Synthesis and photoelectrochemical properties of silver nanoparticles embedded in mesoporous oxides films

L’étude et la compréhension des interactions existantes entre semi-conducteur et nanoparticules métalliques sous irradiation est primordiale pour l’amélioration de leurs performances. Dans cette étude, trois composites oxydes semi-conducteur-métal ont été synthétisés : TiO2-Ag, Fe2O3-Ag et WO3-Ag. La synthèse des films mésoporeux de TiO2, Fe2O3 et WO3 a été effectuée par voie sol gel à l’aide de copolymères à bloc, avec la méthode d’auto-assemblage induit par évaporation (EISA). Les nanoparticules d’argent sont formées dans un deuxième temps par réduction chimique de sels dans la porosité des films. L’étude photo-électrochimique de ces composites a permis de mettre en évidence différents phénomènes : le potentiel d’électroréduction des ions Ag+ dans une matrice de TiO2 mésoporeuse peut être modulé par l’effet de la lumière. Ce phénomène semble résulter d’un effet de passivation des NP Ag par TiO2 qui dépend des conditions d’insolation. Des effets de rechargement de l’électrode poreuse en espèce Ag+ ont aussi été observés, sous l’action simultanée de la chrono-ampérométrie et de l’irradiationThe study and understanding of existing interactions between semiconductor and metal nanoparticles under irradiation is essential for improving their performance. In this study, three semiconductor-metal oxide composites were synthesized: TiO2-Ag, Fe2O3-Ag and WO3-Ag. The synthesis of the mesoporous films of TiO2, Fe2O3 and WO3 was carried out by gel sol method using block copolymers, with the method of self-assembly induced by evaporation (EISA). The silver nanoparticles are formed in a second time by chemical reduction of silver salts in the porosity of the films. The photo-electrochemical study of these composites made it possible to highlight various phenomena: the electroreduction potential of Ag+ ions in a mesoporous TiO2 matrix can be modulated by the effect of light. This phenomenon seems to result from a passivation effect of the NP Ag by TiO2, which depends on the insolation conditions. Charging effects of the porous electrode in Ag+ species have also been observed, under the simultaneous action of chrono-amperometry and irradiatio

Synthèse et propriétés photoélectrochimiques de nanoparticules d’argent intégrées dans des films d’oxydes mésoporeux

The study and understanding of existing interactions between semiconductor and metal nanoparticles under irradiation is essential for improving their performance. In this study, three semiconductor-metal oxide composites were synthesized: TiO2-Ag, Fe2O3-Ag and WO3-Ag. The synthesis of the mesoporous films of TiO2, Fe2O3 and WO3 was carried out by gel sol method using block copolymers, with the method of self-assembly induced by evaporation (EISA). The silver nanoparticles are formed in a second time by chemical reduction of silver salts in the porosity of the films. The photo-electrochemical study of these composites made it possible to highlight various phenomena: the electroreduction potential of Ag+ ions in a mesoporous TiO2 matrix can be modulated by the effect of light. This phenomenon seems to result from a passivation effect of the NP Ag by TiO2, which depends on the insolation conditions. Charging effects of the porous electrode in Ag+ species have also been observed, under the simultaneous action of chrono-amperometry and irradiationL’étude et la compréhension des interactions existantes entre semi-conducteur et nanoparticules métalliques sous irradiation est primordiale pour l’amélioration de leurs performances. Dans cette étude, trois composites oxydes semi-conducteur-métal ont été synthétisés : TiO2-Ag, Fe2O3-Ag et WO3-Ag. La synthèse des films mésoporeux de TiO2, Fe2O3 et WO3 a été effectuée par voie sol gel à l’aide de copolymères à bloc, avec la méthode d’auto-assemblage induit par évaporation (EISA). Les nanoparticules d’argent sont formées dans un deuxième temps par réduction chimique de sels dans la porosité des films. L’étude photo-électrochimique de ces composites a permis de mettre en évidence différents phénomènes : le potentiel d’électroréduction des ions Ag+ dans une matrice de TiO2 mésoporeuse peut être modulé par l’effet de la lumière. Ce phénomène semble résulter d’un effet de passivation des NP Ag par TiO2 qui dépend des conditions d’insolation. Des effets de rechargement de l’électrode poreuse en espèce Ag+ ont aussi été observés, sous l’action simultanée de la chrono-ampérométrie et de l’irradiatio

Electrochemical Observation of the Plasmonic Effect in Photochromic Ag Nanoparticle Filled Mesoporous TiO 2 Films

International audienceWe report photoelectrochemical measurements from mesoporous titanium dioxide filled with silver nanoparticles under illumination. A 200 mV potential switch of silver ion reduction is observed, depending on light wavelength. An easier reduction of silver in the presence of light is linked to plasmon induced charge separation (PICS). SEM and TEM analysis before and after photoelectrochemistry have also shown an electrochemical Ostwald ripening during continuous visible irradiation, with a growth of silver particles at the sample surface. The combined use of mesoporous structures and electrochemical characterization enabled the change in silver reactivity during PICS to be quantified and emphasizes the role of plasmon in photochromism

Hierarchically porous MOF-biopolymer beads for CO2 storage

National audienc

Electroactive Area from Porous Oxide Films Loaded with Silver Nanoparticles: Electrochemical and Electron Tomography Observations

International audienc

Electrochemical Properties of Silver Nanoparticles in Mesoporous Silica and Titania Films: Specific Behavior of Titania Composite

International audienceElectrochemical behavior of silver nanoparticles in mesoporous oxides electrodes is investigated. Mesoporous SiO 2 and TiO 2 films deposited on FTO (Fluorine doped tin oxide) and containing Ag nanoparticles (NPs) are used as electrodes. The study of voltammetric curves (CVs) and the diffusion of Ag + ions out of the films highlight the importance of the retention of Ag + ions by the TiO 2 films. By varying several factors such as the speed rate or the initial potential, we observe the existence of the two potentials anodic peaks. These are explained by the nature of two silver NPs populations created in two distinct areas in the film and with different size distributions, as shown by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) observations. The size distributions of the two NPs populations allow the position and shape of each of the oxidation peaks in the CVs to be adequately simulated

Porous textile composites (PTCs) for the removal and the decomposition of chemical warfare agents (CWAs) – A review

International audienceSince the first use of a chemical warfare agent (CWA), specific methods of protection have been developed to protect human body from such lethal compounds. The first protection systems rely on impermeable clothing or the capture of the toxics species by an adsorbent such as activated carbon. However, both present important limitations, i.e. heat stress for impermeable protection and a risk of saturation or release of toxic compounds for the adsorbent. The optimal protection should therefore be active, i.e. be able to both capture and detoxify CWAs. In this optic, this review describes active porous textiles composites (PTC) used as protective garments against CWAs. To this day, a large variety of porous compounds such as zeolites, metal organic frameworks (MOFs) or aerogels have shown catalytic degradation of CWAs. The integration of these active solids to textile fibers is then detailed, highlighting the importance of the electrospinning technique or the pre-functionalization of fibers. Concerning the detoxification process, MOFs have focused a large part of the PTC research due to their exceptional properties (high surface area and tunable porosity combined to a catalytic activity). More particularly, Zr-based MOFs exhibit exceptional results in terms of CWA detoxification and are currently highly studied. Besides, this present state of art includes other active PTCs (functionalized activated carbon fibers ACFs or zeolite composites) rarely discussed in reviews, to give a full overview of the existing PTC used against CWA

Application of Shaped UiO-66_NH2 Metal-Organic Framework for Gaseous Iodine Capture

International audienceMetal-organic frameworks (MOF) is an emerging class of crystalline and porous materials. Their structure results from the combination of metal clusters (or ions) with multitopic organic linkers. By changing the metal or the linker, or by adding organic functionalities to the linker, the physicochemical properties of the MOF can be tailored for specific applications. For instance, iodine-131 is a major fission by-product which can increase the incidence of thyroid cancers. Following a nuclear meltdown, venting is conducted to avoid overpressurization. The vented steam, containing radionuclides such as 131I2, passes through a filtered containment venting system to capture the contaminants. Typically, a fixed bed of silver-doped ZSM-5 zeolite is used. However, several limitations remain due to the small pore aperture of the zeolite (0.55 nm), hardly accommodating bulky iodine derivatives, and the competitive adsorption of contaminants (mainly CO). Hence adsorbents more specific towards I2 and its derivatives, presenting larger pores and/or higher iodine capture capacity, remain desired.In particular, the UiO-66 MOF presents a good stability against water, a high adsorption capacity, and larger pore sizes (0.8 to 1.1 nm). By adding amino moieties on the terephthalate linker, one can obtain UiO-66_NH2, an adsorbent with high binding energy towards electro-acceptors such as I2 [1]. Recently, our group applied severe nuclear accidental conditions to this MOF, previously shaped as binderless granules, showing high retention of 131I2 and preserved physicochemical properties [2]. In a subsequent step, we studied the preparation of UiO-66_NH2-based extrudates and granules that present both high adsorption capacity towards iodine (see Figure 1) and a significantly improved mechanical resistance [3]. The main results and perspectives of this work will be discussed

MOF/chitosan composites for the capture of gaseous iodine

International audienceMetal-organic frameworks (MOF) is an emerging class of crystalline and porous materials. Their structure results from the combination of metal clusters (or ions) with multitopic organic linkers. By changing the metal or the linker, or by adding organic functionalities to the linker, the physicochemical properties of the MOF can be tailored for specific applications. For instance, iodine-131 is a major fission by-product which can increase the incidence of thyroid cancers. Following a nuclear meltdown, venting is conducted to avoid overpressurization. The vented steam, containing radionuclides such as 131I2, passes through a filtered containment venting system to capture the contaminants. Typically, a fixed bed of silver-doped ZSM-5 zeolite is used. However, several limitations remain due to the small pore aperture of the zeolite (0.55 nm), hardly accommodating bulky iodine derivatives, and the competitive adsorption of contaminants (mainly CO). Hence adsorbents more specific towards I2 and its derivatives, presenting larger pores and/or higher iodine capture capacity, remain desired.In particular, the UiO-66 MOF presents a good stability against water, a high adsorption capacity, and larger pore sizes (0.8 to 1.1 nm). By adding amino moieties on the terephthalate linker, one can obtain UiO-66_NH2, an adsorbent with high binding energy towards electro-acceptor species such as I2. Recently, our group applied severe nuclear accidental conditions to this MOF, previously shaped as binderless granules, showing high retention of 131I2 and preserved physicochemical properties.[1] In a subsequent step, we studied the preparation of UiO-66_NH2-based extrudates and granules with improved mechanical properties by adding biopolymers. With lesser than 5 wt.% of chitosan, the textural properties of the resulting composites are barely affected - in line with the chitosan loading, and as-prepared materials present both high adsorption capacity towards iodine (see Figure 1.A-B) and a significantly improved mechanical resistance.[2] Still, shifting from a fixed bed of powder to a fixed bed of granules has consequences over the adsorption kinetics, with gaseous I2 diffusing in-between the granules. Hence, in a next step, we prepared composite films with up to 60 wt.% of UiO-66_NH2 MOF (Figure 1.C). By doing so, the adsorption equilibrium was reached within 24 h as per the MOF powder. Moreover, the total quantity of I2 adsorbed correspond to the loading of the MOF, meaning that up to 40 wt.% of chitosan, the porosity of the MOF remains fully accessible. The main results and perspectives of these works will be discussed

Microwave-Assisted Synthesis of Porous Composites MOF–Textile for the Protection against Chemical and Nuclear Hazards

International audienceSince the emergence of chemical, biological, radiological, and nuclear risks, significant efforts have been made to create efficient personal protection equipment. Recently, metal−organic framework (MOF) materials have emerged as new promising candidates for the capture and degradation of various threats, like chemical warfare agents (CWAs) or radioactive species. Herein, we report a new synthesis method of MOF−textile composites by microwave irradiation, with direct anchoring of MOFs on textiles. The resistance of the composite has been tested using normed abrasion measurements, and non-stable samples were optimized. The protection capacity of the MOF−textile composite has been tested against dimethyl 4-nitrophenyl phosphate, a common CWA simulant, showing short degradation half-life (30 min). Radiological/nuclear protection has also been tested through uranium uptake (up to 15 mg g−1 adsorbent) and the capture of Kr or Xe gas at 0.9 and 2.9 cm3/g, respectively.Depuis l'émergence des risques chimiques, biologiques, radiologiques et nucléaires, des efforts importants ont été faits pour créer des équipements de protection individuelle performants. Récemment, les matériaux à structure organométallique (MOF) sont apparus comme de nouveaux candidats prometteurs pour la capture et la dégradation de diverses menaces, comme les agents de guerre chimique (CWA) ou les espèces radioactives. Nous rapportons ici une nouvelle méthode de synthèse de composites MOF-textile par irradiation micro-ondes, avec ancrage direct des MOF sur les textiles. La résistance du composite a été testée à l'aide de mesures d'abrasion normées et des échantillons instables ont été optimisés. La capacité de protection du composite MOF-textile a été testée contre le phosphate de diméthyle 4-nitrophényle, un simulant CWA commun, montrant une courte demi-vie de dégradation (30 min). La protection radiologique/nucléaire a également été testée par l'absorption d'uranium (jusqu'à 15 mg g−1 d'adsorbant) et la capture de gaz Kr ou Xe à 0,9 et 2,9 cm3/g, respectivement