Heterometallic antenna−reactor complexes for photocatalysis

Abstract

Metallic nanoparticles with strong optically resonant properties behave as nanoscale optical antennas, and have recently shown extraordinary promise as light-driven catalysts. Traditionally, however, heterogeneous catalysis has relied upon weakly light-absorbing metals such as Pd, Pt, Ru, or Rh to lower the activation energy for chemical reactions. Here we show that coupling a plasmonic nanoantenna directly to catalytic nanoparticles enables the light-induced generation of hot carriers within the catalyst nanoparticles, transforming the entire complex into an efficient light-controlled reactive catalyst. In Pd-decorated Al nanocrystals, photocatalytic hydrogen desorption closely follows the antenna-induced local absorption cross-section of the Pd islands, and a supralinear power dependence strongly suggests that hot-carrier-induced desorption occurs at the Pd island surface. When acetylene is present along with hydrogen, the selectivity for photocatalytic ethylene production relative to ethane is strongly enhanced, approaching 40:1. These observations indicate that antenna−reactor complexes may greatly expand possibilities for developing designer photocatalytic substrates.plasmon | photocatalysis | nanoparticle | catalysis | aluminum I ndustrial processes depend extensively on heterogeneous catalysts for chemical production and mitigation of environmental pollutants. These processes often rely on metal nanoparticles dispersed into high surface area support materials to both maximize catalytically active surface area and for the most cost-effective use of expensive catalysts such as Pd, Pt, Ru, or Rh (1, 2). However, catalytic processes utilizing transition metal nanoparticles are often energyintensive, relying on high temperatures and pressures to maximize catalytic activity. A transition from extreme, high-temperature conditions to low-temperature activation of catalytically active transition metal nanoparticles could have widespread impact, substantially reducing the current energy demands of heterogeneous catalysis.Light-driven chemical transformations offer an attractive and ultimately sustainable alternative to traditional high-temperature catalytic reactions. Metallic plasmonic nanostructures are a new paradigm in photoactive heterogeneous catalysts (3-6). Plasmonic nanoparticles uniquely couple electron density with electromagnetic radiation, leading to a collective oscillation of the conduction electrons in resonance with the frequency of incident light, known as a localized surface plasmon resonance (LSPR). These resonances lead to enhanced light absorption in an area much larger than the physical cross-section of the nanoparticle, and such optical antenna effects result in strongly enhanced electromagnetic fields near the nanoparticle surface. An LSPR can be damped through radiative reemission of a photon, or nonradiative Landau damping with the creation of energetic "hot" carriers: electrons above the Fermi energy of the metal and/or holes below the Fermi energy. In this context, "hot" refers to carri...

Balancing Near-Field Enhancement, Absorption, and Scattering for Effective Antenna–Reactor Plasmonic Photocatalysis

“…[38][39][40][41] Recently it has been shown that Pd nanoparticle-decorated, oxide-coated Al nanocrystals enable efficient plasmon-induced photocatalysis at the Pd surface, where the plasmonic and catalytic functions were effectively distinct. 42 This general structure has been called an "antenna-reactor" complex, where the plasmonic nanoparticle is the antenna and the catalytic particle, which can be interchanged based on desired reactivity, is the reactor. In an antenna-reactor complex, the local field induced by the photoexcited antenna particle drives a "forced" plasmon in the nonplasmonic, catalytic nanoparticle: this forced plasmon can serve as a direct source of hot carriers in the catalytic particle to drive chemical processes without the need for charge transfer between 5 the antenna and the reactor components of the nanocomplex.…”

Plasmonics in the Ultraviolet with Aluminum, Gallium, Magnesium and Rhodium

“…This antenna-reactor complex allows absorption enhancements in poorly light-absorbing catalytic metals [35]. The feasibility of these heterostructures has been demonstrated using Al as "antenna" and Pd as "reactor" heterodimers [35] and decorated spherical nanoparticles [36]. Aluminum-cuprous oxide antenna-reactor nanoparticles have also been proven to be an efficient photocatalytic heterostructure [37].…”

Hot‐Electron‐Mediated Photochemical Reactions: Principles, Recent Advances, and Challenges

“…[1][2][3][4][5][6][7] In particular, heterogeneous photocatalysis that couples light with chemical reactions is of paramount importance in chemistry and energy applications. [8][9][10][11][12][13][14][15][16] Plasmonic enhancement is currently a hot topic in catalysis-driven chemistry and photonic materials due to its important role as the main mediator bridging solar energy with other energy forms. For instance, the photocatalytic water splitting reaction used for biomimetic plant photosynthesis represents a promising solution to the growing demands for clean and sustainable energy.…”