Search

Hybrid photocatalysis/membrane processes constitute promising alternatives for water and wastewater treatment because they combine the efficiencies of filtration membranes technology and the oxidative effect of the photocatalytic process, increasing the lifetime of the membranes. The main challenge of these systems is the incorporation of the titanium dioxide (TiO2) catalyst without altering the filtration properties of the membrane and the photocatalytic activity of the catalyst. One way to achieve this goal is generating the TiO2 layer by direct anodization of titanium supports under controlled conditions to form titanium dioxide nanotubes (TiO2-NTs). This work reports the development of novel photocatalytic titanium membranes based on the formation of TiO2-NT arrays by anodization under both potentiostatic and galvanostatic conditions, and the scaling-up of the most promising systems to operational membrane photoreactors. The results demonstrated that the galvanostatic method displays more controlled tuneability to obtain NTs formation than the potentiostatic method on porous surfaces. However, despite the formation of TiO2-NTs structures, the observed photocatalytic activity is lower than that exhibited by TiO2 nanoparticles deposited directly on the membrane, although in this case the transmembrane pressure is significantly higher, and therefore the operational pumping costs are greater. Synergistic effects of photocatalysis and microfiltration are clearly demonstrated in the application of the hybrid system to the removal of bacteria for water disinfection processes, showing a significant improvement in the inactivation of E. coli bacteria in water with respect to the bare membrane.

This work reports the application of photocatalytic disinfection to the inactivation of Acanthamoeba trophozoites, a free-living pathogenic amoeba. Two types of photocatalytic reactors configurations have been used: i) a slurry reactor using suspended titanium dioxide (TiO2); and, ii) a fixed-bed reactor using immobilized TiO2 onto glass Raschig rings. The effect of the chemical composition of water has been analysed, comparing the efficiency of the process in deionized water (DW) and synthetic wastewater treatment plant effluent (SWTPE). The inactivation of Acanthamoeba spp. has been compared to that of Escherichia coli bacteria, being also analysed the concomitant inactivation of both microorganisms. Our results show that 99% of inactivation of E. coli and Acanthamoeba spp. can be achieved using photocatalysis in both reactor configurations, but interestingly, the kinetics of inactivation of both microorganisms together differs from that found with them separately. Particularly, E. coli seems to be more resistant to the inactivation in the presence of Acanthamoeba spp. which has been justified by the screen effect caused by the bigger size of Acanthamoeba spp. This observation is more pronounced in DW as the composition of the SWTPE prevent the microorganisms from suffering osmotic and/or mechanical stress and protect cellular structures to the attack of reactive oxygen species (ROS). On the other hand, the difference between the inactivation rate of E. coli and Acanthamoeba, points out the importance of the different inactivation mechanisms, suggesting that the entry of small TiO2 particles into the cytoplasm of the Acanthamoeba cells provokes the attack of inner structures and as a consequence a faster inactivation. This mechanism is not possible when the catalyst is immobilized leading to a higher cell resistance to inactivation and consequently lower efficiency of the disinfection process.

The aim of this work was to demonstrate the possibility of using scaled-up photoanodes to inactivate bacteria and oxidise organic compounds as disinfection tertiary treatment of wastewaters. Scaled-up nanoparticulate titania photoanodes were immobilised on conductive glass by dip-coating (141.4 cm2). Photoelectrocatalysis led to a higher disinfection rate in comparison to photocatalysis for all experiments, giving rise to an increase in values of bacterial inactivation kinetic constant from 1.45 up to 2.18 × 104 CFU L−1 min−1 in 0.1 M Na2SO4 and from 1.73 up to 2.23 × 104 CFU L−1 min−1 in simulated wastewaters when using a TiO2 thickness layer of 0.88 ± 0.12 μm and applying +1.0 V. In contrast, photocatalytic oxidation of methanol was not improved when an electric potential bias is applied. It is suggested that electrostatic attraction of negatively charged bacteria to the positively biased photoanodes leads to the enhancement observed. When scaling-up a TiO2/ITO (Indium Tin Oxide) electrode, the change in the way of illumination of the photoreactor has to be carefully taken into account. It led to significant differences in bacterial inactivation, which was noticeably diminished when using a photoreactor with scaled-up photoelectrodes illuminated from the back side of the photoanode. No differences were found out for methanol oxidation. This may be explained by the differences in size between both pollutants, leading to differences in their transport through the TiO2 layer and their feasibility to interact with OH radicals.

A novel integrated photocatalysis/microfiltration hybrid system based on the use of TiO2 immobilized by filtration on porous stainless steel supports has been demonstrated to provide a good efficiency in the removal of bacteria for water disinfection applications. A synergistic effect derived of the physical removal of microorganisms coupled to its photocatalytic inactivation was proved to be achieved. The membrane pore size and the TiO2 loading were found to play a significant role on the efficiency of the process and the value of the transmembrane pressure. An optimal value of 8.5 g·m−2 TiO2 supported over the membranes provides good photocatalytic activity keeping the transmembrane pressures in the range of 1.5–2 bar. Moreover the photocatalytic activity of the membrane was proved to have as an additional advantage the possibility of the simultaneous oxidation of the chemical pollutants present in the feed water. Continuous operation of the photocatalytic membrane reactor in dead-end configuration confirms the accumulation of bacteria on the membrane leading to an increase in the transmembrane pressure, whereas the photocatalytic functionality demonstrated a significant inactivation of the retained cells, confirming the feasibility of the hybrid process for biofouling control.

BiVO samples doped with different contents of Er and Y were prepared by a simple surfactant free hydrothermal method. X-ray diffraction reveals that the doped materials consist of a heterogeneous structure formed by a mixture of tetragonal and monoclinic phases, being found Er and Y co-doping clearly stabilize the tetragonal structure of BiVO. The monoclinic BiVO samples shows a strong absorption in the visible light region leading to band-gap values of around 2.4 eV while the tetragonal BiVO displays higher band-gap values of 2.9 eV. The photocatalytic activity of the catalysts was investigated for the oxidation of methanol and inactivation of Escherichia coli showing that all the BiVO catalysts are photocatalytically active in the oxidation of methanol and are able to inactivate more than 99.99% of bacteria not only under UV light but also under visible light irradiation. The results revealed that the co-doping of Er and Y into BiVO exhibited enhanced photocatalytic activity for methanol oxidation under simulated solar light irradiation. The inactivation of E.coli show similar results for the doped systems although in relative terms of activity the Er,Y-BiVO sample show a better use of the visible light, leading to a higher activity than P25-TiO., The authors gratefully acknowledge the financial support of the European Commission under FP7 project 309846, “Photocatalytic Materials for the Destruction of Recalcitrant Organic Industrial Waste–PCATDES”. The financial support from Junta de Andalucía by project P09-FQM-4570 and Spanish Ministry of Economy and Competitiveness (MINECO) through ENE2011-24412 project is also acknowledged. C. Adán is indebted to the MINECO for its Juan de la Cierva postdoctoral contract (JCI-2010–06430). S. Obregón thanks CSIC for the concession of a JAE-Pre grant.

A novel photoelectrochemical three-dimensional reactor was designed and used to evaluate the photoelectrocatalytic inactivation of bacteria (E. coli) in water using a commercial anode of RuOx/Ti and an illuminated photocatalyst of GAC-TiO2 composite as bipolar electrode. Due to the complexity of the process, the individual phenomena potentially involved in the inactivation mechanism (adsorption, photolysis, electrolysis and photocatalysis) have been evaluated to establish the possible additive, synergistic or antagonistic results of their different combinations. The main oxidizing species formed during the processes (chlorine species and hydroxyl radicals) have been analyzed to elucidate the mechanism. Results show that the use of granular activated carbon (GAC) and GAC-TiO2 composites as third bipolar electrode improves the efficiency of conventional electrocatalysis, but mainly due to the removal effect of the adsorption of bacterial onto the solid particles, and not through a direct impact on the electrochemical generation of disinfecting species. When the GAC-TiO2 composite electrode is illuminated with UV-A light, a significant improvement in the bacterial inactivation efficiency is also observed due to the sum of the adsorption of bacteria and the generation of reactive oxygen species (especially hydroxyl radicals) by the TiO2 photocatalyst. It has been proven that in the electrochemical processes the formation of chlorine species is favored while hydroxyl radical’s generation is favored in the TiO2 photocatalytic system. However, the combination of the photocatalytic process with the electrochemical process (photoelectrocatalytic disinfection) presents a remarkable antagonism derived from the mutual annihilation of the hydroxyl radicals with the chlorine species.

This work reports the application of photocatalytic disinfection to the inactivation of Acanthamoeba trophozoites, a free-living pathogenic amoeba. Two types of photocatalytic reactors configurations have been used: i) a slurry reactor using suspended titanium dioxide (TiO

Línea 1. Procesos de depuración de aguas residuales The use of TiO2 electrodes may solve the two main drawbacks of photocatalytic processes: i) the necessity of recovering the catalyst and ii) the low quantum yield in the use of the radiation. This work focuses on the correlation between the photoelectrochemical properties of TiO2 electrodes and their activity for the photoelectrocatalytic oxidation of methanol. Particulate TiO2 electrodes prepared by deposition of P25-TiO2 nanoparticles on titanium (TiO2/Ti) or conductive glass support (TiO2/ITO) seem to be effective for charge carrier transference on TiO2 surface favouring the formation of ¿OH radicals and consequently, the oxidation of molecules. In contrast, thermal TiO2 electrodes prepared by annealing of titanium (Ti) present better properties for charge carrier separation as a consequence of the application of a potential bias. Despite reducing charge carrier recombination by applying an electric potential bias, the activity of thermal electrodes remains lower than that of P25-particulate electrodes. TiO2 structure of P25-particulate electrodes does not completely allow developing a potential gradient. However, their adequate TiO2 layer characteristics for charge carrier transfer lead to a reduction in charge carrier recombination making up for the lack of charge carrier separation when applying an electric potential bias. TiO2/Ti showed the highest values of activity. Therefore, the combination of the suitable TiO2 surface properties for charge carrier transfer with an adequate conductive support seems to increase the properties of the electrode for allowing charge carrier separation. The scaling-up calculations for a TiO2/ITO electrode do lead to good estimations of the activity and photocurrent of larger electrodes since this photoanode made from ITO as conductive support does not seem to be significantly affected by the applied potential bias. Tecnología Química y Energética

Iron-doped TiO2 catalysts with two different iron contents (0.7 and 3.5 wt.%) as well as the corresponding undoped system, prepared by a combined sol–gel/microemulsion method and calcined at 600 °C, have been examined with respect to their behaviour for photocatalytic degradation of aqueous phenol with H2O2 under solar light. The activity results are complemented with structural/morphological and electronic characterization analysis achieved by XRD, TEM, Raman, SBET, UV–vis DRS and XPS techniques. A detrimental effect of the presence of iron on the photoactivity is detected for the sample with 0.7 wt.% iron. In contrast, some activity enhancement is produced for the sample with highest iron loading. Such irregular catalytic behaviour with respect to iron loading is analyzed on the basis of the presence of additional catalytic contributions from new photoactive species. These are created as a consequence of surface modifications produced under reaction conditions related to the existence of phenomena of iron leaching from the catalysts. Differences in the specific nanostructure present in each case can also play a role on explaining the differences observed in the photoactivity. Finally, an analysis of the photoactivity as a function of the oxidizing agent employed, either H2O2 or oxygen from air, is also performed., Thanks are due to the MEC (projects CTQ2004-03409/BQU, CTQ2006-15600/BQU and CTM2010-14883) and CSIC (project PIF 200420F0280) and Programa de Acceso de Grandes Instalaciones Científicas Españolas GIC-05-17, for financial support. Support from EU COST Action CM1104 is also acknowledged.

Different TiO2 photoelectrodes have been characterized and tested for the photoelectrocatalytic oxidation of methanol. Particulate electrodes (TiO2/Ti and TiO2/ITO) have been shown to notably favour charge-carrier transfer at the electrolyte interface while a thermal electrode (Ti) has been shown to favour charge-carrier separation when applying an electric potential bias according to cyclic voltammetry technique, as a consequence of differences in TiO2 surface between particulate and thermal electrodes. Particulate electrodes lead to a higher photoelectrocatalytic activity for methanol oxidation compared to that of the thermal electrode, probably due to the pure-rutile TiO2 phase composition of the latter and its lower surface area. TiO2/Ti electrode has been shown to be the most effective photoelectrode tested for methanol oxidation since its activity was improved by the combination of the particulate TiO2 layer and the high electrical conductivity of the support. Generally, photocurrent density measured in the photoelectrochemical cell seems to correlate with activity, whereas this correlation is not observed when using a larger photoelectrocatalytic reactor. In contrast, the activity obtained for the scaled-up electrode is found to be similar in terms of surface kinetic constant to that obtained at laboratory scale.

The relation between the amount of incident photons, absorbed photons, oxidant species, reaction products and electrons in the external circuit should be analyzed individually to determine the step limiting the efficiency of the global photoelectrocatalytic processes. This work discusses the evaluation of three different titania electrodes for the oxidation of methanol in a photoelectrocatalytic reactor. The electrode prepared with three titania coating cycles shows a high efficiency in terms of photochemical (photons to product molecules), electrochemical (product molecules to electrons) and photoelectrochemical (photons to electrons) what explain its high activity for the photoelectrocatalytic oxidation of methanol.

A comprehensive report on the correlation between the morphology and the photocatalytic (PC) and photoelectrocatalytic (PEC) activity of TiO2 nanotubes (NTs) electrodes is presented. New insights are provided to support the effect of the anodization conditions on the photon-to-current efficiency of the electrodes based on the dimensional characteristics of the TiO2-NTs. Electrodes with promising properties based on the characterization data were scaled-up to test their activity on the PC and PEC oxidation of methanol. Results indicate that the length of the nanotubes significantly influences the photodegradation efficiency. The enhancement achieved in both PC and PEC processes with longer nanotubes can be explained by the higher surface area in contact with the electrolyte and the increase in the light absorption as the TiO2 layer becomes thicker. However, as the length of the nanotubes increases, a reduction in the enhancement achieved by the application of a potential bias is observed. Kinetic constants of both reactions (PC and PEC) tend to get closer and the charge separation effect diminishes. In relative terms, the effect of the electric potential is more pronounced for electrodes with the shorter NTs. The reason is that once the TiO2 layer is thick enough to absorb the available radiation, a further increase in the NTs length increases the resistance of the electrons to reach the back contact and the diffusional restrictions to the mass transport of the reactants/products along the tubes. Consequently, the existence of a compromise between reactivity and transport properties lead to the existence of an optimal NTs length.

Materials based on niobium oxide (Nb

Titanium dioxide coatings were deposited on the surface of titanium foils by Thermal Plasma Spray (TPS) process. Three different TiO2 coatings were prepared using the commercial TiO2-P25 nanopowder and titanium isopropoxide precursor solution as feed-stocks. Structure and morphology of the TiO2-P25 powder and the plasma sprayed coatings were analyzed by X-ray diffraction (XRD), Raman spectroscopy, N2 adsorption-desorption isotherms, UV-visible spectroscopy and Scanning Electron Microscopy (SEM). XRD and Raman results indicate that the TiO2 coatings were composed of an anatase/rutile mixture that is conditioned by the suspension composition used to be sprayed. Coatings prepared from TiO2-P25 nanoparticles in water suspension (NW-P25) and titanium isopropoxide solution suspension (NSP-P25) are incorporated into the coatings without phase transformation and their anatase/rutile ratio percentage remains very similar to the starting TiO2-P25 powder. On the contrary, when titanium isopropoxide solution is used for spraying (SP), the amount of rutile increases in the final TiO2 coating. SEM analysis also reveals different microstructure morphology, coating thickness, density and porosity of the three TiO2 films that depend significantly on the type of feed-stock employed. Interestingly, we have observed the role of titanium isopropoxide in the formation of more porous and cohesive layers of TiO2. The NSP-P25 coating, prepared with a mix of titanium isopropoxide solution based on TiO2 nanoparticles, presents higher deposition efficiencies and higher coating thickness than the film prepared with nanoparticles suspended in water (NW-P25) or with titanium isopropoxide solutions (SP). This is due to the precursor solution is acting as the cement between TiO2 nanoparticles, improving the cohesive strength of the coating. In sum, NSP-P25 and NW-P25 coatings display a good photocatalytic potential, based on their light absorption properties and mechanical stability. Band gap of the nanoparticulated coatings displays a light absorption at wavelengths below 379 and 399 nm for NW-P25 and NSP-P25 respectively. On the contrary, the SP coating, despite to present lower band-gap value, has bad cohesive properties with surface crackings that makes it mechanically unstable. Therefore, mixtures of P25 nanoparticles with titanium isopropoxide as feed-stock materials can produce promising photocatalytic coatings.

Nanostructured iron-doped TiO 2 catalysts with anatase structure and two different iron contents (0.7 and 3.5 wt.%) have been prepared by a combined sol–gel/microemulsion method and examined with respect to their behaviour for photocatalytic degradation of aqueous phenol with H 2 O 2 under solar light. The activity results are compared with those obtained for similarly prepared undoped systems as well as Degussa P25 reference catalyst and have been complemented with structural/morphological and electronic characterization analyses achieved by XRD, TEM, Raman, S BET , UV–vis DRS and XPS techniques. In contrast to typically observed results, the highest photoactivity is obtained for the catalyst with highest iron loading while that with 0.7% Fe displays lower photoactivity than undoped samples. Such unusual behaviour has been attributed to the contribution of new photoactive iron complexes generated on the surface of the catalyst as a consequence of iron leaching and readsorption processes taking place during the course of phenol photodegradation process.

Different single treatments and a combined process based on two advanced oxidation processes, catalytic wet peroxide oxidation and photocatalysis, have been tested for the purpose of achieving complete mineralization using phenol as target compound at medium-range concentration (200 mg L −1 ). The heterogenous catalysts that were used were a home-made activated carbon-supported iron catalyst (FeCN), and the commercial Aeroxide titania P25. An important improvement in the rate and percentage of TOC removal was achieved by combining both catalysts in a hybrid process based on a mixture of FeCN and TiO 2 P25 (50:50 wt.%) in the same photoassisted reactor in ambient conditions. TOC evolution has been modelled for all the treatments for comparative purposes. The hybrid process allowed a highly efficient use of hydrogen peroxide with the almost complete oxidation of phenol to CO 2 and H 2 O by using the theoretical stoichiometric amount of H 2 O 2 . Among the different advantages of this hybrid process is the rapid and effective degradation of the aromatic compounds adsorbed onto the Fe/CN catalyst surface as a consequence of synergistic effect of the two catalysts in the presence of irradiation light in ambient conditions, achieving a higher degree of mineralization of short-chain organic acids that are resistant and refractory to CWPO treatment. Finally, the stability and durability of this catalytic mixture (FeCN + titania P25) in hybrid mode have been examined through four consecutive cycles. A constant organic matter removal was observed during the last three consecutive cycles in which 90% of total organic carbon conversion was achieved.

A series of nanosized iron-doped titania catalysts has been used for the photocatalytic degradation of ethidium bromide (EtBr) with oxygen. The study shows that EtBr surface adsorption is most favored over basic titania surfaces such as those present in undoped TiO2 and Fe–TiO2 with low iron content. This fact is shown to affect strongly the photocatytic mechanism of EtBr degradation. Based on EtBr adsorption and photocatalytic activity analyses, a titania catalyst with an iron content of 0.7 wt.% has been selected for subsequent studies using H2O2 as oxidant. Parameters as reaction pH and initial hydrogen peroxide concentration were analyzed to establish optimum operating conditions. It is shown that a new strategy based on dosing H2O2 in a controlled way could minimize radical self-scavenging reactions and improves final EtBr mineralization degree. Finally, the stability and durability of catalyst/activity have been examined through five consecutive cycles of H2O2 dosing. A constant activity level is maintained during at least four consecutive cycles in which total EtBr and 80% of Total Organic Carbon conversion is achieved.

The influence of iron content and calcination temperature applied during catalyst preparation on the solar light assisted photo-degradation of phenol over iron-doped titania catalysts have been studied. Pure titania catalysts were also analysed for comparative purpose. An improvement in phenol and TOC removal was detected upon increasing calcination temperature. Although subtle differences in evolution and distribution of short-organic acids were observed upon increasing the calcination temperature, phenol photo-degradation apparently proceeded through the same oxidation pathway over all analysed catalysts. A photo-complex mechanism of iron lixiviates by which the reduced Fe(II) ions in solution become re-adsorbed on the catalyst surface and subsequently re-oxidized by photogenerated holes, leaving the catalyst ready for a new photo-degradation cycle, has been postulated to explain the obtained results. Iron is proposed to be extracted from the catalysts surface through formation of a [Fe-carboxylic acid]2+ complex within a process in which refractory carboxylic acids simultaneously undergo further oxidation. XPS results and the absence of differences in the iron content determined by chemical analysis when comparing fresh and used catalysts confirm the re-adsorption phenomena of iron lixiviates on the catalyst surface.

Photodegradation of phenol was investigated with two types of oxidant agents in water, oxygen and hydrogen peroxide, at two different reaction pH with a series of nanosized iron-doped anatase TiO 2 catalysts with different iron contents. The catalysts have been prepared by a sol–gel/microemulsion method. Firstly, iron-doped titania catalysts were studied with respect to their activity behavior when oxygen was used as oxidant agent in the photocatalytic degradation of aqueous phenol in comparison with un-doped reference catalysts. Secondly, two catalysts (TiO 2 and 0.7 wt.% Fe-doped TiO 2 ) were selected to extend the study for the employment of hydrogen peroxide as oxidant at different concentrations and two initial reaction pHs. An enhancement of the photocatalytic activity is observed only for relatively low doping level (ca. 0.7 wt.%) in catalyst calcined at 450 °C preferably using hydrogen peroxide as oxidant agent which is attributable to the partial introduction of Fe 3+ cations into the anatase structure. Nevertheless, it has been demonstrated that catalyst surface properties can play an important role during phenol photodegradation process on the basis of the analysis of differences found in the photoactivity as a function of reaction pH.

Bi 2 MO 6 (M = W or Mo) have been successfully synthesized using the citrate complex method. The samples were characterized by X-ray diffraction, Brunauer–Emmet–Teller surface area and UV–vis spectroscopy. The solids crystallized in the orthorhombic Aurivillius-type structure and display optimum light absorption properties to be used as photocatalysts. The photoactivity power of the samples was investigated systematically using the rhodamine B degradation under different irradiation wavelengths. The behaviour of the solids and the photodegradation mechanism was studied as a function of the irradiation light (UV or visible) employed. Direct solar light was also employed as irradiation source showing that this type of structures could drive to a plausible strategy for developing finest photocatalyst to degrade wastewaters by using solar light.

The solar light photocatalytic degradation of ethidium bromide (EtBr) in aqueous suspensions has been analyzed over titania-based catalysts. A nanosized titania and an iron-doped TiO2 (with ≈2 wt.% of iron content), synthesized within reverse microemulsions, were compared with a commercial Degussa P-25 titania. Structural and/or light handling properties of a different nature arise upon doping the titania with iron. These include favoring a titania crystal phase transformation from anatase to rutile and lowering the band gap energy. Almost total degradation of EtBr upon solar light assisted photodestruction and with significant total organic carbon (TOC) removal can be achieved over the three studied catalysts although the highest mineralization activity is achieved over the P25 titania sample. The results evidence that heterogeneous photocatalysis can be a promising advanced oxidation process to treat diluted EtBr residues typically generated in biomedical and biomolecular laboratories.

The photocatalytic degradation of ethidium bromide (EtBr), a DNA intercalating pollutant, by TiO2-based catalysts has been analyzed. Three different titanium dioxide samples synthesized by sol–gel within reverse microemulsions at different pH and thermal treatments were characterized and studied for the photocatalytic degradation of EtBr by oxygen in aqueous solutions. A commercial titania, Degussa P25, was also examined as a reference material for comparative purposes. Appreciable differences in the final structural and surface properties of these titania samples are observed which include disparities in the anatase/rutile proportions, optical absorption characteristics, EtBr chemisorption and acid–base properties. EtBr photodegradation results suggest that catalytic acid–base properties are the most relevant to explain EtBr chemisorption and play an important role in their final photocatalytic behaviour. It is stressed that photocatalysis can be an interesting alternative to other chemical or biological methods for mineralization of EtBr diluted in aqueous solutions.

A series of nanosized iron-doped anatase TiO 2 catalysts with different iron content (between 0.4 and 5.1 wt.%) has been prepared by a microemulsion method and examined with respect to their behaviour for UV photocatalytic degradation of aqueous phenol. The activity results have been correlated with structural, electronic and surface examinations of the catalysts done with XRD, Raman, UV–vis, EPR, N 2 physisorption and NH 3 chemisorption. An enhancement of the photocatalytic activity is observed for doping levels up to ca. 1 wt.% which is attributable to the effective introduction of Fe 3+ cations into the anatase structure along with associated modifications of the surface acid/base properties. Achievement of relatively high levels of surface segregation of oxidic iron-containing amorphous phases for higher doping levels results however detrimental to the photoactivity.

Human mitochondrial diseases are associated with a wide range of clinical symptoms, and those that result from mutations in mitochondrial DNA affect at least 1 in 8500 individuals. The development of animal models that reproduce the variety of symptoms associated with this group of complex human disorders is a major focus of current research. Drosophila represents an attractive model, in large part because of its short life cycle, the availability of a number of powerful techniques to alter gene structure and regulation, and the presence of orthologs of many human disease genes. We describe here Drosophila models of mitochondrial DNA depletion, deafness, encephalopathy, Freidreich's ataxia, and diseases due to mitochondrial DNA mutations. We also describe several genetic approaches for gene manipulation in flies, including the recently developed method of targeted mutagenesis by recombinational knock-in. © 2006 Elsevier B.V. All rights reserved., This work was supported by European Union Project QLG1-CT-2001-00966, Ministerio de Ciencia y Tecnologia, Spain (Grants BMC01-1525 and BFU2004-04591) and Instituto de Salud Carlos III, Redes de centros RCMN (C03/08) and Temáticas (G03/011 (to R.G.) and National Institutes of Health Grant GM45295 (to L.S.K.).

The effect of hydrogen peroxide on the photo-oxidation of salicylic acid (SA) in aqueous solutions under UV-irradiation was investigated in both purely homogeneous and photocatalytic conditions. Results obtained show that in absence of photocatalyst and under UV-irradiation, the SA degradation rate increases with increasing the amount of hydrogen peroxide added, although for high concentrations of H 2 O 2 the enhancement of the activity is progressively attenuated. In the case of the photocatalytic degradation, nanocrystallites of anatase immobilised over SiO 2 fibres were used as catalyst. In the present of TiO 2 /SiO 2 , the addition of hydrogen peroxide results in almost a three-fold increment of the photoactivity at low concentration (29.1 mM). In contrast, when the amount of H 2 O 2 added exceeds certain limit, the rate of SA removal becomes slightly lower than those measured in absence of photocatalyst. A simple kinetic model which considers the summation of both photochemical and photocatalytic contributions is used to account for the dependence of the rate on the H 2 O 2 concentration. The efficiency of the SA mineralization was also evaluated by monitoring the evolution of total organic carbon (TOC) with irradiation time. In this respect, remarkable differences are found when comparing pure photochemical degradation, which only reduce the TOC concentration in about a 3% after 300 min of irradiation, with the photocatalytic treatment, which achieve a 38% of SA mineralization in the same period.

We report the cloning and molecular analysis of Drosophila mitochondrial transcription factor (d-mtTF) B1. An RNA interference (RNAi) construct was designed that reduces expression of d-mtTFB1 to 5% of its normal level in Schneider cells. In striking contrast with our previous study on d-mtTFB2, we found that RNAi knock-down of d-mtTFB1 does not change the abundance of specific mitochondrial RNA transcripts, nor does it affect the copy number of mitochondrial DNA. In a corollary manner, overexpression of d-mtTFB1 did not increase either the abundance of mitochondrial RNA transcripts or mitochondrial DNA copy number. Our data suggest that, unlike d-mtTFB2, d-mtTFB1 does not have a critical role in either transcription or regulation of the copy number of mitochondrial DNA. Instead, because we found that RNAi knockdown of d-mtTFB1 reduces mitochondrial protein synthesis, we propose that it serves its primary role in modulating translation. Our work represents the first study to document the role of mtTFB1 in vivo and establishes clearly functional differences between mtTFB1 and mtTFB2.

The application of niobium oxides as photocatalytic materials for the removal of contaminants is scarcely reported in the literature. This work reports the methodology to synthesize four different mesoporous niobium oxide materials and the correlation between the physicochemical properties and the photocatalytic activity. X‐ray diffraction, UV–vis diffuse reflectance spectra (DRS), transmission electron microscopy, and nitrogen adsorption techniques are used to characterize the structure and composition of the obtained materials. The photocatalytic oxidation of methanol is used as reaction test to assess the photocatalytic activities and photonic efficiencies of the materials as a function of the catalyst concentration. Nb2O5 materials display lower reaction rates, which can be attributed to the relatively high average particle size. By contrast, NaNbO3 materials show higher activity, especially for high catalyst loading. No significant differences in absorption and scattering of light are observed among the materials, indicating that the higher photonic efficiency of NaNbO3 should be the result of a lower charge recombination derived from its microstructure, sodium composition, low particle size, and high specific surface area of these materials.

Línea 1. Procesos de depuración de aguas residuales Four bismuth vanadates have been synthesized by using two different precipitating agents (NH3 and triethylamine) following a hydrothermal treatment at 100ºC for 2 hours and at 140ºC for 20 hours. Then, solids were characterized by X-ray diffraction, BET surface area, UVvis spectroscopy and scanning microscopy techniques. The characterization of the synthesized materials showed a well crystallized scheelite monoclinic structure with different morphologies. All materials display optimum light absorption properties for visible light photocatalytic applications. The photocatalytic activity of the catalysts was investigated for the inactivation of Escherichia coli bacteria and the oxidation of methanol under UV-vis and visible light irradiation sources. Main results demonstrate that BiVO4 are photocatalytically active in the oxidation of methanol and are able to inactivate bacteria below the detection level. The activity of the catalyst decrease when using visible light, especially for methanol oxidation, pointing out differences in the reaction mechanism. In contrast with bacteria, whose interaction with the catalyst is limited to the external surface, methanol molecules can access the whole material surface. Tecnología Química y Ambiental

A continuous photoreactor, working in a total recycle mode and irradiated by a low-pressure Hg lamp, has been used to study the bactericidal effect of a photocatalyst, formed by TiO2 embedded in SiO2 fibres, on Legionella pneumophila and a consortium of common gram-negative aerobic bacteria: (Escherichia coli, Klebsiella sp., Pseudomona sp. and Proteus sp.) in water. The kinetic modeling of the inactivation process, carried out with the measured values of viable bacteria concentration at the outlet of photoreactor, evidenced that for each pass inside the photoreactor the ratio between the outlet and inlet cell concentrations was of order of 0.01 for the inactivation of L. pneumophila. For the other aerobic bacteria, which are usually taken as reference in photocatalytic bacteria inactivation studies, this ratio was of order of 0.3 for the first hour of illumination, while upon prolonged irradiation (up to 9 h) this ratio increased to 0.7. Several factors inducing this latter decrease of efficiency are possible, as e.g. competition for photocatalytic attack between microorganisms and organic compounds released by damaged bacteria or photoinduced alteration of a small fraction of still viable bacteria making them less interactive with the photocatalyst. The inactivation mechanism normally proposed for common bacteria involves an initial attack of the photogenerated radicals to the outer membrane; the consequent membrane dispersion allows the radicals to damage the cytoplasmic membrane. The higher lethality of the photocatalytic method observed towards Legionella: (in comparison to the other aerobic bacteria) is explained considering that the radicals attack the Legionella secretion system, which is adapted for high virulence and would become activated for and through adhesion to the TiO2 surface. This attack would then be able to inactivate L. pneumophila without dispersing the outer membrane. Apart from this, the water flow through the catalyst fibres can facilitate the bacteria transport towards the anatase surface, and additionally the generated shear stress may help adhesion, at least for some bacteria as E. coli, contributing further to improve the photokilling efficiency; both factors may contribute to the efficiency of this photoreactor configuration.

et al., DREF [DRE (DNA replication-related element)-binding factor] controls the transcription of numerous genes in Drosophila, many involved in nuclear DNA (nDNA) replication and cell proliferation, three in mitochondrial DNA (mtDNA) replication and two in mtDNA transcription termination. In this work, we have analysed the involvement of DREF in the expression of the known remaining genes engaged in the minimal mtDNA replication (d-mtDNA helicase) and transcription (the activator d-mtTFB2) machineries and of a gene involved in mitochondrial mRNA translation (d-mtTFB1). We have identified their transcriptional initiation sites and DRE sequences in their promoter regions. Gel-shift and chromatin immunoprecipitation assays demonstrate that DREF interacts in vitro and in vivo with the d-mtDNA helicase and d-mtTFB2, but not with the d-mtTFB1 promoters. Transient transfection assays in Drosophila S2 cells with mutated DRE motifs and truncated promoter regions show that DREF controls the transcription of d-mtDNA helicase and d-mtTFB2, but not that of d-mtTFB1. RNA interference of DREF in S2 cells reinforces these results showing a decrease in the mRNA levels of d-mtDNA helicase and d-mtTFB2 and no changes in those of the d-mtTFB1. These results link the genetic regulation of nuclear DNA replication with the genetic control of mtDNA replication and transcriptional activation in Drosophila. © 2013 Elsevier B.V., This work was supported by grants from the Center for Biomedical Research on Rare Diseases (CIBERER) [INTRA/08/743.2] to R.G., the Instituto de Salud Carlos III (grants [PI 07/0167] and [PI 10/0703] to R.G.); the Comunidad de Madrid (grants [GEN-0269/2006] and [MITOLAB S2010/BMD-2402] to R.G); the Università di Bari, Progetto di Ricerca di Ateneo (to M.R.); and the National Institutes of Health (grant [GM45295] to L.S.K.).

In Drosophila melanogaster, the mitochondrial transcription factor B1 (d-mtTFB1) transcript contains in its 5′-untranslated region a conserved upstream open reading frame denoted as CG42630 in FlyBase. We demonstrate that CG42630 encodes a novel protein, the coiled coil domain-containing protein 56 (CCDC56), conserved in metazoans. We show that Drosophila CCDC56 protein localizes to mitochondria and contains 87 amino acids in flies and 106 in humans with the two proteins sharing 42% amino acid identity. We show by rapid amplification of cDNA ends and Northern blotting that Drosophila CCDC56 protein and mtTFB1 are encoded on a bona fide bicistronic transcript. We report the generation and characterization of two ccdc56 knock-out lines in Drosophila carrying the ccdc56 D6 and ccdc56 D11 alleles. Lack of the CCDC56 protein in flies induces a developmental delay and 100% lethality by arrest of larval development at the third instar. ccdc56 knock-out larvae show a significant decrease in the level of fully assembled cytochrome c oxidase (COX) and in its activity, suggesting a defect in complex assembly; the activity of the other oxidative phosphorylation complexes remained either unaffected or increased in the ccdc56 knock-out larvae. The lethal phenotype and the decrease in COX were partially rescued by reintroduction of a wild-type UAS-ccdc56 transgene. These results indicate an important role for CCDC56 in the oxidative phosphorylation system and in particular in COX function required for proper development in D. melanogaster. Wepropose CCDC56 as a candidate factor required for COX biogenesis/assembly. © 2012 by The American Society for Biochemistry and Molecular Biology, Inc., This work was supported, in whole or in part, by National Institutes of Health Grant GM45295 (to L. S. K.). This work was also supported by grants from the Center for Biomedical Research on Rare Diseases (CIBERER), Instituto de Salud Carlos III Grants PI 07/0167 and PI 10/0703 (to R. G), Comunidad de Madrid Grant GEN-0269/2006 (to R. G.), Instituto de Salud Carlos III-Agencia Laín Entralgo Grant PI 08/0021 (to C. U.).

et al., The DREF [DRE (DNA replication-related element)-binding factor], which regulates the transcription of a group of cell proliferation-related genes in Drosophila, also controls the expression of three genes involved in mtDNA (mitochondrial DNA) replication and maintenance. In the present study, by in silico analysis, we have identified DREs in the promoter region of a gene participating in mtDNA transcription, the DmTTF (Drosophila mitochondrial transcription termination factor). Transient transfection assays in Drosophila S2 cells, with mutated versions of DmTTF promoter region, showed that DREs control DmTTF transcription; moreover, gel-shift and Chip (chromatin immunoprecipitation) assays demonstrated that the analysed DRE sites interact with DREF in vitro and in vivo. Accordingly, DREF knock-down in S2 cells by RNAi (RNA interference) induced it considerable decrease in DmTTF mRNA level. These results clearly demonstrate that DREF positively controls DmTTF expression. On the other hand, mtRNApol (mitochondrial RNA polymerase) lacks DREs in its promoter and is not regulated in vivo by DREF. In situ RNA hybridization Studies showed that DmTTF was transcribed almost ubiquitously throughout all stages of Drosophila embryogenesis, whereas mRNApol was efficiently transcribed from stages 11-12. Territories where transcription occurred mostly were the gut and Malpighi tubes for DmTTF, and the gut, mesoderm, pharyngeal muscle and Malpighi tubes for mtRNApol. The partial overlapping in the temporal and spatial mRNA expression patterns confirms that transcription of the two genes is differentially regulated during embryogenesis and suggests that DmTTF might play multiple roles in the mtDNA transcription process, for which different levels of the protein with respect to mtRNApol are required.

Characterization of the basal transcription machinery of mitochondrial DNA (mtDNA) is critical to understand mitochondrial pathophysiology. In mammalian in vitro systems, mtDNA transcription requires mtRNA polymerase, transcription factor A (TFAM), and either transcription factor B1 (TFB1M) or B2 (TFB2M). We have silenced the expression of TFB2M by RNA interference in Drosophila melanogaster. RNA interference knockdown of TF2BM causes lethality by arrest of larval development. Molecular analysis demonstrates that TF2BM is essential for mtDNA transcription during Drosophila development and is not redundant with TFB1M. The impairment of mtDNA transcription causes a dramatic decrease in oxidative phosphorylation and mitochondrial ATP synthesis in the long-lived larvae, and a metabolic shift to glycolysis, which partially restores ATP levels and elicits a compensatory response at the nuclear level that increases mitochondrial mass. At the cellular level, the mitochondrial dysfunction induced by TFB2M knockdown causes a severe reduction in cell proliferation without affecting cell growth, and increases the level of apoptosis. In contrast, cell differentiation and morphogenesis are largely unaffected. Our data demonstrate the essential role of TFB2M in mtDNA transcription in a multicellular organism, and reveal the complex cellular, biochemical, and molecular responses induced by impairment of oxidative phosphorylation during Drosophila development. © 2008 by The American Society for Biochemistry and Molecular Biology, Inc., This work was supported in part by Ministerio de Educación y Ciencia, Spain, Grants BFU2004-04591 (to R. G.) and BFU2005-09071 (to J. J. A.), Instituto de Salud Carlos III, Redes de centros RCMN Grant C03/08 (to R. G. and J. J. A.), Temáticas Grant G03/011 (to R. G.), the Centro de Investigación Biomédica en Red de Enfermedades Raras, and National Institutes of Health Grant GM45295 (to L. S. K.).

Ribonucleic acid (RNA) interference triggered by double-stranded RNA has become a powerful tool for generating loss-of-function phenotypes. It is used to inactivate genes of interest and represents an elegant approach to genome functional analysis by reverse genetics. In Drosophila, RNA interference has been used in both cell culture and animals. We have adopted this approach to reveal the physiological roles of a number of proteins involved in mitochondrial deoxyribonucleic acid metabolism, and present here experimental schemes to induce the stable expression of double-stranded RNA in Schneider cells and in transgenic Drosophila.

In order to study the role of N-glycans in the ER-associated degradation of unassembled immunoglobulin light (Ig L) chains, we introduced N-glycan acceptor sites into the variable domain of the murine Ig L chain kappaNS1, which is unfolded in unassembled molecules. We investigated the fate of kappaNS1 glycosylated at position 70 (K70) and of a double mutant (kappa18/70) in stably transfected HeLa cells. Degradation of both chains was impaired by lactacystin, a specific inhibitor of the proteasome. The mannosidase inhibitor dMNJ also blocked degradation in a step preceding proteasome action, as did two protein synthesis inhibitors, cycloheximide and puromycin. In contrast, ER glucosidase inhibitors dramatically accelerated the degradation of the chains when added either pre- or posttranslationally. The accelerated degradation was sensitive to lactacystin, dMNJ and cycloheximide, too. None of these drugs, except lactacystin, affected the degradation of unglycosylated kappaNS1 chains. We conclude that ER mannosidases and proteasome activities, but not glucose trimming (and therefore, most likely not the calnexin/calreticulin UDP:glucose glycoprotein glucosyl transferase cycle), are essential for ER-associated degradation (ERAD) of soluble glycoproteins. A role for a short-lived protein, acting before or simultaneously to ER mannosidases, is suggested.

Although glycolytic enzymes can be isolated as cytosolic components, some of them are known to bind to proteins from the cytoplasm and other cellular compartments, such as the mitochondria, the nucleus, or the plasma membrane. In some cases these protein-protein interactions are considered significant for the regulation of energy metabolism, as well as for the modulation of other cell functions. Among glycolytic enzymes, phosphofructokinase (PFK) is thought to play a fundamental role in the control of this pathway, because of the number of metabolic signals that can regulate its complex allosteric behavior. No X-ray structure of a characteristic eukaryotic PFK is available yet. However, sequence data indicated that the eukaryotic enzyme originated by duplication, fusion and divergence of an ancestral prokaryotic gene, such that the duplicated fructose 6-phosphate catalytic site in the C-terminal half became an allosteric site for the activator fructose 2,6-bisphosphate. It has been suggested that both sites are shared in the interface between subunits aligned in an antiparallel orientation. To test the contribution of each terminal domain to these two binding sites, chimeric mammalian PFKs involving exchange of their terminal domains have been found to exhibit affinity properties for fructose 6-phosphate and fructose 2,6-bisphosphate that resembled those of the native isozyme that donated the N-terminal half and the C-terminal half, respectively. Further mutational analyses of muscle PFK led us to investigate the composition of the fructose phosphate binding sites and to gain insight into the structural organization of eukaryotic PFK. Data will also be presented evidencing the relationship between mitochondrial function and the operation of glycolysis, as observed after impairment of mitochondrial DNA transcription.