Showing papers in "Journal of Photochemistry and Photobiology A-chemistry in 1997"

An overview of semiconductor photocatalysis

Abstract: The interest in heterogeneous photocatalysis is intense and increasing, as shown by the number of publications on this theme which regularly appear in this journal, and the fact that over 2000 papers have been published on this topic since 1981. This article is an overview of the field of semiconductor photocatalysis : a brief examination of its roots, achievements and possible future. The semiconductor titanium dioxide (TiO 2 ) features predominantly in past and present work on semiconductor photocatalysis; as a result, in the most of the examples selected in this overview to illustrate various points the semiconductor is TiO 2 .

Photocatalytic bactericidal effect of TiO2 thin films : dynamic view of the active oxygen species responsible for the effect

Abstract: The role of active oxygen species in the photocatalytic bactericidal effect was investigated using a thin transparent titanium dioxide (TiO2) film. The viable number of Escherichia coli (E. coli) significantly decreased on the illuminated TiO2 film, and the bactericidal effect was observed even when E. coli was separated from the TiO2 surface with a 50 μm porous membrane. Mannitol, a hydroxyl radical scavenger, inhibited the effect only in the absence of the membrane. In contrast, catalase inhibited the effect in all cases. On the basis of these results, the long-range bactericidal effect of hydrogen peroxide was proposed, together with a cooperative effect due to other oxygen species. © 1997 Elsevier Science S.A.

Relative photonic efficiencies and quantum yields in heterogeneous photocatalysis

Abstract: Quantum yield and quantum efficiency (QY) as used in heterogeneous photocatalysis (solid/liquid or solid/gas systems) have too often been used incorrectly to mean the ratio of the rate of a given event to the rate of incident photons impinging on the (external) rector walls, typically for broadband radiation. There is little accord on how to express process efficiency. At times QY is defined, often ill-defined, and more frequently workers fail to describe how it was assessed. This has led to much confusion in the literature, not only because of the different meaning of QY from that in homogeneous photochemistry, but also because this method of describing photon efficiency precludes a comparison of results from different laboratories because of the variations in light sources, reactor geometries, and overall experimental conditions. It cannot be overemphasized that the reported QY is an apparent quantum yield, indeed a lower limit of the true quantum yield. This position paper addresses this issue, and argues that any reference to quantum yields or quantum efficiencies in a heterogeneous medium is ill-advised unless the actual number of photons absorbed by the light harvester (the photocatalyst) has been determined. The extent of light scattering in a solid/liquid heterogeneous medium is significant. A practical and simple alternative for comparing process efficiencies was recently suggested by defining a relative photonic efficiency ζr. A quantum yield can subsequently be determined from ζr, as φ = ζφphenol, where φphenol is the quantum yield for the photocatalyzed oxidative disappearance of phenol (a standard secondary actinometer) using Degussa P-25 TiO2 as the standard catalyst material.

ESR investigation into the effects of heat treatment and crystal structure on radicals produced over irradiated TiO2 powder

Abstract: Electron spin resonance measurements were carried out at 77 K under irradiation for anatase TiO 2 powders treated by heating at various temperatures in the air. For the untreated powder photoproduced holes were trapped at the surface forming Ti 4+ O − Ti 4+ OH − radicals, while, for the heated powder, they were trapped as Ti 4+ O 2− Ti 4+ O − radicals at the surface. Photoproduced electrons were trapped as Ti 3+ at the desorption of surface hydroxyl groups and the change in the surface accompanied by the crystalline growth. No photoproduced radicals were detected for rutile TiO 2 powder, which may explain the low photocatalytic activity of this crystalline structure.

A highly active photocatalyst for overall water splitting with a hydrated layered perovskite structure

Abstract: Photocatalytic decomposition of H2O into H2 and O2 over a novel photocatalyst, K2La2Ti3O10, was accomplished. K2La2Ti3O10, a layered perovskite-type compound with a hydrated interlayer space, exhibited a high activity for overall water splitting with Ni-loading. The highest activity was obtained over Ni(3.0 wt%)–K2La2Ti3O10 when the reaction was carried out in aqueous KOH solution (0.1 M, pH=12.8). By comparison with other Ni-loaded photocatalysts reported previously, the reaction mechanism of Ni–K2La2Ti3O10 was discussed. © 1997 Elsevier Science S.A.

Synthesis, characterization and photocatalytic properties of iron-doped TiO2 catalysts

Abstract: Fe-doped TiO2 catalysts were prepared by coprecipitation and the sol-gel method. The anatase to rutile phase transformation is dependent on the nature of the precursor used. Sol-gel-derived iron-doped catalysts show the presence of rutile and pseudobrookite phases, whereas coprecipitated catalysts show only the anatase phase. The role of the dopant ion is primarily to improve the charge separation of the photoproduced electron-hole pairs via a permanent electric field. The photocatalytic activity of the iron-doped catalysts can be explained in terms of the heterojunction formed between the Fe/TiO2 and α-Fe2O3 phases for the sol-gel-derived catalyst.

Effect of activated carbon content in TiO2-loaded activated carbon on photodegradation behaviors of dichloromethane

Abstract: The effect of the amount of TiO2 loading on activated carbon support on the photodecomposition of dichloromethane was studied The apparent adsorption constant of the TiO2-loaded activated carbon for dichloromethane was found to decrease with increase of the fraction of the loaded TiO2 It was found that the apparent rate constant of CO2 evolution became small with increase of the activated carbon content, suggesting that the absorbed substrate on the activated carbon support was not easily involved in the photodecomposition reaction However, the use of mixed suspensions of TiO2 and activated carbon showed lower activities than the TiO2-loaded activated carbon for photodegradation of dichloromethane The role of the activated carbon support in the photodecomposition of dichloromethane is discussed

Inhibition of the adsorption and photocatalytic degradation of an organic contaminant in an aqueous suspension of TiO2 by inorganic ions

Abstract: The effect of the inhibition of various adsorbed inorganic ions on the adsorption of dichloroethane (DCE) in a titanium dioxide aqueous suspension was studied. The adsorption of the ions was competitive with that of DCE and the adsorption kinetic constant ka varied only slightly around a value of 0.08 min−1. The kinetics of adsorption were controlled by DCE mass transfer, since the ion mass transfer was much more rapid. The affinity of the ions for TiO2 and the competition with CE adsorption were in the order: Cl− < NO3− < [HCO3−, CO32−] < SO42− < [H2PO4−, HPO42−]. The Langmuir model of adsorption was unsatisfactory for the whole set of experiments, thus suggesting a non-uniform surface. The photodegradation occurred on the surface according to an apparent Langmuir-Hinshelwood mechanism, and the inhibition of the ions for this reaction was in the order: NO3− < Cl− < HCO3−, CO32− < SO42− < H2PO4−, HPO42−. The effect of inhibition on the photocatalytic degradation was about half that on the adsorption of DCE, which could be attributed to the surface heterogeneity and/or to a mass transfer phenomenon.

Photo-oxidation of phenol and monochlorophenols in oxygen-saturated aqueous solutions by different photosensitizers

Abstract: The photo-oxidation of phenol and 2-, 3- and 4-monochlorophenols by irradiation with visible light in aqueous alkaline solution in the presence of photosensitizers and oxygen is described. The reactions were carried out in the absence or presence of detergents. The photosensitizers used were Al(III), Zn(II) and Ga(III) complexes of 2,9,16,23-tetrasulphophthalocyanine (1a–1c), 5,10,15,20-tetrakis(4-carboxy-phenyl)porphyrin (2), a cationically charged perylene tetracarboxylic acid diimide (3), rose bengal (4) and methylene blue (5). The photosensitizers exhibit different activities and photo-oxidative stabilities which are strongly dependent on the pH, hydrolysis sensitivity and aggregation tendency. Singlet oxygen, obtained by photoinduced energy transfer from the excited photosensitizers, dominates the initial steps of photo-oxidation. A reaction sequence is proposed on the basis of the identification of carbon dioxide and maleic or fumaric acid as the products of photo-oxidation in the absence of detergent and the evaluated mass balances.

Photo-induced intramolecular charge transfer and internal conversion in molecules with a small energy gap between S1 and S2. Dynamics and structure

Abstract: A discussion is presented of the fast excited state intramolecular charge transfer (ICT) and dual fluorescence observed with several 4-aminobenzonitriles. The occurrence or absence of this ICT reaction is shown to be determined by the magnitude of the energy gap ΔE (S 1 ,S 2 ) between the two lowest excited states. The strong decrease of the ICT efficiency in the series P8C to P3C of 4-aminobenzonitriles in which the amino nitrogen atom is part of a three- to eight-membered heterocyclic ring, is attributed to the increase with decreasing ring size of the barrier for the configurational change of the amino nitrogen from pyramidal to planar, which is considered to be an important reaction coordinate in the ICT process. Dual fluorescence does not occur with P3C nor with NC in diethyl ether. Application of a pressure of 6000 bar leads to a threefold increase of the CT/LE fluorescence quantum yield ratio for the 4(dialkylamino)benzonitrile DMABN (methyl) in diethyl ether, whereas this ratio only slightly increases for DDABN ( n -decyl) in n -hexane. This difference is attributed to the increase of the solvent dielectric constant with pressure, which effect is much larger for diethyl ether than for n-hexane. These results mean that a large amplitude motion does not occur during the ICT reaction of DMABN and DDABN, in accordance with the model of planar intramolecular charge transfer for dual fluorescence. Dual fluorescence is observed with the rigidized aminobenzonitrile NMC7, showing that a full perpendicular twist of the amino group is not essential for the CT state. I -(Dimethylamino) naphthalene ( I DMAN) undergoes a fast thermally activated internal conversion (IC), for which the activation energy increases with solvent polarity. This IC reaction depends on the magnitude of the ΔE (S 1 ,S 2 ) energy gap and is similar in this respect to the ICT reaction of DMABN.

Phenol decomposition using Mn+ /TiO2 photocatalysts supported by the sol-gel technique on glass fibres

Abstract: The photoactivity of supported TiO2 and Mn+/TiO2 (Mn4  Li+, Zn2+, Cd2+, Ce3+, Co3+, Cr3+, Fe3+, Al3+, Mn2+ and Pt0) layers, fixed on glass fibres by the sol-gel technique, was tested using the reaction of phenol degradation. The concentration of metal dopant in the immobilized photocatalysts was 5 mol.% Mn+ :Ti4+. In addition, the effect of platinum loading in Pt0/TiO2 samples (Pt0 content in the range 0.2–5.0 mol.% Pt0:Ti4+) was investigated. The prepared materials were also characterized by their isoelectric points and reflectance spectra. The photoactivity of the materials prepared is strongly dependent on the character and concentration of the dopant. The best results in terms of phenol decomposition were obtained for dopant-free TiO2 Li+/TiO2Zn2+ /TiO2 and Pt0/TiO2 (Pt content, less than 5 mol.% Pt0:Ti4+). However, using Pt0/TiO2 layers, we observed a slower decomposition of hydroquinone, which is produced as an intermediate by phenol hydroxylation. The presence of Co3+, Cr3+, Ce3+, Mn2+, Al3+ and Fe3+ ions in the TiO2 photocatalyst (5 mol.% Nn+ :Ti4+) has a detrimental effect on its photoactivity.

Photophysical characterization of a 1,4,5,8-naphthalenediimide derivative

Abstract: The photophysical properties of N , N -dibutyl-1,4,5,8-naphthalenediimide ( 1 , Scheme 1) were studied using absorption and fluorescence spectroscopy The absorption and emission spectra of 1 are mirror images and show resolved vibrational structure indicating that 1 is a rigid molecule which does not relax substantially from the initially formed Franck-Condon state The fluorescence of 1 is rather weak (quantum yield, approximately 0002), supposedly due to fast intersystem crossing to a close-lying triplet level Diimide 1 aggregates in acetonitrile and in aqueous medium, but aggregation is prevented by the presence of α-cyclodextrin (α-CD) due to complex formation between α-CD and the butyl substituents of 1 Diimide 1 displays unusual spectral characteristics in aromatic hydrocarbon solvents, which can be attributed to ground state complex formation between 1 and the aromatic compound The addition of benzene, toluene and p -xylene to an acetonitrile solution of 1 was followed by fluorescence spectroscopy, and the data obtained were treated as simple 1 : 1 equilibria Association constants were calculated for the complexes between 1 and the aromatic compounds The magnitude of the constants suggests that these ground state complexes are basically of the π-stacking type, with no charge transfer character In the excited state, however, the complexes show polar character, suggesting that electron transfer occurs following excitation

In vitro photochemical damage to DNA, RNA and their bases by an inorganic sunscreen agent on exposure to UVA and UVB radiation

Abstract: The fate of DNA, RNA and their pyrimidine and purine bases was examined on exposure to UVA and UVB radiation in the presence of a physical sunscreen agent (TiO2 anatase/rutile particles) to assess the potential damage that such an agent may cause on contact with such substrates DNA and RNA were partially decomposed and the bases were converted to carbon dioxide (nitrogen atoms to ammonia and nitrate ions) in a Pyrex reactor under conditions simulating UVA and UVB sunlight The physical and chemical damage inflicted on DNA and RNA was also confirmed by scanning electron microscopy and gel permeation chromatography

Photoassisted titanium dioxide mediated degradation of organophosphorus pesticides by hydrogen peroxide

Abstract: The photooxidation of organophosphorus pesticides (OPP) such as methamidophos, phorate, malathion, diazion and EPN, was investigated in UVTiO 2 , UVH 2 O 2 and UVTIO 2  2 O 2 systems. Apparent first-order rate constants were used to describe the photodecomposition behaviors of OPP. Batch results demonstrate that the degradation efficiencies of OPP increased in the order of phorate > methamidophos > malathion ≈ diazion > EPN. The photooxidation of methamidophos and phorate is primarily attributed to direct photolysis. Whereas the presence of TiO 2 promotes the degradation efficiencies of diazion, malathion and EPN. Hydrogen peroxide was found to be an intermediate in UVTiO 2 system during the photocatalytical reaction process. Longer irradiation decreased H 2 O 2 concentration due to the high electron-hole recombination rate on the surface of TiO 2 . Adding H 2 O 2 is more effective on the photocatalytic oxidation of OPP than TiO 2 . Threefold to tenfold of the quantum efficiency of the UVH 2 O 2 system was obtained for the UVTiO 2 system. Moreover, the quantum efficiencies for degradation of OPP decreased when light intensity is increased from 100 to 450 W, although increasing light intensity can increase the apparent first-order rate constants of OPP.

Processes of formation of NH4+ and NO3− ions during the photocatalyzed oxidation of N-containing compounds at the titania/water interface

Abstract: Nitrogen-containing substrates such as amino acids, amides, succinimide, imidazole, hydroxylamine and urea were photodegraded in illuminated TiO2 suspensions, and the temporal course of formation of NH4+ and NO3− ions was monitored. The hydroxylated nitrogen moiety in a molecule was predominantly converted to NO3− ions, whereas a primary amine and/or an amide were exclusively transformed to NH4+ ions under the prevailing conditions. Heterocyclic nitrogen groups in imidazole were converted to both NH4+ and NO3− ions via the intermediates whose structures were the primary amine and hydroxylamine, respectively. The influence of chemical structure on formation of NH4+ and NO3− ions is discussed from the view point of adsorption behaviours of substrates onto the TiO2 surface.

Photocatalytic reduction of nitrite and nitrate ions to ammonia on M/TiO2 catalysts

Abstract: Noble metal loaded TiO2 catalysts have been employed as catalysts for the photocatalytic reduction of nitrite and nitrate ions to ammonia. The yield of ammonia was found to depend on the nature, amount of metal and the method of metallization. An optimum metal content is beneficial for the activity. Beyond the optimum content the activity decreases.

Nanoporous TiO2 photoanode sensitized with the flower pigment cyanidin

Abstract: The flower pigment cyanidin anchors into nanoporous films of TiO2 by surface complexation. A photoelectrochemical cell made from cyanidin-sensitized nanoporous TiO2, as a film deposited on conducting glass and with the I− + I3− redox couple in acetonitrile, generates high photocurrents of good stability.

Study of the spatial resolution of a new 3D microfabrication process: the microstereophotolithography using a dynamic mask-generator technique

Abstract: In order to manufacture new micromechanical components, a new 3D microfabrication technique called the ‘microstereophotolithography using a dynamic mask-generator’ process has been developed. This technique is based on the use of a liquid crystal display as dynamic mask-generator It obliged us to choose photopolymerizable chemical mixtures, specifically designed for microfabrication, that react to visible wavelengths. The chemical resin we used showed a main disadvantage. It contains an organic dye that undergoes photochemical bleaching. A precise control of the spatial resolution of the physico-chemical process happening during the photoreaction is required in order to manufacture small components. Then, the influence of photobleaching on the photopolymerization resolution has thus been investigated. An experimental study has been compared with a mathematical model describing the phenomenon and allowed to optimize the operating conditions of the microstereophotolitoography device we built, and to manufacture small three-dimensional objects made of a large number of complex layers with a resolution better than 5 μm.

Atmospheric fate of methyl vinyl ketone and methacrolein

Abstract: The rate coefficients for the reaction of OH with methyl vinyl ketone (MVK,CH3C(O)CHCH2) and methacrolein (MACR, CH2C(CH3)CHO) between 232 and 378 K were measured using the pulsed laser photolysis-pulsed laser induced fluorescence (PP-PLIF) technique. The rate coefficient data can be expressed in the Arrhenius form as k1(OH + MVK) = 2.67±0.45) × 10−12exp((452±130)/T) and k2(OH + MACR) = (7.73±0.65) × 10−12exp((379±46)/T) cm3 molecule −1 s−1, where the error limits are 2σ and include estimated systematic error. The UV absorption cross-sections of MVK and MACR were measured over the wavelength range 250–395 nm using a diode array spectrometer. Absolute quantum yields for loss of MVK and MACR were measured at 308, 337, and 351 nm. The MACR quantum yield, ФMACR, was <0.01. The MVK quantum yield was both pressure and wavelength dependent and is represented by the expression:: Ф0(λ,P) < exp[ −0.055 (λ−308)]/(5.5 + 9.2 × 10−19N) where λ is measured in nm and N is the number density in molecule cm−3. Atmospheric loss rate calculations using these results show that the primary loss process for both MVK and MACR is the reaction with OH radicals throughout the troposphere.

The fate of organic nitrogen under photocatalytic conditions : degradation of nitrophenols and aminophenols on irradiated TiO2

Abstract: The photocatalytic transformation of 2-, 3- and 4-nitrophenol (NP) and 2-, 3- and 4-aminophenol (AP) over irradiated titanium dioxide was investigated in aerated aqueous solution. At pH < 6, extensive mineralization (more than 90%) of the substituted phenols occurs, whereas, at pH 11, organic carbon is persistently observed. Photocatalysis converts 80% of the nitro group in nitrophenols to NO3− through the intermediate formation of NO2− ions; the remaining 20% is transformed into NH4+ ions. This implies that, even in aerated solutions, reductive pathways are significant, as confirmed by the detection of aminophenol. By contrast, photocatalytic degradation of aminophenols converts the NH2 group into about 60%–70% NH4+ ions and only about 10% NO3−, when about 20% of the organic carbon remaining. A slow transformation of the ammonium ions into NO3− ions is observed at longer irradiation times.

Solvent effect on the photocatalytic reduction of 4-nitrophenol in titanium dioxide suspensions

Abstract: The selective photocatalytic reduction of 4-nitrophenol to 4-aminophenol in titanium dioxide suspensions prepared in aliphatic alcohols (methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, i-butanol) was investigated. The photoreduction rate is significantly affected by the solvent parameters, such as viscosity, polarity, polarisability, and polarity/polarisability.

Gas-phase ultraviolet absorption cross-sections and atmospheric lifetimes of several C2C5 alkyl nitrates

Abstract: Gas-phase ultraviolet absorption cross-sections of ethyl nitrate, 1-propyl nitrate, 2-propyl nitrate, 2-methyl, 1-propyl nitrate, 1-butyl nitrate and 1-pentyl nitrate have been measured over the wavelength range 220–340 nm using a dual-beam, diode array spectrometer. Each alkyl nitrate spectrum appears to be the sum of at least two Gaussian-shaped absorptions with an intense π−π ∗ band extending from 190–240 nm having a shoulder between 250–340 nm due to a π−π ∗ system. The absorption cross-sections recorded for ethyl nitrate, 1-propyl nitrate, 2-propyl nitrate and 1-butyl nitrate are within 10% of previous data: those of 2-methyl, 1-propyl nitrate and 1-pentyl nitrate have been measured for the first time. For ethyl nitrate, absorption cross-sections between 280–340 nm in the tail of the near-ultraviolet band declined with decreasing temperature from 298-233 K. At two-dimensional numerical model of tropospheric chemistry was used to calculate atmospheric lifetimes with respect to photodissociation and OH radical reaction that are markedly dependent on season, latitude and altitude. Relatively long, surface level atmospheric lifetimes of several days to weeks confirm that the C2C5 alkyl nitrates may act as temporary reservoirs for NOx and suggest that they may also constitute a significant fraction of total reactive odd-nitrogen, NOy, particularly during winter at northern hemisphere high latitudes.

Photocatalytic reduction of CO2 using TiO2 powders in liquid CO2 medium

Abstract: The photocatalytic reduction of CO2 was investigated using TiO2 powders in liquid CO2 medium. The TiO2 powders with liquid CO2 medium were illuminated in a stainless steel vessel. After reducing CO2 pressure to the ordinary state, purified water was added to the vessel containing the TiO2 powders without air contamination. No gaseous reduction products were observed and formic acid was exclusively obtained in the aqueous solution. It seems that formic acid is produced through the protonation of the reaction intermediates on the TiO2 powders with purified water.

Photocatalytic decomposition of organophosphonates in irradiated TiO2 suspensions

Abstract: Kinetic analyses of the TiO 2 -catalyzed photodegradation of dimethyl methylphosphonate (DMMP) and diethyl methylphosphonate (DEMP) in oxygenated aqueous solutions are described. The effects of substrate concentration and solution pH are investigated. A number of kinetic models appear to be applicable in accordance with the initial kinetic parameters. The major products formed from the photocatalytic decomposition of DMMP are methylphosphonic acid, phosphoric acid, formaldehyde and formic acid.

Effect of solvents on photocatalytic reduction of carbon dioxide using TiO2 nanocrystal photocatalyst embedded in SiO2 matrices

Abstract: Photocatalytic reduction of CO 2 in various kinds of solvents was studied using TiO 2 nanocrystals embedded in SiO 2 matrices (Q-TiO 2 / SiO 2 ) as the photocatalyst. It was found that the major reduction products were formate and carbon monoxide, and their total amount increased on increasing the concentration of CO 2 dissolved. The ratio of formate to carbon monoxide was greatly influenced by the kind of solvent, and increased on increasing the dielectric constant of the solvent. If bulk TiO 2 was used as the photocatalyst, the rate of CO 2 reduction was low compared to that obtained with Q-TiO 2 /SiO 2 , but the ratio of formate to carbon monoxide obtained was not greatly different from that obtained with the Q-TiO 2 /SiO 2 . The effect of solvent on the reduction behavior of CO 2 is discussed in terms of stabilization of reaction intermediates.

Fate of amino acids upon exposure to aqueous titania irradiated with UV-A and UV-B radiation Photocatalyzed formation of NH3, NO3−, and CO2

Abstract: The fate of nitrogen in various amino acids was examined following their photooxidative (and/or reductive) transformation catalyzed by UV-A and UV-B illuminated aqueous TiO 2 dispersions. The nitrogens in the amino acids are photoconverted predominantly into NH 3 (analyzed as NH 4 + ) and to a lesser extent into NO 3 − ions; NH 4 + /NO 3 − ratios span the range 3–12 after ca. 8 h irradiation. Extensive evolution of CO 2 is also observed; in some cases it is quantitative. Variations in the NH 4 + /NO 3 − ratio in the transformation of amino acids are dependent on the substrates molecular structure. Some of the steps in an otherwise complex mechanism of the heterogeneous photocatalyzedmineralization are described.

Photophysical characterization of trans-4,4′-disubstituted stilbenes

Abstract: Absorption and emission spectra of twenty trans -4,4′-disubstituted stilbenes have been measured in four solvents: cyclohexane (CH), chlorobenzene (CB), 2-butanone (methylethyl ketone, MEK) and dimethylsulfoxide (DMSO) at room temperature. Fluorescence quantum yields ( Φ f ) and fluorescence lifetimes ( τ f ) have been measured for these stilbenes. The lifetimes and quantum yields of fluorescence were found to be dependent on the donor-acceptor properties of the substituents and correlate with the Hammett ν-constants. In addition, we experimentally observed the appearance of a second emitting state which is close energetically to the lowest exited singlet state 1 t ∗ in cases of strong donor-acceptor substituents in polar solvents.

The study of the photokilling effect and mechanism of ultrafine TiO2 particles on U937 cells

Abstract: The killing effect of photoexcited ultrafine TiO2 particles (UFP TiO2) on U937 cells has been studied. The mechanism concerned has been further investigated by DNA agarose gel electrophoresis. The electrophorogram shows that reactive oxygen species produced by photoexcited UFP TiO2 can damage DNA, which results in cell death. Finally, a new assumption of the way to kill cancer cells is proposed.

A study on dye photoremoval in TiO2 suspension solution

Abstract: TiO2 samples with different characteristics and adsorption ability were prepared via hydrolysis of titanium tetraisopoxide and calcination at four different temperatures. The photoremoval of Acid Red 3B catalyzed by these catalysts was carried out. The results show high firing temperature lead to large TiO2 particle and a low adsorption ability of TiO2. The dye photoremoval reaction fits zero order kinetics well in catalyst-free solution and changes to first order kinetics in the presence of TiO2. The solution pH value has a large effect on the removal efficiency. High dye removal efficiency can be obtained at high pH value. Catalyst addition improves the dye photoremoval efficiency and leads to the change of removal kinetics. Anatase TiO2 fired at 400 °C shows the best catalytic activity and the catalytic activity of TiO2 fired at 800 °C, which is rutile, is the worst of all catalysts. The catalytic ability of TiO2 is influenced mainly by two factors of catalysts: crystalline form and adsorption ability for Acid Red 3B. The crystalline form is a more important factor influencing the catalytic activity than the adsorption ability of TiO2 and the catalytic activity can be enhanced by the high dye adsorption ability of TiO2.

Enhanced photocatalytic activity of Ti1−xVxO2 solid solution on the degradation of acetone

Abstract: Solid solutions of Ti1−xVxO2 (0.00< x ≤0.025) exhibit higher photocatalytic activity than pure TiO2 for the oxidation of acetone. Results from X-ray photoelectron spectrometry, X-ray diffractometry and photoionization detection reveal that the photocatalytic activity of the solid solution increases with increasing V substitution, but decreases with a decrease in the anatase to rutile ratio. The optimum composition in terms of activity is x = 0.015, with an anatase to rutile ratio of 9: 1. Zeta potential measurements indicate that the isoelectric point (in terms of the pH value) is affected by the amount of V substitution. The catalyst with x = 0.015 has the lowest isoelectric point (at pH 5.5). All these results suggest that V substitution may enhance the adsorption of hydroxide ions onto the surface of the catalyst. More hydroxyl radicals can be generated, resulting in a higher photocatalytic activity. The synthesis of the catalyst and the effect of the crystalline form of the catalyst on its activity are also presented.