Showing papers in "Journal of Photochemistry and Photobiology A-chemistry in 1999"
TL;DR: A review of the experimental work on NO2− and NO3− photolysis in the context of recent advances in the understanding of the chemistry of the peroxynitrite anion (ONOO−) in biological experiments is presented in this article.
Abstract: It has long been known that the photolysis of nitrite and nitrate solutions results in the formation of OH radicals. The mechanism of NO3− photolysis has been the subject of considerable controversy in the literature, however. This review summarizes the experimental work on NO2− and NO3− photolysis in the context of recent advances in the understanding of the chemistry of the peroxynitrite anion (ONOO−) in biological experiments. ONOO− has been found to play a far more significant role in the overall reaction mechanism of NO3− photolysis than had previously been suspected. Research on NO2− and NO3− photolysis, as a pathway to the destruction of organic contaminants in natural waters, is summarized. The possible impact of NO2− and NO3− on Advanced Oxidation Technologies (AOTs), in which OH radicals are used to initiate the destruction of hazardous organic pollutants in drinking water and industrial waste streams, is explored.
918 citations
TL;DR: In this paper, the authors deal with doping titania by Cr 3+ and Mo 5+ ions and show the complex interactions between variations in lifetime of charge carriers, adsorption properties and photocatalytic behaviour.
Abstract: Titanium dioxide is one of the most efficient photocatalysts for the detoxification of organically charged waste water. However, this material suffers from the drawback of poor absorption properties because of a band gap of 3.2 eV. Thus, wavelengths shorter than 400 nm are needed for light induced generation of electron–hole pairs. Therefore, doping with transition metal ions is interesting for inducing a batho-chromic shift of the band gap. However, this doping changes other physical properties such as lifetime of electron–hole pairs and adsorption characteristics. This paper deals with doping titania by Cr 3+ and Mo 5+ ions. We want to show the complex interactions between variations in lifetime of charge carriers, adsorption properties and photocatalytic behaviour.
437 citations
TL;DR: In this article, the photobleaching of methylene blue MB, sensitised by TiO2, in an aqueous solution was studied in the absence and presence of oxygen.
Abstract: The photobleaching of methylene blue MB, sensitised by TiO2, in an aqueous solution is studied in the absence and presence of oxygen. In the absence of oxygen and in the presence of a sacrificial electron acceptor (SED), MB is photoreduced to its colourless leuco form, LMB, by the TiO2 photocatalyst. This same photoreduction process is observed even if an SED is not present, indicating that MB itself can act as an SED. The oxidation of LMB by oxygen to regenerate MB is significantly slower if the aqueous solution is acidified (0.01 mol dm−3 HClO4) and, at low partial pressures, the rate of reaction depends directly upon the concentration of dissolved oxygen. The TiO2-sensitised photobleaching of MB is irreversible in an oxygen-saturated aqueous solution, as expected, since the bleaching was due to an oxidative process. However, in an acidified solution (0.01 mol dm−3 HClO4), the photobleaching process, in an oxygen-saturated solution, generates LMB initially. The latter situation arises because, under acidic conditions, LMB reacts only very slowly with oxygen to form MB. The significance of these findings with respect to the popular use of photobleaching of MB as a demonstration of semiconductor photomineralisation is discussed.
383 citations
TL;DR: In this paper, Ru-doped TiO2 particles were prepared and their properties as the photocatalyst were investigated, showing that the oxygen evolution reaction occurred by irradiation of visible light at wavelengths longer than 440nm using iron(III) ions as the electron acceptor.
Abstract: In order to expand the effective wavelength of TiO2 particulate photocatalyst into the visible region, Ru-doped TiO2 particles were prepared and their properties as the photocatalyst were investigated. With this photocatalyst, the oxygen evolution reaction occurred by irradiation of visible light at wavelengths longer than 440 nm using iron(III) ions as the electron acceptor. To clarify the mechanistic aspects of the effect of Ru-doping, photoelectrochemical properties of Ru-doped TiO2 sinter electrodes were investigated.
177 citations
TL;DR: In this paper, the photoactivity of the pure anatase titania was higher than that of Degussa P25 and the anatase/rutile mixed titania prepared from TTIP.
Abstract: Nanophase titania particles were prepared by the sol–gel process using two different precursors; titanium isopropoxide(TTIP) and titanium ethoxide (TEOT). Silica-embedded titania particles was also prepared from TEOT and tera-ethyl-ortho-silicate (TEOS). In the case of nanophase titania particles prepared from TTIP, the rutile/anatase mixed phase had higher photoactivity than the pure anatase in the decomposition of TCE. However, in the nanophase titania prepared from TEOT, the photoactivity was increased with the heat treatment temperature until rutile phase began to be formed. The surface area was decreased with the heat treatment temperature. The photoactivity of the pure anatase titania prepared from TEOT was higher than that of Degussa P25 and the anatase/rutile mixed titania prepared from TTIP. Therefore, we concluded that, in order to achieve high photocatalytic activity, it was important to prepare titania particles at high temperature, preferably without forming rutile phase but not necessarily. This conclusion was confirmed by the experimental result that the silica-embedded titania particle of pure anatase phase had higher photoactivity than that of Degussa P25 and the pure anatase titania prepared from TEOT. The embedding of small amount of silica into anatase titania matrix enhanced the thermal stability of nanophase titaina particle resulting in the suppression of the phase transformation from anatase to rutile phase. This thermal stability enables us to calcine the silica-embedded particles at higher temperature without accompanying the phase transformation and to reduce the bulk defects, which are responsible for the low photocatalytic activity.
172 citations
TL;DR: In this paper, photochromic cyclization reaction efficiency and fluorescence of two dithienylethenes in two solid states, colloidal solutions and amorphous films, were studied.
Abstract: Photochromic cyclization reaction efficiency and fluorescence of two dithienylethenes in two solid states, colloidal solutions and amorphous films, were studied. Colloidal solutions of dithienylethenes were prepared by dilution of concentrated methanol solution into hot water. The diameter of particles of the colloidal solutions was about 1 μm according to observation by a scanning electron microscope. Photochromic cyclization reaction efficiency of colloidal solution of cis-1,2-dicyano-1,2-dithienylethene (1) was as high as that of hexane solution of 1. An amorphous film of 1 also shows high efficiency. On the other hand, neither colloidal solution nor polycrystal of 2,3-bis(2,4,5-trimethyl-3-thienyl)maleic anhydride (2) was photochromic; only an amorphous film of 2 was colored very slightly by UV irradiation. For the dithienylethenes in the solid states, long-wavelength fluorescence which can be assigned to the colored closed-ring form was observed, while deeply colored hexane solution did not give any long-wavelength fluorescence. Fluorescence spectra and fluorescence decay curves indicated the existence of efficient energy transfer from the open-ring form to the closed-ring form of dithienylethenes in the solid states.
169 citations
TL;DR: In this paper, the photoproduction of oxygen and hydrogen from an aqueous suspension containing WO 3, Fe 2+, and Fe 3+ species was studied and a comparison of product yields made between the inner and outer-irradiation systems.
Abstract: The photoproduction of oxygen and hydrogen from an aqueous suspension containing WO 3 , Fe 2+ , and Fe 3+ species was studied and a comparison of product yields made between the inner- and outer-irradiation systems. Prolonged irradiation of the WO 3 –H 2 O–Fe 2+ /Fe 3+ system led to the generation of O 2 and H 2 , and the yields could be sustained for a period of several days. The product yields showed a dependence on the duration of irradiation, illumination wavelength, WO 3 concentration, concentration of Fe 3+ and Fe 2+ cations, type of iron (III) salt, and pH. The optimum photoproduction for O 2 and H 2 was obtained under the following operating conditions: [WO 3 ]: 8 g dm −3 , [Fe 3+ ]: 14–20 mol dm −3 , pH 1.5–2.5, and illumination wavelength: 200–500 nm. The illumination time needed to reach the stationary state was ca. 6 and 30 h for the inner- and outer-irradiation systems, respectively. In addition to these conditions, a ratio of [Fe 2+ ] : [Fe 3+ ] = 2–4 was found to be suitable for the simultaneous production of O 2 and H 2 . The product yields from the annular photoreactor were usually about four times more than those from an outer-irradiation photoreactor. When Fe 2 (SO 4 ) 3 was replaced by Fe(NO 3 ) 3 or FeCl 3 as a source of Fe 3+ species, higher initial O 2 evolution rates were obtained but the long term yields were lower than those from dispersions containing Fe 2 (SO 4 ) 3 . The studied system utilized WO 3 to accomplish the initial light absorption, charge separation and O 2 evolution in the presence of Fe 2+ aq species as an electron acceptor, and then relied on the Fe 2+ aq photochemical process to produce hydrogen. The overall reaction was photodecomposition of water into O 2 and H 2 . Mechanistic implications were considered to account for the probable reaction steps leading to the products observed and the dependence of the yields on the examined reaction parameters.
151 citations
TL;DR: In this article, the photocatalytic efficiency of pure and 0.5 −20 wt.% Fe-containing ZrO 2 samples, prepared by a solgel technique, was tested in the transformation of environmentally important substrates, such as nitrite, EDTA and Cr(VI) and compared with that of TiO2 (Degussa P-25).
Abstract: The photocatalytic efficiency of pure and 0.5‐20 wt.% Fe-containing ZrO 2 samples, prepared by a sol‐gel technique, was tested in the transformation of environmentally important substrates, such as nitrite, EDTA and Cr(VI) and compared with that of TiO2 (Degussa P-25). All samples were active, although the efficiency was lower than that of TiO 2. Nevertheless, the presence of iron increased the activity for nitrite photooxidation, with the maximum efficiency at 5 wt.% Fe content. At higher Fe content, the efficiency decreased but it was always higher than that of the undoped sample. For EDTA oxidation and Cr(VI) reduction, the same trend was observed. Remarkably, Cr(VI) reduction in the presence of EDTA was strongly accelerated, all zirconia samples being as active as P-25, although initial rates were lower and somewhat detrimentally affected by the presence of iron. The photocatalytic activity depends on the structural, surface and optical properties of the sample, on the preparation conditions and on the nature of the photocatalytic reaction. ©1999 Elsevier Science S.A. All rights reserved.
151 citations
TL;DR: In this article, the photo-assisted catalytic degradation of ethylene was studied in the tubular photoreactor packed with TiO2 pellets prepared by sol-gel method, and the dependence of the reaction rate on the light intensity, feed composition (ethylene, oxygen and water vapor) and temperature were investigated.
Abstract: The photo-assisted catalytic degradation of ethylene was studied in the tubular photoreactor packed with TiO2 pellets prepared by sol–gel method. The dependence of the reaction rate on the light intensity, feed composition (ethylene, oxygen and water vapor) and temperature were investigated. More than 95% ethylene was always completely mineralized irrespective of the reaction conditions. The reaction rate for ethylene conversion was greatly suppressed when the water vapor mole fraction was increased in the reactant gas stream. The rate determining step is the oxidation of C2H4OH radicals with oxygen on the catalyst surface. The rate law is expressed as follows to account for the results obtained: − d [ C 2 H 4 ] d t = k 9 K 8 I a φK C 2 H 4 P C 2 H 4 K O 2 P O 2 k OH (1+K C 2 H 4 P C 2 H 4 +K H 2 O P H 2 O )(1+K O 2 P O 2 )
140 citations
TL;DR: In this paper, XPS, TEM and UV-VIS diffuse reflectance spectroscopy was used to study titania with platinum in various oxidation states deposited by a photocatalytic method.
Abstract: Specimens of titania with platinum in various oxidation states deposited by a photocatalytic method, as well as mixture of PtO2 + TiO2, and PtO2 have been studied by means of XPS, TEM and UV-VIS diffuse reflectance spectroscopy. Activities of the specimens in thermal and photocatalytic complete oxidation of gaseous acetone and CO by atmospheric oxygen at 40°C have been evaluated using a flow-circulating reactor. Photocatalytic activity increases with lowering of Pt oxidation state. Possible reasons of this behavior are discussed.
135 citations
TL;DR: In this paper, the physical and photocatalytic properties of the TiO 2 loaded on a unique silica using a TiO2 sols, which was prepared by the hydrolysis of titanium n -butoxide in water (pH = 1.1) containing different alcohols and alcohol concentration, have been examined.
Abstract: The physical and photocatalytic properties of the TiO 2 loaded on a unique silica using a TiO 2 sols, which was prepared by the hydrolysis of titanium n -butoxide in water (pH = 1.1) containing different alcohols and alcohol concentration, have been examined. Compared to the bare TiO 2 prepared in parallel, all the supported TiO 2 showed a higher photoactivity for the oxidation of acetophenone in water. The supported catalyst were mainly anatase crystallites of smaller size, and had a slightly higher adsorptivity toward the organic substrate. Upon the change of alcohols and alcohol concentration in the sol–gel mixture, the supported TiO 2 exhibited different response from the bare TiO 2 in the crystal structures and photoactivity. In addition, the supported TiO 2 showed a higher photoactivity on a silica of smaller particle size than on the silica of larger particles. The results suggest that the dispersion effect of silica is operative, which could be the basic role of any porous support for the TiO 2 photocatalysis.
TL;DR: In this article, the authors show that photogenerated holes in UV-irradiated TiO2 can oxidize As(III) to As(V) and then reduce As (V) to the elemental state.
Abstract: Thermodynamic considerations show that photogenerated holes in UV-irradiated TiO2 can oxidize As(III) to As(V). Similarly, the photogenerated electrons can reduce As(V) to the elemental state. Experimental data are presented in verification of these expectations. An electron acceptor (e.g., O2) is needed for the hole transfer pathway whereas the heterogeneous photocatalytic reduction of As(V) is facilitated by a hole scavenger such as methanol. The oxidation of As(III) to As(V) also proceeds in the dark when a large excess of H2O2 is present. However, this process is very facile with simultaneous UV irradiation of the peroxide. These data point toward the feasibility of a two-step pollution abatement scheme for the initial oxidation and subsequent immobilization of the toxic As(III) species.
TL;DR: In this paper, the quantum yields for the photosensitized production of singlet oxygen and superoxide ion by the quinones 1,4-benzoquinone, BQ, 2-methyl-1,4-, MBQ, NQ2S, AQDS in aqueous buffer (pH 7), at wavelengths above 310nm, have been determined.
Abstract: Quantum yields for the photosensitized production of singlet oxygen and superoxide ion by the several quinones 1,4-benzoquinone, BQ, 2-methyl-1,4-benzoquinone, MBQ, sodium 1,4-naphthoquinone-2-sulfonate, NQ2S, sodium 9,10-anthraquinone-2-sulfonate, AQ2S, 1,4-naphthoquinone, NQ, 2-hydroxy-1,4-naphthoquinone, LWQ, 5,8-dihydroxy-1,4-naphthoquinone, NZQ, 5-hydroxy-1,4-naphthoquinone, JQ, and disodium 9,10-anthraquinone-1,5-disulfonate, AQDS in aqueous buffer (pH 7), at wavelengths above 310 nm, have been determined. Quantum yields for the production of singlet oxygen were found to be smaller than that for the production of superoxide. The quantum yield for the production of the hydroxyl adduct of 5,5-dimethyl pyrroline-1-oxide, DMPO-OH, by NQ was also determined and was found to be oxygen-concentration-dependent while the photoproduction of this adduct by hydroxynaphthoquinones was not observed. Evidence was obtained which suggests that the observed DMPO-OH adduct is produced by the free hydroxyl radical, at least at low NQ concentration.
TL;DR: In this paper, the photocatalytic activity was higher as Rh was richer in the component of metallic and oxidized state, and the results of an X-ray absorption spectroscopic analysis showed that the ratio of Rh in a metallic state to that in an oxidized stale increased along with the increase of the amount of Rh loading on Rh/TiO2.
Abstract: Photoreduction of gaseous carbon dioxide to carbon monoxide with hydrogen over Rh-loading TiO2 was investigated. As the reaction proceeded even in the dark but was enhanced under irradiation, the reaction should be considered as “photo-enhanced reaction”. When Rh in Rh/TiO2 was strongly reduced to be in a fully metallic state, the activity was lowered and the main product changed from CO to CH4. A similar effect was obtained by changing the loading amount of Rh: when the loading amount of Rh was raised, the activity was lowered and the main product shifted from CO to CH4. The results of an X-ray absorption spectroscopic analysis showed that the ratio of Rh in a metallic state to that in an oxidized stale increased along with the increase of the amount of Rh loading on Rh/TiO2. The photocatalytic activity was higher as Rh was richer in the component of metallic and oxidized state.
TL;DR: In this article, the photocatalyzed degradation of 4-chlorophenol (4-CP) in water is comparatively examined with TiO 2 powder, TiO2 /CdS powder,TiO 2 thin film electrodes, and TiO O 2 /S thin-film electrodes in the initial stages of the reaction.
Abstract: The photocatalyzed degradation of 4-chlorophenol (4-CP) in water is comparatively examined with TiO 2 powder, TiO 2 /CdS powder, TiO 2 thin film electrodes and TiO 2 /CdS thin film electrodes in the initial stages of the reaction. The apparent intermediates of 4-CP photodegradation with TiO 2 and TiO 2 /CdS powders in suspensions are found to be 1,4-benzoquinone (BQ) and hydroquinone (HQ), with HQ rapidly converting into BQ with TiO 2 and TiO 2 /CdS electrodes at an applied anodic potential of 0.6 V vs Ag/AgCl. The apparent reaction rate constants using the Langmuir–Hinshelwood equation with TiO 2 /CdS powder and the TiO 2 /CdS electrode are obtained to be about 90% and 33% larger than with TiO 2 powder and the TiO 2 electrode, respectively, indicating that the TiO 2 /CdS catalysts have more photocatalytic activities than the TiO 2 catalysts in the initial stages. The adsorption coefficient ( K ) of 4-CP on TiO 2 /CdS powder is one and a half times larger than that on TiO 2 powder. With the electrode catalysts at 0.6 V, the value of K increases several times with respect to the corresponding powder catalysts and shows essentially no difference between the TiO 2 /CdS electrode and the TiO 2 electrode. Thus, the value of K may strongly depend on the electrostatic interaction between 4-CP and the electrode surface, but not very much on the type of electrode surface.
TL;DR: The excited-state intramolecular proton transfer of 2-(o-hydroxy-3-aryl)benzazoles has been studied by emission spectroscopy.
Abstract: The excited-state intramolecular proton transfer of 2-(o-hydroxyaryl)benzazoles has been studied by emission spectroscopy. Although both 2-(2-hydroxy-3-aryl)benzazole and 2-(1-hydroxy-2-aryl)benzazole consist of an aryl moiety, a benzazol-2-yl group and an OH group, their emission properties are very different for the reasons that can be explained in terms of our previously offered nodal-plane model.
TL;DR: In this paper, the excited state complexation of flavonol derivatives with alkali and alkali-earth metal ions was investigated, and it was found that chelating magnesium complexes are more stable than in the ground state.
Abstract: The excited state complexation of flavonol derivatives with alkali and alkali-earth metal ions were investigated. It was found that in the excited state chelating magnesium complexes are more stable than in the ground state, and they are produced both from normal and from phototautomer forms of flavonols. The ‘external’ barium complexes with flavonols containing electron donor groups in 4 0 -position behave similarly in the excited state. The ‘external’ barium complexes of unsubstituted and 4 0 -methoxy substituted flavonols dissociate in the excited state. Their disruption occurs as a result of the excited state intramolecular proton transfer (ESIPT) in flavonol molecules. Ejection of metal ion from the crown-cycle was found for the magnesium and barium complexes of azacrown-flavonol ‐ M2L. In the case of Ba2L complex the process of cation ejection results in the formation of a complex which does not exist in the ground state. The authors assumed that the short-wavelength band in the emission spectrum of unsubstituted flavonol in acetonitrile might be due to the fluorescence of flavonol molecules forming a hydrogen bond with the solvent. ©1999 Elsevier Science S.A. All rights reserved.
TL;DR: In this paper, the laser characteristics of Rhodamine 6G (Rh6G) doped polymethyl methacrylate (PMMA) rods, modified with ethyl alcohol (EtOH), are examined by nitrogen laser, and second harmonic Nd : YAG laser excitations in a transverse pumping configuration and the variation of small signal gain of the dye in solid medium for different pump powers are studied.
Abstract: Solid state dye doped polymer is an attractive alternative to the conventional liquid dye solution. In this paper, the laser characteristics of Rhodamine 6G (Rh6G) doped polymethyl methacrylate (PMMA) rods, modified with ethyl alcohol (EtOH), are examined by nitrogen laser, and second harmonic Nd : YAG laser excitations in a transverse pumping configuration and the variation of small signal gain of the dye in solid medium for different pump powers are studied. The photobleaching of dye doped polymer rod is also studied.
TL;DR: In this article, the formation of singlet molecular oxygen 1 O 2 photosensitized by rhodamine dyes is directly proved by measuring its IR phosphorescence, and the influence of quenching agents (nitrobenzene and COT) on the formation rate is compared with that expected from the low probability (≈1%) of intersystem crossing of the photosensitizers.
Abstract: By measuring its IR phosphorescence the formation of singlet molecular oxygen 1 O 2 photosensitized by rhodamine dyes is directly proved. The 1 O 2 formation rate is compared with that expected from the low probability (≈1%) of intersystem crossing of the photosensitizers. The quantum yield for triplet population and the triplet lifetime of the investigated dyes is measured by using a laser-scanning-microscopy technique. The influence of quenching agents (nitrobenzene and COT) is discussed. It results that the formation of 1 O 2 can be prevented effectively by quenching of the S 1 or T state of the photosensitizer. The influence of the molecular ground-state oxygen 3 O 2 concentration [ 3 O 2 ] is investigated. The presence of the paramagnetic 3 O 2 leads to an increased S 1 →T intersystem crossing rate of the photosensitizers and therefore to a reinforced formation of singlet molecular oxygen. It is found for rhodamine 6G as well as for rose bengal that in air-saturated acetonitrile nearly the half of the excited dye triplets are quenched by molecular oxygen. The 1 O 2 concentration can be significantly reduced by decreasing the 3 O 2 concentration below its air saturated level.
TL;DR: In this paper, Muller et al. report on the emission characteristics (250650 nm) of various ELECTRONIC discharge lamps (EDL) containing different fill materials (Hg, HgI2, Cd, I2, KI, P, Se, and S).
Abstract: This work expands our previous research on an original
photochemical reactor consisting of the electrodeless discharge
lamp (EDL) inside a reaction mixture that generates ultraviolet
radiation in the microwave (MW) field. The effects of
temperature MW output power of the reactor, and EDL envelope
material, were already published [P. Muller, P. Klan, V.
Cirkva, J. Photochem. Photobiol. A: Chem. 158 (2003) 1]. Now we
report on the emission characteristics (250650 nm) of various
EDLs containing different fill materials (Hg, HgI2, Cd, I2, KI,
P, Se, and S). While distinct line emission peaks were found
for mercury, cadmium and phosphorus fills, iodine, selenium and
sulfur-containing EDLs emitted continuous bands.
Sulfur-containing EDLs are proposed for phototransformations
that are of environmental interest due to the emission flux
comparable to solar terrestrial radiation. It is concluded that
the right choice of EDL envelope fill material can be very
useful in planning an efficient course of photochemical process
without necessity of filtering off the undesirable part of the
UV radiation by other tools, such as glass or solution filters
or monochromators. Quantum efficiency measurements of the
Norrish type II reaction were accomplished to compare
usefulness of the EDLs in photochemical applications. Sulfur
and phosphorus-containing EDLs were found as the most efficient
sources of UV radiation.
TL;DR: In this paper, a triethanolamine (TEOA)-dimethylformamide (DMF) solution was examined for photocatalytic reduction of CO2 using [fac-Re(bpy)(CO)3(4-Xpy)]+ [bpy = 2,2′-bipyridine, py = pyridine py, X = tert-Bu, Me, H, MeCO, CN] in a TEOA-DMF solution and the quantum yields for CO formation were almost identical for each (0.
Abstract: Photocatalytic reduction of CO2 using [fac-Re(bpy)(CO)3(4-Xpy)]+ [bpy = 2,2′-bipyridine, py = pyridine, X = tert-Bu, Me, H, MeCO, CN] in a triethanolamine (TEOA)–dimethylformamide (DMF) solution was examined. The quantum yields for CO formation were almost identical for each (0.03 to 0.04), except for the 4-CNpy complex. Irradiating the solutions caused ligand substitution of these complexes with solvent molecules to produce [fac-Re(bpy)(CO)3(TEOA)]+ and [fac-Re(bpy)(CO)3(DMF)]+, followed by formation of the formate complex [fac-Re(bpy)(CO)3{OC(O)H}], which acts as the real catalyst for CO formation. On the other hand, the much higher CO formation ability observed for the 4-CNpy complex (quantum yield for CO formation = 0.13) was due to the participation of the cyano complex [fac-Re(bpy)(CO)3CN], which is converted from the 4-CNpy complex during irradiation. The photochemical substitution of the initial complexes with the solvent molecules is very rapid (quantum yields >1). This phenomenon is explained by a chain mechanism.
TL;DR: In this paper, the photophysical properties of the dye fluorescein have been studied in alkanols (methanol to decanol), in micellar solutions of SDS, CTAB and Triton X-100 and in the w/o microemulsion system of water/AOT/heptane.
Abstract: The photophysical behaviours of the dye fluorescein have been studied in alkanols (methanol to decanol), in micellar solutions of SDS, CTAB and Triton X-100 and in the w/o microemulsion system of water/AOT/heptane. The alkanols are found to affect the absorption and fluorescence spectra of the dye. On the basis of the solvent adsorption model the binding constants of the dye with the alkanols have been estimated. The absorption and emission spectra of the dye are observed to be influenced by the ionic surfactants SDS, CTAB and not influenced by the non-ionic representative Triton X-100. The results confirm formation of a 1 : 1 complex of the dye with SDS and CTAB micelles. In the w/o microemulsion medium, the photophysical behaviours of the dye are found to be different from non-aqueous and micellar media.
TL;DR: In this paper, a photochemical reaction of perfluorohexylethene with tetrahydrofuran was carried out under microwave and UV combined irradiation using a new simple photochemical reactor developed for organic synthetic reactions.
Abstract: Generation of UV radiation by microwave field has been applied to a photochemical reaction of perfluorohexylethene with tetrahydrofuran. Reactions were carried out under microwave and UV combined irradiation using a new simple photochemical reactor developed for organic synthetic reactions. Comparative experiments with conventional mercury lamps showed the higher efficiency of microwave electrodeless lamps providing high yield of product in shorter reaction time.
TL;DR: In this paper, a free base porphyrin, 5,10,15,20-tetra(4- N -methylpyridyl)porphyrin (TMPyP), was used for the detection of heavy metal ions.
Abstract: The detection of heavy metal ions – Hg 2+ , Pb 2+ , Cd 2+ – by a free base porphyrin, 5,10,15,20-tetra(4- N -methylpyridyl)porphyrin (TMPyP), was studied. The porphyrin was either adsorbed in sol–gel matrix (TMOS) or grafted on glass surfaces. Detection limit was 10 −7 mol/l for mercury and cadmium, and 10 −5 mol/l for lead. Apparent association constants were calculated at pH=7: p K (Cd 2+ )=−5.2; p K (Pb 2+ )=−4; and at pH=4 p K (Hg 2+ )=−5.7. Both the shift of the Soret band and the change in fluorescence lifetime enabled the identification of the metal ions. In sol–gel, detection limits were found to be 10 −3 mol/l but 90% of the metal salts were trapped by the matrix. In sol–gel we have shown that the ions were pumped by the matrix at a concentration of 1.5×10 −5 mol/ml of sol–gel. The sol–gel limits both the reaction time and the detection threshold. No such effect is observed for grafted monolayers. A reaction time of 30 min and a detection limit of 10 −6 mol/l were measured for Hg 2+ salts.
TL;DR: In this article, the photocatalytic degradation of azo dyes in aqueous suspensions of TiO2 is comparatively a good method for the removal of these impurities.
Abstract: The photocatalytic degradation of azo dyes in aqueous suspensions of TiO2 is comparatively a good method for the removal of these impurities. The extent of degradation is followed by UV–visible and IR spectroscopy. The degradation process is performed with various heat treated TiO2, in which anatase form of TiO2 exhibited marked photocatalytic activity.
TL;DR: In this paper, the photo-oxidation of polyvinylpyrrolidone (PVP) has been investigated using the MOPAC system available in the CAChe package.
Abstract: The mechanism of photo-oxidation of the water-soluble polyvinylpyrrolidone (PVP) having a pendant five-membered lactam ring is complicated by the manner by which the macromolecule adsorbs on the TiO 2 particle surface in a heterogeneous dispersion. Experimental results and computer simulation of the initial process(es) infer three major steps for the photodegradation of the PVP structure. The first step is adsorption (or coagulation) of PVP on TiO 2 particles as evidenced by the size distribution of TiO 2 particles by dynamic light-scattering and by the electric charge on the TiO 2 particle surface assayed by ζ -potential measurements. Molecular orbital simulations of initial processes were calculated at the AM1 level using the MOPAC system available in the CAChe package. The second step, namely attack of PVP by OH and/or OOH radicals, involves cleavage of the PVP main chain and opening of the lactam ring in the PVP structure probed by temporal UV spectral changes and by a decrease of the molecular weight using gel permeation chromatographic methods. Additional details of the photo-oxidation mode of the lactam ring was examined by a detailed examination of the photo-oxidation of the model compound 2-pyrrolidone to ascertain formation of OH radical adducts, opening of the lactam ring, and identification of intermediates by HPLC, and 13 C- and 1 H-NMR methods. The final major step in the mechanism involves generation and subsequent conversion of the primary amine (methylamine from opening of the lactam ring) to yield ultimately NH 4 + and NO 3 − ions, and conversion of the propanoic acid to acetic and formic acids and then to CO 2 . The effects of the extent of polymerization and variation in light intensity were examined using PVP samples having different hardness factors (hf) of 15 and 30, and different light intensities (namely, 1, 2, 3 and 4 mW cm −2 ), respectively.
TL;DR: In this paper, small transmission changes observed in terms of triplet formation, photo-isomerization, photodegradation, and thermal heating were analyzed in a diode laser at 812.5nm.
Abstract: Indocyanine green sodium iodide (ICG-NaI) in dimethylsulfoxide (DMSO), methanol, water, and human plasma is excited with a chopped powerful diode laser at 812.5 nm (time resolution 20 μs). Small transmission changes observed are analysed in terms of triplet formation, photo-isomerisation, photo-degradation, and thermal heating. Quantum yields of P-isomer formation and T 1 -triplet formation as well as P-isomer and T 1 -triplet lifetimes are determined. For nitrogen-bubbled ICG-NaI in DMSO a quantum yield of triplet formation of φ T ≈ 5 × 10 −5 and a triplet-state lifetime of τ T ≈ 700 μs are determined. For ICG-NaI in methanol a quantum yield of P-isomer formation of φ P ≈ 2.4 × 10 −4 and a P-isomer lifetime of t P ≈ 430 μs are obtained.
TL;DR: In this article, a comparison between thin film and bulk sol-gel derived matrices produced from the same reaction mixture was made by the incorporation of various concentrations of rhodamine 6G and monitoring the dyes fluorescence behaviour using both steady state and time-resolved fluorescence spectroscopy.
Abstract: A comparison has been made between thin film and bulk sol–gel derived matrices produced from the same reaction mixture. This was carried out by the incorporation of various concentrations of rhodamine 6G and monitoring the dyes fluorescence behaviour using both steady state and time-resolved fluorescence spectroscopy. Measurements were performed on matrices, which were considered to be in a stable condition and unlikely to undergo any further major structural changes. In the thin film matrices the fluorescence decay was non-exponential and appeared to relate to different environments for the dye molecules. This was supported by anisotropy measurements that imply that dye is present adsorbed to the silica matrix as well as solvated within some of the pores. In the bulk matrices the time-resolved fluorescence decay was monoexponential (decay time 4.34 ns) and on increasing the rhodamine 6G concentration the main phenomenon observed was that of self-absorption. Evidence was found for the presence of solvent within the bulk matrix and time-resolved fluorescence anisotropy indicated the existence of two main environments of differing viscosity (7 and 195 mPa s), which can relate to different pore sizes. Measurements of energy transfer from rhodamine 6G to malachite green showed a much greater than expected efficiency at low acceptor concentrations. This is attributed to confinement of the dye within the pore and reflects a distribution of pore sizes.
TL;DR: In this paper, a flash photolysis method employing fluorescence, optical absorption and electrical conductivity measurements was demonstrated for compounds III-V and E-3-phenyl-prop-2-ene-1-yl(anthracene-9-methyl)-ether.
Abstract: Anthracene (III) and the derivatives 9-methoxymethylanthracene (IV), 9-cyanoanthracene (V) and (E-3-phenyl-prop-2-ene-1-yl(anthracene-9-methyl)-ether) (I) were subjected to irradiation at inca347 nm in dilute deoxygenated acetonitrile solution at room temperature. With the aid of the flash photolysis method employing fluorescence, optical absorption and electrical conductivity measurements the monophotonic photoionization and the formation of free ions was evidenced for compounds III‐V. In the case of the bichromophoric compound I a photocurrent was not observed although a transient optical absorption attributable to the radical anion of the arthracene moiety was detected. Moreover, the fluorescence lifetime of I was found to be definitely shorter than that of IV (model compound). On this basis it was concluded that a certain fraction of electronically excited singlet states of I is deactivated via intramolecular electron transfer. The transient zwitter ions formed in this way, overwhelmingly undergo a self-reaction thus regenerating I, but a small portion undergoes an intramolecular Diels‐Alder reaction forming VI, the only photoproduct. The quantum yield is (VI)0.04. # 1999 Elsevier Science S.A. All rights reserved.
TL;DR: In this article, the photoreactivity of Type I and II photointiators, namely, 4-(2-hydroxyethoxy)-phenyl-(2hydroxy2-methylpropyl) ketone (Irgacure 2959, Ciba-Geigy) and 4-hydroxbenzophenone, respectively, have been examined in the free and bound form in melamine and urethane acrylate prepolymers.
Abstract: The photoreactivity of Type I and II photointiators, namely, 4-(2-hydroxyethoxy)-phenyl-(2-hydroxy2-methylpropyl) ketone (Irgacure 2959, Ciba-Geigy) and 4-hydroxybenzophenone, respectively, have been examined in the free and bound form in melamine and urethane acrylate prepolymers. Co-reaction in the prepolymers was undertaken by partial replacement of the hydroxyacrylate components with the photoinitiators in the reaction with the isocyanate component. Both the photoinitiators were also converted into their corresponding acrylate derivatives for study. The free, bound and acrylated derivatives were then analysed by various spectroscopic techniques to evaluate the relationship between their photophysical properties and photoinitiation activity for photocrosslinking of commercial acrylated monomers and prepolymers. Photocuring studies using Hg sources (conveyor and RTIR) indicated that whilst binding the Type I photointiator reduced its efficiency in cure, the Type II photoinitiator was enhanced. The presence of an amine co-synergist, however, generally eliminated these differentials. Acrylation of the Irgacure 2959 also reduced photoactivity. Absorption spectroscopy indicated the presence of a strongly absorbing nπ * transition in the far UV region for both chromophore types which undergoes a blue shift on binding to the prepolymer. Phosphorescence spectra, lifetimes and quantum yields also indicate the presence of low lying triplet nπ * states for both types of chromophore. Binding appears to enhance the triplet lifetime and reduce the quantum yield of emission due to increased electron donation into the chromophore by the resin component and may in part account for their lower photoactivity. Microsecond flash photolysis identified the formation of benzoyl radicals in the case of the Type I system with a small enhancement in radical formation on binding. The Type II system gave ketyl radicals formed by hydrogen atom abstraction which were enhanced in the bound resin system. The latter would account for increased photoactivity for the bound Type II system. Nanosecond laser flash photolysis experiments identified the triplet–triplet absorption in the case of the Type II initiator. In the presence of a tertiary amine (triethylamine) the transient absorption and its lifetime were significantly enhanced due to exciplex formation. However, binding the benzophenone initiator to the resin significantly quenched the transient absorption and significantly reduced its lifetime. In the case of the Type I initiator the benzoyl radical was observed directly, confirming the microsecond flash photolysis data. Binding of the initiator to the melamine acrylate resin also reduced benzoyl radical formation and reduced the radical lifetime. This may account for the reduced photoactivity of the Type I bound initiator. Radical formation was also reduced when bound to the urethane acrylate but the lifetime was enhanced. For the initiator bound resin systems the presence of an amine co-synergist enhanced benzoyl radical formation. The implications of initiator co-reactions are discussed in terms of both the photochemical and commercial benefits.