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Showing papers in "Journal of Photochemistry and Photobiology A-chemistry in 1993"


Journal ArticleDOI
TL;DR: In this paper, the intrinsic processes and mechanisms of proton transfer in relation to the nature of the intramolecular hydrogen bond ring are reviewed. But the authors focus on the intrinsic process and not the mechanisms of transfer.
Abstract: Excited-state intramolecular proton transfer reactions are reviewed. Special emphasis is given to the intrinsic processes and to the mechanisms of proton transfers in relation to the nature of the intramolecular hydrogen bond ring.

647 citations


Journal ArticleDOI
TL;DR: Theoretical models that have been proposed and applied to proton transfer reactions are reviewed in this paper, where simple models, like the Eigen model, Marcus theory and the intersecting state model, are applied to excited-state intermolecular proton transfers.
Abstract: Theoretical models that have been proposed and applied to proton transfer reactions are reviewed in this work. Simple models, like the Eigen model, Marcus theory and the intersecting state model, are applied to excited-state intermolecular proton transfers. The kinetics and thermodynamics of proton transfers occuring in the singlet states of aromatic molecules with OH, NH3+, NH2 and CO substituents are reviewed.

507 citations


Journal ArticleDOI
TL;DR: In this article, the photo-Fenton reaction was used to accelerate the degradation rate of 4-chlorophenol (4-CP) and total organic carbon (TOC) in the presence of H2O2 and Fe2+ significantly compared with the Fe 2+H 2O2 reaction in the dark.
Abstract: A novel photochemical degradation method for organic contaminants, the photo-Fenton reaction, has been investigated. Irradiation of an aqueous solution of 4-chlorophenol (4-CP) with light of greater than 320 nm in the presence of H2O2 and Fe2+ accelerates the degradation rate of 4-CP and total organic carbon (TOC) significantly compared with the Fe2+H2O2 reaction in the dark. The effects of the initial 4-CP and H2O2 concentrations and the intensity of light irradiation on the degradation rates of TOC and H2O2 and the ratio of Fe2+ to Fe3+ are described. Results are compared with the dark Fenton reaction.

329 citations


Journal ArticleDOI
TL;DR: The large fluorescence enhancements observed when DSMI binds to the helix and the poor fluorescence yield of the dye in the absence of DNA suggests that DSMI should be quite useful in the staining of DNA gels and for the detection of very low concentrations of DNA.
Abstract: The cationic styryl dye DSMI binds to the double helical DNA with a high affinity. A red shift of the absorption spectrum and hypochromism accompany the binding of DSMI to calf thymus DNA. The fluorescence yields increase dramatically when DSMI binds to DNA, with no shifts in the emission maximum. These spectral changes are in contrast to the behavior observed with many fluorescent intercalators. Groove binding rather than intercalation of the dye was suggested to be the cause of these spectral changes, based on a variety of experimental results. Consistent with groove binding, the fluorescence enhancements were greater with poly(dA—dT) when compared with poly(dG—dC). The addition of salt or a strong electrolyte to the solution releases the DNA-bound dye cations from the groove and causes a decrease in the fluorescence yield. Therefore, when the dye binds to DNA, the fluorescence quenching with anionic quenchers was enhanced dramatically, in contrast to the expected protection of the probe fluorescence by the DNA helix. Binding of DSMI to DNA inhibits the non-radiative deactivation of the excited state, perhaps owing to the restriction imposed by the narrow minor groove of the DNA. The steric constraints imposed on the dye owing to the binding in the groove result in enhanced fluorescence yields and longer fluorescence lifetimes. Since the lifetimes of the DNA-bound dye were still in the nanosecond range, it is very likely that groove binding of the dye permits twisting in the excited state, which may be important in the excited state dynamics of this class of dyes. The large fluorescence enhancements observed when DSMI binds to the helix and the poor fluorescence yield of the dye in the absence of DNA suggests that DSMI should be quite useful in the staining of DNA gels and for the detection of very low concentrations of DNA.

289 citations


Journal ArticleDOI
TL;DR: In this paper, the kinetics of photomineralization of 4-chlorophenol (4-CP) sensitized by Degussa P25 TiO2 in O2-saturated solution is studied as a function of the following different experimental parameters: pH, [TiO2], percentage O2 [O2]−1, [4CP], T, I, γ and [KNO3].
Abstract: The kinetics of photomineralization of 4-chlorophenol (4-CP) sensitized by Degussa P25 TiO2 in O2-saturated solution is studied as a function of the following different experimental parameters: pH, [TiO2], percentage O2 [O2], [4-CP], T, I, γ and [KNO3]. At pH 2 and T=30°C the initial relative rate of CO2 photogeneration RCO2 conforms to a Langmuir-Hinshelwood-type kinetic scheme and the relationship between RCO2 and the various experimental parameters may be summarized as follows: where λ is a proportionality constant, Ko2 = 0.044±0.005[O2]−1, θ = 0.74 ± 0.05 and K(4-CP) = (29 ± 3) x 103 dm3 mol−1 The overall activation energy for this photosystem was determined as 16±2 kJ mol−1. This work forms part of an overall characterization study in which it is proposed that the 4-CP-TiO2O2 photosystem is adopted as a standard test system for incorporation into all future semiconductor-sensitized photomineralization studies in order to facilitate comparisons between the results of the different studies.

213 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that deposition of a metal on TiO2 considerably accelerated photocatalytic reduction of carbon dioxide to methane and/or acetic acid, and product distribution was dependent on the kind of metal on the surface of TiO 2.
Abstract: Deposition of a metal on TiO2 considerably accelerated photocatalytic reduction of carbon dioxide to methane and/ or acetic acid, and product distribution was dependent on the kind of metal on the surface of TiO2.

201 citations


Journal ArticleDOI
TL;DR: In this article, the spectroscopic and photophysical properties of two 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) derivatives with different substituents on the nitrogen group are reported in 18 solvents.
Abstract: The spectroscopic and photophysical properties of two 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) derivatives with different substituents on the nitrogen group are reported in 18 solvents. The solvatochromic shifts were analysed by correlating with polarity scales. The results, together with the help of modified neglect of diatomic overlap (MNDO) calculations, enable the polarity of the ground and first singlet excited states to be determined. Experiments based on variations in temperature and viscosity establish that the two probes undergo different de-excitation pathways. The possibilities of internal rotation leading to a twisted intramolecular charge transfer (TICT) state in the case of diethylamino-NBD are discussed. A study in binary solvent mixtures outlines specific solvent—solute interactions. Appropriate restrictions are emphasized on the utilization of NBD probes in biological fields.

183 citations


Journal ArticleDOI
TL;DR: In this article, the influence of type, species distribution, standard reduction potential, and concentration of several transition metals on the rate of photocatalytic oxidation of toluene was investigated.
Abstract: The influence of type, species distribution, standard reduction potential, and concentration of several transition metals on the rate of photocatalytic oxidation of toluene was investigated. A significant increase in reaction rate was observed in the presence of 10−5 M Cu(II), Fe(III), and Mn(II) at pH 3, with decreased rates at higher concentrations and pH values. There was no clear correlation between reaction rate and aqueous metal species distribution, nor did the oxidation states of Cu or Fe alter their effects on the reaction rate. Neither Ni(II) nor Zn(II) had a significant influence on the rate of organic oxidation. Negligible adsorption of metals onto TiO2 was measured at the metal concentrations and pH values for which the highest reaction rates were observed, indicating that dissolved metals increase the reaction rate via a homogeneous pathway rather than a TiO2 surface reaction. A mechanism involving formation of a reactive complex between the metal, the organic or its oxidation intermediate, and an oxygen-containing species is proposed to explain the experimental data. The rate of the photocatalytic reaction is described by a Langmuir—Hinshelwood rate form, modified to account for homogeneous catalytic pathways and decreased UV transmittance in the presence of dissolved metals.

180 citations


Journal ArticleDOI
TL;DR: In this article, the results of the temporal variations in the concentrations of 4-CP, CO2, Cl− and the major organic intermediates, namely, 4-chlorocatechol (4-CC), hydroquinone (HQ), benzoquinone and 4chlororesorcinol, are reported.
Abstract: The photomineralisation of 4-chlorophenol (4-CP) sensitised by Degussa P25 TiO2 in O2-saturated solution represents a possible standard test system in semiconductor-sensitised photomineralisation studies. As part of a detailed examination of this photosystem, the results of the temporal variations in the concentrations of 4-CP, CO2, Cl− and the major organic intermediates, namely, 4-chlorocatechol (4-CC), hydroquinone (HQ), benzoquinone and 4-chlororesorcinol, are reported. The observed variations in [4-CP], [4-CC], [HQ] and [CO2] fit those predicted by a kinetic model which utilises kinetic equations with a Langmuir-Hinshelwood form and assumes that there are three major possible routes in which the photogenerated hydroxyl radicals can react with 4-CP, i.e. 4-CP → 4-CC, 4-CP → HQ and 4-CP → (unstable intermediate) → CO2 and that these routes have the following probabilities of occurring: 48%, 10% and 42%.

162 citations


Journal ArticleDOI
TL;DR: In this article, the photocatalytic degradation of six dichlorophenols (DCPs) and three trichlorphenols (TCPs) in TiO2 aqueous suspensions was studied.
Abstract: The photocatalytic degradation of six dichlorophenols (DCPs) and three trichlorophenols (TCPs) in TiO2 aqueous suspensions was studied. The apparent first-order rate constants kapp of disappearance of these CPs and monochlorophenols (MCPs) were found to correlate with their Hammett constants λ and their 1-octanol-water partition coefficients Kow: kaw (h−1)= −10σ+5.2 log Kow−7.5 under the conditions used (correlation coefficient, 0.987, if 2,4,6-TCP was omitted). The aromatic intermediates identified by their UV spectra (high performance liquid chromatography (HPLC) separation) and mass spectra (gas chromatography (GC) separation) corresponded to the hydroxylation of the aromatic nucleus with the following order of reactivity para> ortho>meta. Para-benzoquinones with 0–2 Cl atoms and 0 or 1 OH group and intermediates with two aromatic or quinone rings were also detected. The temporal variations of some intermediates were determined. All of these compounds, in which the C6 ring subsisted, were very unstable, so that their maximum concentration was very low compared with the initial CP concentration. The release of chloride and the evolution of CO2 also followed apparent first- order kinetics within the first part of the degradation. The effects of the number and position of Cl atoms on these fkinetics are discussed.

147 citations


Journal ArticleDOI
TL;DR: In this paper, photo assisted catalytic degradation of trichloroethylene (TCE) in the gas phase was studied in a packed bed reactor using TiO2 pellets.
Abstract: The photoassisted catalytic degradation of trichloroethylene (TCE) in the gas phase was studied in a packed bed reactor using TiO2 pellets. The pellets (size, 0.3–1.6 mm) were prepared by sol—gel techniques. Porosities of 50%–56% and specific surface areas of 160–194 m2 g−1 were obtained for TiO2 sintered at 300°C. The apparent quantum yield for the conversion of TCE was estimated to be in the range 0.4–0.9. A single pass at 300 ml min−1 using four 4 W fluorescent black lights and 0.56 g of TiO2 pellets reduced the TCE concentration from 460 ppm in the influent stream to 3 ppm in the effluent stream, i.e. a 99.3% conversion of TCE.

Journal ArticleDOI
TL;DR: In this paper, the photochemical and thermal degradation of four anthocyanidins (pelargonidin, delphinin, malvidin, and cyanidin) in aqueous acidic media was studied.
Abstract: Photochemical and thermal degradation of four anthocyanidins (pelargonidin, delphinidin, malvidin and cyanidin) in aqueous acidic media was studied. The kinetics of the degradation were followed by absorption spectroscopy and high performance liquid chromatography. All anthocyanidins studied have shown a similar thermal degradation pattern. Chalcone was detected as an intermediary product, which undergoes cleavage yielding the final decomposition products, identified as (i) 2,4,6-trihydroxybenzaldehyde originated from ring A for all four anthocyanidins and (ii) 3,4,5-trihydroxybenzoic acid for delphinidin, 4-hydroxy-3,5-dimethoxybenzoic acid for malvidin, 3,4-dihydroxybenzoic acid for cyanidin, and 4-hydroxybenzoic acid for pelargonidin (all these originated from ring B). During the photochemical degradation, the formation of the same final products as for thermal reaction was observed, but through a different kinetic pathway involving the excitation of the flavylium cation. The substitution of the hydroxyl in position 3 by a glucoside gives rise to a large increase in the thermal stability, and a decrease in the quantum yield of the photochemical reaction.

Journal ArticleDOI
TL;DR: In this paper, the photocatalytic degradation of organophosphorus insecticide, dichlorvos, on glass-supported titanium dioxide was investigated, and the results indicate that photocatalysis can be an effective process for the degradation of dichlorvolvos.
Abstract: The photocatalytic degradation of organophosphorus insecticide, dichlorvos, on glass-supported titanium dioxide was investigated. The photoreactor coated with titanium dioxide was illuminated with a 20 W black-light UV fluorescent tube. The aqueous solution containing dichlorvos was continuously pumped through the photoreactor. Several factors, such as the initial dichlorvos concentration, dissolved oxygen, electrolytes, flow rate and temperature, affecting the oxidation rate of dichlorvos were studied. The results indicate that photocatalysis can be an effective process for the degradation of dichlorvos. The activated energy for the photocatalytic degradation of dichlorvos is 28.4 kJ mol−1. The initial quantum yield for the destruction of dichlorvos is 2.67%. Increasing the flow rate and initial dichlorvos concentration increases the dichlorvos degradation rate. Total mineralization requires a much longer illumination time than the disappearance of dichlorvos. Phosphate-containing intermediates are more stable than chloride-containing intermediates. It is shown that the photocatalytic oxidation of dichlorvos follows the Langmuir—Hinshelwood-type behavior, and reaction byproducts display an inhibiting effect on degradation rate.

Journal ArticleDOI
TL;DR: In this paper, the authors discuss two issues which have led to, and continue to cause, confusion in the heterogeneous photochemical literature: turnover numbers (turnover rates, turnover frequencies) and quantum yields.
Abstract: This paper discusses two issues which have led to, and continue to cause, confusion in the heterogeneous photochemical literature: (i) turnover numbers (turnover rates, turnover frequencies) and (ii) quantum yields. Attention is called to the use of these two parameters when describing the catalytic activity of a photocatalyst on the one hand and the efficiency of a photon on the other. A parameter is defined (relative photonic efficiency) and a simple method is proposed which provides a means of validating data between experiments and between laboratories. In addition, the process efficiency can be assessed and the photocatalytic activity of different materials and a given photocatalyst material from various sources can be validated.

Journal ArticleDOI
TL;DR: In this article, the UV visible absorption spectrum of molecular chlorine at 298 K was investigated in the wavelength range 200-550 nm with a spectral resolution of 0.2 nm, except for minor discrepancies, the absorption cross-sections are in agreement with those found in the literature.
Abstract: The UV—visible absorption spectrum of molecular chlorine at 298 K was investigated in the wavelength range 200–550 nm with a spectral resolution of 0.2 nm. Except for minor discrepancies, the absorption cross-sections are in agreement with those found in the literature. In the region 250⩽λ⩽-550 nm, the Cl 2 spectrum can be adequately described by a semi-empirical function of the wavelength A (in vacuum) and temperature T where tanh=tanh( hc x559.751 cm −1 /2 kT ). The absorption of solar radiation by the weak continuum around λ max =406.5 nm contributes 9% or more of the photodissociation of molecular chlorine in the atmosphere, but the banded Cl 2 features (λ ⩾ 479 nm) are of negligible atmospheric significance.

Journal ArticleDOI
TL;DR: In this paper, the photochromic compounds 1,3-dihydro-1,3,3trimethylspiro[2H-indole-2,3′-[3H]naphth[2,1-b][1,4]oxazine] were degraded under UV light irradiation in toluene solution.
Abstract: The photochromic compounds 1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3′-[3H]naphth[2,1-b][1,4]oxazine], 1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,2′-[3H]naphth[1,2-b]pyran] and 1,3-dihydro-8′-methoxy-6′-nitro-1,3,3-tri- methylspiro[2H-indole-2,2′[3H]benzopyran] were degraded under UV light irradiation in toluene solution. The resulting main photoproducts separated by gas chromatography and high performance liquid chromatography were identified by different couplings with UV—visible diode array detection, mass spectrometry and Fourier transform IR spectroscopy and were compared with synthetic standards. The different nature of the photoproducts involving the chromene part of the molecules could suggest different mechanisms of degradation between the spiropyran and spiro-oxazine series and could explain the better fatigue resistance of the latter.

Journal ArticleDOI
TL;DR: In this article, three pulsed laser techniques have been used to evaluate the absorption spectrum of Ru(bpy) 3 2+ in H 2 O, CH 3 CN and CH 3 O/CH 3 CN mixtures.
Abstract: Three pulsed laser techniques have been used to evaluate the absorption spectrum of ★Ru(bpy) 3 2+ in H 2 O, CH 3 CN and H 2 O/CH 3 CN mixtures: complete conversion of the ground state, energy transfer to anthracene, and benzophenone actinometry. The three techniques give reliable and reproducible values of ϵ 450 =4.6(±0.4) × 10 3 M −1 cm −1 , independent of the solution medium. The ground state spectrum is virtually the same in H 2 O and CH 3 CN with ϵ 452 = 1.46 × 10 4 M −1 cm −1 ; the value of ϵ 450 , the difference in the ϵ values of the excited and the ground states at 450 nm, is −1.0(±0.09)×10 4 M − cm −1 . Ru(bpy) 3 2+ can serve as a reliable actinometer for the 532 nm frequency doubled Nd:YAG pulsed laser line and, with appropriate corrections for the inner filter effect, for the 355 nm frequency tripled line.

Journal ArticleDOI
TL;DR: In this article, the quenching of 1-naphthol fluorescence by carbon tetrachloride (CCl 4 ) has been studied in different solvent mixtures of acetonitrile and dioxane at room temperature.
Abstract: The quenching of 1-naphthol fluorescence by carbon tetrachloride (CCl 4 ) has been studied in different solvent mixtures of acetonitrile and dioxane at room temperature. The quenching is found to be appreciable and a positive deviation from linearity was observed in the Stern-Volmer plot in all the solvent mixtures even at moderate CCl 4 concentrations (0.1 M or less). This could be explained satisfactorily by a static-dynamic model. The static quenching constant K o values indicate that the ground-state complex is weak and independent of solvent polarity, whereas the dynamic quenching constant K sv depends on the solvent polarity.

Journal ArticleDOI
TL;DR: In this paper, the existence of a relationship between phototoxic and photophysical properties of 2,2′:5′,2″-terthiophene (1a ) and related compounds, the singlet-to-triplet intersystem crossing quantum yields of compound 1a and six of its monosubstituted derivatives (1b, 1g ) were determined in 95% ethanol solution.
Abstract: During the course of a study devoted to the investigation of the existence of a relationship between the phototoxic and photophysical properties of 2,2′:5′,2″-terthiophene ( 1a ) and related compounds, the singlet-to-triplet intersystem crossing quantum yields of compound 1a and six of its monosubstituted derivatives ( 1b – 1g ) were determined in 95% ethanol solution. The variations in the phototoxicity of these compounds against some insect and mite species are large in comparison with changes in the quantum yields of triplet state formation. The latter were very similar in the compounds studied (range, 0.88–0.99), with the exception of 5-formyl-2,2′:5′,2″-terthiophene. ( 1c ) (Φ T =0.50). Moreover, a complete characterization of the S 1 decays of compounds 1a – 1g was obtained by combining these data with the corresponding fluorescence quantum yields and lifetimes. Finally, the consequences of the nature and position of the substituents on the measured triplet—triplet absorption and rate constants of the two S 1 decay paths, i.e. fluorescence emission and intersystem crossing, are qualitatively discussed.

Journal ArticleDOI
TL;DR: In this article, the photocatalytic reaction of neat alcohols (ethanol or 2-propanol) by metal-loaded titanium(IV) oxide (TiO2) was conducted under argon at room temperature.
Abstract: The photocatalytic reaction (excitation wavelength, greater than 300 nm) of neat alcohols (ethanol or 2-propanol) by metal-loaded titanium(IV) oxide (TiO2) was conducted under argon at room temperature. The dehydrogenation products hydrogen (H2) and acetaldehyde (or acetone in the case of 2-propanol) were found in the absence of additives. The corresponding acetals, ethers, and alkanes were obtained by the addition of concentrated hydrochloric acid (HCl). The measurement of the product yields during the post-irradiation dark reaction in the presence of photocatalyst (TiO2) loaded with platinum(IV) oxide (PtO2) revealed that the production of ether and ethane and the regeneration of ethanol proceed by the hydrogenation of acetal over loaded metal, presumably via a hemiacetal intermediate. X-ray diffraction (XRD) analyses showed that the loaded PtO2 is reduced to platinum metal during the course of the photocatalytic reaction. For the production of ether from HCl-acidified ethanol, Pd-loaded catalysts, especially prepared by precipitation—reduction, exhibit the highest activity of several metal-loaded TiO2 catalysts. From XRD and X-ray photoelectron spectroscopy studies of Pd-loaded TiO2 particles, it was shown that the smaller the size of the Pd particles, the higher the selectivity for ether production from the acidified ethanol suspension. The application of this photocatalytic O-alkylation to the synthesis of cyclic ethers was demonstrated.

Journal ArticleDOI
TL;DR: In this paper, a new Xe-excimer light source was used for the oxidative degradation of 4-chlorophenol (4-CP) in aqueous solution.
Abstract: A new Xe-excimer light source has been used for the oxidative degradation of 4-chlorophenol (4-CP) in aqueous solution. Owing to the very high absorption cross-section of water at the wavelength of excitation (172 nm), degradation of the organic substrate is initiated by hydroxyl radicals generated by water photolysis. Neither oxygen concentration, nor the presence of carbonates or nitrates affects the rate of 4-CP degradation; however, maximum oxygen concentration is required for higher rates of mineralization of organic carbon. Kinetic investigations are based on 4-CP, TOC and Cl − analysis. VUV photolysis as a means of oxidative degradation of organic pollutants in aqueous systems is showing the potential to compete with other photochemical oxidative processes.

Journal ArticleDOI
TL;DR: In this paper, a hypothesis for increasing the photoefficiency of heterogeneous photocatalytic reactions on TiO 2 particles was proposed and tested for increasing photoefficiency for decomposing organic compounds in water.
Abstract: A hypothesis is proposed and tested for increasing the photoefficiency of heterogeneous photocatalytic reactions on TiO 2 particles. Increasing the photoefficiency is vital for the economic scale-up of photocatalysis for decomposing organic compounds in water. An open-channel reactor was designed to test the following rationale. There is a critical illumination time during which the absorbed UV photons generate the oxidizing species on the particle surface. These species react further to oxidize the organic material in the water. This latter step can take place in the dark. After a critical dark recovery time the particle is illuminated again. Using this light—dark cycling, the photoefficiency for formate decomposition increased by 500% when the illumination time was 72 ms and the dark recovery time was 1.45 s.

Journal ArticleDOI
R.S. Davidson1
TL;DR: In this paper, the development of photoinitiators for curing pigmented films, including those that respond to visible radiation (e.g. from CW lasers), water compatible and cationic photo-initiator, are reviewed.
Abstract: Developments since 1987, of photoinitiators for curing pigmented films, photoinitiators which respond to visible radiation ( e.g. from CW lasers), water compatible and cationic photoinitiators are reviewed. Mechanistic aspects of these reactions are discussed. Some new types of photoinitiators which have been introduced e.g. anionic photoinitiators, bifunctional photoinitiators and those containing peresters are also described.

Journal ArticleDOI
TL;DR: In this paper, the photocatalytic transformation of 4-hydroxybenzylalcohol (HBA) on ZnO or TiO2 leads to a mixture of three photoproducts: 4hydroxy benzaldehyde (HBZ), 3,4-dihydroxy benzyl alcohol (DHBA), and hydroquinone (HQ).
Abstract: The photocatalytic transformation of 4-hydroxybenzylalcohol (HBA) on ZnO or TiO2 leads to a mixture of three photoproducts: 4-hydroxybenzaldehyde (HBZ), 3,4-dihydroxybenzylalcohol (DHBA) and hydroquinone (HQ). In the presence of isopropanol (iPrOH), used as OH quencher, the formation of DHBA is completely inhibited and the formation of HBZ is partly reduced. The product least affected by iPrOH is HQ. However, the oxidation of HBA by OH, produced in the Fenton reaction, leads to HBZ and DHBA, the formation of HQ being almost negligible. These results suggest that positive holes and hydroxyl radicals have different regioselectivities in the photocatalytic transformation of HBA. HQ results from the oxidation by h+, DHBA from the reaction with OH and HBZ is produced by both species.

Journal ArticleDOI
TL;DR: In this article, the results of fluorescence quenching of 2-anthracene sulphonate by cetylpyridinium chloride in ionic and non-ionic micellar environments are presented.
Abstract: The results of the fluorescence quenching of 2-anthracene sulphonate by cetylpyridinium chloride in ionic and non-ionic micellar environments are presented. The static quenching process (lifetime, 4.5 ns) was exploited to estimate the bimolecular quenching rate constants and binding constants between the probe and the quencher from the Stern—Volmer equation, the aggregation number of the surfactant micelles, and the occupancy number of the quencher in the micelle and the binding constant of the quencher with the micelle from the Encinas—Lissi equation. Both ionic and non-ionic micelles, i.e. cetyltrimethylammonium bromide, sodium dodecylsulphate, Triton X-100, Tween-20, Tween-40, Tween-60 and Tween-80, were employed. In the Tween series (Tween-20 to Tween- 80), the micellar aggregation numbers systematically varied. The average occupancy number of the quencher in the micelle and the binding constant of the quencher with the micelle showed a linear correlation with the aggregation number of the micelles.


Journal ArticleDOI
TL;DR: In this paper, the steady state fluorescence emission spectra of various mechanical pulps and celluloses were measured using an excitation wavelength of 320 nm and showed that the peak shapes were influenced by the pulping process, by hydrogen peroxide bleaching and by monochromatic UV irradiation of the sheets.
Abstract: Corrected steady-state fluorescence emission spectra of various mechanical pulps and celluloses were measured using an excitation wavelength of 320 nm. Regardless of its source, cellulose displayed a relatively high characteristic emission. The emission spectra of mechanical pulps were red-shifted with respect to that of cellulose, and peak shapes were influenced by the pulping process, by hydrogen peroxide bleaching and by monochromatic UV irradiation of the sheets. Changes in emission spectra owing to bleaching or UV irradiation occurred principally in the 370–440 nm and 500–550 nm regions, and were similar to changes in reflectance spectra reported in the literature. This suggests that, to a first approximation, emission spectra of mechanical pulps may be interpreted as a decrease in emission of cellulose caused by light absorption by lignin; changes due to bleaching and irradiation may be attributed to changes in lignin absorption.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the quantum yields of photocatalyzed oxidation of I − and of propanal were measured under monochromatic 313 nm irradiation and found that the observed transient signal may arise from a photogenerated hole that undergoes thermalization and surface-trapping with a lifetime of approximately 1 ns.
Abstract: Optically transparent suspensions of (Degussa P25) titanium dioxide which mimic well the photochemical and photophysical properties of the bulk material were prepared by sequential centrifugation. Quantum yields of photocatalyzed oxidation of I − and of propanal were measured under monochromatic 313 nm irradiation and found to be very similar to those estimated for concentrated P25 slurries but higher than those measured in colloidal TiO 2 solutions. A unit limiting quantum yield for propanal photooxidation suggests very efficient utilization of photogenerated holes. Time-resolved absorption spectra were measured in the 50 ps-10 ns time interval following excitation by a 30 ps, 355 nm laser pulse and found to be definitely different from picosecond spectra observed earlier for TiO 2 colloids. It is proposed that the observed transient signal may arise from a photogenerated hole that undergoes thermalization and surface-trapping with a lifetime of approximately 1 ns.

Journal ArticleDOI
TL;DR: In this paper, the visible spectra of safranine T in micellar solutions indicate 1:1 (dye to micelle) charge transfer complex formation with the non-ionic surfactants Triton X 100 (TX 100), Tween 20, Tween 40 and Tween 60.
Abstract: The visible spectra of safranine T in micellar solutions indicate 1:1 (dye to micelle) charge transfer complex formation with the non-ionic surfactants Triton X 100 (TX 100), Tween 20, Tween 40, Tween 60 and Tween 80 as well as with the anionic surfactant sodium dodecyl sulphate (SDS). The non-ionic surfactant micelles show stronger interaction than the ionic micelle SDS, the complexing strengths of the non-ionic micelles following the order Tween 80>Tween 60>TX 100>Tween 40>Tween 20. The fluorescence spectrum of the dye is also affected (intensified) by the surfactant micelles. The results confirm a 1:1 complex and comparable complexing strengths (except the position of TX 100) as revealed by the ground state spectra. Thermodynamic analysis shows that the increased stability of the dye—micelle complex is associated with a systematic increase in exothermic enthalpy and decrease in entropy which compensate each other. The equilibrium constants of the dye—micelle complex are directly proportional to the carbon numbers of the Tweens and inversely proportional to the critical micelle concentration (CMC) of the surfactants.

Journal ArticleDOI
TL;DR: In this paper, the photocatalytic oxidation of cyanide by TiO 2 (anatase and rutile), ZnS, ZnO, CdS, V 2 O 5, SiO 2 and Fe 2 O 3 was investigated and compared with the photo-oxidation in the absence of catalyst.
Abstract: The photocatalytic oxidation of cyanide by TiO 2 (anatase and rutile), ZnS, ZnO, CdS, V 2 O 5 , SiO 2 and Fe 2 O 3 was investigated and compared with the photo-oxidation in the absence of catalyst. Only TiO 2 and ZnO are satisfactory catalysts. Cyanide is first oxidized to cyanate and then via nitrite to nitrate. In most systems cyanide is also volatilized as HCN. The amount of HCN volatilized is a function of the pH of the solution and the surface area of the catalyst and generally increases with decreasing pH and increasing surface area.