(617dv) Photochemical Reactions on Plasmonic Metal Nanoparticles: Underlying Mechanism of Charge Extraction from Nanoparticles to Adsorbates

Plasmonic metal nanoparticles represent a new class of photocatalysts that harvest the energy of visible photons through excitation of localized surface plasmon resonance (LSPR). The relaxation of these excited surface plasmons can lead to the transfer of energetic charge carriers to adsorbates which in turn promote chemical transformations on the surface of the metal nanoparticles.¹ Multiple mechanisms have been proposed for the energetic charge carrier transfer process. The conventional model of photoexcitation in metals suggests the formation of energetic charge carriers in the metal, rapid thermalization, and subsequent transfer of â??hotâ? charge carriers to adsorbates. More recent studies point instead towards the direct transfer of charge from the photo-excited metal to adsorbates avoiding the formation and thermalization of charge carriers in the metal.²

In this presentation, we study the flow of charge for a photo-excited plasmonic metal-adsorbate system in which the presence of the adsorbate opens a new channel for the direct, resonant flow of charge from the metal to the adsorbate. This direct transfer of charge results in the selective heating of the adsorbate molecule without exciting charge carriers in the metal thereby avoiding the heating and loss of energy to the metal nanoparticle. This suggests that the transfer of energy to adsorbates in these photo-excited metal-adsorbate systems can be very efficient. We outline a conceptual model that explains these results and close by discussing the consequences of this energy flow in plasmonic metal-adsorbate systems for applications in photocatalysis.

(1) Linic, S.; Aslam, U.; Boerigter, C.; Morabito, M. Photochemical Transformations on Plasmonic Metal Nanoparticles. Nat. Mater. 2015, 14 (6), 567â??576.

(2) Boerigter, C.; Campana, R.; Morabito, M.; Linic, S. Evidence and Implications of Direct Charge Excitation as the Dominant Mechanism in Plasmon-Mediated Photocatalysis. Nat. Commun. 2016, 7, 10545.