Medium Pressure Mercury Lamp Research Articles

Enhancement of the Photolysis of Nucleic Acid Monomers by Phosphates

Abstract— In the tentative simulation of prebiotic synthesis, it was found that the photolysis yield of nucleic acid bases, nucleosides and nucleotides (NA) undergoing UV irradiation was sharply enhanced by added orthophosphate. Filter experiments demonstrated that the enhancement is due to UV quanta of wavelength less than 215 nm in the emission spectrum of a medium pressure mercury lamp. The phosphate‐induced enhancement of the photolysis of NA constitutes an additional channel of nucleic acid monomer degradation through their interaction with photoionized phosphate radicals.

Curing profiles of the new xenon chloride lamp

The cure rate of a high gloss overprint varnish was compared using a standard medium pressure mercury lamp and a high intensity xenon chloride lamp. Samples with equal photoinitiator concentration cured at a much faster rate using the xenon chloride lamp. It was found that the concentration of the photoinitiator could be greatly reduced and still give rapid rates of curing when the xenon chloride lamp with peak output at 308 nm was used.

Photooxidation of exhaust pollutants—V. Photooxidation and photoreduction of polychlorinated dibenzo-p-dioxins and dibenzofurans on fly-ash

The photochemical decomposition of polychlorinated dibenzo-p-dioxins and dibenzofurans was investigated on fly-ash particles from municipal solid waste. Photodegradation experiments were performed in the solid phase by direct irradiation with medium and low pressure mercury lamps in an oxygen/ozon atmosphere under oxidizing conditions and in an nitrogen/ammonia atmosphere under reductiv conditions. Qualitative and quantitative analysis was performed by GC/MS-spectroscopy. The degradation efficiency mainly depends on the effective irradiation time but also on the reaction temperature and to a small degree on the power output of the UV-lamp. The degradation rates were investigated in special reaction chambers under different conditions and with various additives and lead to a maximum value of about 70%.

Correlation between photolysis rate constants of polycyclic aromatic hydrocarbons and frontier molecular orbital energy

In the present study, pseudo-first-order direct photolysis rate constants of 17 PAHs were determined. Basing on the frontier molecular energy, E homo and E lumo, a QSPR equation was obtained. The obtained equation can be used to predict photolysis rate constants of PAHs under the irradation of medium pressure mercury lamp. As shown in the following equation, the obtained relationship between the logarithm of photolysis rate constants(logk exp) and E lumo-E homo gap was parabolic. logk exp =−32.738+9.770 ( E lumo − E homo )−0.715( E lumo − E homo ) 2 n=17, r=0.921, SE0.322, F=38.911, p=0.0000 Where r is the multiple correlation coefficient, SE is the standard error of estimates for the full regression, F is the F value for analysis of variance, p is the significance level. The obtained parabolic relationship is reasonable when internal and external factors controlling photolysis rate are considered.

Conversion of rhenium alkylidyne complexes that contain unsupported metal-metal double bonds into relatives that contain μ-alkylidyne ligands

Photolysis of compounds of the type [Re(CCMe 2R)(OR′) 2] (R  Me or Ph; OR′  O′Bu, OCMe 2(CF 3), or OCMe(CF 3) 2) in benzene with a medium pressure mercury lamp yields compounds of the type [Re(OR′) 2] 2(μ-CCMe 2R) 2 in an intramolecular and irreversible manner. [Re(CCMe 2R)(OR′) 2] 2 and [Re(OR′) 2] 2(μ-CCMe 2R) 2 (OR′  O′Bu or OCMe 2(CF 3) 2) both react with excess carbon monoxide in several solvents to afford the dimers [Re(OR′) 2(CO)] 2(μ-CCMe 2R) 2 quantitatively. An X-ray study of [Re(O tBu) 2(CO)] 2 (μ-C tBu) 2 shows it to consist of two distorted trigonal bipyramids connected by two symmetrically bridging neopentylidyne ligands. The unbridged dimers of general formula [Re(CCMe 2R)(OR′) 2] 2 do not react readily with simple substrates such as phosphines, olefins, or acetylenes, although [Re(CCMe 2R)(O tBu) 2] 2 can be oxidized by iodine to yield Re(CCMe 2R)(O tBu) 2I 2 in good yield. In contrast, {Re[OCMe(CF 3) 2] 2} 2(μ-C tBu) 2 reacts with one equivalent of phenylacetylene to give a species in which one of the two bridging alkylidyne ligands is retained.

Photocatalytic Degradation of Organophosphoros Pesticides Using TiO 2Supported on Fiberglass

This paper studies the feasibility of photocatalytic degradation of organophosphoros pesticides using supported TiO 2as a catalyst, which is prepared by thermal decomposition and calcination of colloidal solution made from hydrolysis of titanium tetraisopropoxide [Ti(iso-OC 3H 7) 4] on fiberglass cloth. The results show that 0.65 × 10 −4mol/dm 3of dichlorvos, monocrotophos, phorate, and parathion can be completely photocatalytically degraded into PO 4 3−after 200 min illumination with a 375 W medium pressure mercury lamp; the TiO 2supported on the fiberglass is not easily removed and after 120 h illumination there is no significant loss of photocatalytic activity of TiO 2.

A novel photoaddition of 2‐phenylbenzimidazole

AbstractIrradiation of 2‐phenylbenzimidazole (3) in the presence of methyl acrylate (20 equivalents) using a medium pressure mercury lamp gives methyl 2‐(2‐phenylbenzimidazol‐1‐yl)propionate (4) (75%) whose structure has been confirmed by an X‐ray analysis. A similar reaction using acrylonitrile gave only a low yield (1%) of the corresponding propionitrile derivative 5. A mechanism involving photoexcitation of 2‐phenylbenzimidazole (3) followed by sequential single electron transfer, proton transfer and radical coupling is proposed to account for the formation of the novel photoadducts 4 and 5.

Bromate Destruction by UV Irradiation and Electric Arc Discharge

Abstract Bromate ion destruction by UV irradiation using either a low pressure mercury lamp or a medium pressure mercury lamp has been evaluated. A low pressure lamp which emits radiation predominantly at < 200 nm was more effective than the UV lamp which emits radiation at 254 nm, since bromate ion has a peak absorbance of about 195 nm. Bromate ion was shown to be reduced to bromide ion with bromine as an intermediate. Bromate ion destruction using a low pressure mercury lamp (< 200 nm) ranged from 3 to 38% for doses ranging from 23 to 228 mW-s/cm2; 7-46% destruction was achieved using a medium pressure lamp with initial bromate ion concentrations of 11-38 μg/L and doses ranging from 60 to 550 mW-s/cm2. A new innovative electric arc discharge method also has been evaluated and compared with UV irradiation. The electric arc discharge method destroyed 12-45% bromate ion for doses ranging from 130 to 1300 mW-s/cm2.

Photolysis of fluorodiphenylamines

Photolysis of 2-fluoro-2′,5′-dimethyldiphenylamine 1a, in ethanol with a medium-pressure mercury lamp, gave a mixture of 1,4-dimethylcarbazole 7 (53%), 8-fluoro-1,4-dimethylcarbazole 2(11%) and 6-ethoxy-2-fluoro-2′,5′-dimethyldiphenylamine 8(19%). Photolysis of 4-fluoro-2′,5′-dimethyldiphenylamine 1b gave 6-fluoro-1,4-dimethylcarbazole 25 (35%) and 1,4-dimethylcarbazole 7(47%).

Photocatalytic degradation of organophosphorus pesticides using thin films of TiO2

AbstractThis paper studies the feasibility of photocatalytic degradation of organophosphorus pesticides using thin films of TiO2. The results show that 0·65 × 10−4mol dn−3 of dichlorvos, monocrotophos, phorate, parathion can be completely photocatalytically degraded into PO within a short time under illumination with a medium pressure mercury lamp of 375 W. The effect of parameters such as he amount of TiO2 attached, initial concentration of organphosphorus pesticides, initial pH, amount of air flow, concentrations of H2O2 and Fe3+ on the photocatalytic degradation are studied. The possible mechanisms of photocatalytic degradation are discussed. It is our assumption that the degradation reactions occur on the surface of TiO2 via primary produced oxidizing species such as the OH radical and O, after 80 h illumination, there is no significant loss of the photocatalytic activity of TiO2.

Photocatalytic degradation of heparin over titanium dioxide

The photochemical degradation of the homogeneous oxygen-saturated buffered aqueous solutions of sodium heparin salt initiated by the irradiation with medium pressure mercury lamp was compared with the heterogeneous photocatalytic heparin degradation sensitized by titanium dioxide. The obtained results confirmed that UV irradiation of heparin homogeneous aqueous solutions caused negligible changes in the polysaccharidic structure only. The irradiation of heparin in oxygen-saturated physiological saline photosensitized by the TiO2 caused significant changes in the heparin macromolecule. The study of photocatalytic heparin degradation in buffered oxygen-saturated TiO2 suspensions (pH=5–9) ascertained a significant influence of pH on the degradation of heparin. The polymeric chain is predominantly cleaved in the acidic and neutral medium.

Photolytic Destruction and Polymeric Resin Decontamination of Aqueous Solutions of Pharmaceuticals

Amoxicillin, ampicillin, bleomycin, carmustine, cephalothin, dacarbazine, lomustine, metronidazole, norethindrone, streptozocin, sulfamethoxazole, and verapamil were completely degraded in solution, without the production of mutagenic residues, by photolysis using a medium-pressure mercury lamp in an all-quartz apparatus. A stream of air was passed through the solution and for amoxicillin, ampicillin, bleomycin, lomustine, metronidazole, and norethindrone it was necessary to add hydrogen peroxide. Dilute aqueous solutions of ampicillin, bleomycin, carmustine, cephalothin, lomustine, norethindrone, streptozocin, trimethoprim, and verapamil can be decontaminated using polymeric Amberlite resins.

Photochemical reactions of several adducts of metalladithiolenes and metalladithiazoles---dissociation and rearrangement--

The addition products of metalladithiolene and metalladithiazole complexes undergo interesting photochemical dissociation reactions accompanied by rearrangement. Three examples are discussed. Upon irradiation with a medium pressure mercury lamp, the quadicyclane adducts of cobaltadithiolene and rhodiadithiolene dissociate to the free metalladithiolenes and norbornadiene accompanied by the skeletal rearrangement in the hydrocarbon moieties. The tributylphosphine adduct of a cobaltadithiolene eliminates photochemically the coodinated phosphine via the attack of singlet oxygen. In the photoreaction with 254 nm light, the phosphine adduct itself acts as a triplet sensitizer to produce singlet oxygen. The DMAD adducts of 1,2,5-cobaltadithiolene and 1,2,5,3-cobaltadithiazole behave differently upon irradiation: DMAD adduct of the cobaltadithiolene eliminates selectively the alkyne moiety which bridges between Co and S, while DMAD adduct of the cobaltadithiazole eliminates carbonitrile to give the cobaltadithiolenes.

Photooxidation of exhaust pollutants: I. Degradation efficiencies, quantum yields and products of benzene photooxidation

The photochemical decomposition and oxidation of benzene was investigated in the gas phase by irradiation of benzene in an oxygen/ozone atmosphere with ultraviolet light from low and medium pressure mercury lamps. The degradation efficiency depends on the concentration of the pollutant, the power output of the UV-lamp, the ozone concentration and the residence time in the irradiated area. The quantum yields for photooxidation at 1 atm O 2 without addition of O 3 were measured to be < < 1, both at 185 and 254 nm, demonstrating loss channels of the electronically excited benzene which are fluorescence, internal conversion and intersystem crossing as well as the absence of chain reaction steps at both wavelengths.

Preferential displacement of fluorophosphine ligands from fluorophosphinetungstencarbonyl complexes by reaction with trimethylamine oxide

The photolysis of [W(CO) 4dppe] in toluene in the presence of a large excess of PF 3, using a medium pressure mercury lamp, gives [W(PF 3) 4dppe] ( I). The thermal reaction of solutions of cis-[W(CO) 4,(Ph 3P)(CH 3CN)] with fluorophosphine ligands L gives cis-[W(CO) 4(Ph 3P)L] (L=PF 3 ( II), Me 2NPF 2 ( III), MeN(PF 2) 2 ( IV)). Compounds I–IV were characterized by IR, mass and NMR spectroscopy. They react with Me 3NO in acetonitrile, with loss of the fluorophosphine ligand. The CO ligands in II–IV are not attacked by the amine oxide.

Photodegradation of polyimides. 5. An explanation of the rapid photolytic decomposition of a selected polyimide via anhydride formation

Abstract : The photolytic decomposition in air of a polymide film based on a dianhydride and a diarylamine with hexafluoroisopropylidene 6F bridging groups is extremely rapid leading to efficient chain cleavage and subsequent photooxidative decomposition. Relatively short photolysis times with an unfiltered medium pressure mercury lamp are required to give a clean photoablation process of the 6F-6F polyimide films in the air. IR difference spectroscopy shows the appearance of anhydride groups on photolysis in air indicating a photooxidation process via decomposition of the arylimide linkage. A photophysical and photochemical analysis of several model N-arylphthalimides indicates that both solvent polarity and electron withdrawing/donating substituents can greatly after all the efficiency of the photolysis process.

Photodegradation of polyimides. III. The effect of chemical composition, radiation source, atmosphere, and processing

AbstractPolymide films made from diarylanhydrides with oxygen, carbonyl, and hexafluoroisopropylidene 6F bridging groups are photolabile when irradiated with unfiltered light from a medium‐pressure mercury lamp. The presence of oxygen is necessary to the photolytic degradation process, which results in the ultimate oxidative ablation of thin polyimide films. Films based on the 6F dianhydride containing a hexafluoroisopropylidene hinge group are the most unstable. However, photolysis of 6F dianhydride based polyimides in an inert atmosphere with either the unfiltered medium pressure mercury lamp or an electron beam results in no detectable changes even after long exposure times.

Photocatalytic degradation of phenol in the presence of near-UV illuminated titanium dioxide

The photocatalytic oxidation of aqueous phenol solutions in the presence of near-UV illuminated titanium dioxide has been studied at concentrations of 1–100 μM. The titanium dioxide was used as a free suspension and attached to sand. Under identical illumination conditions the degradation rate with the free suspension was approximately 2.6 times faster than with the immobilized catalyst. The quantum yield for the disappearance of phenol from a 100 μM solution in 0.1% TiO 2 suspension illuminated with ‘Blacklight Blue’ 360–370 nm maximum emission radiation was approximately 0.6%. Direct solar illumination gave degradation rates comparable with that achieved with a 100 W medium pressure mercury lamp. In less than 1 h the midday summer sun degraded 90% of a 100 μM phenol solution, of volume 0.5 l in a 145 mm diameter open dish. The disappearance of phenol and the formation of carbon dioxide with illumination time was quantitatively accounted for by numerical integration of simultaneous differential equations based on Langmuir-Hinshelwood kinetics. An unexpected observation emerging from this analysis was a dependence of the adsorption equilibrium constant on the reciprocal of the initial phenol concentration. This dependence occurred at each solution pH studied. A possible explanation for the observation is given in terms of phenol reformation reactions competing with irreversible phenol degrading reactions and free diffusion of OH radicals from the catalyst surface at low solute concentrations.

Dioxetane chemiluminescene detection in liquid chromatography

A study of the potential of dioxetane chemiluminescene (CL) detection in reversed-phase column liquid chromatography is presented. 3,4-Diethoxy-1,2-dioxetane (DEDO) is generated on-line in a post-column photochemical reactor from 1,2-diethoxyethylene (DEE) and single oxygen; the latter is produced photochemically by the eluting compounds via oxygen quenching. CL is obtained by thermal decomposition of DEDO in the detector cell (kept at 70.0°C) in the presence of 9,10-dibromoanthracene (DBA). In the experimental set-up two post-column reagent addition lines are applied, providing DEE in acetonitrile before and DBA in tetrahydrofuran after the photochemical reactor. The photochemical reactor is a kinetic PTFE tube, irradiated with a medium-pressure mercury lamp in combination with a filter cuvette in order to prevent autoxidation of DEE. The experimental conditions were optimized. Reversed-phase chromatograms applying exclusively acetonitrile-water (90 + 10, v/v) are presented and CL detection is compared with UV absorption detection. For a number of analytes the concentration detection limits in both techniques are similar, i.e., in the 10 −8–10 −7 M range. compounds, although providing strong absorption signals, hardly provide any CL, thus indicating the selectivity of the new technique.

Treatment of contaminated water, air and soil with UV flashlamps

AbstractA new and effective method has been developed for the treatment of VOC's, PCB's and other toxic organics. Direct UV photolysis of organics is achieved with this new method with the use of high intensity ultraviolet light of a broad UV spectrum. Standard and novel UV flashlamps can be used for generation of this broad UV spectrum. The pulsing nature of such spectrum helps to increase the efficiency of destruction of toxics. The final products of this destruction process are non‐toxic simple compounds. The energy efficiency of this new process exceeds that of traditional UV aided processes with medium pressure mercury lamps. This article reviews the Direct UV Photolysis Process, gives experimental results, and provides recommendations for applications in the treatment of groundwater, wastewater, contaminated air and soil.