Double-side active TiO2-modified nanofiltration membranes in continuous flow photocatalytic reactors for effective water purification.

A chemical vapour deposition (CVD) based innovative approach was applied with the purpose to develop composite TiO(2) photocatalytic nanofiltration (NF) membranes. The method involved pyrolytic decomposition of titanium tetraisopropoxide (TTIP) vapor and formation of TiO(2) nanoparticles through homogeneous gas phase reactions and aggregation of the produced intermediate species. The grown nanoparticles diffused and deposited on the surface of γ-alumina NF membrane tubes. The CVD reactor allowed for online monitoring of the carrier gas permeability during the treatment, providing a first insight on the pore efficiency and thickness of the formed photocatalytic layers. In addition, the thin TiO(2) deposits were developed on both membrane sides without sacrificing the high yield rates. Important innovation was also introduced in what concerns the photocatalytic performance evaluation. The membrane efficiency to photo degrade typical water pollutants, was evaluated in a continuous flow water purification device, applying UV irradiation on both membrane sides. The developed composite NF membranes were highly efficient in the decomposition of methyl orange exhibiting low adsorption-fouling tendency and high water permeability.

Visible light induced wetting of nanostructured N-F co-doped titania films.

Nitrogen and fluorine co-doped TiO(2) films have been prepared by dip coating of a modified titania sol-gel based on a nitrogen precursor and a nonionic fluorosurfactant as pore template and fluorine source. The modified NF-TiO(2) films absorb in the visible spectral range, between 400-510 nm and undergo reversible hydrophilic conversion under visible light to a final contact angle of 8°, in contrast to the UV limited optical response of their undoped anatase TiO(2) analogues. The phenomenon takes place at a rate slower than the corresponding one observed for the UV stimulated superhydrophilic effect. The wetting response of the N-F doped TiO(2) films correlates well with the variation of their optical properties and surface morphological characteristics and most importantly with their photocatalytic activity, rendering these materials very promising for self-cleaning applications under visible light.

Dye-sensitization of self-assembled titania nanotubes prepared by galvanostatic anodization of Ti sputtered on conductive glass.

Self-organized porous TiO(2) nanotubes (NTs) were prepared on conductive glass by galvanostatic anodizing of sputtered titanium in an NH(4)F /glycerol electrolyte. DC magnetron sputtering at an elevated substrate temperature (500 degrees C) was used to deposit 650 nm thick titanium films. After anodizing, NTs, 830 nm long, with an average external diameter of 92 nm, were grown; this gave a high conversion rate of oxide from titanium (1.9), with a 220 nm thick layer of titanium, which was not oxidized, located at the base of the tubes. The NTs revealed a mainly amorphous structure, which transformed mostly to anatase upon thermal treatment in air at 450 degrees C. The tubes were sensitized by the N719 complex and the resultant photoelectrodes were incorporated into liquid dye solar cells (DSCs) and further tested under back-side illumination. High values of V(oc) (714 mV) were obtained under 1 sun (AM 1.5), assigned to low dark current magnitude and large recombination resistance and electron lifetime. In addition, typical values of fill factors (of the order of 0.62) were attained, in agreement with the estimated ohmic resistance of the cells in combination with low electron transfer resistance at the platinum/electrolyte interface. The overall moderate power conversion efficiency (of the order of 0.3%) was mainly due to the low short-circuit photocurrents (J(sc) = 0.68 mA cm(-2)), which was confirmed further by the corresponding IPCE values (5.2% at 510 nm). The magnitude of J(sc) was attributed to absorbed light losses due to back-side illumination of the cells, the low dye loading (due to the limited thickness of anodic titania) and the high charge transfer resistance at the TiO(2)/conductive substrate due to the presence of barrier layer(s) underneath the tubes. These preliminary results encourage the DSC community to explore further the galvanostatic anodizing of titanium in order to produce highly efficient porous TiO(2) NTs directly on conductive glass. Current work is focusing on achieving complete anodizing of the metal substrate and full transparency for the photoelectrode in order to increase and optimize the resultant cell efficiencies.

Photo-induced effects on self-organized TiO2 nanotube arrays: the influence of surface morphology.

Self-organized TiO(2) nanotubes with packed, vertically aligned morphology and different lateral characteristics were grown on Ti metal substrates by controlled electrochemical anodization in phosphate/HF and ethylene glycol/HF electrolytes. The wetting, photo-induced superhydrophilicity, and photocatalytic activity of the nanotubular materials were investigated under ultraviolet irradiation. The photoactivity of the TiO(2) nanotube arrays was analysed in terms of their morphological characteristics that were determined by means of scanning electron microscopy and atomic force microscopy in conjunction with geometrical modelling. The wetting and the UV-induced superhydrophilicity could be accordingly modelled by the Cassie-Baxter mode arising from the large scale roughness of the nanotubular arrays in combination with the Wenzel mode due to the small scale roughness induced by ridges at the outer tube surface. The photocatalytic activity of the TiO(2) nanotube arrays was further found to correlate quantitatively with the variation of the geometric roughness factor, verifying the strong impact of morphology on the photo-induced properties of the vertically oriented TiO(2) tubular architecture.

Magnetic properties of gamma-Fe2O3/poly(ether-ester) nanocomposites.

The magnetic properties of gamma-Fe2O3 nanoparticles embedded in a thermoplastic elastomer poly(ether-ester) copolymer by the in situ polycondensation reaction process have been investigated by means of magnetization and ferromagnetic resonance (FMR) measurements at low filler concentrations of 0.1 and 0.3 wt% with the magnetic additive introduced in the polymer matrix in powder and solution form. The magnetic behavior of the magnetopolymeric nanocomposites indicates significant interparticle interaction effects that depend mainly on the dispersion state of the magnetic nanoparticles as well as their concentration, consistent with the variation of the particle microstructure characterized by magnetic aggregates in the nanometer and micron scale for the solution and powder dispersions, respectively. The magnetization and FMR results at different filler concentrations and dispersions show a close correspondence to the relaxation processes of the copolymer, implying the coupling of polymeric and magnetic properties.

Dye-sensitized solar cells based on thick highly ordered TiO(2) nanotubes produced by controlled anodic oxidation in non-aqueous electrolytic media.

Dye-sensitized solar cells (DSSCs) were prepared using TiO(2) nanotubes, grown by controlled Ti anodic oxidation in non-aqueous media. Smooth, vertically oriented TiO(2) nanotube arrays, presenting a high degree of self-organization and a length of 20 µm, have been grown using ethylene glycol electrolyte containing HF. As-grown nanotubes exhibit an amorphous structure, which transforms to the anatase TiO(2) crystalline phase upon post-annealing in air at 450 °C. Atomic force microscopy (AFM) revealed the porous morphology together with high roughness and fractality of the surface. The annealed tubes were sensitized by the standard N719 ruthenium dye and the adsorption was characterized using resonance micro-Raman spectroscopy and adsorption-desorption measurements. The sensitized tubes were further used as active photoelectrodes after incorporation in sandwich-type DSSCs using both liquid and solidified electrolytes. The efficiencies obtained under air mass (AM) 1.5 conditions, using a back-side illumination geometry, were very promising: 0.85% using a composite polymer redox electrolyte, while the efficiency was further increased up to 1.65% using a liquid electrolyte.

Magnetic heterogeneity in electron doped La(1-x)Ca(x)MnO(3) manganites studied by means of electron spin resonance.

Electron spin resonance (ESR) has been applied to investigate the magnetic heterogeneity in electron doped La(1-x)Ca(x)MnO(3) (0.80≤x≤0.95). A low field ferromagnetic resonance (FMR) mode is observed for lightly doped compounds (x = 0.90,0.95), signifying the formation of ferromagnetic (FM) spin clusters within the antiferromagnetic G-type AFM phase. The anomalous temperature variations of the resonance field, linewidth and FMR intensity, as well as the observation of thermal cycling effects below T(C), emphasize the non-trivial dynamics of the FM phase, which is attributed to the temperature dependent size evolution of the underlying spin clusters towards canted AFM and FM domains. For heavier electron doping (x = 0.80,0.85), distinct AFM behaviour is evinced in the vicinity of T(N) in the monoclinic C-type AFM phase, characterized by the absence of critical relaxation. Additional weak FMR lines are observed for x = 0.80 and 0.85, whereas a narrow superparamagnetic-like signal is detected for x = 0.95.