Synthesis and Photocatalytic Activity of Porous Bimetallic Plasmonic Nanoparticles Formed on Solid Substrates

Plasmonic catalysis aims to extract useful work from the surface plasmon resonance phenomenon in order to assist or drive a chemical reaction. Nanoparticles (NPs) composed of plasmonic metals such as Au, Ag, Cu and Al resonantly interact with light through the excitation of localized surface plasmon resonance (LSPR) modes which subsequently decay to produce highly energetic "hot carriers". There are two major technical obstacles that prevent the efficient utilization of hot carriers to drive chemical reactions. The first limitation is that plasmonic NPs are frequently synthesized as colloidal suspensions while a number of heterogeneous catalytic reactions require the catalyst to be anchored to a solid-state support. The second limitation arises due to the relative chemical inertness of noble metals, particularly gold, which prevents the adsorption of most types of reactant molecules on the surface of the plasmonic NP catalyst. As a consequence of the second limitation, plasmonic metal NPs often demonstrate low catalytic activity for many chemical reactions. In recent years, there has been growing interest in bimetallic nanostructures that combine the optical characteristics of plasmonic metals with the catalytic properties of metals such as Pt and Pd. In this work, we attempted the precise fabrication of diverse bimetallic plasmonic photocatalysts with a porous structure to overcome both the aforementioned technical problems. Porous bimetallic plasmonic nanoparticles with large surface areas possess an enhanced capacity to adsorb reactant molecules (compared to their monometallic counterparts) increasing their overall catalytic efficiency. In this work, we present a dealloying technique to fabricate porous bimetallic nanostructures on solid substrates and investigate their activity for the vapor phase transformation of CO_² and H₂O into hydrocarbons at close to room temperature. We also analyze the photocatalytic ability of the as-fabricated porous bimetallic nanostructures in the decolorization of methylene blue (MB) dye. Scavenger studies indicate photogenerated electrons to be the active species responsible for photocatalytic activity. In both CO₂ photoreduction and dye photodegradation, bimetallic porous AuPt NPs outperform monometallic porous Au NPs by nearly 33%. These results have important implications for more energy efficient, sustainable heterogeneous catalysis under milder conditions of temperature and pressure. This work also presents the application potential for the use of porous bimetallic plasmonic catalysts in water remediation and the generation of solar fuels.