Search

International audience; Photocatalytic production of fuels, even in small quantities, from the mineralization of hazardous pollutants, is a promising and renewable way of recycling wastewater. In the present work, the potential of methyl functionalized inorganic aluminosilicate nanotubes (methyl imogolite/Imo-CH3) as photocatalytic nanoreactors for this application is demonstrated. Using the phototoxic polycyclic aromatic hydrocarbon dibenzo(a,h)anthracene (DBAN) as a model pollutant, we show that DBAN molecules can be efficiently trapped inside Imo-CH3 nanotubes from an aqueous medium to undergo subsequent oxidative photo-degradation under UV light. The kinetics of this photo-degradation were shown to depend strongly on both the initial DBAN concentration in the nanotubes and the presence/absence of dissolved dioxygen. The photo-degradation process followed a complex mechanistic pathway, consisting of combined photo-oxidation and photo-cycloaddition reactions, where detection of carbon dioxide (CO2) as a photo-oxidation product confirmed the mineralization of encapsulated DBAN. CO and CH4 molecules were also formed, however these could arise from the further photo-reduction of CO2 on the external surface of the nanotubes. Moreover, dihydrogen (H2) was produced upon UV illumination under anaerobic conditions due to water reduction reactions on the external surfaces of Imo-CH3 nanotubes. The possible mechanistic pathways of these processes are proposed, and the dual capability of Imo-CH3 nanotubes for simultaneous pollutant degradation and H2 production is then demonstrated – a rare feat for a single photocatalyst material.

Formation of highly stable metal nanostructures in a Nafion® membrane with various aspect ratios has been of considerable research interest in recent years. However, there is a need for a proper understanding of the growth mechanism of such nanostructures in Nafion® (sometimes larger than the size of water–sulfonate ionic clusters of the membrane). In this work, the early growth kinetics of silver nanoparticles (NPs) in Nafion®-117 ion-exchange membrane during in situ L-ascorbic acid reduction of Ag+ ions by time resolved in situ small-angle X-ray scattering (SAXS) using synchrotron radiation with a time resolution of 50 ms are revealed for the first time. The SAXS analyses, corroborated by transmission electron microscopy, showed that the sizes of NPs increase rapidly together with their number density until they attain a certain size that could be accommodated in the ∼5 nm water–sulfonate ionic clusters. Further growth takes place either by self-agglomeration of the particles ejected out from the water–sulfonic acid clusters or by continuous reduction of metal ions on the existing NP surfaces (uniformly or on a specific plane) leading to formation of bigger nanostructures with various aspect ratios. The time resolved information of NP growth provides an opportunity for the controlled synthesis of metal NPs with a definite size, shape and size distribution for a specific application. The catalytic properties of Ag NPs formed in the membrane were examined using borohydride reduction of a model dye methylene blue. It was observed that smaller Ag NPs with a mean diameter ∼3 nm, confined in the hydrophilic clusters of the Nafion® matrix, have reasonably good catalytic activity and a lower lag time for the onset of reduction.