Synthèse et caractérisation d'hydrogels macroporeux contenant des nanoparticules pour des procédés catalytiques hétérogènes en écoulement continu

RÉSUMÉ : Les nanoparticules (NPs) métalliques catalysent un grand nombre de réactions chimiques dans des conditions relativement douces et vertes, mais également avec une sélectivité élevée. C’est pourquoi l’industrie chimique s’est orientée de plus en plus vers les procédés « nanocatalysés » depuis les deux dernières décennies. Le problème principal, relié à l’utilisation de nanoparticules catalytiques, provient de leurs petites dimensions : la taille nanoscopique (~ 1 – 10 nm) rend les particules thermodynamiquement instables et en conséquence, elles s’agglomèrent, coalescent, et perdent leur propriétés catalytiques. De surcroît, la récupération des nanoparticules dispersées dans le milieu réactionnel nécessite des procédés sophistiqués et dispendieux.---------ABSTRACT : Metallic nanoparticles (NPs) catalyze a large number of chemical reactions under relatively mild and green conditions, and with high selectivity. As a result, during the last two decades, the chemical industry has become increasingly focused and interested on « nanocatalyzed » processes. The main problem with the use of catalytic nanoparticles arises from their dimensions : the nanoscopic size (~ 1 – 10 nm) renders the particles thermodynamically unstable and as a result, they agglomerate, coalesce, and lose their catalytic properties. In addition, nanoparticles recovery from the reaction medium requires sophisticated and expensive processes

Enhancing and Tuning the Response of Environmentally Sensitive Hydrogels With Embedded and Interconnected Pore Networks

Porous and temperature-sensitive poly­(<i>N</i>-isopropylacrylamide) (PNIPAam) hydrogels with tunable and enhanced response properties were prepared by using porous poly­(ε-caprolactone) (PCL) molds. The molds were obtained from melt-processed cocontinuous polymer blends of ethylene propylene diene monomer (EPDM) and PCL. Quiescent annealing of the blends resulted in microstructure coarsening, and subsequent extraction of the EPDM phase yielded the molds. Ultimately, it allowed control over the average gel pore size from 20 to 300 μm. The gelling solution was injected within the molds, which were subsequently extracted, yielding hydrogels with fully interconnected pores. The porous gels display enhanced thermoresponsive properties in water: tunable, fully reversible and significantly faster swelling and deswelling responses following a temperature change across the PNIPAam lower critical solution temperature, as compared to nonporous gels. The fabrication process is compatible with a broad choice of gel chemistries, and allows the fabrication of complex 3D shapes of various sizes

Tailored Macroporous Hydrogels with Nanoparticles Display Enhanced and Tunable Catalytic Activity

This work demonstrates that a model system of poly­(<i>N</i>-isopropylacrylamide) (PNIPAam) macroporous hydrogels, with tailored microstructures and comprising gold (Au) or silver (Ag) nanoparticles, display enhanced and tunable catalytic activity. These nanocomposites are prepared using polymer templates obtained from melt-processed cocontinuous polymer blends. The reaction rate, controlled by both hydrogel porosity and the PNIPAam lower critical solution temperature, increases by more than an order of magnitude as compared to nonporous gels, and is comparable to micro- or nanocarrier-based systems, with easier catalyst recovery. The fabrication process is scalable, and is compatible with broad choices of polymer blend, gel, and nanoparticle chemistries