Kinetics Of Photodecomposition Research Articles

Comparison of palladium/zinc oxide photocatalysts prepared by different palladium doping methods for congo red degradation

ZnO nanoplates were synthesized by microwave-hydrothermal methods. Pd doped ZnO photocatalysts were prepared by microwave irradiation, UV irradiation, and borohydride reduction methods. The Pd/ZnO photocatalysts were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and UV–vis spectrophotometry. The obtained FESEM results confirmed the dispersion of Pd nanoparticles on the surface of ZnO nanoplates. The optical band gap value was calculated as 3.25eV from UV–Vis diffuse reflectance spectra of ZnO and different Pd/ZnO photocatalysts. Since the preparation method of the photocatalyst is of great importance for determining the photocatalysis, the effect of this on photocatalysis was investigated. The results of the photocatalytic degradation of congo red in aqueous solutions under the UV-light showed that Pd/ZnO prepared by borohydride reduction method exhibited higher photocatalytic activity than the other ones. A plausible mechanism for the enhanced photocatalytic activity by Pd doped ZnO was proposed. The kinetics of photodecomposition of congo red, and the identification of photoproducts were investigated by using liquid chromatography–mass spectrometry (LC–MS). The possible photodegradation pathway of congo red was also proposed according to the structures of the photoproducts obtained from LC–MS data.

Adsorption kinetics and degradation mechanism study of water persistent insecticide quinalphos: for heterogeneous photocatalysis onto TiO2

The kinetics of adsorption and photodecomposition of the water polluting insecticide quinalphos (QP), in aqueous suspensions of TiO2 were evaluated under laboratory conditions. Langmuir and Freundlich models were applied to describe the adsorption process and the model proposed by Langmuir–Hinshelwood was used to illustrate the kinetics of the photodecomposition reactions of QP. The adsorption capacity of TiO2 observed to increase from 7.86 to 20.04 mg g−1 with the increase in initial QP concentration from 5 to 25 mg L−1, respectively. About 45.8% adsorption of 20 mg L−1 QP was observed in just 60 min at pH 6 with 5 g L−1 TiO2 loading and 25 ± 1°C temperature. TiO2 was found to have a maximum adsorption capacity of 23.7 mg g−1 for QP. Photocatalytic treatment of 200-mL solution (20 mg L−1) under least harmful UV-A radiations (365 nm/30 W m−2) with 0.5 g L−1 TiO2 loading gives nearly 89.67% degradation in 3 h. The photodecomposition rate of QP was significantly higher at slightly acidic conditions (pH 6). Increasing light intensity from 20 to 35 W m−2 and aperture to volume ratio of the photoreaction from 0.515 to 1.327 cm2 mL−1 shows a notable increase in the decomposition rate of QP. Formation of two complex intermediates (m/z 282 and 284) and a few smaller compounds (m/z 104, 108, and 149) were detected by the gas chromatography–mass spectrometry analysis of the reaction sample after 3 h UV irradiation in the presence of TiO2. These intermediates were further dissociated to simpler hydrocarbons, possibly, by reacting with ⋅OH and ⋅O species.

Photodegradation of Hexythiazox in Different Solvent Systems under the Influence of Ultraviolet Light and Sunlight in the Presence of TiO2, H2O2, and KNO3 and Identification of the Photometabolites

The photodegradation of the carboxamide acaricide hexythiazox in three different solvent systems (aqueous methanolic, aqueous isopropanolic, and aqueous acetonitrilic solutions) in the presence of H(2)O(2), KNO(3), and TiO(2) under ultraviolet (UV) light (λ(max) ≥ 250 nm) and sunlight (λ(max) ≥290 nm) has been assessed in this work. The kinetics of photodecomposition of hexythiazox and the identification of photoproducts were carried out using liquid chromatography-mass spectrometry. The rate of photodecomposition of hexythiazox in different solvents followed first-order kinetics in both UV radiation and natural sunlight, and the degradation rates were faster under UV light than under sunlight. Hexythiazox was found to be more efficiently photodegraded in the presence of TiO(2) than in the presence of H(2)O(2) and KNO(3). Two major photoproducts were separated in pure form using column chromatography and identified according to IR, (1)H NMR, and mass spectral information as cyclohexylamine and 5-(4-chlorophenyl)-4-methylthiazolidin-2-one. Another nine photoproducts were identified according to LC-MS/MS spectral information. The plausible photodegradation pathways of hexythiazox were proposed according to the structures of the photoproducts.

Kinetics and mechanism of the photodecomposition of trifluorobromomethane and tetrafluorodibromoethane under the action of light with a wavelength of 253.7 nm

The kinetics of photodecomposition of Halons CF3Br and C2F4Br2 was studied at different times of the irradiation of a mixture of these substances with oxygen at the wavelength λ = 253.7 nm. Kinetic data were obtained from changes in the absorption spectra in the region of Halon absorption and at a wavelength of 416 nm, which corresponds to the absorption maximum of molecular bromine. Kinetic schemes were proposed for the photodecomposition of CF3Br and C2F4Br2 at λ = 253.7 nm, and the quantum yields of their photodecomposition at this wavelength were determined.

Resolution, Line-Edge Roughness, Sensitivity Tradeoff, and Quantum Yield of High Photo Acid Generator Resists for Extreme Ultraviolet Lithography

Ultrahigh loadings of photoacid generators (PAGs) in phenolic extreme ultraviolet (EUV) resists have generated the highest known film quantum yields (FQYs). We evaluate the performance of these resists in terms of resolution, line-edge roughness (LER), and sensitivity and collectively evaluate these three parameters (known as RLS) in terms of KLUP and Z-Parameter figures of merit. An analytical model describing the kinetics of photodecomposition was developed to explain the relationship between film quantum yield and PAG concentration. Resists were prepared using a broad range of concentrations of iodonium (DTBPI-PFBS), sulfonium (TPS-PFBS), and non-ionic (NDI-PFBS) PAGs. The model fits the experimental data (correlation coefficient R2 = 0.998, 0.994, and 0.995) and compares the rate at which electrons react with PAGs or recombine with holes. Resists prepared with 15–20 wt % of iodonium nonaflate PAG exhibit both high quantum yields and the best RLS performance as determined using both KLUP and Z-Parameter methodologies. The improvement in RLS performance correlates with the increase in FQY at higher PAG concentrations.

Resolution, Line-Edge Roughness, Sensitivity Tradeoff, and Quantum Yield of High Photo Acid Generator Resists for Extreme Ultraviolet Lithography

Ultrahigh loadings of photoacid generators (PAGs) in phenolic extreme ultraviolet (EUV) resists have generated the highest known film quantum yields (FQYs). We evaluate the performance of these resists in terms of resolution, line-edge roughness (LER), and sensitivity and collectively evaluate these three parameters (known as RLS) in terms of KLUP and Z-Parameter figures of merit. An analytical model describing the kinetics of photodecomposition was developed to explain the relationship between film quantum yield and PAG concentration. Resists were prepared using a broad range of concentrations of iodonium (DTBPI-PFBS), sulfonium (TPS-PFBS), and non-ionic (NDI-PFBS) PAGs. The model fits the experimental data (correlation coefficient R2 = 0.998, 0.994, and 0.995) and compares the rate at which electrons react with PAGs or recombine with holes. Resists prepared with 15–20 wt % of iodonium nonaflate PAG exhibit both high quantum yields and the best RLS performance as determined using both KLUP and Z-Parameter methodologies. The improvement in RLS performance correlates with the increase in FQY at higher PAG concentrations.

Photodegradation of Flumorph in Aqueous Solutions and Natural Water under Abiotic Conditions

Flumorph is an oomycete fungicide that is now used extensively in China (Hu, J. Y.; Liu, C.; Yan, H. Degradation of flumorph in soils, aqueous buffer solutions, and natural waters. J. Agric. Food Chem. 2008, 56, 8574-8579). The photodegradation of flumorph in aqueous solutions and natural water have been assessed under natural and controlled conditions in this work. The kinetics of photodecomposition of flumorph was determined using the high-performance liquid chromatography (HPLC)-diode array detector (DAD), and the identification of photoproducts was carried out with HPLC-mass spectrometry (MS) [electrospray ionization (ESI) positive mode]. The rate of photodecomposition of flumorph in aqueous solutions and natural water followed first-order kinetics in both UV radiation and natural sunlight, and the Z isomer of flumorph could convert to the E isomer. The degradation rates were faster under UV light than sunlight, with the half-lives (t(1/2) = ln 2/k) of 36.5-64.2 min and 36.3-73.1 days, respectively. One major photoproduct was detected in UV light and tentatively identified according to HPLC-MS spectral information as (E or Z)-3-(3, 4-dimethoxyphenyl)-3-(4-fluorophenyl)-2-acrylamide. Photosensitizers, such as H(2)O(2) and riboflavin, could enhance photolysis of flumorph in natural sunlight. The results obtained indicated that photoreaction was an important dissipation pathway of flumorph in natural water systems.

Photodecomposition of Molybdenum andTungsten Carbonyl Complexes

The photodecomposition of four different colored organometallic molybdenum and tungsten carbonyl complexes, i.e. [Mo(CO)5)2LA] (complex I), [(Mo(CO)3(bipy))2LB] (complex II), [(W(CO)3(tmen))2LB] (complex III) and [Mo(CO)2LC]2 (complex I V) where LA 2‐phenyl‐1,3‐indandione)bis(2‐methyl anilines, LB 2‐phenyl‐1,3‐indandione) bis (4‐hydroxy anilines and LCbis (2‐hydroxo‐benzalydine) benzidine ion have been performed at 365 nm in chloroform at 25 °C under oxygen atmosphere. The absorbance spectrum of these complexes has been recorded with the time of irradiation in order to examine the kinetics of photodecomposition. The rate of the photodecomposition process was investigated and the relative values of the rate constants of dissociation (Kd) for the first‐order reaction are tabulated. The apparent rate constant of photodecomposition was found to be (8.33‐11.50) × 10-5 s-1.

Kinetics of Photocatalytic Decomposition of Methylene Blue

To treat dyeing and finishing industrial wastewater effluents by an advanced oxidation process, the decomposition kinetics of methylene blue by nanofine sol TiO2/UV was systematically studied in two batch slurry reactors. The factors of study include agitation speed, recirculation flow rate, initial dissolved oxygen concentration, initial methylene blue concentration, reaction temperature, TiO2 dosage, and UV light intensity. By using the network reduction technique, the general rate equation has been developed from considering the reaction mechanism. The rate equation uses a systematic reaction network reduction technique to avoid the need of more restrictive assumptions commonly used, such as a rate-determining step or equilibrium steps. The resulting rate equation is applicable to a wider range of reaction conditions. After applying the resulting rate equation to predict the transient concentrations of other dye compounds, we expect it can be applied for the kinetics of photodecomposition of other orga...

Synthesis, photochemical stability and photo-stabilizing efficiency of probes based on benzothioxanthene chromophore and Hindered Amine Stabilizer

New types of combined chromophore–HAS (Hindered Amine Stabilizer) fluorescence probes were prepared and their photo-stability as well as their photo-stabilizing efficiency was tested in polypropylene film. The chromophore was benzothioxanthene and HAS was 2,2,6,6-tetramethylpiperidine. They were prepared by a one-step synthesis from benzothioxanthene-3,4-dicarboxylic anhydride (BTXA) by condensation with 4-amino-2,2,6,6-tetramethylpiperidine to obtain the probe in the form of parent amine (BTXI-NH) and 4-amino-1-oxy-2,2,6,6-tetramethylpiperidine in the case of stable nitroxyl radical form (BTXI-NO). Kinetics of BTXA photo-decomposition followed by UV spectroscopy were similar to kinetics of photo-decomposition for derivatives with covalently linked HAS i.e. BTXI-NH and BTXI-NO. It consists of two parts, slower in the beginning and very fast at the end of the process. Better stability of BTXI-NO in comparison with BTXI-NH can be explained by the presence of stable nitroxyl radical in its structure. The rate of decomposition of the fast part is similar for both additives. As soon as the decomposition starts there is no influence of NO or NH on this process. Times represented the start of the fast decomposition of probes correspond to the induction period of photo-oxidation of PP films. Possible effect of mutual interaction of chromophore and HAS coupled in one molecule (BTXI-NH or BTXI-NO) during photo-oxidation was followed by comparison with the course of photo-oxidation of PP film containing physical mixture of chromophore in the form of BTXA and HAS in the form of parent amine (4-hydroxy-2,2,6,6-tetramethylpiperidine) and stable nitroxyl radical (4-hydroxy-2,2,6,6-tetramethylpiperidin- N-oxyl).

Abiotic Degradation of Iodosulfuron-methyl-ester in Aqueous Solution

The abiotic degradation of iodosulfuron-methyl-ester was investigated under both alkaline and acidic pH conditions in the dark, and results showed it to be a rather stable molecule in neutral or slightly alkaline environments. Photochemical reactions were studied using a high-pressure mercury arc lamp, and results showed that direct phototransformation is possible under normal environmental conditions (lambda > 290 nm). High-performance liquid chromatography (HPLC-UV and HPLC-MS) analyses were used to identify the degradates and to study the kinetics of photodecomposition and hydrolysis. Five main products of iodosulfuron-methyl-ester degradation were tentatively identified, and one of them (4-methoxy-6-methyl-1,3,5-triazin-2-amine) was confirmed using an authentic standard. Among the phototransformation mechanisms, photosubstitution of the iodide atom by a hydroxyl group, photodissociation of the N-S bond, and photoassisted hydrolysis were observed. The quantum efficiencies (multiwavelength quantum yield) of the photodegradation under different conditions were determined, and values of 0.054 +/- 0.02 (pH 9.6), 0.08 +/- 0.02 (pH 7), and 0.044 +/- 0.008 (pH 5.3) were obtained.

Primary processes of photodecomposition of 2-(5′-nitro-2′-furanyl)ethenyl-4-{N-[4′-(N,N-diethylamino)-1′-methylbutyl] carbamoyl} quinoline: Effect of oxygen and compound concentration

The study of the kinetics of photodecomposition of 2-(5′-nitro-2′-furanyl)ethenyl-4-{N-[4′-(N,N-diethylamino)-1′-methylbutyl] carbamoyl} quinoline (Quinifuryl, Q) was studied using steady-state and time resolved absorption spectroscopy. We detected the formation of the Q triplet state, which is characterized by the absorption maximum at 550nm, triplet state energy ET = 18,200 ± 500cm−1 and a decay constant k0=1.8×104s−1. This triplet state is quenched by Q molecules in its ground state with the constant kq1=2.6×108M−1s−1 and by molecular oxygen with the constant kq2=2.0×109M−1s−1. The initial rate of Q photodecomposition under continuous irradiation by visible light (Vi) increases when the Q concentration is increased. In air and oxygen saturated solutions Vi is linearly proportional to Q concentration and does not depend on the O2 concentration. Our kinetic model of the process supposed two ways of Q photodecomposition: the reaction between Q molecules in triplet and ground states and the photodecomposition directly from the Q singlet excited state.

The impact of UV irradiation on the radical initiating capacity of dissolved dyes

The kinetics of photodecomposition of three model dyes dissolved in isopropylalcohol (IP)–water mixture has been determined after exposure to UV radiation. An equation has been constructed and applied for the calculation of the radical initiating rate of the irradiated dye molecules on IP. The average radical initiating rate of the dye was found to be similar to that of azo-bis-isobutyronitrile. The number of cycles between the first radical formation and the last regeneration of the dye molecule was calculated in the presence and absence of oxygen in the system.

Photochemistry of Long-Lived [(CF 3 ) 2 CF] 2 C · C 2 F 5 Radicals in a Hexafluoropropylene Trimer Matrix

The kinetics of photodecomposition of long-lived [(CF3)2CF]2C·C2F5 radicals (I) in glassy and liquid hexafluoropropylene trimer was studied at 77 and 300 K, respectively. It was found that the phase state of the hexafluoropropylene trimer matrix did not affect the photodecomposition mechanism. In both cases, I eliminates ·CF3 radical from the perfluoroethyl fragment. The molar absorption coefficient of I was determined: e250 = 49 m2 mol–1. It was shown that the photodecomposition of I in a liquid matrix at 300 K led to the formation of other long-lived radicals. One of these species is [(CF3)2CF]3C· radical, which results from addition of ·CF3 radical to the double bond of a hexafluoropropylene trimer molecule.

Photochemical behaviour of carbendazim in aqueous solution.

To elucidate the photochemical behaviour of carbendazim (or MBC) in superficial waters, photolysis studies have been carried out in aqueous solutions at several pH using a UV light source (high pressure mercury arc lamp) or a solar light simulator (xenon arc lamp). The kinetics of photodecomposition of carbendazim was determined using HPLC-DAD and the identification of photoproducts was carried out with HPLC-MS (ESI negative and positive mode). According to the experimental results carbendazim is a rather stable molecule in the dark or in environmental conditions. The pH influence of the environmental medium on the photodegradation rate has been confirmed. The photochemical process can be considerably accelerated in alkaline solutions using HPK-quartz irradiation (quantum efficiency at pH 9 phi = 3.1 x 10(-3) degraded molecule per absorbed photon) while the photodegradation is not as efficient under a simulated sun irradiation (quantum efficiency in the suntest phi = 10(-4) at pH 7). Three photoproducts have been tentatively identified in pure water: 2-aminobenzimidazole, benzimidazole isocyanate and monocarbomethoxy-guanidine (issued from the cleavage of the benzimidazole ring). The last one seems very stable and could be accumulated in the environment.

INFLUENCE OF AN SiO2/CYCLOHEXANE INTERFACE ON THE PHOTOCHEMISTRY OF ANTHRACENE

AbstractWe have investigated the effect of added Si02 on the photochemistry of anthracene, 1, in cyclohexane. Adsorption of 1 onto the Si02 surface from cyclohexane follows a Freundlich adsorption isotherm indicating interactions between 1 and the surface over a distribution of adsorption sites. In the absence of oxygen, addition of Si02 to a cyclohexane solution of 1 leads to a significant increase in the rate of photolysis without a large concomitant change in product identity. The 9,10‐photodimer of 1 is the major product under oxygen‐deficient conditions. In the presence of oxygen, added Si02 has dramatic effects on both the photoproduct distribution and the kinetics of photodecomposition. The complicated mixture of oxygenated products formed from photolysis in oxygen‐containing slurries is proposed to arise from thermal decomposition of a single primary photoproduct, anthracene‐9,10‐endo‐peroxide. The polarity/polarizability of the Si02/cyclohexane interface is considered to be a major factor influencing the rate of photolysis in the oxygenated Si02/cyclohexane slurries.

Photodecomposition du bioxyde de chlore et des ions chlorite par irradiation U.V. en milieu aqueux—partie I. Sous-produits de reaction

Literature data about the photochemistry of oxychlorine compounds in aqueous solutions (flash photolysis, pulse radiolysis, solar radiation) indicate that the products (ClO, Cl, O, O −,…) generated from the primary photochemical reactions of decomposition of chlorine dioxide and hypochlorite can then initiate complex reactions which lead to the formation of many secondary products (Cl 2O 2, Cl 2O 1, ClO −,…) and of chlorate, chloride and molecular oxygen as end-products (Table 1). The aim of this work was to study the photodecomposition of aqueous solutions of chlorine dioxide and chlorite in u.v. reactors equipped with low pressure mercury vapour lamps in order to show the effects of pH and of the initial concentrations on the nature of photoproducts and on the rate of photodecomposition of ClO 2 and ClO 2 −. This paper presents the data obtained for the identification of photoproducts. The kinetics of photodecomposition will be presented in another paper (Part II).

Photodecomposition du bioxyde de chlore et des ions chlorite par irradiation u.v. en milieu aqueux-partie II. Etude cinetique

The decomposition of ClO 2 and ClO 2 − by u.v. radiation leads to the production of chlorate, chloride and oxygen as end-products via complex reactions which are initiated by the products generated by the primary reactions of photolysis (Buxton and Subhani, 1972a; Mialocq et al., 1973; Karpel Vel Leitner et al., 1992). As far as the rate of decomposition is concerned, Bowen and Cheung (1932) and Zika et al. (1985) have shown that the quantum yield of photodecomposition of chlorine dioxide (overall reaction) increases when the wavelength decreases [Zika et al. (1985): φ = 0.46 at 366 nm and 1.4 at 296.7 nm]. However, the values of the quantum yield of photodecomposition of ClO 2 and ClO 2 − at 253.7 nm as well as the quantum yields for the primary reactions of photolysis of ClO 2 and ClO 2 − at different wavelengths are not given in the literature. The aim of this work was to study the kinetics of photodecomposition of chlorine dioxide and of chlorite by u.v. irradiation.

Solid state decomposition studies of fluoroperoxo species of transition metals VIII: photodecomposition of Rb 3Zr 2(O 2) 2F 7·H 2O and Cs 3Zr 2(O 2) 2F 7·2H 2O

The kinetics of photodecomposition of the solids Rb 3Zr 2(O 2) 2F 7·H 2O and Cs 3Zr 2(O 2) 2F 7·2H 2O were studied under vacuum as a function of both intensity and temperature by measuring the pressure of the oxygen evolved with a McLeod gauge. Similar to other fluoroperoxozirconates the photolysis kinetics of these compounds are deceleratory throughout the decomposition reaction. The pressure—time curves are parabolic and the data fit the rate equation p = kt 1 2 . Also the rate of photodecomposition is a linear function of the intensity, indicating a monoexcitation process for the photolysis. The probable mechanism of photodecomposition can be visualized as the interaction of peroxo groups in excited states at special sites: ▪

Solid state decomposition studies on fluoroperoxo species of transition metals. IV. Photodecomposition of K 3Zr 2(O 2) 2F 7 · 2H 2O

The kinetics of photodecomposition of solid K 3Zr 2(O 2) 2F 7 · 2H 2O have been studied under vacuum as a function of intensity and temperature by measuring the evolved oxygen with the help of a McLeod Gauge. Pressure-time curves are parabolic in nature and the data fit the empirical equation p = kt 1 2 . The rate of photodecomposition is a linear function of intensity. The activation energy determined from an Arrhenius plot, in the temperature range 15–55°C, of the title compound is 2.15 kcal mole −1 (9.00 kJ mole −1).