Self-assembled titanium oxide nanotubular (NTs) arrays with vertical arrangement, tailored morphological properties and variable thickness were prepared by electrochemical anodization in ethylene glycol containing electrolytes. The NTs present significant UV photocatalysis against toluene and benzene at ppb concentrations, under normal conditions of temperature and pressure. The photocatalytic activity depends on the length of the NT arrays, showing a tendency of saturation for thickness above 2.5 μm and maximum efficiency for samples with thickness of 12 μm. The optimum NT structures outperform over standard Degussa P25 films rendering them very promising for outdoor photocatalytic applications. © 2010 Elsevier B.V. All rights reserved.

Interacting properties of colloidal CdSe quantum dots (QDs) and polypyridyl ruthenium dyes employed as cosensitizers of mesoporous TiO2 electrodes as well as the effect of QDs coating and anchoring mode (direct and linker adsorption) have been investigated by photoluminesce (PL), Raman, and transient absorption (TAS) spectroscopies. Direct adsorption of QDs on TiO 2 leads to a more efficient PL quenching compared to that of QDs attached by means of a molecular linker (cysteine). This fact suggests higher electron injection for the former anchoring mode. Coating of ZnS on CdSe QDs sensitized TiO2 electrodes passivates the QDs surface states and partially releases quantum confinement effects, as is observed in colloidal core-shell nanoparticles. Subsequent cosensitization with a ruthenium molecular dye dramatically quenches the PL of the QDs/TiO2 electrodes, even in the presence of ZnS coating, indicating the presence of strong photoinduced charge transfer between the CdSe QDs and the dye molecules. This is firmly supported by TAS spectroscopy on the interfacial recombination kinetics that points to the fast hole transfer from the photoexcited QDs to the dye. The regenerating action of molecular dyes for QD sensitizers can have important implications in the development of efficient photovoltaic devices based on the synergistic action of dye-QD-TiO2 heterostructures. © 2010 American Chemical Society.

In this work, titanium dioxide (TiO2) has been used as an additive in lime binder (Ca(OH)2), in order to benefit from its photocatalytic properties and study both the photocatalytic properties of the produced mixtures and the effect of photocatalytically produced carbon dioxide on the carbonation process of lime. TiO2 was added in three different portions (3, 6 and 10% w/w) in lime mixtures and their physicochemical and photocatalytic properties were studied and compared to those of a reference, made exclusively of lime. The photocatalytic properties of the mixtures were studied through the photo-oxidation of an organic model pollutant solution (methyl orange) to a colorless form, as well as by studying the microstructure and carbonation depth in different groups of mixtures subjected to photocatalysis cycles in the laboratory and exposed for a 2 month period in the open air (urban environment). Laboratory results confirmed that lime-TiO2 composite mixtures exhibit photocatalytic properties in both UV radiation conditions and direct exposure to sunlight. Moreover, analytical results indicated an enhanced carbonation of lime-TiO2 composites. TiO2 can be added to lime successfully and can have applications in lime-based mortars used in the conservation of architectural heritage, enhancing their performance against soiling and amenity loss. © 2009 Elsevier B.V. All rights reserved.

This study describes the application of a novel chemistry method based on a modified sol-gel technique for the fabrication of nanostructured non-metal doped TiO2 photocatalytic films that can be activated under both visible and UV light. A self-assembling surfactant was employed as a pore-directing agent and a nitrogen-containing compound as doping precursor. Different surfactant ratios were explored to tailor-design the desired structural properties of TiO2 (i.e., high surface area, small crystal size) and enhanced the photocatalytic activity under visible light illumination. The films were characterized by XRD, ESEM, TEM, AFM, EPR, micro-Raman, XPS, UV-vis spectroscopy and N2 porosimetry. The photocatalytic evaluation of the films was tested for the degradation of microcystin-LR and the effects of NOM, pH, alkalinity, and dissolved oxygen under visible light irradiation were investigated. The multifunctional behavior exhibited for the non-metal doped TiO2 films can lead to important photoinduced applications including environmental protection (water disinfection, self-cleaning surfaces) and sustainable solar energy conversion to electricity (dye-sensitized solar cells).

In this study, immobilized nitrogen and fluorine co-doped TiO2 (NF-TiO2) was synthesized employing a fluorosurfactant-based sol-gel method to tailor-design the nanoparticulate, structural and photocatalytic properties of the catalyst. Besides the co-doping of nitrogen and fluorine observed for visible light photoresponse, the nanostructure of the dip-coated films was effectively controlled by modifying the molar ratio of the fluorosurfactant. The synthesized films were evaluated for the destruction of two emerging contaminants, hepatotoxin microcystin LR (MC-LR) and herbicice Amitrole. NF-TiO2 films showed high photocatalytic activity for the degradation of both MC-LR and Amitrole compared to control experiments under both visible and solar light irradiation. Moreover, NF-TiO2 nanostructured films also exhibited high mechanical stability and no irreversible changes were observed during photocatalysis after 3 cycles under visible light. These results are promising for further development of sustainable remediation technologies for the treatment of water contaminated with MC-LR and other persistent micropollutants, based on advanced oxidation processes driven by solar light as a renewable source of energy.

This study reports on the synthesis, characterization and environmental application of immobilized nitrogen and fluorine co-doped TiO2 (NF-TiO2) photocatalyst. A fluorosurfactant-based sol-gel approach was employed to enhance the physicochemical properties and photocatalytic activity of NF-TiO2 under visible and UV light for the degradation of the hepatotoxin microcystin-LR (MC-LR). The films were characterized by XRD, environmental scanning electron microscope (ESEM), TEM, AFM, EPR, micro-Raman, X-ray photoelectron spectroscope (XPS), UV-vis spectroscopy and porosimeter analysis. The results revealed that by modifying the molar ratio of the fluorosurfactant, we could effectively control the physicochemical properties and obtain films with high BET surface area and porosity, small crystallite size and narrow pore size distribution. UV-vis spectroscopy showed an increase in the absorption capacity of NF-TiO2 in the visible light range compared to reference films. The existence of interstitial nitrogen and substitutional fluorine in the titanium dioxide (TiO2) lattice was determined by XPS. Comparative EPR measurements between the co-doped and reference samples identified distinct N spin species in NF-TiO2, with a high sensitivity to visible light irradiation. The abundance of these paramagnetic centers verifies the formation of localized intra-gap states in TiO2 and implies synergistic effects between fluorine and nitrogen dopants. Micro-Raman spectroscopy showed the growth of small amounts of brookite concomitantly with the major anatase TiO2 phase, which could promote the system's photocatalytic activity through the formation of anatase/brookite heterojunctions. Analysis of the lower frequency Eg anatase Raman mode indicated the occurrence of size effects reflecting phonon confinement in the anatase nanocrystallites as well as deviations from stoichiometry due to structural defects in the co-doped sample. NF-TiO2 films effectively degraded MC-LR under visible and UV light compared to reference film. Similar MC-LR degradation rates under visible light after three cycles revealed high mechanical stability and no irreversible changes of the film during photocatalysis. This process has the potential of providing environmentally benign routes for drinking water treatment with solar powered photocatalytic systems. © 2010 Elsevier B.V.

The magnetic and electronic properties of composites consisting of oxidized multiwall carbon nantubes (MWNTs) dispersed in elastomeric poly(ether-ester) segmented block copolymer have been studied by means of electron spin resonance (ESR) and dc magnetization measurements. A marked reduction in the MWNT diamagnetic response is identified, indicative of substantial hole doping related to the oxygen functional groups on the oxidized carbon nanotube's surface. Both ESR and the static magnetization reveal considerable enhancement of the spin susceptibility due to an excessive increase in the density of paramagnetic defects, which are sensitive to the dynamical polymer relaxation and thus to the MWNT-polymer interfacial coupling. © 2010 American Institute of Physics.

Although hollow nanostructures, such as nanotubes, represent a major portion of nanoscaled materials with a tremendously large application range, a detailed evaluation of their internal characteristics still remains elusive. Transmission electron microscopy is the most common analytical technique to examine the internal configuration of these structures, yet it can only provide evidence of a minimal portion of the overall material, thus, it cannot be accurately generalized. In the present paper, in addition to electron microscopy and other spot-size analysis methods (X-ray diffraction, Raman spectroscopy, etc.), a combination of techniques including adsorption, permeability, and relative permeability are employed in order to provide important insights into various crucial details of the overall internal surface and hollow-space characteristics of carbon nanotube (CNT) arrays and membranes. The CNT arrays are fabricated using anodized alumina as a template in a flow-through chemical vapor deposition (CVD) reactor. This is the first systematic approach for investigating the internal configuration of template-based CNT arrays in detail. Key findings are made fiar the customized optimization of the resulting nanotube membranes for a variety of applications, including separations, nanofluidics and nanoreactors, biological capturing and purification, and controlled drug delivery and release. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhelm.

Environmental pollution abatement and especially the growing demand for clean water pose one of the most severe challenges worldwide. Besides the scarcity of water resources, the presence of hazardous chemicals with serious adverse health effects, even at extremely low concentrations, impose serious considerations for the quality of drinking water. The rapid evolution of nanoscale science and technology has dramatically expanded the materials' application potential towards radically new or multifunctional properties rendering nanotechnology an indispensable component in shaping modern environmental science. The nanoscale-perspective maintaining the integrity of the environment is currently the stimulus for the development of innovative and cost-effective functional materials and sustainable processes for water treatment and purification. The CLEAN WATER (EU FP7 collaborative project) aims at the development of an innovative and efficient water detoxification technology exploiting solar energy and nano-engineered titania photocatalysts in combination with nanofiltration membranes. In this approach, nanostructured titania with high UV-visible response will be synthesized and stabilized on nanotubular membranes of controlled pore size and retention efficiency as well as on carbon nanotubes exploiting their high surface area to achieve photocatalytically active nanocomposite membranes. Comparative evaluation of the UV-visible and solar light efficiency of the modified titania photocatalysts for water detoxification will be intensively investigated on various target pollutants ranging from classical water contaminants such us phenols, pesticides and azo-dyes to the extremely hazardous cyanobacterial toxins and emerging endocrine disrupting compounds in order to evaluate/optimize the materials performance and validate their competence on water treatment. Particular efforts will be devoted to the analysis and quantification of degradation products as well as their toxicity. All these will be the crucial components for the fabrication of innovative continuous flow photocatalytic-disinfection-membrane reactors for the implementation of sustainable and cost effective water treatment technologies based on nano-engineered materials. © Springer Science+Business Media B.V. 2010.