2017 Lord Lewis Lecture (I) Sustainable plasmonics: abundant materials for modular photocatalysis
Metallic nanoparticles, used since antiquity to impart intense and vibrant color into materials, have more recently become a central tool in the nanoscale manipulation of light. Metal nanoparticles can support surface plasmons, the collective oscillations of their conduction electrons, which give rise to their optical properties. In addition, the nonradiative decay of surface plasmons results in the generation of hot electrons and holes within the metal; charge transfer of these hot carriers between the metal and adsorbate molecules can induce chemical transformations. Since metallic nanoparticles provide direct optical excitation of surface plasmons and the ability to tune the plasmon energies through control of nanoparticle geometry, they are ideal structures for the controlled generation of hot carriers for photocatalysis. We have recently shown that room temperature dissociation of H2 at Au nanoparticle surfaces- an “impossible reaction”- can be driven by hot electron injection into the LUMO level of the molecule. [1-3] In a device geometry where we were able to distinguish between “hot” carriers due to plasmon decay and “cold” carriers resulting from direct excitation of electrons, we found that the generation rate of hot carriers is proportional to the local electromagnetic field within the plasmon-excited metal. We have applied this discovery to design a new type of photocatalyst using a modular approach, combining a metallic nanoparticle with a good plasmonic response as an “antenna”, coupled to a catalytically active but poorly optically absorbing metal nanoparticle, as a “reactor”, situated within the antenna nanoparticle’s fringing field. One highly promising candidate for the antenna in this modular design is Aluminum, the most abundant metal on earth. We will show how this “antenna-reactor” concept can be realized to control the reactivity of the catalytic “reactor” particle, as well as control the selectivity of chemical reaction outcomes.  S. Mukherjee et al., Nano Letters 13, 240-247 (2012).  S. Mukherjee, et al., Journal of the American Chemical Society 136, pp 64–67 (2014).  L. Zhou et al., Nano Letters 16, 1478-1484 (2016).  B. Y. Zheng et al., Nature Communications 6, 7797 (2015).  D. F. Swearer et al., PNAS 113, 8916–8920 (2016).