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The adsorption of dye monolayers on nanocrystalline titanium dioxide surfaces leads to high photoelectrochemical yields in the visible range, which gives a renewal of interest in the use of this system in solar energy. A high resonance effect in these dyes enabled the attainment of the Raman spectra of the adsorbed molecules; further, a new series of Raman peaks appeared during the polarization of TiO{sub 2} modified by Ru-bipyridinium compounds in the presence of an electron donor. They correspond to a molecular configuration in which an electron is exchanged during the measurement between a particular ligand and a substrate titanium atom. This configuration appears then to be similar to the short-lived excited state of the metal ligand charge-transfer complex (MLCT).

Nanomaterials are receiving particular interest due to their novel physical and chemical properties, which are important for a wide range of applications, including environmental remediation. This article presents an overview of the currentadvances on the most relevant nanomaterials and nanotechnologies employed for environmental remediation. Particular emphasis is given to nanostructured semiconductors for photocatalysis; the use of nanomaterials such as nano-silver, single-walled carbon nanotubes, fullerenes, and titania for disinfection purposes; reactive metal nanoparticles, in particular zero-valent iron; ferrate and membrane nanotechnologies. These nanomaterials and nanotechnologies have been used for water and air purification or for the remediation of contaminated groundwater, soil, and sediments. Keywords: nanoparticles; TiO2; photocatalysis; membranes; metal nanoparticles; zero-valent iron; ferrate; disinfection; nanosilver

International audience; Nanostructured titanium materials with high UV-visible activity were synthesized in the collaborative project Clean Water FP7. In this study, the efficiency of some of these catalysts to degrade endocrine disruptor compounds, using bisphenol A as the model compound, was evaluated. Titanium dioxide P25 (AEROXIDE (R) TiO2, Evonik Degussa) was used as the reference. The photocatalytic degradation was carried out under the UV part of a simulated solar light (280-400 nm) and under the full spectrum of a simulated solar light (200 nm-30 gm). Catalytic efficiency was assessed using several indicators such as the conversion yield, the mineralization yield, by-product formation and the endocrine disruption effect of by-products. The new synthesized catalysts exhibited a significant degradation of bisphenol A, with the so-called ECT-1023t being the most efficient. The intermediates formed during photocatalytic degradation experiments with ECT-1023t as catalyst were monitored and identified. The estrogenic effect of the intermediates was also evaluated in vivo using a ChgH-GFP transgenic medaka line. The results obtained show that the formation of intermediates is related to the nature of the catalyst and depends on the experimental conditions. Moreover, under simulated UV, in contrast with the results obtained using P25, the by-products formed with ECT-1023t as catalyst do not present an estrogenic effect. (C) 2013 Elsevier Ltd. All rights reserved.

The ample use of nanomaterials has led to increasing demand in the chemical industry. Hence, many chemicals such as solvents, raw materials, reagents, and template materials, have been utilized in order to produce nanomaterials. In addition, the production of toxic or hazardous intermediates and products, as well as wastes has increased through reactions aiming at preparing desirable chemicals. The concept of green chemistry was introduced to chemical science and industry to reduce or eliminate the generation of undesirable products and to decrease the use of hazardous materials in chemical processes. This chapter will discuss green routes that have been applied in chemical processes to synthesize various nanomaterials.

Ca alginate polymer fibers were developed to effectively disperse and stabilize an efficient photocatalyst such as AEROXIDE (R) TiO2 P25 in their matrix. The biopolymer/TiO2 fibers were prepared and tested either in the hydrogel non-porous form or in the highly porous aerogel form prepared by sc-CO2 drying. Batch photocatalytic experiments showed that the porous, Ca alginate/TiO2 fibers, exhibited high efficiency for the removal of methyl orange (MO) from polluted water. In addition, their high porosity and surface area led to high MO degradation rate which was faster than that observed not only for their non-porous analogs but also of the bulk P25 TiO2 powder. Specifically, 90% removal for 20 mu M MO was achieved within 220 min for the porous sc-CO2 dried fibers while for their non-porous analogs at 325 min. The corresponding value (at 60 mu M MO) for the porous sc-CO2 dried fibers was 140 min over 240 min for the AEROXIDE (R) TiO2 P25 as documented in the literature. Furthermore the composite alginate/photocatalyst porous fibers were combined with TiO2 membranes in a continuous flow, hybrid photocatalytic/ultrafiltration water treatment process that led to a three fold enhancement of the MO removal efficiency at 400 ml of 20 mu W MO total treated volume and to dilution rather than condensation in the membrane retentate as commonly observed in filtration processes. Furthermore the permeability of the photocatalytic membrane was enhanced in the presence of the fibers by almost 20%. This performance is achieved with 26 cm(2) and 31 cm(2) of membrane and stabilized photocatalyst surfaces respectively and in this context there is plenty of room for the up-scaling of both membranes and fibers and the achievement of much higher water yields since the methods applied for the development of the involved materials (CVD and dry-wet phase inversion in a spinning set-up) are easily up-scalable and are not expected to add significant cost to the proposed water treatment process. (C) 2012 Elsevier Ltd. All rights reserved. Water Res

This chapter summarizes the use of green chemistry on the synthesis of nanomaterials as well as their environmental applications. Green routes for the synthesis of nanomaterials are discussed, including those using nontoxic solvents and natural template materials, such as ionic liquid, leaf and tea extract, natural cellulose, sucrose, starch, and plant leaves. Such methods could decrease the use of hazardous chemicals in chemical processes and reduce or eliminate undesirable products during the synthesis process. The employment of micro-organisms for the green synthesis of nanoparticles is also described. In addition, the use of nanomaterials as photocatalysts, Fenton's catalysts, and disinfectants is reported for environmental remediation including the degradation of organic contaminants and the inactivation of pathogenic micro-organisms in water. Finally, the importance of immobilization of nanomaterials onto substrates for their sustainable application to environmental remediation, in particular, contaminated water and wastewater treatment is presented.

Direct decomposition and reaction of hydrogen peroxide inside a titanium dioxide/hexadecylamine slurry dispersion results in a foaming, inorganic/organic hybrid composite material containing TiO2 with intercalated hexadecylamine with extended, sponge-like, porous structure. The complex structure of the synthesized foams can be described by a self-assembly of the amine moieties between the TiO2 nanoparticles. The surfactant molecules, held together by hydrophobic interactions between the alkyl chains, are intercalated inside thin planar TiO2 walls in a way that a lamellar nanostructure is formed. The XRD basal distance of 46.8 A is consistent with a crystal unit containing two surfactant molecules with alkyl chains perpendicular to the titanium dioxide walls. The hydrophilic amine headgroups are oriented with strong affinity to the hydroxyl groups present on the oxide surface.

Poly(ethylene oxide)/titania polymer electrolyte based photoelectrochemical cells have been fabricated with Ru(dcbpy)2(NCS)2 complex as the sensitizer and nanoporous TiO2 films as photoanodes. The ...

The presence of specific chemical additives in the redox electrolyte results in an efficient increase of the photovoltaic performance of dye-sensitized solar cells (DSCs). The most effective additives are 4-tert-butylpyridine (TBP), N-methylbenzimidazole (NMBI) and guanidinium thiocyanate (GuNCS) that are adsorbed onto the photoelectrode/electrolyte interface, thus shifting the semiconductor's conduction band edge and preventing recombination with triiodides. In a comparative work, we investigated in detail the action of TBP and NMBI additives in ionic liquid-based redox electrolytes with varying iodine concentrations, in order to extract the optimum additive/I2 ratio for each system. Different optimum additive/I2 ratios were determined for TBP and NMBI, despite the fact that both generally work in a similar way. Further addition of GuNCS in the optimized electrolytic media causes significant synergistic effects, the action of GuNCS being strongly influenced by the nature of the corresponding co-additive. Under the best operation conditions, power conversion efficiencies as high as 8% were obtained.

The present review article traces the discoveries that were instrumental to the evolution of DSSCs, taking a critical look at the principles of the operation mechanism and insisting on the most important recent developments in the field. We draw our attention mainly to the dye (photosensitizer); the primary processes that take place inside a solar cell, and which are affected by the dye, are also reviewed along with some of the most significant recent information found in literature that one should keep in mind before designing a novel ruthenium sensitizer. Specific emphasis is given in trying to answer vital questions like defining the optimum number of -COOH anchoring groups and protons that an efficient dye should carry, the correct choice of preparing either a homoleptic or a heteroleptic complex, as well as which counterions are the most suitable. Phenomena such as the role of the adsorption geometry, electrical fields at the double layer, dye-redox couple interaction and recombination effects are also analyzed, in order to show how these factors influence the photoelectrochemical characteristics of the cell. Next, the contributions from our group in the direction of designing, synthesizing, characterizing and evaluating novel ruthenium(II)-based complexes, utilized as photosensitizers in DSSCs, are thoroughly discussed. Two types of Ru(II) complexes are examined: one family mimicking the standard N719 dye, bearing bidentate ligands, and another, carrying tridendate ligands, resembling the " black dye" © 2010 Elsevier B.V.

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.

Two new ruthenium(II) complexes bearing terpyridine- or 2,6-dipyrazinylpyridine ligands have been prepared and characterized by one- and two-dimensional NMR techniques, ESI mass spectrometry, as well as by UV-vis, emission, FTIR, Raman, and cyclic voltammetry studies. The structure of the terpyridine-coordinated complex resembles that of black dye (tris(thiocyanato) (2,2′:6′,2″-terpyridyl-4,4′,4″-tricarboxylato) ruthenium(II) tris(tetra butylammonium) salt), while the spectral data of the 2,6-dipyrazinylpyridine-coordinated complex are consistent with an unanticipated, unsymmetrical binuclear structure. The ruthenium(II)/(III) oxidation potential of the terpyridine-coordinated dye was measured at +0.87 V (vs. Ag/AgCl), about 200 mV higher than the oxidation potential of black dye. According to a series of desorption experiments, both new dyes were found to adsorb on TiO2 to a greater extent than black dye. The photo-electrochemical properties of both dyes were investigated and compared to that of black dye; while the 2,6-dipyrazinylpyridine-coordinated complex was found to be a very poor sensitizer, the cells obtained from the terpyridine-coordinated dye show power-conversion efficiencies which are more than half of that attained by black dye. Finally, preliminary electron dynamics studies of the cells constructed with the terpyridine dye were carried out and the results are compared to that of black dye cells. © 2010 Elsevier B.V.

The non-biomimetic splitting of water has been achieved using a single photocatalyst-catalyst (tris-[1-(4-methoxyphenyl-2-phenyl-1,2-ethylenodithiolenic-S,S′]tungsten), and a reversible electron acceptor (methylviologen). The average quantum yield (in equivalents) in the effective wavelength range in the visible (400–500 nm) is about 4%. The oxidation and reduction cycles of water are fully coupled, in fact they are integrated, in the sense that they are part of a single cycle, rather than of the separate hypothetical cycles with contact points proposed in the literature.

Electrochemical properties are reported for a montmorillonite-modified graphite electrode intersalated by the complex salt [Fe(bpy) 3 ] 2 Fe(CN) 6 ] at loadings in excess of the cation-exchange capacity of the clay. The presence of a multilayer assembler in the clay galleries was indicated by a basal spacing of ∼27 A, as compared to 17 A for homoionic Fe(bpy) 3 4- -montmorillonite.

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.

Particle vs tube: The present paper systematically investigates a range of fundamental geometrical and structural features of TiO(2) nanotube layers and their effect on the dye-sensitized solar cell conversion efficiency, to deduce the most promising strategies for improvement. It is found that the performance of the cells strongly depends on the morphology and crystalline structure of the nanotubes.

Transparent counter electrodes were prepared on transparent conductive glass (TCG) substrates from a hexachloroplatinic acid (H 2 PtCl6) solution applying the thermal decomposition method in combination with the spin-coating deposition technique. The effect of the precursor concentration and the number of deposited platinum layers on the surface characteristics of the Pt films was examined, and the relation between those surface characteristics and the electrochemical properties of the corresponding modified Pt/TCG electrodes was defined. Four types of counterelectrodes were prepared, differing in the concentration of the H 2 PtCl 6 solution (0.03M and 0.15M) and in the number of Pt layers (one or two Pt layers); their performance as counterelectrodes was evaluated after their incorporation into dye-sensitized solar cells (DSSCs) employing a solid state redox electrolyte. The obtained results show that solar cells using counterelectrodes prepared from the 0.03M H 2 PtCl 6 solution and consisting of two Pt layers (Pt032 electrode) exhibited the best performance characteristics (diffusion coefficient D * I 3 _ =1.58 X 10 -5 cm 2 s -1 , conversion efficiency η=2.16%, fill factor ff =62.14%, and short circuit photocurrent I sc =4.71mA cm -2 ). The electrochemical behavior of the modified counterelectrodes is consistent with the surface characteristics of the Pt film that formed on the conductive glass substrate, which seems to be significantly affected by the adopted method and the adjusted experimental parameters (Pt concentration and number of Pt layers). Specifically, this type of electrodes beside their low roughness (R q = 11.5 nm), also presents a high complexity (Df =2.3). As a result, for this kind of solid state DSSCs, the less rough but the more complex the Pt/TCG electrode surface, the higher the efficiency of the corresponding solar cells.

Titania nanospheres were prepared using the sol-gel technique following a core-shell approach based on polystyrene substrates. Thermal treatment of the titanium alkoxide modified polymer core structures resulted to formation of monodisperse TiO

TiO2 mesostructured films have been made on glass slides by a dip-coating process, using ethanolic solutions containing titanium iso-propoxide and poly(ethylene glycol) oligomers of various chain lengths. This convenient and easy procedure provides a means of controlling the size of titania nanoparticles, as well as the fractality and the roughness of the film surface by simply choosing the size of the oligomer chain length.

New composite PEO-based polymer-gel electrolytes were developed, using propylene carbonate (PC) plasticizer and iodide/triiodide (I-/I-3(-)) redox couple. The iodide anion was introduced in the form of the corresponding metal salts: CsI, RbI and LiI and the influence of the metal cation was examined. The non-volatile and high polar character of the PC plasticizer results to excellent ionic conductivity values of the electrolyte samples (up to 1.6 mS cm(-1)), as well as remarkable stability over time. Linear sweep voltametry measurements revealed noticeable triiodide diffusion coefficient values (in the order of 2 x 10(-6) cm s(-1)). The thermograms confirm the amorphicity of the electrolytes (crystallinity values below 20%). All the experimental results showed that the introduction of inorganic titania filler (Degussa P25) into the polymer matrix reduces even more the crystallinity of the samples and enhances the mobility of the redox couple. Nanocrystalline photoelectrochemical solar cells were fabricated with the newly developed composite electrolytes and were tested with I-V measurements. All cells presented high efficiency values for this type of composite electrolytes, with the best performance attained in the case of the PEO-TiO2-PC(CSI/I-3(-)) electrolyte, with overall energy conversion efficiency (eta) of 2.87% under standard AM1.5 simulated solar irradiation. Our results clearly support the redox couple mobility dependence on the cation nature. (C) 2007 Elsevier B.V. All rights reserved. Journal of Photochemistry and Photobiology a-Chemistry

International audience; The calcareous deposit formation on a marine structure under cathodic protection is depending on a large number of parameters. The influence of clay in suspension in artificial sea water has been mostly studied with montmorillonite, but some results with kaolinite are also presented. For both types of clays, the chronoamperometric curves show a delay for the calcareous deposit with respect to the situation without sediments and the deposition kinetics themselves are not modified whatever the clay concentration. This delay is proportional to the clay concentration in the particular case of montmorillonite. Conversely, the clay effect is negligible on the deposition kinetics of the Ca-based film in the absence of Mg2+ and small for the Mg-based film in the absence of Ca2+. A qualitative model is proposed to explain the role of clay suspension.

Novel polymer gel electrolytes have been prepared by incorporating LiI-I(2) solutions into a polyethylene oxide matrix supported by a TiO(2) filler. The gel electrolytes, based on either acetonitrile or propylene carbonate solvents are compared with liquid standard ones and are examined by (7)Li solid state nuclear magnetic resonance relaxometry and diffusion measurements. In parallel, the triiodide apparent diffusion coefficient has been determined by linear sweep voltammetry. The results are correlated with atomic force microscopic images of the electrolytes and give insight of the dynamic properties of the ions in the constrained polymer medium. Furthermore, the dissociation of the ions is estimated by relating the ionic conductivity to the ionic diffusion. As a prime application, the polymer gel electrolytes were incorporated in dye sensitized solar cells and the measured energy conversion efficiencies were successfully correlated with their morphological, diffusive and conducting properties.

Magnetic NdFeB thick films were prepared by screen printing a NdFeB-based ink. The films are isotropic and the thickness varied from 30 microns to 1 mm. The printing parameters were optimized with respect to the mechanical and the magnetic properties of the films. After curing at 390 K good adhesive non porous films were obtained. The magnetization of films are 400 emu/cc, the coercive field Hc is 1 Tesla, the Br is 4 kG and the energy product is 2.7 MGOe (21.5 kJ/mc). Rotors with those magnetic properties tested in stepper motors with promising efficiency.

A screen printing process was used for the preparation of Nd-Fe-B thick films directly on a variety of suitable substrates: Si, glass, stainless steel, Al, Ta and Mo. Then, the samples were cured at approx. 130 /spl deg/C, for 10 minutes in air. The magnetic properties of the films were measured at room temperature using a vibrating sample magnetometer and a superconducting quantum interference device magnetometer. All samples showed a typical ferromagnetic, single-phase hysteresis loops and an almost square loop with high coercive field and remanence. These properties are with technical interest and promising for MEMs applications.

New dyes of the type Ru(II)(bdmpp)(bpy) [where bdmpp is 2,6-bis(3,5-dimethyl-N-pyrazoyl)pyridine and bpy is 2,2'-bipyridine-4,4'-dicarboxylic acid] are prepared and characterized by infra-red (IR), mass (MS) and electrospray mass spectroscopy (ES-MS) as well as 1H NMR (1D and 2D) spectroscopies. The compounds present broad and very high intensity MLCT absorption bands in the visible and can be chemically anchored on TiO2 films via ester-like linkage involving carboxylato groups. These complexes have been tested with success as potential molecular antennas in dye-sensitized solar cells. Both opaque and transparent nanocrystalline TiO2 thin film electrodes obtained by a doctor blade technique sensitized by these complexes were incorporated in a sandwich type regenerative photoelectrochemical solar cell containing 0.1M LiI +0.01M I2 in propylene carbonate as well as a platinized conductive glass counter electrode. The cell was characterized by Raman spectroscopy under anodic and cathodic bias. Two new vibration bands were observed in the lower frequency region. The first one at 112 cm-1 is due to tri-iodide formed on the photoactive electrode, and the second one at 167 cm-1 is a sign of the dye/iodide interaction and corresponds to a vibration in a chemically stable "DI" intermediate species. Under direct sunlight illumination (solar irradiance of 60 mW/cm2) by using a composite polymer solid state electrolye, the cell ITO/TiO2/(Ru(II)(bdmpp)(bpy)(NCS))(PF6)/electrolyte/Pt-ITO produced a continuous photocurrent as high as 4.29mA/cm2, and gave IPCE values about half of the corresponding values obtained by the standard N3 dye under the same conditions. The photovoltage is about 600 mV and the overall energy conversion cell’s efficiency is as high as 1.72%.

Raman spectroscopy (RS) was used to study the interfacial species due to the presence of a redox couple in the electrolyte during the operation of dye-sensitized solar cells (DSSC). Two bands appear in the Raman spectra of polypyridinium (ppy) dyes adsorbed on nanocrystalline anatase. They can be directly connected to the presence of iodine/iodide couple because they are not present when hydroquinone/quinone (HQ/Q) redox couple is used. The band at 112 cm -1 has already be assigned to the presence of tri-iodide; it disappears only at very high cathodic polarization. The band at 167 cm -1 is due to the formation of an intermediate compound between the oxidized form of the dye , D + , and iodine; it involves a Py-I bonding. The use of different focusing proves that this compound is located below the adsorbed tri-iodide. Electrochemical Impedance Spectroscopy (EIS) allows to determine the charge transfer kinetics at the three main interfaces of the cell and to characterize the diffusion of tri-iodide species. Three different cell functioning regimes (photocurrent plateau, recombination, accumulation) were described. The Raman intensities of the two iodide-connected bands are investigated in each of the three regimes. The “Py-I” band is strong in the photocurrent plateau range and disappears in the recombination range.

Surface modification by suitable dyes of electrodes used in photoelectrochemical cells allows noticeable increase of their photo‐to‐electrical conversion efficiency. Several bis or trisbipyridylruthenium(II) complexes, containing different functional groups (in particular, carboxylation of the pyridine ring is necessary to obtain a strong adsorption) were studied. All of them were identified by "normal" (without any "artificial" enhancement) ex situ Raman spectroscopy. The differences (in peak position and intensity) of their spectra, typical of the pyridine rings, carboxylated or not, yields the position of the molecule with respect to the oxide surface. It is the first time that such a monolayer‐on‐oxide substrate was studied by Raman spectroscopy; the laser light must stimulate the charge transfer in the Ti‐molecule surface complex.

Publisher Summary This chapter illustrates the concept of mesoporous materials based on manganese and enriches them with other heterocations, such as A1, La, Ce, at will. The materials thus formed have been tested for important environmentally catalytic reactions: CH 4 /NO/O 2 (lean de-NO x ) and CH 4 /O 2 (combustion). Their corresponding catalytic performances were found superior to those reported in the open literature for a large number of catalysts tested under similar experimental conditions. A large number of techniques were employed for the surface and bulk characterization of the present materials. These include X-ray photoelectron spectroscopy (XPS) for surface composition, X-ray diffraction (XRD) for crystal phases, surface area measurements (BET) and AFM/Tapping mode experiments for surface texture, and transient methods for in situ determination of adsorption capacities and interaction characteristics of the reaction molecular species with the catalyst surface. The results obtained from these techniques were correlated with the catalytic performance results obtained.

Innovative redox electrolytes for dye-sensitized solar cells (DSCs) were prepared using binary mixtures of 1-methyl-3-propylimidazolium iodide (MPII) with 1-alkyl-methylimidazolium tricyanomethanide, C(nu)mimTCM (nu = 2, 4, 6, 8) ionic liquids (ILs) to lower the high viscosity of MPII. The investigation of the physicochemical properties of the IL blends as a function of temperature has shown that both density and viscosity strongly depend on the kind of the C(nu)mim cation in the mixture. The corresponding Raman spectra were dominated by the vibrational modes of the IL components in an additive way and confirmed the absence of any specific interaction, independent of the C-nu alkyl chain length. The electrochemical properties (triiodide diffusion coefficients, specific conductivity), determined in symmetrical thin layer cells using polarization and electrochemical impedance spectroscopy (EIS) measurements, have shown that both diffusion and conductivity decreased with increasing viscosity, and further confirmed the electrolytes' compatibility with the cathode. Incorporation of the novel electrolytes in DSC devices revealed a systematic dependence of the cell photovoltaic performance on the alkyl chain length of C(nu)mimTCM; the maximum power conversion efficiency exceeded 5 and 6.5% under 1 and 0.1 sun AM 1.5 G illumination, respectively, for the ionic liquid with the shortest alkyl chain. The solar cells were further characterized by EIS (IMPS) spectroscopy, exploring charge recombination dynamics and identifying conduction band edge shifts. Solidification of the electrolytes with silica nanoparticles, demonstrated that the ionic liquid electrolytes with long chain length (nu > 4) not only retain their efficiencies, but also exhibit a 22% efficiency enhancement, which is most pronounced for the electrolytes employing ionic liquids with the longest (hexyl-and octyl-) alkyl chains.

A surface-blocking triphenylamine-based organic dye (named as D35) is utilized for the fabrication of efficient dye solar cells (DSCs) employing solvent-free ionic liquid electrolytes. The prepared DSCs present power conversion efficiencies of 5.2% under 1 sun AM 1.5G illumination conditions, a performance very similar to solar cells using a reference electrolyte with identical amount (0.2 M) of iodine dissolved in a standard acetonitrile–valeronitrile solvent mixture. Despite the high concentration of recombining species inside the electrolyte, the IL-based cells are able to afford a photopotential (Voc) of 0.76 V. Electrochemical Impedance Spectroscopy (EIS) has explored the recombination dynamics and conduction band edge shifts, proving the role of the dye's molecular structure on attaining such a high value of Voc. The obtained short-circuit photocurrent (Jsc) values are discussed and justified in terms of mass-transport limitation processes in the viscous ionic liquid electrolyte.

The adsorption on a titanium dioxide substrate of organic monolayers used in the nanocrystalline dye sensitized solar cells was investigated by Raman spectroscopy, owing to the high resonance effect in these molecules. During the polarization of TiO2 modified by Ru-bi or ter pyridinium compounds in a photoelectrochemical cell, an enhancement affect appeared, allowing us to scrutinize the part of the complex which is in contact with the substrate. This affect remains to a large extent unexplained; it could be attributed to SERRS (surface enhanced Raman resonance). Noticeable differences appeared in the function of the nature of the pyridil ligands. In the case of bipy, in addition to the `normal' (ground state) Raman bands, a new series of bands appeared which correspond to the particular ligand exchanging electrons with the substrate titanium atoms. The Raman intensity of these new peaks is directly related to the electric field (i.e., to the potential magnitude independently of its cathodic or anodic nature). In the case of terpy, the enhancement mechanism seems different. The similarity of the molecular configuration created by the adsorption with the radical anion formed by the excitation of the metal ligand charge transfer complex has to be emphasized. Very interesting prospects for the understanding of the adsorption mechanisms are therefore opened.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An innovative solidified redox electrolyte for dye-sensitized solar cells (DSCs) was prepared by incorporating amorphous silica nanoparticles in a liquid system containing the Co2+/Co3+ shuttle dissolved in methoxypropionitrile; the novel material was characterized by Raman spectroscopy and its optical properties were examined by UV-Vis spectroscopy. Electrochemical properties (diffusion, conductivity, electrolyte compatibility with the cathode) were studied in symmetrical thin layer cells using polarization and electrochemical impedance spectroscopy (EIS) measurements. Quasi-solid DSCs were fabricated by incorporating this electrolyte and attained an efficiency of about 2.6% under 1 sun (under 1000 W m−2) AM1.5G illumination, corresponding to 73% of that gained by the reference liquid electrolyte; the cell efficiency depends on the light illumination conditions, significantly increased up to more than 4% under 0.23 sun. The solar cells were further characterized by EIS and intensity modulated photocurrent spectroscopy (IMPS) to investigate charge transport and recombination dynamics, possible conduction band edge shifts, alterations of the interfacial and ohmic resistances, and variations of the diffusion rate through the photoelectrode. It was confirmed that the solidified electrolyte-based DSC presented a slightly enhanced photopotential in comparison with that of the liquid electrolyte due to a negative TiO2 conduction band edge shift upon contact with the electrolyte, accompanied with a decreased photocurrent mainly stemming from the restricted diffusion of the Co3+ species through the pores of the TiO2 photoelectrode.

We have demonstrated heterogeneous photocatalytic degradation of microcystin-LR (MC-LR) by visible light activated carbon doped TiO(2) (C-TiO(2)) nanoparticles, synthesized by a modified sol-gel route based on the self-assembly technique exploiting oleic acid as a pore directing agent and carbon source. The C-TiO(2) nanoparticles crystallize in anatase phase despite the low calcination temperature of 350 °C and exhibit a highly porous structure that can be optimized by tuning the concentration of the oleic acid surfactant. The carbon modified nanomaterials exhibited enhanced absorption in the broad visible light region together with an apparent red shift in the optical absorption edge by 0.5 eV (2.69 eV), compared to the 3.18 eV of reference anatase TiO(2). Carbon species were identified by x-ray photoelectron spectroscopy analysis through the formation of both Ti-C and C-O bonds, indicative of substitution of carbon for oxygen atoms and the formation of carbonates, respectively. Electron paramagnetic resonance spectroscopy revealed the formation of two carbon related paramagnetic centers in C-TiO(2), whose intensity was markedly enhanced under visible light illumination, pointing to the formation of localized states within the anatase band gap, following carbon doping. The photocatalytic activity of C-TiO(2) nanomaterials was evaluated for the degradation of MC-LR at pH 3.0 under visible light (λ > 420 nm) irradiation. The doped materials showed a higher MC-LR degradation rate than reference TiO(2), behavior that is attributed to the incorporation of carbon into the titania lattice.

There is an error in the scale bar of the inset of Fig. 1b in the original manuscript. The corrected figure is presented here in Fig. 1. As the originally used figure (see Fig. 2a here) was not very representative for TiO2 nanotubes grown under the described conditions we now provide a more representative picture (Fig. 2b) confirming an average thickness of ∼2.5 µm (as given throughout the paper). No statement or other scientific content of the article is affected by this correction. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The optical and structural properties of cadmium and lead sulfide nanocrystals deposited on mesoporous TiO2 substrates via the successive ionic layer adsorption and reaction method were comparatively investigated by reflectance, transmittance, micro-Raman and photoluminescence measurements. Enhanced interfacial electron transfer is evidenced upon direct growth of both CdS and PbS on TiO2 through the marked quenching of their excitonic emission. The optical absorbance of CdS/TiO2 can be tuned over a narrow spectral range. On the other side PbS/TiO2 exhibits a remarkable band gap tunability extending from the visible to the near infrared range, due to the distinct quantum size effects of PbS quantum dots. However, PbS/TiO2 suffers from severe degradation upon air exposure. Degradation effects are much less pronounced for CdS/TiO2 that is appreciably more stable, though it degrades readily upon visible light illumination.

The effect of applied potential on the morphology, growth efficiency, and composition of self-organized titanium oxide nanotubes, generated in 0.2 M N H4 F /glycerol electrolyte, has been examined by electron microscopy, Rutherford backscattering spectroscopy, and nuclear reaction analysis. A linear increase in nanotube diameter, length, and wall thickness, with increasing applied potential is evident up to 40 V, whereas the growth efficiency decreases with increase of the applied potential. Due to the semiconductive properties of the titanium oxide, at potentials above 40 V some of the oxygen anions migrating across the barrier layer lose electrons and generate oxygen gas within the oxide. This results in a morphological transition above 40 V, characterized by the degeneration of nanotube geometry and uniformity, and the appearance of oxygen-filled voids within the barrier layer and nanotubes walls. © 2010 The Electrochemical Society.

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.

Polarized micro-Raman spectroscopy was applied to investigate the phase composition and transformation from the amorphous to the crystalline state, size effects, and the crystallographic orientation and antenna polarization effects on self-organized anodic TiO2 nanotubes (NTs). The morphological characteristics of the NTs were tailored by electrochemical anodization in both aqueous (phosphate buffer) and organic (ethylene glycol) electrolytes as well as in perchlorate/chloride-containing electrolytes. Postgrowth thermal annealing was confirmed to reduce markedly the organic and inorganic species encapsulated in the as-grown arrays and drive the transformation of the amorphous titania to nanocrystalline anatase. Crystallite size and shape effects as well as oxygen nonstoichiometry were investigated through the variation of the low-frequency Eg anatase mode for the TiO2 NT arrays produced in different electrolyte media, and the results were compared with the predictions of the phonon confinement model for a...

Ru(PPh3)2(dcbipy)Cl2 (PPh3=triphenylphosphine, dcbipy=2,2′-bipyridyl-4,4′-dicarboxylate) was prepared to use as a TiO2 sensitizer in wet regenerative photoelectrochemical cells. The complex has been structurally characterized by IR, Raman, ES-MS and NMR spectroscopies. The broad bands in the visible spectrum as well as the reversibility of the redox couple RuII–RuIII, established by cyclic voltammetry, make this complex potentially beneficial for the photosensitization process.

Dye-sensitized photoelectrochemical cells (DSSC) are characterized by electrochemical impedance spectroscopy (EIS) and Raman spectroscopy during their polarization. Cells realized with a dye recently synthesized in one of our laboratories, containing two terpyridyl (terpy) ligands, are compared with cells using commercial dyes (Ru535 and Ru620) containing isothiocyanates and either bipyridyl (bpy) or terpy ligands. Here, two points are emphasized, first, the role of the functional group (carboxylate or phosphonate) which ensures the linkage to TiO 2 and, second, the role of the redox couple (I /I - 3 ) present in the electrolyte which can react with the dye D to give unwanted intermediate species. Two species, each of them giving a characteristic Raman band in the low wavenumber range, are characterized by Raman spectroscopy. The first of these species is triiodide; the nature of the second one, which directly implies the oxidized form of dye, D + , is discussed. During the DSSC functioning, EIS allows one to discriminate three potential ranges, the photocurrent plateau, the recombination range, and the direct current range when the voltage decreases from anodic to cathodic. The second intermediate exists only in the photocurrent plateau, while I - 3 exists also in the recombination range. These results do not depend on the nature (bpy or terpy) of the ligand.

WO3 films grown by anodic oxidation have been studied by different optical and structural techniques. Their growth kinetics have been investigated by multichannel optical analysis; a very fast initial growth step must be responsible for their particular (hexagonal) crystallographic structure. Reflection high energy electron diffraction and Raman spectroscopy allowed us to follow the structural changes related to the coloration of the oxide by different intercalated ions: H+, Na+ and above all Li+. In fact, no changes in WO3 composition (stoichiometry) or in the crystalline order can be detected: the main effect is a profound chemical perturbation of the lattice leading to the formation of W=O in place of the initial WO bonds.

Thin WO3 films, grown by anodic oxidation of tungsten, show excellent electrochromic properties, including a coloration absorption band in the visible wavelength range, fast kinetics, and high stability during long oxidation/bleaching cycles. These properties are described here, together with the choice of the polarization conditions that ensure the best electrochromic film performance.

Anodic oxydation of tungsten in sulfuric solutions gives thin films with the uncommon hexagonal structure. When the films have grown at low voltages, the hexagonal channels are distorted with a lack of long-distance order. These films present very interesting electrochromic properties, over all when the coloration is done in an organic medium with insertion of Li + . The coloration absorption band is then centered in the visible wavelengths range. The optical indices in the bleached and colored states are obtained by a sophisticated statistical method of reflectance curves fitting. The kinetics of coloration/bleaching are studied by Multichannel Optical Analysis (OMA), and the lattice perturbations created by the insertion are followed by Raman spectroscopy. The electrical and optical reversibilities are perfect after more than 2x10 6 coloration/ bleaching cycles and, in reason of the position of the coloration band in the visible wavelengths range, the coloration yield is high.