Oxidation of Styrene in a Silent Discharge Plasma

A silent discharge plasma reactor has been developed to study the oxidation of styrene vapor in argon/oxygen mixtures. A number of analytical techniques were employed to determine the destruction efficiency and to characterize the intermediate products. The destruction efficiency was measured as a function of initial styrene concentration, temperature, and energy density of the plasma. The formation of solid products was observed in most experiments. At low temperature (100°C), the solid deposit was polymeric in nature, while at high temperature (300°C) the solid appeared to be amorphous carbon. A combination of high temperature and high energy density resulted in high destruction efficiency and minimal production of solid films. The destruction efficiency vs. energy density is shown to be more complex than a simple model predicting exponential behavior. Several reasons for the discrepancy are suggested. The e-folding energy density for the destruction of styrene is compared to literature values for other organic compounds, measured using similar types of plasma reactors.     

Abatement of Trichloromethane by Using Nonthermal Plasma Reactors

This work investigated the destruction of a halogenated carbon (trichloromethane) using different types of nonthermal plasma reactors. Three reactors, i.e., a surface discharge reactor, a dielectric-packed bed reactor and a barrier discharge reactor with a perforated dielectric tube, were compared with respected to the trichloromethane destruction efficiency. The effect of oxygen content and input power on the trichloromethane destruction was examined, and the byproducts were analyzed to elucidate the destruction pathways. The dielectric-packed bed reactor was found to show better performance in the trichloromethane destruction than the other two reactors. The increase in the oxygen content decreased the destruction efficiency, and the highest destruction efficiency was obtained at oxygen content 0.5%. The calculations for electron-molecule collisions indicated that the most abundant reactive species initiating the destruction of trichloromethane are metastable nitrogen molecules. The major byproducts were CO and Cl₂, and the formations of NO₂ and N₂O were also significant.     

Oxidative Destruction of Anthraquinone and Indigoid Compounds in Aqueous Solutions of Sodium Hydroxymethylsulfinate

Kinetics of quinone-hydroquinone equilibria of tetrabromoindigo, benzopyrene quinone, and dimethoxybenzanthrone in the presence of a reducer and atmospheric oxygen were studied by spectrophotometry. The reason for the destruction of the dyes both in acidic and alkaline media is the molecular oxygen primarily present in the system. The destruction mechanism is considered on an example of disodium 5,5-indigosulfonate.     

Study of quenching of S2 emission by addition of oxygen to a hydrogen flame in molecular emission cavity analysis

Interferences of oxygen on S₂ emission were measured for a hydrogen-oxgen flame in molecular emission cavity analysis and are discussed in terms of the emission intensities and temperatures in different regions of the flame. When a little oxygen is added to a hydrogen flame, S₂ emission is usually quenched. It also brings about a reduction in temperature in the lower region of the flame, where a cavity is introduced. However, in a “lower burnt hydrogen-oxygen flame”, in which hydrogen reacts instantly with added oxygen at the burner top, S₂ emission is not quenched by addition of oxygen, and the intensity and the flame temperature increase linearly with increasing oxygen flow-rate. Therefore, it is apparent that an increase in flame temperature is not responsible for the quenching. It is suggested that the existence of unburnt oxygen in the lower region of the flame can cause the quenching owing to the destruction of S₂ molecules to form sulphur-oxygen compounds.     

Development of a Submerged Thermal Plasma Process for Combustion of Organic Liquid Waste

Plasma Chemistry and Plasma Processing - A process for the destruction of organic liquid waste has been developed in which a nontransferred arc plasma torch is operated with oxygen as the plasma...     

Polymer treatment in the flowing afterglow of an oxygen microwave discharge: Active species profile concentrations and kinetics of the functionalization

The surface treatment of different polymers and their corresponding model surfaces in the flowing afterglow of an oxygen microwave plasma is investigated. The concentration profiles of tire long-lived species issued from the plasma are measured and calculated in the downstream area The influence of atomic and singlet molecular oxygen in the behavior of different polymers is investigated. It appears that the evolution of the surface energy can be explained by an initiation of the functionalization by the oxygen atoms impinging upon the surface followed by reaction of the radicals formed with molecular oxygen. The concentration of functions at the sureface is limited due to their destruction by reaction with oxygen atoms. Furthermore, the functionalization level is higher in the /lowing afterglow than in the plasma, without any significant degradation of the polymer surface. Therefore, the treatment in the flowing afterglow is more efficient to increase suface energy in particular, for polymers which undergo high backbone chain scission.Died April 27, 1993.     

PHOTOSENSITIZED CARCINOGEN DEGRADATION AND THE POSSIBLE ROLE OF SINGLET OXYGEN IN CARCINOGEN ACTIVATION

Abstract— Dye sensitized photo-oxidation of various chemical carcinogens including 2-acetylaminofluorene, benzo(a)pyrene, 9,10-dimethyl-1,2-benzanthracene and 4-nitroquinoline- N -oxide has been studied in the presence and absence of oxygen. Visible light from a filtered 150 W Xe arc was used for photolysis. and carcinogen destruction was monitored spectrophotometrically. The carcinogens were solubilized in aqueous solution within micelles of various lipid-like surfactants. Photosensitized destruction of carcinogens by several triplet sensitizers has been observed. Enhanced damage in the presence of oxygen is also found. These results are consistent with photochemical oxidative damage to carcinogens being produced in aerated solutions via the sensitizer triplet state, possibly involving singlet oxygen. These manifold reactions are catalysed by micelles which concentrate polycyclic hydrocarbons in the non-polar environment within the micelles where the exclusion of water probably increases reactive species lifetimes. This model photochemical system mimics the aerobic metabolic activation of chemical carcinogens, which in part is believed to be mediated by various forms of activated oxygen.     

Characterisation of the photocatalyst Pilkington Activ™: a reference film photocatalyst?

Pilkington Glass Activ™ represents a possible suitable successor to P25 TiO₂, especially as a benchmark photocatalyst film for comparing other photocatalyst or PSH self-cleaning films. Activ™ is a glass product with a clear, colourless, effectively invisible, photocatalytic coating of titania that also exhibits PSH. Although not as active as a film of P25 TiO₂, Activ™ vastly superior mechanical stability, very reproducible activity and widespread commercial availability makes it highly attractive as a reference photocatalytic film. The photocatalytic and photo-induced superhydrophilitic (PSH) properties of Activ™ are studied in some detail and the results reported. Thus, the kinetics of stearic acid destruction (a 10⁴ electron process) are zero order over the stearic acid range 4–129 monolayers and exhibit formal quantum efficiencies (FQE) of 0.7×10⁻⁵ and 10.2×10⁻⁵ molecules per photon when irradiated with light of 365±20 and 254 nm, respectively; the latter appears also to be the quantum yield for Activ™ at 254 nm. The kinetics of stearic acid destruction exhibit Langmuir–Hinshelwood-like saturation type kinetics as a function of oxygen partial pressure, with no destruction occurring in the absence of oxygen and the rate of destruction appearing the same in air and oxygen atmospheres. Further kinetic work revealed a Langmuir adsorption type constant for oxygen of 0.45±0.16 kPa⁻¹ and an activation energy of 19±1 kJ mol⁻¹. A study of the PSH properties of Activ™ reveals a high water contact angle (67°) before ultra-bandgap irradiation reduced to 0° after prolonged irradiation. The kinetics of PSH are similar to those reported by others for sol–gel films using a low level of UV light. The kinetics of contact angle recovery in the dark appear monophasic and different to the biphasic kinetics reported recently by others for sol–gel films [J. Phys. Chem. B 107 (2003) 1028]. Overall, Activ™ appears a very suitable reference material for semiconductor film photocatalysis.     

Thermal Destruction of Polydimethyl-Siloxane on a Phosphorus-containing Silica Surface

Thermogravimetry, differential thermal analysis, and IR spectroscopy were used to investigate the process of thermal destruction of adsorbed polydimethylsiloxane (PDMS) in air. The disperse adsorbents were pristine fumed silica and modified fumed silica whose surface contained oxygen compounds of phosphorus. It was shown that under the given experimental conditions the thermal destruction of PDMS on the fumed silica surface was accompanied by the complete transformation of the adsorbed PDMS to SiO₂. In the case of phosphorus-containing silica, the thermal destruction proceeded in a different way. It was found that at 140–300°C depolymerization of the siloxane chains of a certain part of the adsorbed polymer took place with the concurrent removal of volatile products of the reaction. However, the remaining part of the adsorbed PDMS interacted with the modified silica surface to form chemisorbed dimethylsilyl structures. The thermal destruction of the chemisorbed fragments of PDMS in air was initiated at 400°C or above for both types of silica investigated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Plasma Destruction of Ozone Depleting Substances

The literature on the plasma destruction of ozone depleting substances (ODS) such as CCl₂F₂ and CBrF₃ is reviewed, and compared with more recent work on the decomposition of CCl₂F₂ and CBrClF₂ in oxygen and steam. A comprehensive kinetic scheme for the decomposition of CBrClF₂, which includes the decomposition of CCl₂F₂ and CBrF₃, is presented. Simulations performed with this scheme, and experimental results, demonstrate the importance of allowing for the interconversion of ODS in the assessment of plasma destruction devices.Both experimental and modeling results show that the efficiency of operation of a practical plasma ODS destruction device can be quantified in terms of a throughput parameter, the feed to plasma power ratio (units mol (kWh)^-1), or in terms of the thermochemical mixing temperature, T_m, of the plasma, ODS and oxidant. At low throughputs and high T_m, essentially complete destruction may be achieved, with below-ppm quantities of ODS remaining in the plasma exhaust gases. As throughput rises and Tm falls, a threshold is reached above which the ODS residual rises steeply towards the practical working limit set for ODS destruction by the Montreal Protocol (a destruction level of 99.99%). The assessment of this limit must include all ODS in the exhaust gases, weighted for ozone depleting potential. The use of steam, rather than oxygen, as the oxidizing gas gives superior destruction performance.     

Fringelite D, a Model of the Protist Photosensory Pigments of the Stentorinand Blepharismin Types: The Hypericinand Fringelite D PhotosensitizedDestruction of Bilirubin

 Using the hypericin and fringelite D photosensitized destruction of bilirubin together with fluorescence spectroscopy it was found that in contrast to fringelite D hypericin behaves as an effective photodynamic agent producing mainly singlet oxygen. This makes fringelite D and concomitantly the related stentorin and blepharismin pigments better suited for the photosensory transduction chain where, as shown recently, an initial proton expulsion reaction plays the fundamental role. Thus, in organisms using these photosensory pigments the production of deleterious oxygen species becomes diminished as compared to hypericin. In addition it was found that complexation with albumin further inhibits bilirubin destruction.     

Low-temperature destruction of carbon tetrachloride over lanthanide oxide-based catalysts: from destructive adsorption to a catalytic reaction cycle

The catalytic destruction of carbon tetrachloride in the presence of steam, CCl(4) + 2 H(2)O-->4 HCl + CO(2), was investigated at 200-350 degrees C over a series of lanthanide (La, Ce, Pr and Nd) and alkaline-earth metal (Mg, Ca, Sr and Ba) oxide-based catalysts with kinetic experiments, Raman spectroscopy, X-ray photoelectron spectroscopy, IR spectroscopy, X-ray diffraction, and DFT calculations. This new catalytic reaction was achieved by combining destructive adsorption of CCl(4) on a basic oxide surface and concurrent dechlorination of the resulting partially chlorinated solid by steam. The combination of the two noncatalytic reactions into a catalytic cycle provided a rare opportunity in heterogeneous catalysis for studying the nature and extent of surface participation in the overall reaction chemistry. The reaction is proposed to proceed over a terminal lattice oxygen site with stepwise donation of chlorine atoms from the hydrocarbon to the surface and formation of the gas-phase intermediate COCl(2), which is readily readsorbed at the catalyst surface to form CO(2). In a second step, the active catalyst surface is regenerated by steam with formation of gas-phase HCl. Depending on the reaction conditions, the catalytic material was found to transform dynamically from the metal oxide state to the metal oxide chloride or metal chloride state due to the bulk diffusion of oxygen and chlorine atoms. A catalyst obtained from a 10 wt % La(2)O(3)/Al(2)O(3) precursor exhibited the highest destruction rate: 0.289 g CCl(4) h(-1) g(-1) catalyst at 350 degrees C, which is higher than that of any other reported catalyst system.     

On the formation of ozone in oxygen-rich solar system ices via ionizing radiation

The irradiation of pure molecular oxygen (O(2)) and carbon dioxide (CO(2)) ices with 5 keV H(+) and He(+) ions was investigated experimentally to simulate the chemical processing of oxygen rich planetary and interstellar surfaces by exposure to galactic cosmic ray (GCR), solar wind, and magnetospheric particles. Deposited at 12 K under ultra-high vacuum conditions (UHV), the irradiated condensates were monitored on-line and in situ in the solid-state by Fourier transform infrared spectroscopy (FTIR), revealing the formation of ozone (O(3)) in irradiated oxygen ice; and ozone, carbon monoxide (CO), and cyclic carbon trioxide (c-CO(3)) in irradiated carbon dioxide. In addition to these irradiation products, evolution of gas-phase molecular hydrogen (H(2)), atomic helium (He) and molecular oxygen (O(2)) were identified in the subliming oxygen and carbon dioxide condensates by quadrupole mass spectrometry (QMS). Temporal abundances of the oxygen and carbon dioxide precursors and the observed molecular products were compiled over the irradiation period to develop reaction schemes unfolding in the ices. These reactions were observed to be dependent on the generation of atomic oxygen (O) by the homolytic dissociation of molecular oxygen induced by electronic, S(e), and nuclear, S(n), interaction with the impinging ions. In addition, the destruction of the ozone and carbon trioxide products back to the molecular oxygen and carbon dioxide precursors was promoted over an extended period of ion bombardment. Finally, destruction and formation yields were calculated and compared between irradiation sources (including 5 keV electrons) which showed a surprising correlation between the molecular yields (～10(-3)-10(-4) molecules eV(-1)) created by H(+) and He(+) impacts. However, energy transfer by isoenergetic, fast electrons typically generated ten times more product molecules per electron volt (～10(-2)-10(-3) molecules eV(-1)) than exposure to the ions. Implications of these findings to Solar System chemistry are also discussed.     

The structures of the active intermediates in Catalyst-Enhanced Molten Salt Oxidation and a new method for the complete destruction of chemical warfare arsenicals

Catalyst-Enhanced Molten Salt Oxidation (CEMSO) is our improvement of the earlier process, Molten Salt Oxidation (MSO), originally employed for the destruction of hazardous materials by high temperature oxidation in a carbonate melt. MSO was abandoned because it was slow and only partially oxidized cotton, paper, and plastics. It was very efficient for many other chemicals and had oxidized the nerve gas sarin with >99.9999% efficiency. We came to realize that the concentration of the oxidizing species, superoxide and peroxide ions, produced from the oxygen entering the carbonate melt, could be increased and maintained by the addition of nitrate ions as catalyst. The structure and interatomic distances for the various possible adducts between nitrate and nitrite with oxygen and peroxide have been calculated for the first time by Density Functional Theory (DFT). Their calculated enthalpies, as a function of temperature, revealed which adducts can be formed in the carbonate melt. The Japanese still have large stocks of the chemical warfare arsenicals Clark I and Clark II awaiting a destruction procedure that ensures removal of all volatile As(III) compounds. We have established that As(V) salts are stable at high temperature and here discuss how CEMSO can efficiently achieve this for the Clark arsenicals.     

Effect of polyethylenimine, a cell permeabilizer, on the photosensitized destruction of algae by methylene blue and nuclear fast red

The present study reports the effect a cell permeabilizer, polyethylenimine (PEI) has on the photodynamic effect of methylene blue (MB) and nuclear fast red (NFR) in the presence of hydrogen peroxide (H2O2). The photosensitized destruction of the algae Chlorella vulgaris under irradiation with visible light is examined. The photodynamic effect was investigated under aerobic and anaerobic conditions. The presence of a permeabilizer during the photosensitized destruction of C. vulgaris does not enhance the activity of the MB, MB/H2O2 system or the NFR, NFR/H2O2 system under aerobic conditions. However under anaerobic conditions we have determined that when a cell permeabilizer was added to the MB/H202 system, the photosensitized destruction of C. vulgaris proceeded via a combination of Type I and Type II mechanisms. The presence of PEI enforces MB/H2O2 to be active toward the destruction of C. vulgaris whether oxygen is present or absent. Under aerobic and anaerobic conditions the activity of NFR was suppressed in the presence of PEI as a result of electrostatic interactions between the photosensitizer and the cell permeabilizer. The decrease in fluorescence recorded is indicative of destruction of the chlorophyll a pigment.     

Fringelite D, a Model of the Protist Photosensory Pigments of the Stentorinand Blepharismin Types: The Hypericinand Fringelite D PhotosensitizedDestruction of Bilirubin

Summary.  Using the hypericin and fringelite D photosensitized destruction of bilirubin together with fluorescence spectroscopy it was found that in contrast to fringelite D hypericin behaves as an effective photodynamic agent producing mainly singlet oxygen. This makes fringelite D and concomitantly the related stentorin and blepharismin pigments better suited for the photosensory transduction chain where, as shown recently, an initial proton expulsion reaction plays the fundamental role. Thus, in organisms using these photosensory pigments the production of deleterious oxygen species becomes diminished as compared to hypericin. In addition it was found that complexation with albumin further inhibits bilirubin destruction. Received June 29, 2000. Accepted July 18, 2000     

Trichloroethylene Combustion in a Submerged Thermal Plasma: Results and Chemical Kinetics Model

This work deals with incineration of organic liquid wastes using an oxygen thermal plasma jet, submerged in water. The results presented here concern incineration of trichloroethylene (TCE). During a trial run, the CO₂ and CO content in the exhaust gas is continuously measured; samples taken periodically from the solution are analyzed by appropriate methods: total organic carbon and chlorine content are measured. Process efficiency during tests with a few L/h of TCE is given by the mineralization rate. The trapping rate of chlorine as HCl is near 100 %. The TCE destruction and removal efficiency, measured by MS/GC, is better than 99.9999 %. A simplified kinetic model of gas quenching was constructed from a single-phase plug-flow reactor model taking into account 14 species and 34 reactions. It satisfies the requirements of heat balance and major components analysis, and reveals the major role of the OH radical on the concentrations of CO as well as HCl and/or Cl₂ in the off-gas stream.     

Ceramic-based nanoparticles entrapping water-insoluble photosensitizing anticancer drugs: a novel drug-carrier system for photodynamic therapy

A novel nanoparticle-based drug carrier for photodynamic therapy is reported which can provide stable aqueous dispersion of hydrophobic photosensitizers, yet preserve the key step of photogeneration of singlet oxygen, necessary for photodynamic action. A multidisciplinary approach is utilized which involves (i) nanochemistry in micellar cavity to produce these carriers, (ii) spectroscopy to confirm singlet oxygen production, and (iii) in vitro studies using tumor cells to investigate drug-carrier uptake and destruction of cancer cells by photodynamic action. Ultrafine organically modified silica-based nanoparticles (diameter approximately 30 nm), entrapping water-insoluble photosensitizing anticancer drug 2-devinyl-2-(1-hexyloxyethyl) pyropheophorbide, have been synthesized in the nonpolar core of micelles by hydrolysis of triethoxyvinylsilane. The resulting drug-doped nanoparticles are spherical, highly monodispersed, and stable in aqueous system. The entrapped drug is more fluorescent in aqueous medium than the free drug, permitting use of fluorescence bioimaging studies. Irradiation of the photosensitizing drug entrapped in nanoparticles with light of suitable wavelength results in efficient generation of singlet oxygen, which is made possible by the inherent porosity of the nanoparticles. In vitro studies have demonstrated the active uptake of drug-doped nanoparticles into the cytosol of tumor cells. Significant damage to such impregnated tumor cells was observed upon irradiation with light of wavelength 650 nm. Thus, the potential of using ceramic-based nanoparticles as drug carriers for photodynamic therapy has been demonstrated.     

Anodic-Cathodic Electrocatalytic Degradation of Phenol with Oxygen Sparged in the Presence of Iron(Ⅱ)

IntroductionAs typical contaminants,phenolic pollutants,are toxic and are found in oil refinery and coke,chemical and plastic industries. Conventionaltreatment processes such as activated carbonadsorption,extraction and biological treatment cannot make the pollutants complete mineralization orwill lead to recontamination. Recently,electrochemical techniques have been extensivelyapplied to such a kind of wastewater treatment,mainly because of their amenability to automation,high efficiency and …     

FLUOROMETRIC STUDY OF TRYPTOPHAN PHOTOLYSIS

Abstract— Measurements of fluorescence spectra and fluorescence intensity for tryptophan solutions at different pH show an effective decarboxylation and deamination of tryptophan molecules under UV irradiation. The nonexponential dose-relationship of decrease in total fluorescence of tryptophan solutions is due to the formation of the products retaining indole ring in the course of these reactions. Dose-relationships and quantum yields of indole ring photolysis, deamination and decarboxylation are determined for tryptophan at 254 nm irradiation. Indole ring destruction accounts for about 60% of the total photolysis of tryptophan. Decarboxylation of tryptophan is two times more effective than its deamination. In the absence of oxygen quantum yield of indole photolysis in tryptophan and in the products of decarboxylation and deamination is reduced by a factor of two and by approximately an order of magnitude, respectively. Tryptophan photolysis products which, when excited at 365 nm. fluoresce in the visible region are formed from an intermediate product of indole ring destruction.