Br−, and 127I−. The observations support the following points: (1) there are few systematic differences between behavior of anion shifts in dilute and moderately concentrated aqueous solution, (2) anion shifts commonly show larger sensitivity to solvent than counter ion over convenient ranges of variation so that "solvent shift" may be easily measured. Using the concept of collision effects on shifts developed by Richards and his collaborators, it is possible to separate, in many cases, the large effects arising from contact, or primary solvation sphere, collisions from the smaller effects of outer sphere interactions.We find no preferential solvation of F−by H2O in mixtures with CH3OH; at most, small preference over C2H5OH and formamide, and a small opposite preference in favor of diols. However, water appears strongly preferred in the primary solvation shell over acetone, acetonitrile, dioxane, and (in contrast to other halides), dimethylsulfoxide. Solvation by amines involving both outer and inner sphere site occupation is considered.The inter-anion effects on fluoride ion chemical shifts tend to undermine the concept of additivity of ionic effects on shifts.

The photolysis of Co(EDTA)−in the ultraviolet is unlike analogous reactions of Fe(III) complexes. The ratio of products Co(II) to CO2is 1:1 but we find only as much CH2O. For Fe(EDTA)−, yields of photolysis products Fe(II):CO2:CH2O are 2:1:1. This is consistent only with a mechanism where primary photolysis yields Co(II), CO2, and a radical which attacks EDTA in preferenceto reduction of the slowly reducible metal oxidation state, Co(III). Use of 2-propanol as a scavenger diagnostic of primary radicals is questioned because it is shown that LMCT excited states of Co(III) complexes exhibit the same outer sphere oxidations of alcohols earlier recognized in the photochemistry of a variety of Fe(III) complexes.

The irradiation of ferric perchlorate in the presence of tert-amyl alcohol produces Fe(II) with a quantum yield of 0.110 ± 0.002, 12% lower than the yield obtained when tert-butyl alcohol was used as scavenger. Other tertiary alcohols studied, 3-methyl-2-pentanol and 3-ethyl-3-pentanol, exhibited similar lower yields. It is shown that this reduction is due to the formation of γ-hydroxyalkyl radicals which do not reduce ferric ion to ferrous. The addition of copper causes these radicals to be oxidized. The Fe(II) quantum yield for the irradiation with tertiary amyl alcohol as scavenger in the presence of copper is in good agreement with the tertiary butyl alcohol results in the absence of copper (0.124 ± 0.003).Quantum yields are observed which are independent of scavenger concentration indicating outer sphere photooxidations are not taking place. This result supports the suggestion that an H on the carbon bearing oxygen is necessary for direct reaction between scavenger and the ferric charge transfer excited state.

Relative initial quantum yields for the disappearance of 1-propanol and propanal were estimated based on total light intensity entering the reaction vessels. Two types of photocatalytic reactor geometries were compared, a commercial prototype flow reactor with immobilized TiO2and a conventional reactor with TiO2dispersion. A maximum relative quantum yield, , was extrapolated for pure propanol and propanal in both geometries. The high quantum yields were attributed to efficient competition of substrate oxidation with electron–hole recombination, at high surface coverage. Propanal was identified as the primary intermediate generated from 1-propanol in both reactor systems, but yields of propanal were systematically 10 times lower than 1-propanol loss, indicating that there was an effective pathway for propanal oxidation on the surface prior to desorption. The inhibition of 1-propanol reaction caused by accumulation of product arises because both reactant and product compete for active sites on the photocatalyst surface. These propositions were confirmed by introducing propanal into the feed. The relative quantum yields converge to unity for pure substrates, suggesting that they are true yields. That is to say, absorption by TiO2of light entering the reactor is efficient in these geometries.

The rates of nickel(II)–murexide complex formation were studied in dimethylsulfoxide/nitromethane mixed solvents at 25 °C with the latter being an "inert" solvent, to elucidate the mechanism of the reaction. Results do not fit in detail with a D mechanism and the five-coordinated intermediate interpretation. Idmechanisms are able to explain the observations with and without invoking a nitromethane-containing intermediate, Ni(DMSO)5NM2+. Both mechanisms were tested with the aid of nmr data on solvation (second coordinate sphere nitromethane population). Ligand solvation unavoidably plays a major role in the determination of the encounter as well as the complex formation equilibrium. The simplest mechanism assumes an Idprocess in which the probability of encounter between Ni(DMSO)62+and murexide ion is quite sensitive to solvent composition.

In this report, determination of unbound aquo iron species is accomplished by a kinetic methodinvolving reaction with sulfosalicylic acid (SSA) on a time scale which is very short with respect to reaction of SSA with the glutathione complexes of iron. The data are used to calculate conditional binding constants for Fe(III) to glutathione. Binding constants in 0.1 Mionic strength media were obtained between pH 1 and 2.4 by the kinetic method, and near pH = 3 by spectrophotometry andby examination of the ratio of rate of complex formation and dissociation. The conditional binding 'constant' betweenpH 1 and 3 is represented as pK = −1.96 – 0.50pH. This is consistent with the importance of reactions involving only very limited proton release. Spectrophotometric data show that the —OH group on Fe(OH)2+is lost on glutathione complexing. Kinetics of the complex formation reaction between aquo iron(III) species and glutathione are slower than rates of reaction of iron(III) with simple ligands.The glutathione system is regarded as a model system important to natural water chemistry because it is a widely distributed biological sulfur-containing chelating agent.