On-line measurement of oxidative degradation kinetics for trace gasoline contaminants in aqueous solutions and natural water by membrane introduction tandem mass spectrometry.

Membrane introduction mass spectrometry (MIMS) was used to directly monitor the loss of trace gasoline contaminants (benzene, toluene, 2-methylthiophene and methylcyclohexane) in nanomolar (ppb) aqueous solutions under a variety of UV-induced advanced oxidation processes (AOP). The decay kinetics of these contaminants were followed simultaneously in "real-time" via tandem mass spectrometric techniques by re-circulating the reaction mixture in a closed loop over a semi-permeable membrane interface. The photocatalyzed degradations were observed to follow pseudo-first-order kinetics with rate constants ranging from 0.006 to 0.2 min⁻¹ depending on the reaction conditions. We report rate enhancements for several UV-based advanced oxidative processes using physiosorbed titanium dioxide (TiO2/UV, TiO2/UV/O2, TiO2/UV/H2O2) and compare these to the direct photolysis of H2O2 under otherwise identical conditions. The relative degradation rates of 4 trace contaminants are reported for reactions carried out in the same solution. The degradation kinetics were also monitored directly in a natural surface water spiked with the same contaminant suite. The observed decay kinetics in the presence of TiO2 in air-saturated natural water were similar to those carried out in deionized water. However, when the photo-oxidation was enhanced by the addition of H2O2, the degradation was markedly slower in natural water relative to deionized water due to competition for photons by dissolved organic matter. This work further demonstrates the use of MIMS as a sensitive on-line measurement technique for "in-situ" reaction monitoring of organic contaminants at environmentally relevant concentrations in complex solutions and reactive media.

Solvent effects on the spectroscopic and photophysical properties of the trans-(1,4,8,11-tetraazacyclotetradecane)diisothiocyanatochromium(III) ion, trans-[Cr(cyclam)(NCS)(2)]+.

The spectroscopy and photophysics of trans-[Cr(cyclam)(NCS)2]+ (where cyclam is 1,4,8,11-tetraazacyclotetradecane) were studied in a range of solvents. The cyclam NH stretching vibration [nu(NH)] wavenumber correlates with the Gutmann donor number, whereas the thiocyanate CN stretching vibration [nu(CN)] wavenumber correlates with the Snyder solvent strength (P') scale. These results signify that there is a difference in the solvent interactions with the two types of ligands. The energy of the ligand-to-metal charge transfer absorption maximum between 310 and 320 nm and the energy of the spin-forbidden (doublet-quartet) absorption and emission bands above 700 nm correlate with the nu(CN) wavenumber. This establishes the dominant role of solvent effects at the NCS- ligand in "tuning" the energy of these spectroscopic features. Quantum yields phirx for photosubstitution are <0.02 at 54 degrees C and <0.002 at 22 degrees C, demonstrating that photochemical reaction is a very minor pathway. The effects of solvent and temperature on the nonradiative decay of the doublet excited-state were investigated by observing the time-resolved phosphorescence between 700 and 750 nm. Below 30 degrees C, the lifetimes are relatively temperature-independent, whereas at higher temperatures, a strong Arrhenius-type dependence is observed. Values for the preexponential factor (A) and the activation energy (Ea) are solvent-dependent and follow a Barclay-Butler-type correlation. These observations are consistent with a dominant back-intersystem crossing pathway for nonradiative decay in the higher-temperature region. From trends observed between ln(A) and the nu(CN) frequency, it appears that solvent effects at the thiocyanate ligand play a dominant role in influencing the rate of nonradiative decay in the high-temperature region.

Monitoring the TiO2-photocatalyzed destruction of aqueous environmental contaminants at parts-per-trillion levels using membrane introduction mass spectrometry (MIMS).

Membrane introduction mass spectrometry (MIMS) was used to directly monitor the TiO2/UV-photocatalyzed destruction of acetophenone, toluene, and chloroform in H2O at ppm to pptr concentrations. The instrument response time was sufficiently rapid for these environmental contaminants (1-6min) that "real-time" monitoring of their degradation was possible. This method was used to follow the loss of toluene at pptr levels and the concomitant formation of one of its primary photo-oxidation intermediates, methylphenol. These results illustrate the potential use of MIMS as a sensitive on-line measurement technique for monitoring photocatalytic destruction of trace organic contaminants in water at environmentally relevant levels.

Photolysis of naphthenic acids in natural surface water.

Naphthenic acids are toxic and corrosive substances in oil sands leachates comprising a group of saturated aliphatic and alicyclic carboxylic acids in hydrocarbon deposits (petroleum, oil sands bitumen, and crude oils). In the current study, photolysis was applied to naphthenic acid mixtures and individual compounds to determine the efficacy of a variety of UV/vis radiation sources for reducing both concentration and aryl hydrocarbon (Ah) receptor binding as a measure of toxicity. The results show that the concentrations of neither the compounds nor the mixtures were significantly reduced in Athabasca River water, although compositional changes occurred within the mixtures and Ah receptor binding potential was affected by photolysis. Photolysis at UV254 was the most effective radiation source applied in all instances.

Solvent dependence of intramolecular electron transfer in a helical oligoproline assembly.

The helical oligoproline assembly CH3-CO-Pro-Pro-Pro-Pra(Ptzpn)-Pro-Pro-Pra(RuIIb2m2+ -Pro-Pro-Pra(Anq)-Pro-Pro-Pro-NH2, having a spatially ordered array of functional sites protruding from the proline backbone, has been prepared. The 13-residue assembly formed a linear array containing a phenothiazine electron donor, a tris(bipyridine)ruthenium(II) chromophore, and an anthraquinone electron acceptor with the proline II secondary structure as shown by circular dichroism measurements. Following RuII --> b2m metal-to-ligand charge-transfer (MLCT) excitation at 457 nm, electron-transfer quenching occurs, ultimately to give a redox-separated (RS) state containing a phenothiazine (PTZ) radical cation at the Pra(Ptzpn) site and an anthraquinone (ANQ) radical anion at the Pra(Anq) site. The redox-separated state was formed with 33-96% efficiency depending on the solvent, and the transient stored energy varied from -1.46 to -1.71 eV at 22 +/- 2 degrees C. The dominant quenching mechanism is PTZ reductive quenching of the initial RuIII(b2m*-) MLCT excited state which is followed by m*- --> ANQ electron transfer to give the RS state. Back electron transfer is highly exergonic and occurs in the inverted region. The rate constant for back electron transfer is solvent dependent and varies from 5.2 x 10(6) to 7.7 x 10(6) s-1 at 22 +/- 2 degrees C. It is concluded that back electron transfer occurs by direct ANQ*- --> PTZ*+ electron transfer. Based on independently evaluated kinetic parameters, the electron-transfer matrix element is HDA approximately 0.13 cm-1.

Photolysis and biodegradation of selected resin acids in River Saale water, Germany.

The River Saale is the Elbe's major tributary flowing through the state of Thuringia, Germany and receives organics inputs from several industrial facilities including pulp and paper mills. Resin acids constitute a major class of polar organics and environmental toxins derived primarily from pulp and paper processing of softwoods. Since wastewater treatment methods at pulp and paper mills are not always capable of removing the persistent resin acids prior to effluent discharge, alternative or complementary degradation methods may be required. Here, the facile photodegradation of four resin acids--abietic, dehydroabietic, isopimaric, and pimaric--was observed with pseudo-first-order kinetics when exposed to broad band and UV254-radiation. Further experimentation in rotating annular biofilm reactors with UV-exposed and unexposed River Saale water spiked with abietic and dehydroabietic acids indicated that photolysis is an effective pretreatment method for resin acid biodegradation. The bacterial toxicity of the aqueous resin acids solutions as measured with Microtox luminescence assays decreased with exposure time. Consequently, photo- and biodegradation of the resin acids did not generate any notable amounts of toxic intermediates and/or the intermediates formed were further degraded into compounds of lower toxicity than the parents. With tandem photo- and biological treatment at pulp and paper mills, as well as in-situ degradation by solar radiation and natural biofilms within the River Saale, resin acid inputs can be reduced in both concentration and toxicity to near undetectable levels with little or no ecological significance.

Preparation and Photophysical Properties of Amide-Linked, Polypyridylruthenium-Derivatized Polystyrene.

The polymer poly(4{2-[N,N-bis(trimethylsilyl)amino]ethyl}styrene), prepared by anionic polymerization and of low polydispersity (M(w)/M(n) = 1.10-1.18), has been derivatized by amide linkage to [Ru(II)(bpy)(2)(4-(CO-)-4'-CH(3)-bpy)-](2+) (bpy is 2,2'-bipyridine; 4-(CO-)-4'-CH(3)-bpy is 4-carbonyl-4'-methyl-2,2'-bipyridine). Unreacted amine sites were converted into acetamides by treatment with acetic anhydride to give derivatized polymers of general formula [PS-CH(2)CH(2)NHCO(Ru(II)(n)()Me(m)())](PF(6))(2)(n)(), where m + n = 11, 18, or 25, PS represents the polystyrene backbone, and Ru(II) and Me represent the attached complex and acetamide, respectively. Spectral and electrochemical properties of the derivatized polymers are similar to those of the model [Ru(bpy)(2)(4-CONHCH(2)CH(2)C(6)H(5)-4'-CH(3)-bpy)](2+) (4-CONHCH(2)CH(2)C(6)H(5)-4'-CH(3)-bpy is 4'-methyl-2,2'-bipyridinyl-4-(2-phenylethylamide)), but emission quantum yields (phi(em)) and time-resolved emission decays are slightly dependent on the level of Ru(II) loading, with nonexponential, irradiation-dependent decays appearing at high loadings. The decays could be fitted satisfactorily to the first derivative of the Williams-Watts distribution function. These results are discussed with reference to possible structural and multichromophoric effects on excited-state decay.