Gold and gold-palladium branched nanocrystals for applications in plasmonic catalysis and electrocatalysis

Abstract

The harvesting of solar light is one of the main challenges in science. The outstanding optical properties of plasmonic in the visible and near-infrared ranges due to the localized surface plasmon resonance (SPR) has emerged as a promising approach for the solar-tochemical energy conversion. Specifically, it has been demonstrated that the SPR excitation in the visible range in silver (Ag) and gold (Au) nanoparticles can drive and accelerate chemical transformations. This field, coined plasmonic catalysis, enables one to merge catalytic and optical properties in the nanoscale and use visible or near-infrared light as a sustainable energy input to accelerate molecular transformations. In the first part of this thesis. we developed Au branched nanostructures to be employed as plasmonic catalysts. In this case, we aimed at investigating the effect of the sharp tips at their surface over their plasmonic catalytic performance, as it is established that tips can concentrate higher electric field enhancements relative to rounded surfaces as a result of the lightning rod effect, which, in turn, can translate into higher plasmonic catalytic performances. Here, the plasmonic-catalytic performances were tested using the SPR mediated oxidation of paminothiophenol and benzylamine as model transformations. While the Ag and Au nanoparticles support LSPR excitation in the visible and near-infrared ranges, their catalytic properties are limited in terms of versatility. Conversely, metals that are important in catalysis, such as palladium Pd, do not support SPR excitation in the visible or near-infrared range. In the second part of this thesis, we developed multimetallic nanoparticle morphologies, composed of both Au and Pd, that enabled us to marry catalytic and plasmonic component in order to address this challenge. We focused on plasmonic core-catalytic shell structures, in which the shell displayed a branched morphology. Parameters such as shell thickness could be controlled, and structure performance relationships were established towards the methanol electro-oxidation under plasmonic excitation.