RESUMO
Plasmonic catalysis enables the use of light to accelerate molecular transformations. Its application to the control reaction selectivity is highly attractive but remains challenging. Here, we have found that the plasmonic properties in AgPd nanoparticles allowed different reaction pathways for tunable product formation under visible-light irradiation. By employing the hydrogenation of phenylacetylene as a model transformation, we demonstrate that visible-light irradiation can be employed to steer the reaction pathway from hydrogenation to homocoupling. Our data showed that the decrease in the concentration of H species at the surface due to plasmon-enhanced H2 desorption led to the control in selectivity. These results provide important insights into the understanding of reaction selectivity with light, paving the way for the application of plasmonic catalysis to the synthesis of 1,3-diynes, and bringing the vision of light-driven transformations with target selectivity one step closer to reality.
RESUMO
This article reports on the fabrication and investigation of low-emissivity (low-E) coatings based on random networks of silver nanowires (AgNWs). The transparent layers based on AgNWs do exhibit low emissivity while being still transparent: an overall emissivity as low as 0.21 at 78% total transmittance was obtained. A simple physical model allows to rationalize the emissivity-transparency dependence and a good agreement with experimental data is observed. This model demonstrates the role played by AgNWs which partially reflect IR photons emitted by the substrate, exacerbating then the presence of AgNWs and lowering the total emissivity. The potential use of such layers in functional devices is hampered by the poor intrinsic surface adhesion of the AgNWs, which renders the coating fragile and prone to mechanical damaging. Two very efficient encapsulation processes based on the deposition of a conformal alumina thin film using the spatial atomic layer deposition technique and the solution processed layer deposition of a polysiloxane varnish have been developed to thwart this weakness. Both coatings combine sturdy mechanical resistance relying on a strong interfacial adhesion and excellent optical transmittance properties. The performances for the mechanically resistant low-E coatings achieve an overall emissivity as low as 0.34 at 74% total transparency. The set of optical properties and mechanical resistance of the reported AgNWs based low-E coatings combined with the ease of fabrication and the cost-effective production process make it an excellent candidate for a wide set of applications, including smart windows for energy-saving buildings.
RESUMO
Localized surface plasmon resonance (LSPR) in plasmonic nanoparticles (NPs) can accelerate and control the selectivity of a variety of molecular transformations. This opens possibilities for the use of visible or near-IR light as a sustainable input to drive and control reactions when plasmonic nanoparticles supporting LSPR excitation in these ranges are employed as catalysts. Unfortunately, this is not the case for several catalytic metals such as palladium (Pd). One strategy to overcome this limitation is to employ bimetallic NPs containing plasmonic and catalytic metals. In this case, the LSPR excitation in the plasmonic metal can contribute to accelerate and control transformations driven by the catalytic component. The method reported herein focuses on the synthesis of bimetallic silver-palladium (Ag-Pd) NPs supported on ZrO2 (Ag-Pd/ZrO2) that acts as a plasmonic-catalytic system. The NPs were prepared by co-impregnation of corresponding metal precursors on the ZrO2 support followed by simultaneous reduction leading to the formation of bimetallic NPs directly on the ZrO2 support. The Ag-Pd/ZrO2 NPs were then used as plasmonic catalysts for the reduction of nitrobenzene under 425 nm illumination by LED lamps. Using gas chromatography (GC), the conversion and selectivity of the reduction reaction under the dark and light irradiation conditions can be monitored, demonstrating the enhanced catalytic performance and control over selectivity under LSPR excitation after alloying non-plasmonic Pd with plasmonic metal Ag. This technique can be adapted to a wide range of molecular transformations and NPs compositions, making it useful for the characterization of the plasmonic catalytic activity of different types of catalysis in terms of conversion and selectivity.
