堀越 智

This review article summarizes research directed toward microwave heating in the oil chemistry. Topics to be discussed include microwave synthesis of surfactants, extraction methods, modification of crude oil properties, and degradation of surfactants. The specific effects of microwave heating, which cannot be obtained by conventional heating in particular, are explained.

For the first time, this comprehensive handbook presents the emerging field of microwave technology for the synthesis of nanoparticles. Divided into three parts--fundamentals, methods, and applications--it covers topics including microwave theory, scale-up, microwave plasma synthesis, characterization, and more. This offers both an important volume for academic researchers, and a resource for those in industry exploring the applications of nanoparticles in semiconductors, electronics, catalysis, sensors, and more. © 2013 Wiley-VCH Verlag GmbH &amp Co. KGaA.

The photocatalyzed degradation and mineralization of branched C4 and C5 acids {2-methylpropanoic acid (2-MPA), 2-methylbutanoic acid (2-MBA), 3-methylbutanoic acid (3-MBA), and trimethylacetic acid (TMA)} and oxidized C4 and C5 carboxylic acids {e.g., 2-hydroxybutanoic acid (2-HBA), 2-hydroxy-2-methylbutanoic acid (2-OH-2-MBA), 2-hydroxyvaleric acid (2-HVA), and 2-ketovaleric acid (2-KVA)} were examined in UV-irradiated air-equilibrated aqueous TiO2 dispersions to assess: (a) the extent of (dark) adsorption; (b) the relationship between the extent of adsorption and degradation dynamics; and (c) the dynamics of mineralization (loss of total organic carbon (TOC)). Branching had little, if any impact on the adsorption process by comparison with analogous linear acids reported earlier. Complete degradation of the branched acids occurred in relatively short time (less than or equal to 2 h), whereas mineralization required longer irradiation times (3-4.5 h). The trends correlate with C-H bond strengths. Branched acids degrade at rates slightly greater than unbranched acids with degradation dynamics decreasing with increase in chain length. The 2-HVA and 2-KVA acids degraded at nearly identical rates. Methylation of 2-HBA had no effect on the dynamics of degradation. However, oxidized carboxylic acids (2-HVA and 2-KVA) degraded five-fold faster than the corresponding linear valeric acid; similarly for 2-OH-2-MBA, which degraded four-fold faster than 2-MBA. These observations explain the difficulty in detecting primary hydroxylated intermediates in (OH)-O-.-radical oxidized linear carboxylic acids. (C) 2004 Elsevier B.V. All rights reserved.

Thermal and nonthermal effects originating when a system is subjected to a microwave radiation field in the TiO2-photocatalyzed transformation of model substances containing various functional groups (e.g., benzoic acid, phthalic acid, o-formylbenzoic acid, phthalaldehyde, succinic acid, dimethyl phthalate, diethyl phthalate, and phenol) have been examined under simultaneous irradiation by ultraviolet (UV) and microwave (MW) radiations. Characteristics of the microwave effects and the fate of each substrate during the microwave-assisted photocatalytic process were monitored by UV absorption spectroscopy, HPLC methods, total organic carbon assays, and identification of intermediates using electrospray mass spectral techniques. Microwave thermal and nonthermal effects were delineated by comparing results from MW-generated internal heat versus conventional external heating, and at constant ambient temperature under a microwave field. Factors involved in the nonthermal component of the microwave radiation were inferred for the initial adsorption of the substrate and its subsequent degradation occurring on the surface of TiO2 particles. Microwave effects bear on the mechanism through which a model substrate undergoes oxidative degradation. A characteristic feature of these effects was briefly examined by considering the behavior of polar (dipole moments) substrates in a microwave radiation field.

The photodegradation of the endocrine disruptor 4,4'-isopropyldiphenol (bisphenol-A, BPA; 0.1 mM) was examined in aqueous TiO2 dispersions to assess thermal versus non-thermal effects of the microwave radiation assisted photocatalytic process driven by UV radiation. The effects were examined by comparing the results of the photodegradative process from the hybrid UV/microwave irradiation (PD/MW) with a UV/conventional heating method (PD/TH) and with UV illumination alone (PD). Mechanistic considerations followed from monitoring the process by UV/Vis absorption spectroscopy (cleavage of benzene rings), total organic carbon (TOC) assays, identification of intermediates by electrospray mass spectral techniques, and from calculations of frontier electron densities and partial charges of all non-hydrogen atoms in the BPA skeleton. Near-quantitative mineralization of BPA occurred after only 90 min of irradiation by the PD/MW and PD/TH routes, contrary to the PD route, which accounts for only 67% mineralization under identical conditions. Microwave radiation alone on a solution of BPA (no TiO2) had no effect on the TOC, except for an increase of the pH of the solution (6.7-7.2) and formation of a small quantity of formic acid (ca. 0.005 mM) originating from oxidation of the isopropyl methyl groups after a 30 min irradiation period. For the other three routes, other intermediates were identified in addition to acetic acid and formic acids: 4-hydroxyacetophenone (PD/MW, PD/TH, PD), 4-hydroxybenzaldehyde (PD/MW, PD/TH), 4-hydroxyphenylisopropanol (PD/TH, PD), phenol and hydroquinone (PD/TH), and 3-hydroxy-1,3,5-hexatriene (PD/MW). Mechanistic differences are attributed to adsorption mode variations of the BPA substrate on the TiO2 particle surface. (C) 2004 Elsevier B.V. All rights reserved.

The photocatalyzed degradation of phenol and catechol was re-examined to assess their adsorption/desorption behavior on a TiO2-coated (sol-gel technique) quartz crystal microbalance (QCM) sensor. The QCM senses changes in mass occurring during the photodegradation, which of necessity implicates photoinduced adsorption and desorption of molecules of the original substrate and its degradation intermediates. The temporal loss of spectral features of the benzene ring with irradiation time was monitored by fluorescence spectroscopy. The increase in the quantity of TiO2 deposited on the QCM sensor scaled linearly with the number of dip-coatings (five). Water adsorption on QCM in the dark was relatively independent of pH. Adsorption of the organic substrates was pH dependent since the surface charge of TiO2 varies with pH. Thus, both phenol and catechol tended to be adsorbed more at neutral pH 7 than at the other pHs examined and within the concentration range of substrate 0 to 0.012 mM. For phenol, adsorption reached near saturation around 0.007 mM in the order pH 7 &gt pH 9 &gt pH 5. Catechol showed a similar behavior except at the higher concentrations (around 0.010 mM). Mass changes occurring during the photodegradation of phenol and catechol on the TiO2-coated QCM sensor surface are reported.

Bisphenol A (BPA) can be decomposed photocatalytically under UV-illumination in aqueous TiO(2) dispersion. The two methyl groups in BPA were initially attacked with (.)OH and/or (.)OOH radicals having strong oxidizing power, followed by the cleavage of the two phenyl moieties. Finally, the photomineralization to CO(2) gas occurred via oxidative processes involving carboxylic acids and aldehydes. The decomposition of structurally similar substances of 4,4'-ethylidenebisphenol (EBP) and 4,4'-methylenebisphenol (MBP) was compared. The decomposition of BPA gave more kinds of intermediates such as 4-isopropylphenol, 4-ethylphenol, etc. On the other hand, that of EBP gave mainly 4-isopropylphenol and that of MBP gave a predominant product of 4-hydroxybenzaldehyde. These photooxidative pathways were proposed on the base of the evidence of oxidative intermediate formation. (C) 2003 Published by Elsevier Science Ltd.

Formation of .OH radicals during TiO2 photocatalyzed oxidations driven by simultaneous UV and microwave radiation was probed by the electron spin resonance technique employing a novel setup in which the ESR sample (contained the DMPO spin-trap agent and P-25 TiO2 or pure anatase or pure rutile in aqueous media) could be irradiated by both UV light and microwave radiation; the microwave generator was coupled through an N connector to the ESR sample cavity and to a photoreactor in which phenol was photooxidized by simultaneous irradiation with UV light and microwaves to assess whether the photooxidative process correlated with the concentration of OH radicals formed. (C) 2003 Elsevier B.V. All rights reserved.

Bisphenol A (BPA) widely used includes drain water, consequently causing a serious health threat owing to its endocrine disruptor action. The pH dependence on BPA photodegradation in TiO2 dispersion under UV-irradiation was examined at different pH in BPA solution (0.1 mM) containing TiO2 (100 mg). BPA photodegradation was assessed by UV spectroscopy, and total organic carbon (TOC). Change in ζ-potential and ·OH radicals formation were determined by ESR spin-trapping technique for each solution. Decrease in ratio of UV absorption and TOC at pH 11 occurred more slowly than that at pH 4, 6.3 or 10. This was due to conversion of two -OH groups in BPA to -O2- the pH 11. Anionic BPA and negative TiO2 surface thus separate by simple coulombic force. ·OH radical intensity at pH 11 was greater than at other values. The photooxidation rate was influenced by the initial absorption between partially charged BPA and TiO2 surface regardless of the number of ·OH radicals. © 2003, Japan Oil Chemists' Society. All rights reserved.

The photodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D) taking place in UV irradiated aqueous TiO2 dispersions was revisited to obtain mechanistic details on the basis of similar degradation of the related 2,3-dichlorophenoxyacetic acid (2,3-D), 4-chlorophenoxyacetic acid (4-M) and phenoxyacetic acid (PhA). Mechanistic changes were inferred from the different positions of the chlorine substituents. As well, the compounds were compared for differences in degradation rate and initial adsorption on the TiO2 surface as a function of the number of chlorines. The initial mechanistic sequence(s) in the TiO2-photocatalyzed oxidation of each substrate was predicted theoretically by molecular orbital ( MO) calculations of frontier electron densities and point charges of all the atoms in the phenoxyacetic acid structures.

Refractory atrazine and cyanuric acid were degraded under hydrothermal and supercritical aqueous media (HY-SC) conditions, as well as in the presence of ozone (HY-SC/O-3) and UV-illuminated ozone (HY-SC/UV/O-3) to assess whether the efficacy of the decomposition process could be enhanced using a single-pass flow-through treatment device under a constant pressure of 23 MPa. The progress of the degradation was evidenced by the extent of removal of total organic carbon (TOC) in solution, by UV absorption spectroscopy (opening of the atrazine and cyanuric acid heterorings), and by the extent of deamination (formation of NH4+) and dechlorination (release of Cl- ions) of the two compounds. Loss of atrazine was confirmed by LC-MSD techniques in the positive ion mode. Formation of various intermediates from the degradation of atrazine was substantiated by positive and negative ion mode MSD analyses. Dechlorination of atrazine occurred around 100 degreesC under hydrothermal conditions for the HY-SC and HY-SC/O-3 processes but not for HY-SC/UV/O-3; it did increase rapidly at higher temperatures (beginning at ca. 220-230 degreesC) for all three methods: HY-SC through HY-SC/UV/O-3. Deamination, removal of TOC, and loss of atrazine mass spectral features began around 260-280 degreesC in hydrothermal aqueous media. Degradation of cyanuric acid showed a similar behavior. For the treated effluent solution in the collector reservoir, ozonation enhanced somewhat both dechlorination and mineralization, but had no significant effect on the deamination of either atrazine or cyanuric acid.

The photostabilities of a random set of commercially available sunscreen lotions and their active ingredients are examined spectroscopically subsequent to simulated sunlight UV exposure. Loss of filtering efficacy can occur because of possible photochemical modifications of the sunscreen active agents. Changes in absorption of UVA/ UVB sunlight by agents in sunscreen lotions also leads to a reduction of the expected photoprotection of human skin and DNA against the harmful UV radiation. The active ingredients were investigated in aqueous media and in organic solvents of various polarities (methanol, acetonitrile, and n-hexane) under aerobic and anaerobic conditions. The UV absorption features are affected by the nature of the solvents with properties closely related to oil-in-water (o/w) or water-in-oil (w/o) emulsions actually used in sunscreen formulations, and by the presence of molecular oxygen. The photo stabilities of two combined chemical ingredients (oxybenzone and octyl methoxycinnamate) and the combination oxybenzone/titanium dioxide were also explored. In the latter case, oxybenzone undergoes significant photodegradation in the presence of the physical filter TiO2.

The characteristic features of a novel double-quartz cylindrical plasma photoreactor (DQCPP) were assessed by examining the photodegradation of rhodamine-B dye (RhB+) in aqueous TiO2 dispersions irradiated simultaneously by both microwave radiation and UV/visible radiation emitted from a microwave-powered (MW, 2,45 GHz) electrodeless mercury lamp. The features of the DQCPP lamp are given and discussed in terms of the experimental output UV energy in the wavelength ranges 210-300 and 310-400 nm for applied MW powers from 74 to 621 W. The DQCPP and a watercooled DCICPP reactor absorbed more than 50% MW radiation (50-88 and 50-75%, respectively). The emitted light irradiance scaled sublinearly with applied MW power. Relative to the DQCPP lamp, loss of irradiance by the watercooled DQCPP lamp was similar to28-46% at 250 nm and similar to41-58% at 360 nm in the range of MW power used. The smallest loss occurred at 178.9 W at which the degradation of RhB+ was subsequently examined by UV/visible spectroscopy and by total organic carbon analyses. Highly intense mercury lines were seen at 365, 404, 435, 546, and 579 nm (those below 365 nm were more than 10 times weaker). About 80% of the RhB+ solution was photomineralized after 60 min of irradiation of the aqueous RhB+/TiO2 dispersion with the DGCPP lamp; no UV/visible spectral features of RhB+ were evident at wavelengths below 250 nm after 30 min. Possible effects of microwave radiation and temperature on the degradative process are described.

In this brief article we examined the characteristics of a novel UV-VIS-microwave integrated irradiation device and explore its usefulness using the now well-established photo-degradation of a cationic dye (rhodamine-B; RhB) as a test substrate. The device consisted of a double quartz cylindrical plasma photoreactor (DQCPP) equipped with a microwave (MW) powered electrodeless Hg/Ne irradiation source. The latter is activated only by the MW radiation. The integrated MW-UV-VIS radiations so produced and incident on the DQCPP reactor significantly enhanced the decomposition of the RhB dye through simultaneous photocatalytic and photosensitization processes. (C) 2002 Elsevier Science B.V. All rights reserved.

Simulated wastewaters that contain methylene blue (MB) were bleached in a photocatalytic aqueous TiO2 dispersion illuminated by concentrated sunlight using a parabolic round concentrator reactor (PRCR). The kinetic analysis was carried out well when the temporal concentration variation was a function of the concentrated light energy irradiated. The photocatalyzed N-demethylation of NIB takes place concurrently with photocatalytic decomposition of MB by pseudo-first-order kinetics. The dependence of the photo-decomposition kinetics on the initial concentration of MB is consistent with the Langmuir-Hinshelwood model. Elimination of TOC (total organic carbon) also occurs by pseudo-first-order kinetics prior to full bleaching of the aqueous TiO2 dispersion, after which the TOC level decreases only slightly. Also, compared with the open to air, the photodegradation of MB is not influenced by molecular oxygen bubbling continuously through the reactant suspensions during illumination. TiO2 loadings and flow rates markedly affect the degradation of MB. Under concentrated sunlight, the relative photonic efficiency of MB photodegradation is zeta(rel) = 0.49 (relative to phenol). The efficiency zeta(rel) for the degradation of MB is independent of photoreactor geometry (cylindrical bottle reactor versus round-bottomed flask), of light sources (solar light concentrator versus a Hg lamp) and of the operating mode used (flow versus batch operation). (C) 2002 Elsevier Science B.V. All rights reserved.

Simulated wastewaters that contain methylene blue (MB) were bleached in a photocatalytic aqueous TiO2 dispersion illuminated by concentrated sunlight using a parabolic round concentrator reactor (PRCR). The kinetic analysis was carried out well when the temporal concentration variation was a function of the concentrated light energy irradiated. The photocatalyzed N-demethylation of NIB takes place concurrently with photocatalytic decomposition of MB by pseudo-first-order kinetics. The dependence of the photo-decomposition kinetics on the initial concentration of MB is consistent with the Langmuir-Hinshelwood model. Elimination of TOC (total organic carbon) also occurs by pseudo-first-order kinetics prior to full bleaching of the aqueous TiO2 dispersion, after which the TOC level decreases only slightly. Also, compared with the open to air, the photodegradation of MB is not influenced by molecular oxygen bubbling continuously through the reactant suspensions during illumination. TiO2 loadings and flow rates markedly affect the degradation of MB. Under concentrated sunlight, the relative photonic efficiency of MB photodegradation is zeta(rel) = 0.49 (relative to phenol). The efficiency zeta(rel) for the degradation of MB is independent of photoreactor geometry (cylindrical bottle reactor versus round-bottomed flask), of light sources (solar light concentrator versus a Hg lamp) and of the operating mode used (flow versus batch operation). (C) 2002 Elsevier Science B.V. All rights reserved.

In an attempt to improve the understanding of the basic mechanisms on the degradation of pollutants in water by TiO(2) photocatalysis, we discussed the primary degradation mechanism of three triazolidine derivatives, such as 1,2,4-triazolidine-3,5-dione (TRIANE), 4-hydroxy-1,2,4-triazolidine-3,5-dione (OH-TRIANE) and 4-phenyl-1,2,4-triazolidine-3,5-dione (Ph-TRIANE) and one triazole derivative of the 4-phenyl-1,2,4-triazole-2,5-dione (Ph-TRIOLE), on the basis of the experimental results together with molecular orbital (MO) calculation of frontier electron density and partial charge. The above four heterocycles were selected as molecular probe, principally because the highest frontier electron density was situated at different places of the molecule, while their structures were very similar, two major pathways have been revealed by LC/MS analysis for each heterocyclic compound. The pathway (a) corresponded to the hydroxylation of the atom bearing the highest electron density, via oxidation on nitrogen atom of azo group with respect to the photodegradation of TRIANE, OH-TRIANE and Ph-TRIOLE and opening of aromatic ring when Ph-TRIANE was used. This initial attack occurred with the preferential electrophilic attack of OH(circle) radicals. The pathway (b) was caused by the attack of active species on to carbon atom of carbonyl group. Considering the calculation of the relative electrophilic density of this carbon atom for the four heterocyclics and the evolution of large amount of N(2) gas at the initial degradation step, it has been suggested that this step (b) was favored by adsorption of carbonyl group on TiO(2) surface as theoretically determined by partial charge and confirmed by IR analysis. The participation of hole (h(+)) to form R-C=O(+circle) was envisaged in this step. The presence of 1,2,4,5-tetrazixane-3,6-dione also agrees with the participation of TiO(2) surface. The nitrogen inorganic analysis (N(2), NH(4)(+) and NO(3)(-)) determined by gas chromatography and ion liquid chromatography, show that the hydrazo group were photoconverted mainly into N(2) gas and partially to NH(4)(+) ions. No nitrate ions were observed at the beginning of the degradation even when a OH substituent was present on one nitrogen atom (case of OH-TRIANE). However, the presence of -OH group increased the NO(3)(-) /NH(4)(+) ratio observed after a few hours of irradiation. The presence of OH also improved the total mineralization of carbon atom into CO(2), which was attributed to mesomeric effect of -OH group. (C) 2002 Elsevier Science B.V. All rights reserved.

The photodegradation of p-nonylphenol polyethoxylate (NPE-9) has been examined in a large-scale circulating photoreactor to assess a set of different procedures to construct hybrid TiO(2) films immobilized on a flexible fiberglass cloth (TiO(2)-FGC). The method consisted of pasting active TiO(2) particles onto the fiberglass cloth support (PA method; 0.24 nm thick; weight, 210 g m(-2)), followed by a number of dip-coatings in a titania sol-gel solution (SG method). Various TiO(2) particulates from different sources have been screened. The Degussa P-25 titania exhibited the greater photocatalytic activity. The hybrid TiO(2)-FGC specimens retained a greater quantity of the TiO(2) catalyst on the FGC support than did the corresponding PA and SG samples. Comparison of the photodegradation of NPE-9 taking place in the various hybrid TiO(2)-FGC specimens with processes occurring in TiO(2) aqueous dispersions, on PA TiO(2)-FGC and SG Ti02-FGC specimens reveals that the hybrid TiO(2)-FGC specimens were the more photocatalytically active. Formic and acetic acids are two of the photo-oxidation intermediates identified in the degradation of NPE-9. Experimental conditions used in the present study to assess the cylindrical photoreactor containing the hybrid TiO(2)-FGC specimens show that such a reactor can be useful in a large-scale treatment of wastewaters. (C) 2002 Elsevier Science B.V. All rights reserved.

In an attempt to improve the understanding of the basic mechanisms on the degradation of pollutants in water by TiO(2) photocatalysis, we discussed the primary degradation mechanism of three triazolidine derivatives, such as 1,2,4-triazolidine-3,5-dione (TRIANE), 4-hydroxy-1,2,4-triazolidine-3,5-dione (OH-TRIANE) and 4-phenyl-1,2,4-triazolidine-3,5-dione (Ph-TRIANE) and one triazole derivative of the 4-phenyl-1,2,4-triazole-2,5-dione (Ph-TRIOLE), on the basis of the experimental results together with molecular orbital (MO) calculation of frontier electron density and partial charge. The above four heterocycles were selected as molecular probe, principally because the highest frontier electron density was situated at different places of the molecule, while their structures were very similar, two major pathways have been revealed by LC/MS analysis for each heterocyclic compound. The pathway (a) corresponded to the hydroxylation of the atom bearing the highest electron density, via oxidation on nitrogen atom of azo group with respect to the photodegradation of TRIANE, OH-TRIANE and Ph-TRIOLE and opening of aromatic ring when Ph-TRIANE was used. This initial attack occurred with the preferential electrophilic attack of OH(circle) radicals. The pathway (b) was caused by the attack of active species on to carbon atom of carbonyl group. Considering the calculation of the relative electrophilic density of this carbon atom for the four heterocyclics and the evolution of large amount of N(2) gas at the initial degradation step, it has been suggested that this step (b) was favored by adsorption of carbonyl group on TiO(2) surface as theoretically determined by partial charge and confirmed by IR analysis. The participation of hole (h(+)) to form R-C=O(+circle) was envisaged in this step. The presence of 1,2,4,5-tetrazixane-3,6-dione also agrees with the participation of TiO(2) surface. The nitrogen inorganic analysis (N(2), NH(4)(+) and NO(3)(-)) determined by gas chromatography and ion liquid chromatography, show that the hydrazo group were photoconverted mainly into N(2) gas and partially to NH(4)(+) ions. No nitrate ions were observed at the beginning of the degradation even when a OH substituent was present on one nitrogen atom (case of OH-TRIANE). However, the presence of -OH group increased the NO(3)(-) /NH(4)(+) ratio observed after a few hours of irradiation. The presence of OH also improved the total mineralization of carbon atom into CO(2), which was attributed to mesomeric effect of -OH group. (C) 2002 Elsevier Science B.V. All rights reserved.

The photodegradation of p-nonylphenol polyethoxylate (NPE-9) has been examined in a large-scale circulating photoreactor to assess a set of different procedures to construct hybrid TiO(2) films immobilized on a flexible fiberglass cloth (TiO(2)-FGC). The method consisted of pasting active TiO(2) particles onto the fiberglass cloth support (PA method; 0.24 nm thick; weight, 210 g m(-2)), followed by a number of dip-coatings in a titania sol-gel solution (SG method). Various TiO(2) particulates from different sources have been screened. The Degussa P-25 titania exhibited the greater photocatalytic activity. The hybrid TiO(2)-FGC specimens retained a greater quantity of the TiO(2) catalyst on the FGC support than did the corresponding PA and SG samples. Comparison of the photodegradation of NPE-9 taking place in the various hybrid TiO(2)-FGC specimens with processes occurring in TiO(2) aqueous dispersions, on PA TiO(2)-FGC and SG Ti02-FGC specimens reveals that the hybrid TiO(2)-FGC specimens were the more photocatalytically active. Formic and acetic acids are two of the photo-oxidation intermediates identified in the degradation of NPE-9. Experimental conditions used in the present study to assess the cylindrical photoreactor containing the hybrid TiO(2)-FGC specimens show that such a reactor can be useful in a large-scale treatment of wastewaters. (C) 2002 Elsevier Science B.V. All rights reserved.

Photocurrent is generated during the photooxidation of nonylphenol polyethoxylate surfactants (NPE-n; n = 1, 5, 7, 9 and 10), precursors of 4-nonylphenol (NP), on illuminated TiO2/OTE electrodes on which TiO2 semiconductor particles were immobilized by a pasting (PA), a sol gel (SG), or both techniques (HY). The photooxidative process of NP and NPEs was examined by absorption spectroscopic methods monitoring the cleavage of the benzene ring moiety, and by the evolution of CO2 gas. The kinetics of photooxidation and the magnitude of the generated photocurrent scaled with the length of the ethoxyl side-chain for NPEs where n = 0, 1, 5, 7 and 10. The relative order of adsorption of NPEs on the positive TiO2 surface was predicted from calculated partial negative point charges of all the C and O atoms in the NPEs using molecular orbital methods. Both photodegradation and photocurrent generation were enhanced for the NPE-9 substrate using the HY TiO2/OTE electrode compared to the PA and SG electrodes. Although, biodegradation of NPEs yields NP in rivers, no formation of NP was observed during the photooxidation of NPE-9 because of predominant opening of the benzene ring. Photooxidation of NPEs is facilitated under an applied bias of +0.3 V and scales with the number of ethoxylate groups.

Photocurrent is generated during the photooxidation of nonylphenol polyethoxylate surfactants (NPE-n; n = 1, 5, 7, 9 and 10), precursors of 4-nonylphenol (NP), on illuminated TiO2/OTE electrodes on which TiO2 semiconductor particles were immobilized by a pasting (PA), a sol gel (SG), or both techniques (HY). The photooxidative process of NP and NPEs was examined by absorption spectroscopic methods monitoring the cleavage of the benzene ring moiety, and by the evolution of CO2 gas. The kinetics of photooxidation and the magnitude of the generated photocurrent scaled with the length of the ethoxyl side-chain for NPEs where n = 0, 1, 5, 7 and 10. The relative order of adsorption of NPEs on the positive TiO2 surface was predicted from calculated partial negative point charges of all the C and O atoms in the NPEs using molecular orbital methods. Both photodegradation and photocurrent generation were enhanced for the NPE-9 substrate using the HY TiO2/OTE electrode compared to the PA and SG electrodes. Although, biodegradation of NPEs yields NP in rivers, no formation of NP was observed during the photooxidation of NPE-9 because of predominant opening of the benzene ring. Photooxidation of NPEs is facilitated under an applied bias of +0.3 V and scales with the number of ethoxylate groups.

The enhancement of photocurrent and photodegradation of organic pollutants was investigated using hybrid TiO2 thin films prepared by a combined paste/sol-gel technique to immobilize the TiO2 Particles onto optically transparent electrodes (OTEs); they were connected in series in a continuous flow, bench-top, two-compartment photoreactor. The benzene sulfonate (BS) of the model substrate surfactant used was photodegraded in aqueous media to test the efficacy of the TiO2/OTE electrode preparation and the construction of the photoreactor. Results indicate that the hybrid TiO2 film/OTE electrodes were more efficient than either the pasted TiO2/OTE electrode or the sol-gel TiO2/OTE electrode for the photo degradation of BS, as evidenced by the evolution of carbon dioxide and the photocurrent generated. The extent of ring opening and generated photocurrent during the photodegradation of BS with the hybrid (HY) electrode was correlated to the pasted TiO2 electrode and to the number of dip-coatings in the sol-gel. High photocurrents were generated in the cylindrical large photoreactor under continuous flow of the aqueous BS solution. Optimization of experimental factors for optimal efficiency of the setup was addressed with regard to the preparation of the HY electrodes, and to their size and location in the photoreactor. (C) 2001 Elsevier Science B.V. All rights reserved.

The photocatalytic degradation of six-membered heteroaromatics (pyridazine, pyrimidine and pyrazine) in aqueous TiO(2) suspension was investigated. The initial mechanistic sequence(s) in the TiO(2)-photocatdyzed oxidation of the constituent heterorings was predicted theoretically by molecular orbital (MO) calculations such as frontier electron densities and point charges on all the atoms. The cleavage of the heterocyclic moiety was examined by UV-VIS spectroscopy. The evolution of N(2) and CO(2) gas was determined by gas chromatography. The formation of NH(4)(+) and NO(3)(-) ions was assessed by ion-HPLC, and that of carboxylic acid intermediates by HPLC. The disappearance of six-membered heteroaromatics and the formation of intermediates were observed by LC-MSD. The heterorings containing an N=N fragment lead to the evolution of Nz gas, and those containing a C-N=C fragment lead to the generation of a large amount of NH(4)(+) ions and a minor amount of NO(3)(-) ions. The photodegradation of these heteroaromatics is closely related to the position of the nitrogen in the heterorings. The mechanism of the photodecomposition of the heterocyclic aromatics was revealed through comparison of experimental data with the analytical simulation. (C) 2001 Elsevier Science B.V. Ail rights reserved.

In this study we focus on elucidating the mechanism of the photocatalyzed transformation of the primary, secondary and tertiary amines found in ethanolamine, diethanolamine and triethanolamine when present in illuminated aqueous titania dispersions. Photodecomposition of these ethanolamines leads to the evolution of CO2 through prior formation of various intermediate species. Ammonium (NH4+) and nitrate ions (NO3-) are the ultimate products formed in the photoconversion of the amine nitrogen atoms, with NH4+ cations produced in greater quantity than NO3- anions for all three ethanolamines. Photooxidation of triethanolamine yields various intermediates, including a 3-pyrrolidone derivative, diethanolamine, and then ethanolamine, before complete mineralization occurs. The nature of the initial steps in the photodegradation was predicted by computer-aided molecular orbital (MO) calculations of point charges, and by frontier electron densities of all atoms in the ethanolamine structures.

Sodium benzene sulfonate (BS) was decomposed in aqueous TiO(2) dispersions under highly concentrated solar light illumination to examine the photocatalytic characteristics of a parabolic round concentrator (PRC) reactor to degrade the pollutant without visible light absorption. The effects of such operational parameters as initial concentration, volume of the aqueous BS solution, oxygen purging, and TiO(2) loading on the kinetics of decomposition of BS were investigated. An effective photodegradation necessitates a suitable combination of initial volume and concentration of BS solution. Relative to atmospheric air, oxygen purging significantly accelerates the degradation process at high initial concentrations of BS (0.40 mM or 1.0 mM). Optimal TiO(2) loading was 9 g l(-1), greater than previously reported. Elimination of TOC (total organic carbon) followed pseudo first-order kinetics in the initial stages of the photodegradation process. The relative photonic efficiency for the photodegradation of BS is zeta (rel) = 1.0. (C) 2001 Elsevier Science Ltd. All rights reserved.

This study reports on a comparative assessment of the efficiencies of TiO2/SnO2-doped OTE thin film electrodes fabricated by three different deposition methods. Process efficiencies, as measured by the kinetics of degradation, were examined by monitoring the photo-oxidative fate of two test substrates, namely the anionic surfactant sodium dodecylbenzenesulfonate (DBS) and the model compound sodium benzenesulfonate (BS). Methods chosen to fabricate the TiO2/OTE electrodes comprised (i) pulsed laser deposition, (ii) deposition of a TiO2 paste on the OTE plate, and (iii) sol-gel deposition. Both DBS and BS are readily photo-oxidized and, under our conditions, were partially mineralized to CO2 with the process being made particularly more efficient when the TiO2/OTE electrodes were anodically biased at +0.3 V, which generated a photocurrent during the photoelectrolysis. The sol-gel {C} and anatase {B1} electrodes proved especially useful under the +0.3 V bias. In the absence of any bias, however, DBS photodegraded faster on the TiO2-pasted electrode. Under otherwise similar conditions, the pulsed laser rutile TiO2/OTE electrode showed very little photoactivity. Some of the characteristics of the TiO2 film, such as the TiO2 crystalline form, film thickness, surface roughness, and film transparency appear to have some effect on the overall photodegradative process efficiency. (C) 2001 Elsevier Science B.V. All rights reserved.