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Water disinfection using visible light-active photocatalyst has recently attracted more attention due to its potential to inactivate microbes. In this study, we have investigated the efficiency of photocatalysis (TiO

Water disinfection using visible light-active photocatalyst has recently attracted more attention due to its potential to inactivate microbes. In this study, we have investigated the efficiency of ...

Solar photocatalytic inactivation of Gram-negative bacteria with immobilized TiO2-P25 in a fixed-bed reactor was modeled with simplified kinetic equations. The kinetic parameters are the following: the photocatalytic inactivation coefficient (kd,QUV), the initial bacterial reduction rate (A) in the contact with the disinfecting agent, and the threshold level of damage (n) were determined to report the effect of QUV/TiO2-P25 on bacterial cultivability and viability and to compare the response of bacterial strains to photocatalytic treatment. In addition, the integration of the reactivation coefficient (Cr) in the photocatalytic inactivation equation allowed evaluating the ability of bacterial reactivation after photocatalytic stress. Results showed different responses of the bacteria strains to photocatalytic stress and the ability of certain bacterial strains such as Escherichia coli ATCC25922 and Pseudomonas aeruginosa ATCC4114 to resuscitate after photocatalytic treatment.

International audience; Among the possible solutions for the intensification of photocatalytic reactions, the use of microreactors is emerging. Such an approach was applied to the photodegradation of Ifosfamide in a flow microreactor with an immobilized catalyst composed of ZnO sensitized with CuInZnxS2+x quantum dots. The conversion yield at a low flow rate was investigated. A computational flow simulation allows to determine an apparent constant rate and the diffusion coefficient towards the photocatalyst surface. Photocatalytic degradation of Ifosfamide can be fitted by the Langmuir-Hinshelwood model. The Sherwood number and the average value of Damköhler show that the photocatalytic reaction under our experimental conditions is limited by the mass transfer.

In a previous paper, we have demonstrated a facile and low-cost synthesis of ZnO/In2S3 core/shell nanowires (NWs) on indium tin oxide substrates by a two-step electrochemical method. The main objective of the present study was to demonstrate the potentiality of this system in visible and solar photocatalysis for water treatment applications. The morphological, structural and photophysical properties of the core/shell NWs were investigated through TEM, XRD, Raman, wettability and UV–vis absorption. The photocatalytic activity of the ZnO/In2S3 core/shell NWs was investigated under solar light and visible light irradiation using mainly methylene blue in aqueous solutions. The influence of the materials (In2S3 shell thickness) as well as the operating parameters, including the nature and the intensity of the incident light irradiation (visible and solar), the nature and the concentration of the pollutants (methylene blue, methyl orange, and salicylic acid), and the pH of the solution were examined. The hydroxyl radicals involved in the photodegradation process were also addressed at different excitation wavelengths. The experimental results pointed out that the pollutants can be degraded completely within 120 min by the ZnO/In2S3 core/shell and their photodegradation rate were 5 times faster than those of pure ZnO nanowires. The reusability test highlighted that the ZnO/In2S3 NWs arrays still maintained high photocatalytic activity over five cycles. The as-synthesized ZnO/In2S3 core/shell provide a facile, low cost, large photocatalytic efficiency, and high reusability, which shall be also promising in many related areas, such as solar energy conversion, water splitting, and energy storage.

International audience; Porous Mn-doped ZnO (ZnO:Mn) nanoparticles with an average diameter of ca. 21 nm were prepared by a simple and cheap solvothermal process involving no templates, post-synthetic annealing or etching. The particles produced were characterized by XRD, Raman spectroscopy, SEM, TEM, XPS, diffuse reflectance spectroscopy and BET surface area measurements and the effects of Mn2+-doping on the structural, optical and photocatalytic properties of ZnO particles were investigated. The particles doped with 3 mol% Mn2+ were found to exhibit the highest catalytic activity toward the photodegradation of the Orange II dye under solar light irradiation. Our results demonstrate that Mn2+-doping shifts the optical absorption to the visible region, increases the specific surface area of the photocatalyst and reduces the recombination of electron-hole pairs. The influence of various operational parameters (amount of catalyst, concentration of dye and pH) on the photodegradation and the photocatalytic mechanism were studied. Finally, we demonstrated that the ZnO:Mn photocatalyst is stable and can be easily recycled up to ten times without any significant decrease in photocatalytic activity.

International audience; ZnO nanorods (NRs) with an average length and diameter of 186 and 20 nm, respectively, were prepared through a mild solvothermal route and used as photocatalysts either as dispersed powder or immobilized on glass slides. The ZnO NRs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Dispersed ZnO NRs and, to a lesser extent, immobilized ZnO NRs were demonstrated to exhibit high photocatalytic activity under simulated sunlight of low intensity (5.5 mW/cm 2) both for the degradation of the Orange II dye and for Escherichia coli bacterial decontamination (2.5-fold survival decrease after 180 min irradiation for immobilized NRs). SEM, atomic force microscopy (AFM), fluorescence spectroscopy, and epifluorescence microscopy demonstrate that cell surface damages are responsible of bacterial inactivation. The immobilized ZnO NRs could be reused up to five times for bacterial decontamination at comparable efficiency and therefore have great potential for real environmental applications.

International audience; Al-doped ZnO (ZnO:Al) rods with Al doping varying from 0 to 20% were successfully prepared via a solvothermal method. ZnO:Al rods exhibit the hexagonal wurtzite crystalline structure and their length were found to decrease from 127 to 12 nm when increasing the dopant percentage from 0 to 20%. Simultaneously, their specific surface area increased from ca. 21 to 82 m2/g. ZnO:Al (20%) rods exhibit high adsorption capability towards some negatively charged dyes like Orange II, Acid red 88 or Alizarin, which was attributed to the high specific surface of ZnO:Al rods and to the defects induced by the Al doping as demonstrated by XRD and Raman spectroscopy.

International audience; We report a facile synthesis of ZnO/Fe2O3 heterostructures based on the hydrolysis of FeCl3 in the presence of ZnO nanoparticles. The material structure, composition, and its optical properties have been examined by means of transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and diffuse reflectance UV-visible spectroscopy. Results obtained show that 2.9 nm-sized Fe2O3 nanoparticles produced assemble with ZnO to form ZnO/Fe2O3 heterostructures. We have evaluated the photodegradation performances of ZnO/Fe2O3 materials using salicylic acid under UV-light. ZnO/Fe2O3 heterostructures exhibited enhanced photocatalytic capabilities than commercial ZnO due to the effective electron/hole separation at the interfaces of ZnO/Fe2O3 allowing the enhanced hydroxyl and superoxide radicals production from the heterostructure.

Chemical reactions in a microreactor can offer new possibilities for many chemical engineering application fields and have been employed in photocatalysis studies. The purpose of this work is to investigate the photocatalytic degradation of salicylic acid (SA) as a pollutant model, in a continuous flow microchannel reactor in order to evaluate the influence of radial concentration profile on the photocatalytic efficiency. The study has been developed on both experimental and theoretical aspects. Microreactors have been manufactured by stereolithography in epoxy resin (Accura® SI 30) and are composed of a channel with a rectangular cross-section of about 1 mm2 with different aspect ratios defined as width/depth. Photocatalytic experiments have been performed at different flow rates. Results can be predicted by the Langmuir-Hinshelwood (LH) kinetic model coupled with surface diffusion. Computational fluid dynamics (CFD-Comsol Multiphysics) can model phenomena and confirmed the reliability of our experimenta...

International audience; This paper illustrates the electrowetting behavior of aqueous dispersions of quantum dots (QDs) functionalized with 3-mercaptopropionic acid. The pH, QD concentration, type of QDs (core/shell CdSe/CdS versus CdTe/CdS) and the polarity of the voltage have been varied. The major parameter that controls the electrowetting properties is the polarity of the applied potential. This is explained by the electrophoretic transport of the negatively charged QDs to the in-liquid electrode (air/water interface) or to the fluoropolymer surface depending on the polarity of the electric field. In the negative range of applied voltage, the reversibility is excellent and contact angle hysteresis is minimal (1-2). The electric field favors the accumulation of the QDs at the air/water interface which reduces the liquid/vapor surface tension. The contact angle values depend mainly on the QD concentration regardless of pH and QD composition. For positive applied voltages, the electrowetting behavior becomes different. The adsorption of the QDs onto the fluoropolymer surface is observed when the electric field is applied. The adsorption increases with both the pH (negative zeta potential of the QDs) and the QD concentration. The surface roughness in the presence of adsorbed QDs leads to non-reversible electrowetting and significant contact angle hysteresis. The large contact angle change versus voltage at basic pH and high QD concentration is attributed to the enhancement of the capacitance of the fluoropolymer dielectric layer due to the presence of highly insulating QDs adsorbed onto the fluoropolymer surface.

International audience; An original photocatalytic reactor for the treatment of polluted air is designed. The titanium dioxide is supported on various supports that consist in photopolymers and are built using the stereolithography technique and placed in a glass tube illuminated from the outside, while the air containing the pollutant to be removed flows through the glass tube and the photocatalyst support. It is shown that the gas-solid mass transfer plays a role only at the very smallest gas velocities investigated. The global depollution kinetics are then determined for the different geometrical forms of the phorocatalyst support and the efficiency of the forms compared.

International audience; The advantage of using electrowetting as a novel principle for a reflective display has been previously demonstrated. The principle is based on the controlled two-dimensional movement of an oil/water interface across a hydrophobic fluoropolymer insulator. The main objective of this paper is to show experimentally the influence of surfactants on the electro-optic behavior of a single electrowetting pixel. The concentration and type of nonionic surfactant (Tween 80 and Span 20) have been varied. The experimental data are compared with calculations from the electro-optic model developed previously. The electro-optic performance is significantly affected by the nature and the concentration of surfactant. In the presence of Tween, at concentrations lower than the critical micelle concentration (CMC), and mixtures of Tween and Span the electro-optic behavior can be related to the interfacial tension. When decreasing the oil/water interfacial tension, the amplitude of the driving voltage required for obtaining a given oil displacement decreases and the switching curve becomes steeper. These effects can be accurately reproduced bymeans of the previously developed electro-optic model. Mixtures of Tween and Span produce a significant synergetic reduction of the driving voltage. For Tween concentrations higher than the CMC and Span, a strong disagreement is observed between the previously developedmodel and experimental data. Here a new physical model is reported that describes the electro-optic behavior of electrowetting-based optical elements in the presence of surfactants. The model takes into account the actual voltage used to control the liquid movement in electrowetting (lower than the applied voltage), the amount of surfactant adsorbed at the decane/water interface, and the dipole moment of the surfactant molecules. The calculated results are in very good agreement with experimental data without employing fitting parameters. The dipoles interact with the applied field and lower the actual applied field. This reduction of the effective electric field across the solid-liquid interface induces a decrease in the charge density at the solid-liquid interface and reduces the electrowetting force. For surfactant concentrations higher than theCMC, the electro-optic performance does not depend on the surfactant concentration. This demonstrates that the reduction of the electrowetting field due to the large dipole moment of the surfactant molecules occurs at the oil/water interface. A new method for the test cell fabrication is also presented.

International audience; This review presentse the stereolithography fabircaztion of epoxy and acrylate syntactic foams based on hollow glass microspheres. Physicochemicakl analysis has been performed on the fabricated 3D syntactic foam items containing different amounts of microspheres. The surface free energies, light transmuittance, densityb of the syntactic foams were investigated. Criteria for the choice of a polymeric binder are discussed.

International audience; The constructal approach, proposed by Bejan is an emergent notion which quickly develops at the international level and in a multidisciplinary frame. It is a method of optimization of the conception of objects and ‘‘components'' which allows finding the geometry of a multi-scale system in view of an optimal performance. The constructal concept, as the fractal concept, is a way of connecting the geometry of a microscopic world (the structures of an equipment or a material at the finest scales) with the macroscopic world in which it is immersed, through several intermediate scales. Essential differences with the fractal object are that the constructal object optimizes the passages from one scale to the other, that the geometry is not necessarily invariant from one scale to the other, and that there maybe some thermodynamic content to the optimization, such as minimizing entropy production. The present paper addresses these issues through several aspects: general introduction to the constructal approach; discussion of some examples of multi-scale components (heat exchanger, fluid distributor, coupling of fluid distributor to heat exchanger, mixer and its coupling to a micro reactor); manufacturing issues; perspectives for applications and for further scientific research.

Optical profilometry and real-time infrared (RTIR) spectroscopy have been performed to determine the influence of oxygen diffusion in ceramics suspensions on stereolithography accuracy. As expected, oxygen tends to lower both polymerized depth and width by inhibiting the polymerization and scavenging the radicals. Researches concern the influence of process parameters (atmosphere composition and temperature) and dispersion formulation, through viscosity, its filler content or tertiary amine addition, on oxygen diffusion. Models, such as those of Wilke–Chang and Mackie and Meares, were used to fit the oxygen diffusivity in the piezoelectric ceramics suspensions. This study has led to the modification of the stereolithography process in order to allow piezocomposites fabrication with a higher accuracy.

The study of the rheological behaviour of PZT suspensions is essential to a better understanding of piezocomposites fabrication through stereolithography process. Research concerns the influence of fillers contents, surfactant doses, temperature and resin nature on suspensions rheological behaviour. They have led to the choice of two photosensitive suspensions suitable for stereolithography purpose; which use depends on the fillers content. Furthermore, the stereolithography process has been modified owing to the balance between suspensions rheological and photochemical properties in order to shape piezoelectric ceramics. Thanks to these improvements, PZT ceramics/polymer composites dedicated to transducers and medical imaging applications have been fabricated.

In order to obtain three dimensional micro-objects, we developed a new microstereolithography apparatus based on the use of a dynamic mask generator which allows the manufacture of a complete layer by only one irradiation, the part being still layered. In order to improve the mechanical properties of the fabricated micro-objects and the resolution of the process, a mixture of alumina and photopolymer is used. By controlling the fabrication parameters, we present a movable microgimbal which has been realised in only one fabrication step.

The characteristics of PZT suspensions have been studied and fit to stereolithography restraints. On one hand, researches concern the influence of fillers contents, dispersant concentration, temperature and resins nature and amount on suspensions rheological behaviour. On the other hand, the influence of photoinitiator and PZT concentrations, density of energy and nature of the resin on suspension reactivity was investigated. These experiments have led to the choice of two photosensitive suspensions suitable for stereolithography purpose; which use depend on the fillers content. Furthermore, the stereolithography process has been modified owing to the balance between suspensions rheological and photochemical properties in order to shape piezoelectric ceramics. Thanks to these improvements, PZT ceramics/polymer composites dedicated to transducers and medical imaging applications have been fabricated.

International audience; The main objective of this paper was to evaluate the influence of mass transfer on the photocatalytic efficiency at a low flow rate in the order of several mL per hour. Several continuous flow microchannel reactors have been used to study the degradation of salicylic acid (SA) taken as a model pollutant. The photocatalytic degradation of salicylic acid, under UV illumination of 1.5 mW cm−2, was assessed from the outlet concentration measured by liquid chromatography HPLC. It was shown that the degradation of SA by UV was limited by mass transfer. Numerical simulations have allowed establishing a relationship of the Sherwood number valuable for all the microchannel geometries. Computational fluid dynamics with Comsol Multiphysics is useful for predicting the degradation yield for a given geometry of the microreactor. The best representation of the experimental data is obtained by introducing a kinetic law taking into account mass transfer limitation.

International audience; Laser stereolithography (SL) is an additive manufacturing technology which is increasingly being used to produce customized end-user parts of any complex shape. It requires the use of a photo-curable resin which can be loaded with ceramic powders or carbon fibers to produce composite parts. However, the range of available materials compatible with the SL process is rather limited. In particular, photo-curable resins reinforced by metal particles are difficult to process, because of fundamental limitations related to the high reflectivity of intermetallics in the UV-visible range. In this work, the unique properties of Al-based quasicrystalline alloys are being used to develop a new UV-curable resin reinforced by such metal particles. The optical properties of the quasicrystalline particles and of the filled resin are studied and they are found to be compatible with the SL process. The volume fraction of the filler particles in the liquid resin is optimized to increase the polymerization depth while preserving suitable rheological behaviour. Finally, 3D composite parts are being built by SL. The composite parts have improved mechanical properties compared to the unfilled resin (higher hardness, reduced wear losses and lower friction coefficient) and compete favourably with the other commercial photo-curable resins.

Ceramic three‐dimensional parts can be produced by a stereolithography (SL) process using a ceramic suspension containing alumina powder, UV curable monomer, diluent, photoinitiator and dispersant. The monomer reacts to UV radiation (argon ionized laser) and is transformed into a solid polymer which is then removed by thermal treatment (debinding). Subsequent sintering of green parts leads to dense ceramic parts. The effect of each component on the rheology of the alumina suspensions has been studied first. Both the addition of dispersant and diluent and the increase in temperature allow a significant decrease of the viscosity of the suspensions. The highly loaded (more than 55 vol. per cent), homogeneous and stable suspensions have a shear thinning behaviour which is favourable for casting the layers. Adequate cured depth (above 200μm) and satisfactory transversal resolution have been obtained and these allow the production of ceramic parts, which demonstrates the feasibility of the process. Sintering at 1,580°C leads to dense ceramic parts with homogeneous microstructure. The process still needs to be optimized to improve even more the mechanical properties.

Ceramic three dimensional parts have been fabricated by a Stereolithography (SL) process using a ceramic slurry containing alumina powder, UV curable monomer, diluent, photoinitiator and dispersant, subsequent removal of organic components and sintering. The SL process consists of fabricating parts with complex shapes layer by layer by laser polymerization of a ceramic/resin mixture. The effects of each component on the rheology of the ceramic suspension were investigated. Both, the addition of dispersant and diluent to the curable monomer and the increase in temperature decrease the viscosity down to suitable values for tape casting of the layers and for SL. The homogeneous and stable high ceramic concentration suspensions (53 vol%) exhibited a shear thinning behavior, which is favorable for casting the layers. Adequate cured depth (above 200 μm) and width were obtained even at high scanning speeds with an argon ionized laser.

The stereophotolithography process allows a three-dimensional object to be built by layer-by-layer, space-resolved, light-induced polymerization of a liquid monomer into a solid polymer. The relationship between the light penetration depth in the photoreacting medium, the scanning speed of the laser beam on the surface of the resin and the laser power has been studied. Experimental measurements have been performed and compared with a kinetic model. Empirical laws of evolution of the polymerized depth vs. macroscopic parameters have also been determined allowing the optimal operating conditions in stereophotolithography to be defined.

A new laser microstereophotolithography process has been developed in our laboratory to manufacture three-dimensional parts with a high accuracy. As usual in laser stereophotolithography or laser microstereophotolithography, the part is manufactured layer by layer by a light-induced space-resolved polymerization. Until now, in all the already existing microstereophotolithography devices a layer is manufactured vector by vector, by moving the part beneath the initiating light source which remains motionless. We developed a simpler and easier process, in which we can manufacture an entire layer by irradiating its whole surface only once: we used a liquid crystal display as a dynamic generator of masks. In the device we set up, we need only one mobile element, the z translator, all the others are fixed. We manufactured several different 3D microparts, in particular a piece of bevel microgearing with helicoidal cogs, the volume of which is less than half a cubic millimetre.

International audience; Cu-doped ZnS quantum dots (QDs) were synthesized in aqueous solution using 3-mercaptopropionic acid (MPA) as stabilizer. Transmission electron microscopy (TEM) results indicate that the Cu:ZnS nanocrystals distribute uniformly and the size is ca. 2.9 ± 0.5 nm. These nanocrystals were successfully associated to anatase TiO2 nanoparticles to yield TiO2/Cu:ZnS photocatalysts. Morphological and optical properties of TiO2/Cu:ZnS nanocomposites were characterized by X-ray diffraction (XRD) analysis, TEM, and UV-vis and fluorescence spectroscopies. Photocatalytic activities of TiO2/Cu:ZnS nanocomposites were evaluated by the oxidation of salicylic acid aqueous solutions under UV light irradiation. Enhanced performances compared either to pure TiO2 nanoparticles or to undoped TiO2/ZnS nanocomposites were observed. Effects of the mass ratio of the TiO2and Cu:ZnS and of the pH of the aqueous solution containing salicylic acid on the photocatalytic activities of TiO2 nanoparticles sensitized with Cu:ZnS QDs were also investigated.

International audience; In recent years, purification and stabilization of environmental waste by titanium dioxide (TiO2) photocatalysis has gained increasing attention due to its biological and chemical inertness and strong oxidizing power. Recently, metal-sulfide like ZnS and CdS have been intensively studied because of their unique catalytic functions compared to TiO2. Association of ZnS to TiO2 enhances charge separation and minimizes or inhibits charge-carrier recombination. When both semiconductors are illuminated, electrons accumulate at the low-lying conduction band of one semiconductor while holes accumulate at the valence band of the other material. These processes of charge separation are very fast and the efficiency of reduction or oxidation of the adsorbed organics remarkably increases. To further improve the photoefficiency of these processes as well as the response into the visible part of the spectrum, doping with transition metal like copper can also be undertaken. Indeed, copper can efficiently trap charge carriers and thus reduce electron-hole recombination. On the basis of these considerations, in this work we report a study concerning the use of a Cu-doped ZnS/TiO2 nanocatalysts immobilized in a microreactor for the degradation of salicylic acid.

The laser stereophotolithography is a process which allows the manufacture of 3D parts by a light-induced space-resolved polymerization. In view to obtain microparts, it is necessary on one hand to reduce the polymerization depth and on the other hand the polymerization width in thex-y plane. The addition of an unreactive highly absorbing chemical succeeded in a significant reduction of the polymerization depth (8 to 10 times thinner). We studied the influences of the light flux, of the initiator and the absorbing unreactive chemical concentrations. The experimental data are in good agreement with the theoretical model. The narrowing of the width is disappointing except with one resin. These results nevertheless led us to set up a new apparatus to reduce the beam diameter by a factor of ten. Despite the increase of the light flux, some of the first results are promising.

Brevet Français déposé le 11 mai 2012 par NOVAGRAAF TECHNOLOGIES

The objective of this article is to find the optimal design of rectangular microchannel reactors, in terms of reactor dimensions and materials, in order to increase the photocatalytic activity. Microchannel reactors with immobilized titanium dioxide (TiO2) as photocatalyst have been designed, fabricated, and tested. The photocatalytic degradation of salicylic acid is investigated as a function of microchannel size, materials that constitute the reactor, contaminant concentration and flow rate. All the reactors exhibit the same behavior. Higher degradation is observed for low pollutant concentrations and flow rates. The nature of the constituent element of the reactor has practically no influence on the photocatalytic process. The degradation performance is affected by the microchannel dimensions. The reactor with the largest channel width and length, and the lowest channel height displays the highest photocatalytic activity. For an optimal design of the rectangular microchannel reactors a relation between the degradation ratio X and the dimensions of the microchannel is reported. A linear relationship between X and wL/h2 (L: length, w: width, h: height of the channel) is found experimentally. The product wL emphasizes the uniform irradiance over the entire catalyst surface and confirms that the bottom of the channel covered with TiO2 is photoactivated. The term in 1/h2 is necessary to take into account the mass transfer limitation.

One of the main restrictions to the industrial development of the manufacturing process of three-dimensional objects by photopolymerization induced by laser derives from the variation in volume between the liquid monomer and the solidified polymer. In this paper, we describe the simulation model of the warping of a bar made by laser photopolymerization. This model is based on a previously published kinetics and volume variation model (A.M. Duclos, J.Y. Jezequel and J.C. Andre, J. Photochem. Photobiol. A: Chem., 70 (1993) 285–299), and we assume that warping occurs when the reactive medium is still viscous, i.e. before the complete hardening of the object. We deduce from this model that the deformation increases when the translation speed of the laser beam is increased.

International audience; The main objective of this article is to evaluate quantitatively the kinetic constants of a photocatalytic reaction in micro-channel reactors despite the presence of a radial concentration profile (mass-transfer limitation) and axial dispersion. Photocatalytic micro-channel reactors with immobilized titanium dioxide as photocatalyst have been fabricated using stereolithography process. The photocatalytic degradation of salicylic acid is investigated as a function of rectangular micro-channel size, contaminant concentration, flow rate and incident UV light intensity. All the micro-channel reactors exhibit the same tendency. Higher degradation is observed for high incident light intensities, low pollutant concentrations and flow rates. A simple equation for the determination of the kinetic constants during the photocatalytic degradation is reported. The equation includes the hydrodynamic properties and a surface reaction model for the photocatalytic reaction (monomolecular Langmuir-Hinshelwood kinetics). In the experimental system, we demonstrate that some external mass-transfer limitation and axial dispersion occur. They are included in the modeling with calculated values of the mass-transfer coefficient of salicylic acid from the solution to the catalyst surface and the axial dispersion coefficient. A single couple of values of the reaction rate constant k and the adsorption equilibrium constant K represent properly the experimental degradation ratios for all reactor dimensions, flow rates and pollutant concentrations. The major parameter that controls the values of the reaction rate constant is the incident light intensity. The dependence of the reaction rate on the incident light intensity is first order.

Stereolithography (SL) is a rapid prototyping method for three-dimensional polymer part fabrication [3, 34, 49, 53, 63]. The technique is based on the process of photopolymerization, in which a liquid resin is converted into a solid polymer under laser irradiation [4, 34]. The models are produced by curing successive layers of the resin material until a three-dimensional object is formed. The advantages of stereolithography are its flexibility in manufacturing parts with different geometries and dimensions, its accuracy and its quickness. The challenge is to extend the stereolithography method to directly fabricate parts with complex shapes and good mechanical properties [30, 47, 58]. Recently, polymer/ceramic composite were successively fabricated by stereolithography [29, 46, 52, 62]. The manufacturing process requires the formulation of a photoreactive medium containing a photocurable resin and powders prior to laser exposure. Once polymerized, the photopolymer constitutes a though matrix around ceramic particles.

Laser stereophotolithography is a technology which allows the space-resolved phototransformation of a product. In this paper we describe the different basic processes with their limits. We present several ways to override these limits and discuss new application areas.

This paper describes a process for the manufacture of three-dimensional objects, layer by layer, using thermal irradiation by moving the beam of a computer controlled CO2 laser. Computer simulations of the system performance under different experimental conditions (for example, irradiation time, characteristics of the reactive medium), combined with experiments prove the feasibility of the process. The objects are spatially well resolved since the reactive area is matched with the laser beam surface area. On decrit dans cet article un procede de fabrication par irradiation thermique d'objets tridimensionnels, couche par couche, base sur le deplacement d'un faisceau laser au CO2 controle par ordinateur. Des simulations par ordinateur de l'efficacite du systeme dans differentes conditions operatoires (par exemple, temps d'irradiation, caracteristiques du milieu reactif), combinees a des experiences reelles, demontrent la faisabilite du procede. La resolution des objets sur le plan spatial est tres bonne car la surface reactive est adaptee a la surface du faisceau laser.

The influence of porous additives with various structures on the shrinkage of resins used for stereolithographic applications was studied by measuring the dependence of the specific gravity of the charged polymer material as a function of the charge fraction. The investigations were conducted on difunctional monomers photopolymerized either by a radical (acrylate) or a cationic (epoxy) mechanism. The improvement resulting from the incorporation of charges in the formulation is accounted for in a semi-quantitative way by an adsorption-desorption equilibrium of monomer molecules between the pores and the bulk phase

International audience; Photocatalytic micro-channel reactor was built by using stereolithography process. A reactor with a micro-channel as a support of TiO2 photocatalyst was designed in order to reduce dimensions while improving the efficiency. Photocatalytic activity of the micro-reactor at various flow rates was evaluated by the inlet and outlet concentrations of salicylic acid as a model of pollutant. Influence of the initial pollutant concentration, the irradiation intensity on the rate of degradation of the pollutant was studied. A model with the kinetic parameters for the given support geometry was applied to reactor design and scale-up.

International audience; Vitamin A is used as a generic term for all vitamin A derivatives with retinol-like biological activity. Retinol is the main parent compound for vitamin A. It derives from carotenoids (provitamin A) and also directly from the pre-formed vitamin A contained in the diet. The term “retinoid” is a generic descriptor of compounds structurally related to vitamin A and the synthetic analogues of retinol with or without biological activity. Retinoic acid is the active cellular catabolite. Vitamin A/retinoids have been given cancer-preventive functions and subsequently used in clinical trials to reduce lung cancer incidence in high-risk individuals. The results obtained have been in contradiction with both in vivo and in vitro promising studies. It seems therefore necessary to develop a better understanding of the vitamin A/retinoids signalling pathways in the lung. With this aim, we summarise the relevant knowledge focussed on thelung.

International audience; The main objective of this research was to define a structured and functionalized support for future biomedical applications (model of “low-density bioarray”). The experiments were carried out by using stereolithography process with a special SU-8 photoresist and the reproducibility of the method was studied by analyzing the surface profile of the support. Finally, a matrix of regular controlled sized wells was fabricated. Chemical reactions leading to covalent grafting were run to demonstrate that the inner surface of the wells remains still reactive after polymerization. The grafting of fluorophores with carboxylic functions activated by N-hydroxysuccinimide was studied as function of time, in order to determine the best reactions, conditions. Then, the grafting of two distinct fluorescent probes was led simultaneously inside the wells, showing the possibility of spatial localization of diverse reactions on the same support. The covalent and localized bindings were confirmed by fluorescence spectroscopy and microscopy analyses.

The accuracy of the conventional stereolithography process has been improved to shape microstructures, especially for chemical engineering applications. Thus, a new recoating system has been developed to allow the deposition of resin or suspension layers with thickness ranging from 5 to 40 μm. Moreover, the influences of photomaterial formulation and of oxygen inhibition have been discussed with regard to polymerization kinetics and process accuracy. As a consequence, lateral and vertical resolutions of conventional stereolithography have been improved to 50 and 5 μm respectively. Finally, microstructures such as microtransducers, micropumps and heat exchangers have been created by stereolithography. As a result, the contribution of these microstructures to process intensification and local control has to be considered.

Un dispositif de deposition de couches uniformes de suspensions de ceramiques a ete mis au point en vue d'applications pour le prototypage rapide. Le systeme de raclage se compose d'une buse d'injection de gaz de hauteur, d'angle d'attaque et de pression reglables. L'homogeneite des couches etalees ainsi que la reproductibilite du procede ont ete etudiees. La mise en place d'un plan d'experience a egalement conduit a la caracterisation de l'influence de chaque parametre sur l'epaisseur de couche deposee et a permis de proposer un modele mathematique fiable en vue d'optimiser le dispositif de depot. A system to coat uniform layers of ceramic suspensions has been developed for rapid prototyping applications. The metering system is made of a gas injection nozzle which height, angle of attack and pressure can be adjusted. The coated layer homogeneity and the process reproducibility have been studied. The effect of each parameter on the coated layer thickness has been characterized using a design of experiments approach and a reliable mathematical model is proposed to optimze the coating system.

In this study, stereolithography of PZT films or composites has been successfully carried out. With regard to the PZT suspensions formulation, the process was modified to allow the deposition of films with thickness ranging between 8 to 40 μm. 1-3 and 0-3 piezocomposites as well as other highly loaded structures (maximum 45 % in volume) have been elaborated. Moreover, PZT thick films have been deposited on metallic substrates and silicon wafers. After sintering, crack-free PZT films with thickness ranging between 12 to hundreds of microns have been metallized and polarized. The properties of these microstructures have been studied with permittivity and piezoelectric coefficients measurements. Experiments have shown that the piezoelectric properties of PZT ceramics fabricated by stereolithography are promising (d 33 up to 200 pC/N and g 33 greater than 30×10 -3 Vm/N), which implies that such structures could be integrated in MEMS for microactuators or sensors applications. Finally, simultaneous fabrications by conventional stereolithography of polymer micropumps and their related piezoelectric transducers have been tested. The upper polymer membrane of the micropump is 100 μm thick and the inner diameter of the pump is 5 mm. Researches are in progress to improve the micropump flow rate and to manufacture a drop-on-demand inkjet device.

The mini heat-exchangers presented here are cubic, cross-flow type exchangers with several specific features, concerning the internal design, the material, and the method of fabrication. The overall dimensions are of the order of several centimetres, while the internal channels have characteristic dimension in the millimetre range. The different “layers” or plates and their channels may be designed in such way as to produce an important local mixing of the fluid in three dimensions, in order to improve the fluid-side heat transfer. Different internal geometries have been designed.

Laser stereolithography deals with the manufacture of three-dimensional objects that are made by space-resolved laser-induced polymerization. In order to obtain three dimensional microobjects, we developed a new microstereolithography apparatus based on the use of a dynamic mask-generator which allows the manufacture of a complete layer by only one irradiation, the part being manufactured layer by layer. This process uses a broad-band visible light source, that leads to the elimination of speckle effects resulting from the conventional use of a laser beam. A lateral resolution of 2 μm * 2 μm has been demonstrated with this new process.

Laser stereolithography deals with the manufacture of 3D objects that are made by space-resolved laser-induced polymerization. In order to obtain 3D micro-objects, we developed a new microstereolithography apparatus based on the use of a dynamic mask generator which allows the manufacture of a complete layer by only one irradiation, the part being manufactured layer by layer. This process is compared of a broad-band visible light source, that leads to the elimination of speckle effects resulting from the conventional use of a laser beam, and of a liquid crystal display as the dynamic mask generator. A lateral resolution of 2 micrometers has been demonstrated, and some examples of high aspect ratio micro-objects are presented.

An induction period has been observed in the pyrolysis of ethane in a continuous-flow stirred tank reactor at 530°C. The rate constants of the initiation, determining propagation and termination steps, have been determined.

In recent decades, the water pollution has become a problem worldwide. Indeed, the strong growth in water demand due to population growth as well as industrial developments, agricultural and urban, generates huge amounts of waste water discharges. These are released into nature with or without treatment and may constitute a danger via the transmission of diseases as well as for irrigation of lands that are surrounding the site of release. The objective of this study is the treatment of aqueous waste through the use of a new technology "heterogeneous photocatalysis." This method is based on the use of a semiconductor irradiated by a light source of appropriate wavelength and is simple to implement and inexpensive. ZnO / Fe2O3 semiconductors, ZnO morphology "nanorods" and Mn2+ doped ZnO were synthesized and tested in various photocatalytic applications. The results showed an improvement in catalytic efficiency compared to the commercial ZnO. The developed materials can reduce the recombination of charges and, therefore, improve the photocatalytic activity when the degradation of chemical pollutants (salicylic acid, Orange II) and biological (bacteria) under solar irradiation. Furthermore, we have demonstrated recyclability of these catalysts without specific treatment. In the second part of our work, we studied the solar photocatalysis mechanism on a reference strain E. coli MG1655 using ZnO nanorods either in suspension or immobilized on an inert support. The results show a loss of cultivability of E. coli with damage essentially localized in cell membranes and proteins. The genetic material remaining intact. The response of three bacterial strains (Escherichia coli, Pseudomonas aeruginosa and Salmonella enterica Typhi) to oxidative stress of photocatalysis showed differences can be attributed to morphology, metabolism and genetics of each strain. (Some strains can be reactivated after treatment). Studies performed on the strain Pseudomonas aeruginosa (ATCC 4114) show that there is a loss of cultivability but that the bacterium retains its ability to activate its virulence and characters after treatment, Ces dernières décennies, la pollution de l’eau est devenue un problème se posant avec insistance dans le monde entier. En effet, la forte croissance des besoins en eau due à l’accroissement démographique ainsi qu’aux évolutions industrielles, agricoles et urbaines, engendrent des quantités énormes de rejets d’eaux usées. Ces derniers sont déversés dans la nature avec ou sans traitement et peuvent constituer un danger via la transmission de maladies ainsi que pour l’irrigation des terres qui se trouvent aux alentours du site de rejet. L’objectif de cette étude est le traitement des rejets aqueux par l’utilisation d’une nouvelle technologie appelée « photocatalyse hétérogène ». Ce procédé est basé sur l’utilisation d’un semiconducteur irradié par une source lumineuse de longueur d’onde appropriée et est simple à mettre en œuvre et peu coûteux. Des semiconducteurs ZnO/Fe2O3, ZnO de morphologie « bâtonnets » et ZnO dopé Mn2+ ont été synthétisés et testés dans diverses applications photocatalytiques. Les résultats obtenus ont montré une amélioration de l’efficacité catalytique par rapport au ZnO commercial. Les matériaux développés permettent de réduire la recombinaison des charges et, par conséquent, d’améliorer l’activité photocatalytique lors de la dégradation des polluants chimiques (acide salicylique, Orange II) et biologiques (bactéries) sous l’irradiation solaire. De plus, nous avons démontré la recyclabilité de ces catalyseurs sans traitement particulier. Dans la seconde partie de notre travail, nous avons étudié le mécanisme de la photocatalyse solaire sur une souche de référence E. coli MG 1655 en utilisant les bâtonnets ZnO soit en suspension soit immobilisés sur un support inerte. Les résultats montrent une perte de cultivabilité de la bactérie E. coli avec des dommages essentiellement localisés au niveau membranaire et des protéines, le matériel génétique restant intact. La réponse de trois souches bactériennes (Escherichia coli, Pseudomonas aeruginosa et Salmonella enterica Typhi) au stress oxydant de la photocatalyse a montré des différences pouvant être attribués aux différences morphologiques, métaboliques et génétiques des souches (certaines souches peuvent se réactiver après traitement). Des études réalisées sur la souche Pseudomonas aeruginosa (ATCC 4114) montrent qu’il y a une perte de cultivabilité mais que la bactérie conserve sa capacité de se réactiver ainsi que ses caractères de virulence après traitement

This study aimed at developing new materials for additive manufacturing. We focused on producing parts containing complex metallic alloys (CMA) using a UV laser used for stereolithography. The selected intermetallic is a quasicrystalline alloy dominated by the icosahedral phase in the system AlCuFeB. The raw powders produced by gas atomization were characterized by X-ray diffraction and differential thermal analysis. The powders exhibit good optical absorption properties in the UV-visible range allowing direct laser sintering as evidenced by the formation of bridges between the grains at a temperature of about 820°C. In a second step, we have considered the manufacturing of parts made of a suspension of CMA powders in a binder. We have studied the wetting properties of the particles AlCuFeB and optimized a mixture consisting of an epoxy resin filled with 20 % vol. of CMA particles. The optical absorption of the suspension in the UV range was sufficient to produce composite parts by stereolithography. The particle size used was smaller than 25 micrometers. We have managed to make parts reaching 14 mm in height by adding layers with a thickness of 50 microns. Using test samples, we have characterized the hardness and the tribological properties of this new composite material. The hardness of the parts produced by stereolithography is larger than that of epoxy parts and reaches 88 Shore D. We have also shown a 30 % reduction of the friction coefficient as well as a 40 % reduction of wear losses compared to the epoxy matrix. These properties make attractive this new composite material for stereolithography applications, Cette étude s'inscrit dans le cadre du développement de nouveaux matériaux pour la fabrication additive. Notre objectif est la fabrication de pièces comprenant un alliage métallique complexe (CMA) à l'aide d'un laser UV de stéréolithographie. L'alliage choisi est un alliage quasicristallin dominé par une phase icosaédrique du système AlCuFeB. Des poudres brutes d'atomisations ont été caractérisées par diffractions des rayons X et analyse thermique différentielle. Nous avons montré une bonne absorbance optique de la poudre dans le domaine UV-visible qui rend possible un début de frittage sous l'effet du laser correspondant à la formation de pontages entre les grains à une température d'environ 820°C. Concernant la fabrication à partir d'une suspension de poudres dans un liant, nous avons étudié les propriétés de mouillage des particules AlCuFeB et optimisé un mélange avec une résine époxy chargée par 20 % vol. de particules CMA. L'absorption optique de la suspension dans le domaine UV est suffisante pour fabriquer une pièce composite par stéréolithographie. La granulométrie utilisée est inférieure à 25 µm. Nous avons ainsi réussi à fabriquer des pièces de 14 mm de hauteur, en additionnant des couches de 50 µm. À partir des pièces réalisées, nous avons caractérisé la dureté et les propriétés tribologiques de ce nouveau matériau composite. La dureté des pièces ainsi fabriquées est supérieure à celle de la résine seule et atteint 88 Shore D. Nous avons également mis en évidence une amélioration de 30 % du coefficient de frottement et une diminution du volume d'usure de 40 % par rapport au matériau de la matrice époxy. Ces propriétés rendent attractif ce nouveau matériau composite pour la fabrication par stéréolithographie