Gas-Directed Production of Noble Metal-Magnetic Heteronanostructures in Continuous Fashion: Application in Catalysis.

Abstract

Complex nanomaterials produced by scale-up batch processes lack suitable control of shape, size distribution, chemical composition, and quality, because heat and mass transfer are seriously affected as the reactor volume increases. Here we use a novel continuous synthesis procedure, the active gas-liquid segmented flow, to produce noble metal-magnetic heteronanostructures with enormous interest in the fields of catalysis, biomedicine, environmental sensors, food monitoring, and chemical analysis. The microreactor technology proposed scales down the reaction volume to gain advantage of the large surface area to volume ratio with respect to conventional batch-type reactors, improving heat and mass transport and, consequently, promoting a uniform heating and mixing. The gas phase was introduced in the chemical reactor as gas slugs of nanoliter scale with a dual role: (1) passive mixing and (2) chemical directing agent to tune the crystallization of nanostructures in a continuous fashion. The shape, size, and magnetic properties of the resulting heteronanostructures, as well as the density, size, and composition of noble metal nanoparticles were tuned to show the versatility of the proposed approach in a timeline of 4 min. We demonstrated that the produced nanostructures provide excellent catalytic properties in the catalyzed hydrogenation of nitrophenols to aminophenols. Electron microscopy, UV-vis spectroscopy, and cyclic voltammetry studies showed the remarkable catalytic performance of the produced heteronanostructures.