Temperature dependent photoluminescence of anatase and rutile TiO 2 single crystals: Polaron and self-trapped exciton formation

International audienc

One step synthesis of niobium doped titania nanotube arrays to form (N,Nb) co-doped TiO 2 with high visible light photoelectrochemical activity

International audienceThe chemical modification of aligned titanium dioxide nanotube (TiO2-NT) arrays provides new doping possibilities to improve their photoelectrochemical activity under visible light. Niobium doped TiO2-NTs containing up to 15% of Nb in the near-surface region are prepared by a flexible single step procedure using a fluoroniobate complex simultaneously acting as a source of the doping element and fluoride anions required for nanotube formation. This negatively charged complex allows an efficient insertion of Nb in the forming TiO2-NT structure during the anodization process. These nanotube arrays are further modified with nitrogen to achieve (Nb,N) co-doped nanotubes with noticeable visible light photoelectrochemical activity

Sols et gels photosensibles à base d'oxyde de titane pour applications photovoltaïques

Au coté de leur indice de réfraction élevé justifiant l emploi des dioxydes de titane comme pigment blanc, de nouvelles applications dans le domaine de l environnement succitent un engouement croissant auprès de la communauté scientifique durant cette dernière décennie. Ces applications exploitent leurs propriétés photoactives: photocatalyse, photovoltaïque, matériaux auto-nettoyants . Les études précédemment menées au sein de l Institut des Matériaux Jean Rouxel, ont permis de synthétiser différentes variétés d oxyde de titane utilisables pour ces différentes applications. L objet de ce travail concerne de nouveaux sols et gels hybrides, présentant des propriétés photosensibles originales. Une étude approfondie des mécanismes de formation de ces sols et gels a été menée. Le rôle actif du solvant organique dans le processus de poly-condensation a été mis en évidence par spectroscopie Raman et RMN 1H et 13C. Le contrôle de l hydrolyse du précurseur de titane permet d obtenir des sols et des gels dont la partie inorganique, structurée à l échelle nanométrique, a été caractérisée par spectroscopie d absorption des rayons X (XANES et EXAFS). L étude de leurs propriétés photochromes a été menée par spectroscopie d absorption UV-visible. Les études par magnétométrie et XPS ont permis de proposer un mécanisme réactionnel expliquant le phénomène photochimique observé sous irradiation UV. Il implique une réduction du Ti(IV) en Ti(III) et la participation des espèces organiques adsorbées sur le matériau. Une cellule photovoltaïque de type cellule à colorant a été développée afin de tester les possibilités d utilisation du gel pour la conversion de l énergie solaire. Les expériences de photoélectrochimie réalisées sur l électrode photoactive montrent un stockage des charges lors de l irradiation. Cette propriété autorise la réalisation d un dispositif permettant la conversion et le stockage de l énergie solaire: une photobatterie rechargeableBeside to their white pigment properties, known for several years, new applications of the titanium oxides induces a lot of new scientific works during the past decade. All these new applications, like photodepollution of water through photocatalysis, air cleaning, dye sensitized solar cells (DSSC), self cleaning surfaces are based on the photoactive properties of this material. The previous studies done at the Institut des Materiaux Jean Rouxel, lead to the synthesis of various forms of titanium oxide that can be used for this different applications. During this study, we focus on new hybrid sols and gels, having original photosensitive properties. The formation mechanisms of these sols and gels have been studied. The Raman and 1H and 13C NMR spectroscopies have shown that the organic solvent is directly involved in the condensation mechanism. In particular the hydrolysis of the organic solvent produces dimethylammonium chloride and methanoic acid, both strongly interacting with the inorganic nanostructured framework. The extension of the latter controls the sol-gel transformation and was characterised by X-ray absorption spectroscopy (XANES and EXAFS). The photochromic properties were investigated by UV-visible spectroscopy. Using the magnetic results and XPS studies, we proposed a reaction mechanism, involving the reduction of Ti(IV) to Ti(III), for the blue coloration appearing under UV irradiation. The importance of the organic part from the solvent in this mechanism has also been pointed out. A photovoltaic cell, based on the principle of DSSC, has been developed to evaluate the possibilities of the gel for solar energy conversion applications. The photo-electrochemical experiments done on the photoactive electrode show a chemical storage of the charges formed under irradiation. This property enables the development of a device that could convert and store solar energy : a rechargeable photobatteryNANTES-BU Sciences (441092104) / SudocSudocFranceF

Investigation of interactions between organophosphorus compounds and TiO₂ modified microcantilevers for molecule detection in air

International audienceIn order to develop a detector working in the gas phase for organophosphorus molecules, resonant microcantilever surfaces were chemically modified with pristine and functionalized TiO 2 nanorods. By using a solvothermal synthesis method a homogeneous film, composed of nanorods with square facets, covering completely the surface of the levers was obtained. The synthesized rods mainly exhibit [110] oriented crystals and this facet has especially demonstrated a high loading ability for grafted sensing molecules. Experimental results showed that the sensing response is three times higher when the TiO 2 sensor is functionalized with amine terminated molecules while no significant response is observed for bare cantilevers exposed to a DMMP simulant. The in situ IR analysis highlighted the formation of hydrogen bonds between the characteristic groups of DMMP and the TiO 2 surface at room temperature. The strength of this bond depends on the chemical groups present at the oxide surface. Molecules containing hydroxyl or amino functions form stronger hydrogen interactions with the OP simulant compared to the fluorine group. The kinetics of adsorption are characterized by a fast initial reaction followed by gradual slowing to a steady-state for all the samples

Influence of the anatase/rutile ratio on the charge transport properties of TiO 2 -NTs arrays studied by dual wavelength opto-electrochemical impedance spectroscopy

International audienceThe modification of photo-generated charge transport properties in aligned titanium dioxide nanotubes(TiO2-NTs) regarding the anatase/rutile ratio was studied by photo-electrochemical methods. TiO2-NTsobtained by anodization were thermally treated under air flux at different temperatures to significantlymodify the proportion of TiO2 anatase and rutile phases in the tubular structure. Material characterisationmethods (XRD, SEM, UV-visible spectroscopy) were used to determine the characteristics of the differentTiO2-NT electrodes in terms of dimensions, proportion of each phase and optical properties. The solar tochemical energy conversion efficiency of these electrodes during an oxidation process was investigated inbasic aqueous solution, using methanol as a sacrificial agent, by cyclic voltametry and Incident Photon toCurrent conversion Efficiency (IPCE) measurements. TiO2-NTs with a high rutile content absorb photonsof higher wavelengths, but despite this red shifted optical band gap, they exhibit the lowest photoelectrochemicalconversion efficiency. To further investigate the transport properties in thesephotoelectrodes, Intensity-Modulated Photocurrent Spectroscopy (IMPS) was used with two differentirradiation wavelengths to determine the transport and recombination properties of anatase and rutileseparately. The results obtained by this set of experiments indicate that the presence of the rutile at thebottom of the nanotubes is the major factor limiting the photo-generated electron transfer

Design of an efficient measurement cell for characterizing sensing properties of nanostructured sensitive layers coated on chips

International audienc

Enhanced visible-light-photoconversion efficiency of TiO2 nanotubes decorated by pulsed laser deposited CoNi nanoparticles

International audienc

Double side nanostructuring of microcantilever sensors with TiO2-NTs as a route to enhance their sensitivity

International audienceWe reported a new strategy to enhance the sensing performances of a commercial microcantilever with optical readout in dynamic mode for the vapor detection of organophosphorus compounds (OPs). In order to increase significantly the surface area accessible to the molecules in the vapor phase, we nanostructured both sides of the microcantilever with ordered, open and vertically oriented amorphous titanium dioxide nanotubes (TiO2-NTs) in one step by an anodization method. However, due to the aggressive conditions of anodization synthesis it remains a real challenge to nanostructure both sides of the microcantilever. Consequently, we developed and optimized a protocol of synthesis to overcome these harsh conditions which can lead to the total destruction of the silicon microcantilever. Moreover, this protocol was also elaborated in order to maintain a good reflection of the laser beam on one side of the microcantilever towards the position sensitive photodiode and limit the light diffusion by the NTs film. The results related to the detection of dimethyl methylphosphonate (DMMP) showed that TiO2 and the nanostructuring on both sides of the microcantilever with NTs indeed improved the response of the sensor to vapors compared to a microcantilever nanostructured on only one side. The dimensions and morphology of NTs guaranteed the access of molecules to the surface of NTs. This approach showed promising prospects to enhance the sensing performances of microcantilevers

TiO2 Nanotube arrays: Influence of tube length on the photocatalytic degradation of Paraquat

International audienc

Hydrolysis and Complexation of N , N -Dimethylformamide in New Nanostructurated Titanium Oxide Hybrid Organic–Inorganic Sols and Gel

International audienc