Showing papers in "Journal of Photochemistry and Photobiology A-chemistry in 2000"

Quantum yields of active oxidative species formed on TiO2 photocatalyst

Abstract: The quantum yield of hydroxyl radical (⋅OH) production during TiO2 photocatalysis was estimated to be 7×10−5 in aqueous solution by means of a method using terephthalic acid as a fluorescence probe. This value is much lower than the quantum yield of ordinary photocatalytic reactions (∼10−2). Conversely, the quantum yield of hole generation estimated by iodide ion oxidation was equivalent (5.7×10−2) to that of ordinary photocatalytic reactions. This implies that oxidative reactions on TiO2 photocatalyst occur mainly via photogenerated holes, not via ⋅OH.

Bactericidal mode of titanium dioxide photocatalysis

Abstract: When exposed to near-UV light, titanium dioxide (TiO 2 ) exhibits a strong bactericidal activity. However, the killing mechanism(s) underlying the TiO 2 photocatalytic reaction is not yet well understood. The aim of the present study is to investigate the cellular damage sites and their contribution to cell death. A sensitive approach using o -nitrophenol β- d– galactopyranosideside (ONPG) as the probe and Escherichia coli as model cells has been developed. This approach is used to illustrate damages to both the cell envelope and intracellular components caused by TiO 2 photocatalytic reaction. Treatment of E. coli with TiO 2 and near-UV light resulted in an immediate increase in permeability to small molecules such as ONPG, and the leakage of large molecules such as β- d– galactosidase after 20 min. Kinetic data showed that cell wall damage took place in less than 20 min, followed by a progressive damage of cytoplasmic membrane and intracellular components. The results from the ONPG assay correlated well with the loss of cell viability. Cell wall damage followed by cytoplasmic membrane damage leading to a direct intracellular attack has therefore been proposed as the sequence of events when microorganisms undergo TiO 2 photocatalytic attack. It has been found that smaller TiO 2 particles cause quicker intracellular damage. Evidence has been obtained that indicated that the TiO 2 photocatalytic reaction results in continued bactericidal activity after the UV illumination terminates.

Photodegradation of the aminoazobenzene acid orange 52 by three advanced oxidation processes: UV/H2O2, UV/TiO2 and VIS/TiO2: Comparative mechanistic and kinetic investigations

Abstract: This paper presents the results obtained from the oxidation of the aminoazobenzene dye AO52 by the UV/H2O2, UV/TiO2 and VIS/TiO2 systems. In the former case, we investigated the formation of first by-products by means of GC/MS, HPLC and 1H NMR. spectroscopy. We conclude that hydroxyl radicals are added to aromatic rings in the ipso position with respect to the sulfonate group or to the azo-linkage-bearing carbon. The reaction of the inorganic radical with the N,N-dimethylamino substituent, leading to demethylation, adds to the multiplicity of the possible pathways. Degradation by the UV/TiO2 system is pH dependent. Whereas hydroxyl radicals are the main oxidative agent in neutral and alkaline solutions, positive hole-induced oxidation competes with the reduction of the protonated dye molecules in acid media. Moreover, FTIR spectroscopy of AO52/TiO2 wafers provided an insight to the nature of the photoproducts. This process is very efficient since only ultimate breakdown products, i.e. aliphatic acids and inorganic salts, are detected. Similar results were obtained using visible light as the irradiation source in the case of wafers whereas in heterogeneous solutions, the dye seems to be resistant to degradation.

Time-resolved photoluminescence of particulate TiO2 photocatalysts suspended in aqueous solutions

Abstract: TiO2 powders showed a broad emission band. The peak position of the emission band for rutile powders was about 450 nm, and that of anatase powders was about 500 nm. The time-resolved photoluminescence of TiO2 powder was investigated with 30 ps laser pulses at 355 and 266 nm. Decay profiles of emission were successfully traced by the extended exponential equation. In the case of rutile powders, the lifetime of the emission lengthened in the relation to the increase of particle size. Their lifetime was also dependent on the wavelength of excitation; i.e., it was longer at 355 nm of excitation than at 266 nm. Based on these results, the decay profiles of rutile particles were concluded to be determined by the migration of carriers from the bulk of the particles to the surface. In contrast, the decay profiles of the emission of small anatase particles were considered to be determined chiefly by the recombination process at the surface. The effects of Fe(III) ions and 2-propanol on the respective decay profiles of the emission from rutile and anatase powders are also discussed.

Steady hydrogen evolution from water on Eosin Y-fixed TiO2 photocatalyst using a silane-coupling reagent under visible light irradiation

Abstract: A chemical fixation of xanthene dyes on platinized TiO 2 particles via silane-coupling reagent was attempted in order to construct a stable dye-sensitized photocatalyst system in water. The Eosin Y fixed Pt-TiO 2 (E.Y-TiO 2 ) exhibited steady H 2 production from aqueous triethanolamine solution (TEOA aq.) under visible light irradiation for long time, and the H 2 evolution reproduced even after the exchange of TEOA aq., while the H 2 evolution from the mixture of Eosin Y (E.Y) and Pt-TiO 2 ceased in 10 h. The turnover number of the dye molecule fixed on TiO 2 surface reached more than 10,000, and the quantum yield of the E.Y-TiO 2 at 520 nm was determined to be about 10%.

Ferrocene and ferrocenyl derivatives in luminescent systems

Abstract: Owing to their fairly high stability under visible irradiation, ferrocene and ferrocenyl derivatives are widely used in luminescent systems. They are classical quenchers of excited states. Both energy and electron transfer may be involved, depending on the nature of the excited species. Inter- or intramolecular quenching are encountered. Applications span from the study of reaction mechanisms to that of organized or biological media. Recently, dyads and polyads designed for their ability to mimic photosynthetic centers or for their photodiode properties have also been obtained. Finally, the incorporation of a ferrocenyl derivative in a luminescent system does not necessarily lead to luminescence quenching. New applications are emerging, in which advantage is taken of the presence of ferrocene acting as a redox center: this gives optically and electrochemically active sensors. The present review encompasses the literature up to November 1999.

Photocatalytic mineralisation of methylene blue using buoyant TiO2-coated polystyrene beads

Abstract: The photocatalysed mineralisation of methylene blue has been carried out using TiO2 coated onto naturally buoyant polystyrene beads. Titanium dioxide is coated onto polystyrene using a thermal treatment procedure. The coated beads show high mechanical stability as well as impressive photocatalytic activity. Thermogravimetric analysis of the beads, post-treatment, indicates that there is no destructive degradation of the Polystyrene support by the photocatalytic process. The catalyst activity remains appreciably high for up to 10 successive runs. For the buoyant particles, suspension is only possible for situations where pulsatile mixing is applied. Reaction rates in this system are found to increase with increase both in the catalyst loading and the pulsing conditions.

Factors affecting the efficiency of a photocatalyzed process in aqueous metal-oxide dispersions: Prospect of distinguishing between two kinetic models

Abstract: The photooxidative degradation of phenol in aqueous TiO2 dispersions has been revisited to determine the dependencies of the rate on the concentration of phenol and on the photon flow (ρ) of the actinic light at 365 nm. The principal objective was to assess the factors that influence the efficiency of the photocatalytic process, the rate of which is described by the function d C d t (ρ,C)=( const )C n ρ m where n and m are orders of the reaction with respect to concentration and photon flow (light intensity), respectively. The reaction order m varies with reagent concentration C, whereas the order n depends on photon flow ρ. The description indicates that m→1 if n→0, whereas n→1 if m→0. Therefore, the reaction orders m and n of phenol photodegradation are interdependent. A detailed kinetic description of the process is given based on two well-known mechanistic/kinetic models, namely (i) the Langmuir–Hinshelwood (LH) model whereby the organic reagent is pre-adsorbed on the photocatalyst surface prior to UV illumination, and (ii) the Eley–Rideal (ER) model for which the organic reagent diffuses from the solution bulk onto the photocatalyst surface to interact with the activated state of the photocatalyst. The kinetic treatment infers that it is possible (under certain conditions) to delineate between the LH and ER mechanistic models on the basis of the magnitude of the Langmuir constant KL at very high photon flow, i.e. when ρ→∞ {for the LH pathway, KL→K; for the ER model KL→0}, and on the dependence of kobs of the process on ρ. For the ER model, kobs scales linearly with ρ at high photon flow, whereas for the LH pathway kobs displays a sub-linear dependence on ρ and tends toward saturation at high photon flow.

TiO2-mediated photodegradation of liquid and solid organic compounds

Abstract: The photocatalytic degradation of several liquid and solid organic compounds, including polymers, with molecular weights covering a wide range from 600 to 500,000 was studied on TiO2 thin films on glass under UV illumination. Nearly exact agreement was found between the weight losses of the solid compounds octadecane and stearic acid and the weights of CO2 produced during photocatalytic degradation. No other gas-phase degradation product was detected for these two compounds other than CO2, which means that potentially harmful products are not expected to pose a problem. For convenient comparison of degradation rates for various compounds and measurement methods, the values were converted to numbers of moles of carbon reacted per square centimeter per hour. Under appropriate conditions (50C, relative humidity 10% in air), octadecane was completely decomposed (<400 ng cm 2 ). In contrast, stearic acid did not decompose completely, even after more than 80 h of UV illumination. This may be due to the formation of a photocatalytically inert reaction product that blocks the TiO2 surface. The decomposition rates for all of the compounds examined spanned less than two orders of magnitude, suggesting that the photocatalytic reactions involved are rather versatile. © 2000 Published by Elsevier Science B.V.

Kinetics of photocatalytic degradation of aniline in water over TiO2 supported on porous nickel

Abstract: The photocatalytic degradation of aniline was studied in annular photoreactor, with 2×6 W (Emax=365 nm) UV lamp as light source, borosilicate glass as wave filter and titanium dioxide immobilized on porous nickel as catalysts. Parameters such as the initial concentration, flow rate, initial pH, dissolved oxygen, electrolyte, hydrogen peroxide addition, temperature and external potential bias affecting the degradation rate of aniline were studied. The results showed that photocatalysis is an effective process for the degradation of aniline. The activated energy for the photocatalytic degradation of aniline is 6.13 kJ mol−1. The initial quantum yield is 1.89% for aniline 1.10×10−4 mol l−1. Total mineralization requires a much longer illumination time than the disappearance of anilines. The external potential bias can largely improve the efficiency of photocatalytic degradation of aniline. The degradation kinetic of aniline can be described by Langmuir–Hinshelwood equation.

Variation of Langmuir adsorption constant determined for TiO2-photocatalyzed degradation of acetophenone under different light intensity

Abstract: The Langmuir–Hinshelwood (L–H) kinetic model has been used to describe semiconductor photocatalysis. In this report, the L–H rate constant (kL–H)and the Langmuir adsorption constant (K) have been determined under different light intensity for the photocatalytic degradation of poorly adsorbed acetophenone over TiO2 of Degussa P25 in aqueous medium (pH 6.2). The result shows that K decreases when the irradiation is performed at higher light intensity, while kL–H increases expectedly. It is also demonstrated that the initial time interval selected for the initial rate calculation is quite critical to the final determination for the constants.

Solar cells based on dyes

Abstract: From early developments to recently developed stages of solar cells have been discussed in details, considering the effect of different parameters. In this paper, primitive photoelectrochemical (PEC) cell and PEC cell with Fe–thionine and different dyes-reducing agent have been reviewed. Solar cell with phenazine dyes have also been pointed out separately since these dyes give more output in solar cell. The use of inorganic semiconductor electrode (e.g. SnO2, In2O3 and ZnO) and utilization of semiconducting properties of organic dyes in PEC cell have been mentioned. Furthermore, utilization of surfactant media for storage of solar energy and production of hydrogen from solar cell using dye are also included.

Photocatalytic decomposition of NO by TiO2 particles

Abstract: The effects of initial NO concentration, gas-residence time, reaction temperature and ultraviolet (UV) light intensity on the photocatalytic decomposition of NO have been determined in an annular flow-type and a modified two-dimensional fluidized-bed photoreactors. The decomposition of NO by photocatalysis increases with decreasing initial NO concentration and increasing gas-residence time. The reaction rate increases with increasing UV light intensity. The light transmission increases exponentially with the bed voidage at superficial gas velocity above 1.3 times the minimum fluidizing velocity ( U mf ) in the two-dimensional fluidized-bed photoreactor. In the two-dimensional fluidized-bed photoreactor, NO decomposition reaches >70% at the gas velocity of 2.5 U mf . A two-dimensional fluidized-bed photoreactor is an effective tool for high NO decomposition with efficient utilization of photon energy.

Photoassisted degradation of dyes in the presence of Fe3+ and H2O2 under visible irradiation

Abstract: The homogeneous photocatalytic degradation of cationic acridine orange monohydrochloride (AO) and anionic alizarin violet 3B (AV) in photo-Fenton system under visible irradiation was studied. The generated intermediates and degradation processes of AO were investigated by EPR, IR and GS–MS. It was found that visible irradiation not only enhances apparently the generation of hydroxyl radicals but also accelerates effectively the degradation of the dyes in the presence of Fe3+ and H2O2. N,N-dimethyl formaldehyde and N,N-dimethyl acetamide were found during the degradation of AO. Ammonium ions were also formed during the degradation of AO through the ion-selective electrode analysis.

Photocatalytic oxidation of nitrogen monoxide over titanium(IV) oxide nanocrystals large size areas

Abstract: The titania prepared by high-temperature hydrolysis of titanium alkoxides in a hydrocarbon solvent is highly active for the photocatalytic oxidation of NO to NO 2 and NO 3 . The photocatalytic oxidation activity decreases with an increase in post-calcination temperature of the titania. The surface area and crystal size of the titania make some contributions to the photocatalytic oxidation activity. IR spectra show that ultraviolet (UV) irradiation of the titania promotes the formation of nitrate species. The data of ESR and IR lead to the conclusions that NO, when irradiating the titania with UV rays, reacts with O 2 − to form NO 2 and NO 3 − , but the radicals generated as a result of secondary products of O − make no contribution to the photocatalytic oxidation. In addition, the concentration of free electron and O 2 − decreases significantly with an increase in post-calcination temperature of the titania.

Post-irradiation effect and reductive dechlorination of chlorophenols at oxygen-free TiO2/water interfaces in the presence of prominent hole scavengers

Abstract: Heterogeneous photocatalysis with TiO2 nanoparticles for the detoxification of waste-waters and other media is typically achieved by oxidative pathways involving ultimately photogenerated surface-trapped holes (i.e. surface-bound OH radicals). However, reductive pathways may coexist. The degradation of 2,4-dichlorophenol (2,4-DCP) and pentachlorophenol (PCP) was examined in irradiated O2-free aqueous media in the presence of prominent hole scavengers such as polyethyleneimine (PEI), triethylamine (TEA), 2-propanol (IPA) and ethylenediaminetetraacetic acid (in the EDTA 4 state) to assess the role of photogenerated electrons. The presence of these scavengers imparts a blue-violet color to the nanoparticles corresponding to a broad absorption band in the 400‐850 nm region. A post-irradiation effect was observed when irradiation was terminated, which we ascribe to an electron transfer from radical species formed by hole scavenging to the TiO2 particles (reminiscent of the doubling current phenomena in semiconductor electrodes). The two chlorophenols degraded in oxygen-free media, a process inhibited by PEI, TEA and IPA. In the presence of EDTA, degradation of 2,4-dichorophenol occurred by dechlorination only after a 120-min induction period, a process attributed to the accumulated electrons on the particle surface. HPLC analyses revealed that the intermediate products were not those expected from typical oxidative pathways in aerated aqueous media. The degradative process is inferred to take place first by electron attachment to the halophenol to yield phenoxy related radicals and then by secondary reactions with water and/or with each other. © 2000 Elsevier Science S.A. All rights reserved.

TiO2 photocatalytic oxidation of monochloroacetic acid and pyridine: influence of ozone

Abstract: The influence of ozone on the photocatalytic oxidation of monochloroacetic acid and pyridine with TiO 2 (0.5 g/l) at pH 3 (H 2 SO 4 ) was investigated. Illumination was performed in a batch reactor (400 ml), with UV-lamp (360–420 nm; 7×10 −6 Einstein s −1 ) with continuous introduction of oxygen or ozone containing oxygen. The photocatalytic ozonation of monochloroacetic acid and pyridine which does not react with ozone alone under given conditions leads to 6 and 24 times higher degradation rates than without TiO 2 and 4 and 18 times higher rates than without ozone. Moreover the photocatalytic ozonation shows the lowest specific energy consumption (kW h/g DOC-reduction) of the different processes under the experimental conditions.

The photostabilities of naturally occurring 5-hydroxyflavones, flavonols, their glycosides and their aluminium complexes

Abstract: The photostabilities of luteolin, in solution, in the presence of aluminium ions, and deposited on a cellulosic substrate have been determined and compared with those of quercetin and other 5-hydroxyflavonols and their 3-O-glycosides. In aqueous methanol solution, luteolin and flavonol 3-glycosides exhibited no degradation over periods of up to 15 h of UV irradiation. However, the flavonols studied were all found to degrade and their relative photostabilities correlate with their redox potentials. Quercetin was the least stable. In the presence of aluminium ions, all the flavonoids, including luteolin, were degraded by UV irradiation. In contrast to the absorption spectra in dilute solution, the reflectance spectra of both quercetin and luteolin deposited on a cellulosic substrate exhibited strong absorptions beyond 400 nm. On this substrate these flavonoids displayed the characteristic yellow colour associated with flavonoids in some environments. Although the quercetin yellow faded rapidly on exposure to UV radiation, the colour of luteolin darkened. This was due to the formation of a photoproduct absorbing maximally at 450 nm. The relevance of these observations to cellulosic dyeing and flower colouration are discussed.

Sensitization of TiO2 particles by dyes to achieve H2 evolution by visible light

Abstract: Sensitization of titanium dioxide particles platinized and suspended in water was carried out by Ru(bpy) 3 2+ , tris(bipirimidine)Ru(II) (Ru(bpym) 3 ) and porphines to induce dihydrogen evolution by visible light in the presence of sacrificial electron donor, EDTA. It was found that Ru(bpym) 3 2+ is an efficient sensitizer for H 2 formation. High concentration of the Ru(bpy) 3 2+ was required to achieve the photosensitization suggesting adsorption of the sensitizer on the TiO 2 . Photochemical deposition of platinum from K 2 [PtCl 4 ] was important to prepare active Pt-loaded TiO 2 photocatalyst. Simple mixing of the TiO 2 and Pt powders in a mortar as usually done for preparing conventional photocatalyst was not effective for the present system showing that electronic channeling between the TiO 2 bulk and the Pt is more important than for usual photocatalysts. The H 2 evolution showed an optimum point at pH 7, which was interpreted by the adsorption of the dye on TiO 2 . For the tetrakis(4-carboxyphenyl)porphine and tetrakis(4-sulfonicphenyl)porphine sensitizers, only the absorption of light at Q band was effective.

Photocurrent generated on a carotenoid-sensitized TiO2 nanocrystalline mesoporous electrode

Abstract: Photocurrent was observed upon monochromatic illumination of an ITO electrode coated with a TiO2 nanocrystalline mesoporous membrane with carotenoid 8 0 -apo-b-caroten-8 0 -oic acid (ACOA) deposited as a sensitizer (illuminated area 0.25 cm 2 ) and immersed in an aqueous 10 mM hydroquinone (H2Q), 0.1 M NaH2PO4 solution (pH = 7.4) purged with argon, using a platinum flag counter electrode (area 3.3 cm 2 ) and a SCE reference electrode. The carotenoid-sensitized short-circuit photocurrent reached 4.6 mA/cm 2 upon a 40mW/cm 2 incident light beam at 426 nm, with an IPCE (%, incident monochromatic photon-to-photocurrent conversion efficiency) as high as 34%. The short-circuit photocurrent was stable during 1 h of continuous illumination with only a 10% decrease. An open-circuit voltage of 0.15 V was obtained (upon 426 nm, 40mW/cm 2 illumination) which remained at a constant value for hours. The observed open-circuit voltage is close to the theoretical value (0.22 V) expected in such a system. The action spectrum resembled the absorption spectrum of ACOA bound on the TiO2 membrane with a maximum near 426 nm. No decay of the ACOA on the TiO 2 surface was observed after 12 h, presumably because of rapid regeneration of ACOA from ACOA C at the surface by electron transfer from H2Q. ©2000 Elsevier Science

A study of the photocatalytic oxidation of formaldehyde on Pt/Fe2O3/TiO2☆

Abstract: Preparation of TiO2 photocatalysts loaded with noble metal or transition-metal oxide and the influences of preparing procedures on the photocatalytic activity for degradation of formaldehyde are reported The products and intermediates in the photocatalytic oxidation of formaldehyde were detected, and a reasonable mechanism of reaction was suggested

Excited-state intramolecular proton transfer (ESIPT) in 2-(2′-hydroxyphenyl)-oxazole and -thiazole

Abstract: The azoles 2-(2 0 -hydroxyphenyl)oxazole (HPO) and 2-(2 0 -hydroxyphenyl)-4-methylthiazole (HPT) have been synthesised and studied in order to compare their photophysical characteristics. Their absorption and emission properties are reported in non-polar, alcoholic and aqueous media. Ground and excited state pK data were determined by spectroscopy and a model is proposed to explain the behaviour of HPT and HPO as a function of the pH. Excitation spectra and quantum chemical calculations suggest an equilibrium of ground state conformers. The calculations also predict a small energy barrier for rotation in the first excited singlet state for the proton transferred tautomers. The resulting twisted structure of the tautomer form possesses a biradicaloid nature, and is near-degenerate in energy with the first excited triplet state. ©2000 Elsevier Science S.A. All rights reserved.

Photocatalytic degradation of lindane, p,p′-DDT and methoxychlor in an aqueous environment

Abstract: Aqueous solutions containing 40 mg/dm3 of lindane, p,p′-DDT and methoxychlor were photodegraded in a UV/TiO2/O2 system yielding different degradation products. Powdered anatase and rutile, and anatase supported on glass hollow microspheres served as photocatalysts. The destruction degree of pesticides was evaluated and oxidation products identified by gas chromatography with an electron capture detector (GC–ECD) and a mass spectroscopy detector (GC–MS). From 68 to 90% of pesticides investigated was eliminated after 30 min irradiation in the presence of anatase supported on glass microspheres. The lowest efficiency was obtained for rutile as a catalyst. One hundred and fifty minutes of processing resulted in 50% elimination for γ-HCH, 85% for DDT and over 99% for methoxychlor.

Study of the photolysis of folic acid and 6-formylpterin in acid aqueous solutions

Abstract: Folic acid and 6-formylpterin solutions of pH in the range 4.5–6.0 were photolysed at 350 nm at room temperature. The photochemical reactions were followed by UV–VIS spectrophotometry, thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). In the presence of oxygen, folic acid is photochemically cleavaged yielding 6-formylpterin and p-aminobenzoylglutamic acid. As the photolysis proceeds, 6-carboxypterin arises from 6-formylpterin, as observed when solutions only containing the latter compound are irradiated in the presence of oxygen. In the absence of oxygen, folic acid is not light-sensitive. However, when oxygen free solutions of 6-formylpterin are irradiated, a ‘red intermediate’ is observed, which is thermally oxidised producing 6-carboxypterin on admission of oxygen. The quantum yields of substrates disappearance and of photoproducts formation are reported.

VOC photodegradation at the gas–solid interface of a TiO2 photocatalyst

Abstract: The gas–solid heterogeneous photocatalytic oxidation of 1-butanol and 1-butylamine in air was investigated using supported TiO2 as a catalyst. The supported catalyst was prepared using a sol–gel method and irradiated employing two different light sources, a medium pressure mercury lamp or a xenon-chloride excimer lamp. The experimental set-up was especially designed for generating a gas stream containing stable and defined concentrations of the model pollutants. The gas stream at the reactor exit was analyzed on line by gas chromatography and the structures of the intermediates were established by gas chromatography coupled with mass spectrometry. Six major intermediates (butanal, butanoic acid, 1-propanol, propanal, ethanol and ethanal) were identified in the case of the photocatalytic degradation of 1-butanol. 1-Butylamine was less efficiently adsorbed on the catalyst and its degradation was slower. Three intermediates could be identified in this case (N-butylidene-1-butylamine, N-ethylidene-1-butylamine and N–butylformamide). Based on these results, a degradation mechanism is proposed for both compounds. Mineralization could be achieved under various conditions of concentrations and flow rates and was confirmed by infrared spectroscopy.

Photolysis of polycyclic aromatic hydrocarbons (PAHs) in dilute aqueous solutions detected by fluorescence

Abstract: Photodegradation kinetics of anthracene, pyrene, benz[ a ]anthracene and dibenz[ a,h ]anthracene were studied in aqueous solutions at pH 5.6 and 7.6 with purging gases of nitrogen, oxygen or synthetic air. Photolysis of PAHs was performed in an immersion well reactor at 254 nm and was followed as decreasing fluorescence intensities. Photodegradation of PAHs was fast in all cases with anthracene and benz[ a ]anthracene being the fastest decomposed. The photochemical reactions followed a first order equation, and the apparent rate constants, k r , varied from 10 −3 to 10 −4 s −1 . Oxygen concentration had minor effect upon the photodegradation rates of PAHs. At pH 5.6 the values of the rate constants were higher than those at pH 7.6, anthracene was an only exception of this. Based on photodegradation kinetics and fluorescence lifetime measurements, a simple scheme for a mechanism is proposed containing non-emissing excited intermediate species in equilibrium with the excited singlet state.

TiO2-coated optical fiber bundles used as a photocatalytic filter for decomposition of gaseous organic compounds

Abstract: An optical fiber-based, filter-type photocatalytic reactor was designed and the decomposition reaction of gas phase isopropanol was studied using a recirculating reaction system. Compared to the conventional TiO 2 -coated glass plate or honeycomb monolith, both higher efficiency of light utility and larger processing capacity were obtained. This good combination was achieved by employing both high input light intensities (1.6×10 16 to 2.6×10 17 quanta cm −2 s −1 ) and a large number of glass fibers (18 000 pieces, 125 μm diameter) in the reactor, which makes it possible for the reaction to occur with a high reaction rates while maintaining a high quantum efficiency. These characteristics can be understood by considering a TiO 2 -coated single fiber as a micro-reactor distributed with low photon flux, and the corresponding fiber bundles being composed of large number of such micro-reactors.

Substituent effects on intramolecular charge-transfer behaviour of styrylheterocycles

Abstract: To understand the influence of substituents on intramolecular charge transfer (ICT), absorption and emission spectra were measured for several derivatives of 2-styrylquinoline (2-StQ), 2-styrylpyridine (2-StP) and 2-styrylthiophene (2-StT) systems. A strong donor, such as an N,N-dimethylamino group can produce an ICT compound in these systems, and the excited state dipole moments were measured using a solvatochromic method. Quinoline and pyridine can only act as acceptors. Depending on substituents, the thiophene ring could be a donor or an acceptor. For same donor in our systems, the strength order of different acceptors is quinoline>naphthalene>pyridine>thiophene. Besides electronic effect, steric conformation is also an important factor in ICT molecules. Protonation and hydrogen bonding at acceptor site show red-shift in absorption maxima. The degree of shift depends on the substituents. Interaction at a donor site gives the opposite result. There is a linear relation between excited state dipole moments and absorption energy.

Photochemical and photocatalytic reduction of nitrobenzene in the presence of cyclohexene

Abstract: Irradiation with light of wavelength higher than 350 nm of deaerated mixtures of nitrobenzene and cyclohexene leads to the reduction of the nitro-compound, with the formation of C 6 H 5 N(O)NC 6 H 5 (32%), C 6 H 5 NNC 6 H 5 (21%), C 6 H 5 NH 2 (15%), C 6 H 5 N(H)C 6 H 9 (32%). The same stable reduction products are obtained when the photochemical experiments are carried out in the presence of powder dispersions of TiO 2 or WO 3 or CdS. On the other hand, the photocatalytic contribution of these semiconductors plays an important role in the relative product distribution, which is observed to depend on both competitive adsorption–desorption equilibria of the involved reagents and intermediates on the solid surface and the different reducing power of the photoexcited semiconductors. Cyclohexene participates in the photoinduced reduction of nitrobenzene, undergoing oxidation, and producing the required electrons and protons. Experimental evidence for the formation of radical species deriving from the oxidation of this alkene is obtained by ESR spin trapping investigation. We report here for the first time, the photoinduced allylic amination of cyclohexene with nitrobenzene to give the important building block of synthetic interest C 6 H 5 N(H)C 6 H 9 .

Supramolecular sensitizer: complexation of meso-tetrakis(4-sulfonatophenyl)porphyrin with 2-hydroxypropyl-cyclodextrins

Abstract: 5, 10, 15, 20-tetraphenyl-21 H, 23 H-porphine tetrasulfonic acid, tetrasodium salt (TPPS4) forms in ground state 1 : 1 supramolecular complexes with 2-hydroxypropyl-cyclodextrins (hp-CD) in aqueous neutral solutions. It was investigated with UV–VIS absorption and fluorescence spectroscopy. The complexing ability of CD’s exhibits marked differences for hp-α-CD, hp-β-CD and hp-γ-CD. The hp-β-CD was found to bind the porphyrin the strongest with K b about two order of magnitude greater when compared to native β-CD. It suggests that the binding site on the porphyrin moiety predominantly interacts with the primary face of the modified CD’s. Complexation of TPPS4 significantly prevents protonation of pyrrole nitrogens, induce deaggregation of J-aggregates and slows down metalation indicating that the porphyrin moiety is shielded from bulk solution. The presence of hp-CD’s considerably prolong the lifetimes of the triplet states of the title porphyrin; simultaneously, the rate constants of quenching of the triplet states by oxygen are decreased. In the presence of hp-β-CD the quantum yields of the triplet states and of singlet oxygen formation remain unchanged. The addition of hp-β-CD prevents staining effect of TPPS4 on the cellular membranes and greatly affects the uptake of TPPS4 by human Caucasian acute lymphoblastic leukemia CCRF-CEM cells. In conclusion, TPPS4 in a supramolecular complex represents an efficient sensitizer, which is due to shielding effect of hp-CD’s (against protonization, aggregation, metalation, or interaction with membrane proteins) much less sensitive towards the influence of its environment.