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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 ...

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; 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; 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.

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.

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.

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.