Radiation-initiated dechlorination of organochlorine ecotoxicants

The yields of chloride ions produced by the action of γ-radiation on aqueous, aqueous alcohol, and alcohol solutions of trichloroethylene, hexachlorocyclohexane, sodium 2,4-dichlorophenoxyacetate, pentachlorophenol, hexachlorobenzene, and Sovtol-10 (polychlorinated biphenyl) were measured. The effect of alkali and oxygen on the dehalogenation of these compounds was examined. Dechlorination in an aqueous medium is effected by e_aq and OH radicals, as well as by hydrolysis of the radicals produced from the compounds in question. In an alkaline alcohol, chain dehalogenation processes involving electron transfer from the alcohol radical anion to a chlorinated organic molecule develop. It was found that Sovtol-10 is almost completely (by 99.7%) dechlorinated in a 1% solution at a dose of ≤20 kGy.     

Removal of pentachlorophenol from aqueous solutions by dolomitic sorbents

The partial decomposition of dolomite carried out within the temperature range 600-1000 degrees C provides new sorbents, called dolomitic sorbents. Their surface properties and identification by X-ray diffraction are discussed. The lowest specific surface area value was found for the raw dolomite, while the highest value was achieved by the D-1000 sample. The adsorption equilibrium of pentachlorophenol from aqueous solutions on the examined sorbents was investigated at 30, 40, and 50 degrees C via a bath process. Langmuir, Freundlich, Langmuir-Freundlich, and Redlich-Petersen models were fitted to experimental equilibrium data, and their goodnesses of fit are compared. The adjustable parameters of Langmuir-Freundlich and Redlich-Petersen isotherms were estimated by nonlinear least-squares analysis. Langmuir and Freundlich models were found insufficient to explain the adsorption equilibrium, while Langmuir-Freundlich and Redlich-Petersen isotherms provide the best correlation of the pentachlorophenol adsorption onto dolomitic sorbents.     

Oxidative decomposition of pentachlorophenol in aqueous solution

OH-radical-induced dechlorination of pentachlorophenol (PCP) has been studies pulse and γ-radiolytically. OH radicals react with PCP by both electron transfer (53%) and addition followed by very rapid HCl-elimination to form phenoxyl radicals. The phenoxyl radicals decay to form products (e.g. chloranil) that unstable in alkaline aqueous solution and release some more Cl⁻, therefore G(Cl⁻) is high. Primary HPLC–MS analysis reveals that some quinones among the final products, whose toxicity remains unclear. Ozone can also oxidize PCP very rapidly, and this oxidation may destroy the benzene ring of PCP.     

Complete dechlorination of pentachlorophenol using palladized bacterial cellulose in a rotating catalyst contact reactor

A rotating catalyst contact reactor (RCCR) was developed which consisted of palladized bacterial cellulose immobilized on acrylic discs for hydrodechlorination of pentachlorophenol (PCP). More than 99% of 40 mg L(-1) PCP was dechlorinated to phenol in the presence of hydrogen in batch mode at initial pH values of 5.5 and 6.5 within 2 h of reaction with stoichiometric release of free chloride. The rate of PCP dechlorination was found to be independent of rotational speed of discs. PCP (40 mg L(-1)) hydrodechlorination experiments were also conducted using RCCR in continuous flow mode at hydraulic retention times of 1 and 2 h. The average outlet PCP concentrations revealed that liquid phase in RCCR closely resembled that of a continuous flow complete mix reactor (CFMR). Approximately 12 and 11 L of 40 mg L(-1) PCP (pH 6.5) could be treated in RCCR with 99 and 80% efficiencies in batch and continuous flow modes, respectively without any appreciable loss of the catalytic activity. These results suggested reusability of palladized bacterial cellulose which in turn is expected to substantially reduce the cost of treatment process. Thus RCCR seems to have high potential for treatment of ground water contaminated with chlorinated organic compounds. Dried palladized bacterial cellulose has been used as a material for electrodes in a fuel cell. However, its application as a hydrodechlorination catalyst in a reactor operating under room temperature and atmospheric pressure has not been reported to the best of our knowledge. Scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analyses suggested the irreversible deposition of palladium (Pd 0) particles on the bacterial cellulose fibrils.     

Kinetics of acid-assisted hydrolysis of pentachlorophenol in aqueous media

The rate of acid catalyzed hydrolysis of pentachlorophenol (PCP) can be described by the general equation-d[PCP]/dt = k _exp[PCP]. The experimental pseudo-first order rate constant generally increases with increase of the H⁺ concentration, but this dependence has a complex character. A kinetic model, which takes into account the pK _a of PCP and a combination of catalyzed and uncatalyzed reactions, was suggested. This model is consistent with experimental results in the whole range of pH studied.     

Radiation-initiated telomerization of tetrafluoroethylene in 1,2-dibromotetrafluoroethane

The kinetics of the radiation telomerization of tetrafluoroethylene in 1,2-dibromotetrafluoroethane has been studied. It has been shown that the process occurs very efficiently in the perfluorinated solvent; small doses of γ-radiation (~2 kGy) are required for the complete conversion of the monomer. Telomers with a chain length of 120–360 tetrafluoroethylene units and high thermal stability are formed in the reaction. The structure and properties of the telomers have been studied by IR spectroscopy, thermogravimetry, and elemental analysis.     

Supercooling behavior in aqueous solutions

Using the emulsion method, we measured the homogeneous nucleation temperature depression, DeltaT(f,hom), and equilibrium melting points depression, DeltaT(m), of various aqueous solutions and then calculated lambda for each solute using the linear relationship DeltaT(f,hom) = lambdaDeltaT(m). We defined lambda as the solute-specific supercooling capacity and examined its correlation with some known hydration characteristics. The results showed that lambda is correlated with D0, the self-diffusion coefficient of solute molecules in infinite dilution.     

Ionic radii in aqueous solutions

The aqueous ionic radii of 35 ions have been calculated from published data of the average distances between the ions and the nearest water molecules, obtained by diffraction and computer simulation methods.     

Methionine equilibrium in aqueous solutions

Stepwise dissociation constants of D,L-methionine in aqueous solution at 298 K were measured by spectrophotometric method, and a possibility of analytical determination of the amino acid concentration was estimated. The integral enthalpy of dissolution of D,L-methionine in water, enthalpies of protonation of the amino group and neutralization of the carboxy group at 298 K were measured using a calorimetric method.     

Hydrolysis of cyanides in aqueous solutions

The hydrolytic destruction of cyanides in aqueous solutions is studied. The reaction can be described by a first-order equation with respect to cyanide, and its rate depends on pH. An analysis of the parameters of the Arrhenius equation and reaction rate coefficients implies that molecular prussic acid is predominantly involved in the hydrolysis. A mathematical model is created for predicting the development of cyanide removal over time at different pHs and temperatures     

Radiopolarography of mendelevium in aqueous solutions

The possible existence of a monovalent ion of mendelevium has been examined further by radiopolarography. Experiments were conducted in several aqueous media with ²⁴¹Am, ²⁴⁹Cf, ²⁵⁴Es, ^255,256Fm and ²⁵⁶Md tracers. Half-wave amalgamation potentials of Md in tetramethylammonium perchlorate and in LiCl were identical within the experimental errors at −1.755 ± 0.005 V vs the saturated calomel electrode, in good agreement with an earlier study by radiocoulometry in an ammonium acetate medium. No shift in the half-wave potential of Md was observed due to NH₄⁺ or Cl⁻ ions; hence, these ions do not act as complexing agents for Md ions present during electrochemical reductions. The shift in the half-wave potential observed in the presence of citrate as a complexing agent was characteristic of the reduction process Md²⁺ → Md⁰(Hg). In noncomplexing media, the slope of the logarithmically transformed wave of Md was ∼ 30 mV, consistent only with a reversible, two-electron reduction process. All of our results provide evidence for electrochemical reduction of the Md²⁺ ion only and disprove the existence of an the intermediate Md⁺ ion in aqueous solution with properties like those of Cs⁺, Ag⁺ or Cu⁺.     

Complexation in aqueous solutions of lignosulfonates

The capability of lignosulfonates for donor-acceptor interaction with d-metal cations in aqueous solutions was studied. A quantitative estimation of the complexing properties of lignosulfonates was made.     

Photochemistry of metalloporphyrins in aqueous solutions

The fluorescence spectra of Ga(III), In(III), Ge(IV) and Sn(IV) tetramethyl pyridine porphyrin showed a small stokes shift ca 400 ± 100 cm⁻¹ attributed to the similarity between their ground and excited states. The one and two electron reduction products of the metalloporphyrins were studied by steady-state method. The nature of the product was dependent upon the pH of the reaction medium. Chlorin and phlorin were obtained at low and high pH's, respectively. Sn TMPyP was the only metalloporphyrin which yielded the Π-radical anion whose stability is due to the high electronegativity of Sn(IV).     

Recognition of caffeine in aqueous solutions

Binding of caffeine in aqueous solutions has been achieved for the first time by using water-soluble, tetracationic peptide-porphyrin conjugates Zn-1 as the receptor molecules. The association constant for caffeine with receptor Zn-1 is in some cases as high as 6000 M(-1), only 5-6 times lower than the highest binding constant reported for an artificial caffeine receptor in low polarity aprotic solvents. The binding mechanism has been studied by a combination of experimental techniques such as UV-visible and NMR spectroscopy and microcalorimetry. Recognition of caffeine involves both stacking with the porphyrin ring and metal coordination. Subtle variations of the receptor structure affect the complexation. Receptors Zn-1 have also been investigated for the recognition of molecules structurally related to caffeine, for example, 1-methylimidazole. Selectivity towards oxopurine derivatives (caffeine and theophylline) have been found.     

A facile method for the dechlorination of mono- and dichlorobiphenyls using Raney Ni-Al alloy in dilute aqueous solutions of alkali hydroxides or alkali metal carbonates

Raney Ni-Al alloy in a dilute aqueous alkaline solution of NaOH, KOH, CsOH, LiOH, or Ca(OH) ₂ or of alkali metal carbonates such as Na₂CO₃, K₂CO₃ becomes a very powerful reducing agent and dechlorinates the polychlorobiphenyl(PCB) congeners mono- and dichlorobiphenyls effectively to afford biphenyl and/or phenylcyclohexane, respectively. The reactions are run under mild conditions without the use of organic solvents. The reductive dechlorination of dichlorobiphenyls with a Raney Ni-Al alloy under ultrasonication was investigated, also.     

Radiation-initiated homogeneous grafting of styrene to benzylcellulose

Graft copolymers of benzylcellulose and styrene were prepared by direct irradiation of benzylcellulose–styrene solutions with ⁶⁰Co γ-radiation. The solutions remained homogeneous during irradiation. The amount of styrene grafted to benzylcellulose increased in dilute solutions and was dose-dependent up to 4.0 MR. The graft copolymer consisted of both branched and linear structures with one in every 140–1020 benzylated anhydroglucose units carrying a grafted polystyrene chain. Grafted polystyrene was isolated from the graft copolymer by hydrolysis of the benzylcellulose substrate. The number-average molecular weight and molecular weight distribution of the grafted polystyrene were the same as those for hompolymer formed in the same solution, indicating that the substrate is fully accessible to the monomer and polymerization conditions are uniform throughout the solution during the grafting procedure. The existence of a true graft copolymer was proved by the solubility behavior, intrinsic viscosity, number-average molecular weight, and density-gradient sedimentation of the product of the grafting procedure. Column elution fractionation of the gross products of the grafting procedure failed to isolate the benzylcellulose–styrene copolymer which was eluted with ungrafted benzylcellulose.     

Proton transfer in aqueous urea solutions

The rates of proton dissociation from the first excited state of aromatic alcohols (8-hydroxypyrene-1,3,6-trisulfonate and -naphthol-6-sulfonate) were measured by steady-state fluorimetry in aqueous solutions as a function of urea concentration. The measured acid dissociation rate constants (k _off ^/* ) of the probes were independent of urea concentration up to 3M. These results, together with the decrease of k _off ^/* with salt and other additives, demonstrate that the changes in k _off ^/* are not related unequivocally with the activity of water. A urea-H₂O cluster of properties similar to pure water is proposed to account for the observed results.     

Mixing schemes in ternary aqueous solutions

The enthalpic interaction functions introduced by us earlier were evaluated in some ternary aqueous solutions. They are determined purely experimentally without resorting to any model system. From them, the pair interaction coefficients based on the virial expansion were evaluated, which will serve for a future theoretical development based on the McMillan-Mayer theory of solution. Secondly, our new methodology of using the mole fraction dependence of the enthalpic interaction function as a probe to elucidate the effect of a third component on the molecular organization is introduced. The conclusions for selected third components in ternary aqueous 1-propanol are reviewed. This revised version was published online in August 2006 with corrections to the Cover Date.