Photochemical & Photobiological Sciences

Augugliaro, Vincenzo; Loddo, Vittorio; López-Muñoz, María José; Márquez-Álvarez, Carlos; Palmisano, Giovanni; Palmisano, Leonardo; Yurdakal, Sedat

2009 Photochemical & Photobiological Sciences

doi: 10.1039/b818353hpmid: 19424540

TiO2catalysts of anatase, rutile and brookite phase were prepared at low temperature and tested for carrying out the photocatalytic partial oxidation of 4-methoxybenzyl alcohol to 4-methoxybenzaldehyde (p-anisaldehyde) in organic-free water suspensions. Traces of 4-methoxybenzoic acid and open-ring products were the only by-products present, CO2 being the other main oxidation product. Rutile exhibited the highest yield to p-anisaldehyde (62% mol) at a rate of the same order of magnitude of that showed by the other samples. Commercial rutile and anatase photocatalysts were also used for the sake of comparison. The samples have been characterised by an in situATR-FTIR investigation carried out in conditions simulating the photoreaction ones.

Maver, Ksenija; Štangar, Urška Lavrenčič; Černigoj, Urh; Gross, Silvia; Cerc Korošec, Romana

2009 Photochemical & Photobiological Sciences

doi: 10.1039/b817475jpmid: 19424539

Transparent TiO2 and TiO2–ZrO2 (molar ratio Zr/Ti = 0.1) thin films were produced by low-temperature sol–gel processing from nanocrystalline aqueous based solutions. The structural features and compositions of the films treated at room temperature, 100 °C and 500 °C were investigated by X-ray diffraction, X-ray photoelectron spectroscopy and thermal analysis. Addition of zirconia increased specific surface area (140–230 m2 g−1) and hindered the growth of anatase crystallites, exhibiting a constant size of 6–7 nm in the whole temperature range. These significant changes with respect to pure TiO2 in anatase crystalline form did not result in significantly and systematically different photocatalytic activity, which was evaluated in terms of aqueous pollutant degradation (azo-dye in water) and self-cleaning ability (fatty contaminant deposit). The films treated at only 100 °C showed excellent photocatalytic activity towards azo-dyedegradation. Contact angle measurements of aged and contaminated surfaces revealed a fast or sharp hydrophilicity gain under UVA illumination. Accordingly, the results of this study confirmed the potential application of advantageous low-temperature films in water treatment as well as for self-cleaning surfaces.

Camera-Roda, Giovanni; Santarelli, Francesco; Panico, Mauro

2009 Photochemical & Photobiological Sciences

doi: 10.1039/b817351fpmid: 19424547

The experimental results obtained for the photocatalytic degradation of a model organic dye in an annular slurry reactor are analyzed with the aid of a mathematical model. The model is used also to study the effects on the performances of many operative conditions: flow rate, photocatalyst concentration, power of the lamp, size of the photocatalytic particles, dimensions of the reactor. The investigation demonstrates that the rate of the process is often limited by the radiant energy transfer and that some simple rules can be followed in order to optimize different yields and the observed rate of reaction.

Sirtori, Carla; Zapata, Ana; Malato, Sixto; Gernjak, Wolfgang; Fernández-Alba, Amadeo R.; Agüera, Ana

2009 Photochemical & Photobiological Sciences

doi: 10.1039/b817247apmid: 19424537

In this study, degradation of Flumequine (FLU) and nalidixic acid (NXA) in distilled water by two solar photocatalytic processes, TiO2 and photo-Fenton, was evaluated. Intermediates and acute toxicity of the photoproducts generated were also studied. Degradation efficiency by heterogeneous photocatalysis with TiO2 was similar for NXA and FLU, which were completely degraded after 25 min of illumination. Less NXA mineralisation was reached after 80 min of illumination. Photo-Fenton degradation of both substances was very quick (<25 min of illumination time), and the same mineralisation was reached in both cases. The kinetic parameters of the two substances were calculated for comparison of their photocatalytic degradation. In all cases, photocatalytic processes were associated with a reduction in toxicity, as evaluated by Vibrio fischeri bioassay. Furthermore, a sharp decrease in inhibition was observed from the beginning of the treatment, even when FLU and NXA were still present in the reaction solution (first samples). These results demonstrate that in both photocatalytic processes studied, toxicity decreases significantly, producing a phototreated sample within safe toxicity limits. The intermediates formed during photocatalytic degradation were studied by liquid chromatography-time of flight-mass spectrometry (LC-TOF-MS).

Meichtry, Jorge M.; Rivera, Verónica; Di Iorio, Yesica; Rodríguez, Hernán B.; Román, Enrique San; Grela, María A.; Litter, Marta I.

2009 Photochemical & Photobiological Sciences

doi: 10.1039/b816441jpmid: 19424532

Hydroxoaluminiumtricarboxymonoamide phthalocyanine (AlTCPc) adsorbed at different loadings on TiO2 Degussa P-25 was tested for Cr(vi) photocatalytic reduction under visible irradiation in the presence of 4-chlorophenol (4-CP) as sacrificial donor. A rapid reaction takes place in spite of the presumable aggregation of the dye on the TiO2 surface. The removal of Cr(vi) is fairly negligible under visible-light irradiation, either without photocatalyst or in the presence of bare TiO2. The fast capture of conduction band electrons by Cr(vi), which forms a surface complex with TiO2, inhibits the formation of reactive oxygen species in the reductive pathway. This fact and the easier oxidation of 4-CP as compared to AlTCPc hinder the photobleaching of the dye and make feasible Cr(vi) reduction under visible irradiation. The consumption of Cr(vi) follows a pseudo-first order kinetics; the decay constant depends, in the studied range, on the photocatalyst mass, but it is barely affected by dye loading. The presence of 4-CP is essential, but its concentration has no effect on the Cr(vi) decay rate. Oxidation products of 4-CP, such as hydroquinone, catechol or benzoquinone, are not observed. Direct evidence of the one-electron reduction of Cr(vi) to Cr(v) was obtained by EPR spectroscopy using citric acid as Cr(v) trapping agent. In this case, disappearance of Cr(v) also follows a first order decay, but conduction band electrons do not seem to be involved. The fact that oxidation products of 4-CP are not observed is consistent with the fast dark removal of reaction intermediates by Cr(v), proved by EPR.

Ubomba-Jaswa, Eunice; Navntoft, Christian; Inmaculada, M.; Fernandez-Ibáñez, Pilar; McGuigan, Kevin G.

2009 Photochemical & Photobiological Sciences

doi: 10.1039/b816593apmid: 19424529

The effect of solar UV-A irradiance and solar UV-A dose on the inactivation of Escherichia coliK-12 using solar disinfection (SODIS) was studied. E. coliK-12 was seeded in natural well-water contained in borosilicate glass tubes and exposed to sunlight at different irradiances and doses of solar UV radiation. In addition, E. coliK-12 was also inoculated into poly(ethylene) terephthalate (PET) bottles and in a continuous flow system (10 L min−1) to determine the effect of an interrupted and uninterrupted solar dose on inactivation. Results showed that inactivation from approximately 106CFU mL−1 to below the detection level (4 CFU/mL) for E. coliK-12, is a function of the total uninterrupted dose delivered to the bacteria and that the minimum dose should be>108 kJ m−2 for the conditions described (spectral range of 0.295–0.385 μm). For complete inactivation to below the limit of detection, this dose needs to be received regardless of the incident solar UV intensity and needs to be delivered in a continuous and uninterrupted manner. This is illustrated by a continuous flow system in which bacteria were not fully inactivated (residual viable concentration ∼102CFU/mL) even after 5 h of exposure to strong sunlight and a cumulative dose of>108 kJ m−2. This has serious implications for attempts to scale-up solar disinfection through the use of re-circulatory continuous flow reactors.

Konti, Georgia; Chatzivasiloglou, Evaggelia; Likodimos, Vlassis; Kantonis, Georgios; Kontos, Athanassios G.; Philippopoulos, Athanassios I.; Falaras, Polycarpos

2009 Photochemical & Photobiological Sciences

doi: 10.1039/b817470apmid: 19424549

cis-[Ru(bpy)2(Ln)]Cl2 (n = 1, L1 = 4-carboxy-2-(2′-pyridyl)quinoline (2); n = 2, L2 = 2,2′-pyridine-4,4′-dicarboxylic acid (4)); and cis-[Ru(bpy)2(L′)2)]Cl2 (L′ = 4-pyridinecarboxylic acid (6)) complexes, with surface anchoring groups, are prepared from the reaction of cis-[Ru(bpy)2Cl2] (1) with the appropriate ligand (L1, L2, L′). Ion exchange in aqueous solution with NH4PF6 gives the corresponding bis(hexafluorophosphate) derivatives cis-[Ru(bpy)2(L1)](PF6)2 (3), cis-[Ru(bpy)2(L2)](PF6)2 (5) and cis-[Ru(bpy)2(L′)2](PF6)2 (7), respectively. The photo-electrochemical properties of the dyes (2–7) are investigated and the efficiency of the corresponding dye sensitized solar cells is compared to a N719 sensitized device, under similar fabrication and testing conditions.

Klementová, S.; Kříž, D.; Kopáček, J.; Novák, F.; Porcal, P.

2009 Photochemical & Photobiological Sciences

doi: 10.1039/b817044dpmid: 19424528

Fluorophore types and their photochemical stability have been tested in two samples of humic acids (HA) and four types of fulvic acids (FA) extracted from upper soil horizons (O and A horizons) in Norway spruce forest mountain ecosystems. Only one type of fluorophore occurred in all samples, with an excitation maximum at 310 nm for both HA and FA samples and emission maxima between 420–435 and 440–450 for HA and FA, respectively. HA weak native fluorescence increased significantly during irradiation in the first 12 h. Fluorophores in FA were uniformly degraded from the beginning of irradiation. Addition of metal (aluminium or ferric) ions did not affect the positions of fluorescence maxima in any of the studied samples; mild effects on fluorescence intensities were observed.

Arslan-Alaton, Idil; Tureli, Gokce; Olmez-Hanci, Tugba

2009 Photochemical & Photobiological Sciences

doi: 10.1039/b817423gpmid: 19424535

Treatability of synthetic Acid Blue 193 and Reactive Black 39 production wastewaters and real Reactive Black 39 production effluent via photo-Fenton-like process was investigated. The Central Composite Design technique was used to study the effect of some critical process parameters of the photo-Fenton process (e.g. reaction time, initial COD and Fe3+:H2O2 molar ratio) on synthetic Acid Blue 193 production wastewater treatment efficiency in terms of color, chemical oxygen demand (COD) and total organic carbon (TOC) removals. Selected process parameters were optimized to obtain maximum color, COD and TOC removal efficiencies. Optimum working conditions were established as 45 min reaction time and a Fe3+:H2O2 molar ratio of 0.073 for wastewater having an initial COD (CODo) of 200 mg L−1. Under these conditions, 99% color, 83% COD and 58% TOC abatements were experimentally obtained. In case of real Reactive Black 39 production effluent, photo-Fenton-like treatment efficiency was found to be considerably lower than that of the synthetic acid and reactive dye production wastewaters, which was attributable to the relatively high chloride (i.e. a well known ˙OHradical scavenger) content of the real effluent.

Mori, Kohsuke; Araki, Takashi; Takasaki, Tomoya; Shironita, Sayoko; Yamashita, Hiromi

2009 Photochemical & Photobiological Sciences

doi: 10.1039/b817049epmid: 19424538

Supported Pd catalysts were synthesized using various semiconductor materials by a photo-assisted deposition method under UV-light irradiation. The Pd precursor was deposited and partially reduced by the direct interaction with the photo-excited state of the semiconductor materials, and subsequently transformed into metal particles by H2reduction. CO adsorption and Pd K-edge XAFS measurements demonstrated that the mean diameter of the deposited Pd particles can be controlled by the type of employed semiconductor materials. The catalytic activities in the direct synthesis of hydrogen peroxide (H2O2) using H2 and O2 gases under atmospheric pressure were strongly dependent on the type of supports. Here, the use of TiO2 comprising a mixed phase of anatase and rutile was the most efficient based on the amount of Pd. The photo-assisted deposition also provides a simple and straightforward method to synthesize PdAu alloy nanoparticles. For the structural model of PdAu nanoparticles, we suggest that most of the Au atoms are preferentially located in the core region, whereas the Pd atoms are preferentially located in the shell region. The PdAu/TiO2catalysts prepared by the photo-assisted deposition method were shown to perform significantly better than the pure Pd/TiO2catalysts.