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

Abstract

Efficient photocatalysis requires multifunctional materials that absorb photons and generate energetic charge carriers at catalytic active sites to facilitate a desired chemical reaction.Antenna-reactor complexes are an emerging multifunctional photocatalytic structure where the strong, localized near field of the plasmonic metal nanoparticle (e.g. Ag) is coupled to the catalytic properties of the non-plasmonic metal nanoparticle (e.g. Pt) to enable chemical transformations. With an eye towards sustainable solar driven photocatalysis we investigate how the structure of antenna-reactor complexes governs their photocatalytic activity in the light- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 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 the antenna and the reactor components of the nanocomplex. In the initial demonstrations of antenna-reactor coupling, however, the optimal geometric configuration of the constituent materials to maximize photocatalytic performance was not addressed. Furthermore, while it is relatively straightforward to conclude that localizing a plasmonic particle near a non-plasmonic catalytic particle will enhance light absorption in the non-plasmonic particle, it is not clear how this translates to enhanced photocatalysis in the light-limited regime, where all photons must be utilized in a 3-D packed bed of catalytic particles. Optimizing photocatalytic complexes for highest efficiency photon management in the light-limited regime is of critical importance for further development of this approach.In the work reported here, a series of antenna-reactor complexes consisting of core@shell/satellite (Ag@SiO 2 /Pt) heterostructures with varying Ag core diameter (12,25,50 and 100 nm) were synthesized and their photocatalytic properties for the kinetically well-defined CO oxidation reaction were quantitatively compared. Rigorous quantum yield measurements in the light-limited regime demonstrate that for heterostructures with Ag nanoparticles (Ag NPs) in an intermediate size range of 25 and 50 nm diameter, plasmon-enhanced photocatalytic performance was observed at rates more than four times larger than for either smaller (12 nm diameter) or larger (100 nm diameter) Ag particles. Using optical and Monte Carlo simulations, it was shown that if the Ag NPs were too large, the heterostructures scattered light out of the catalyst bed, reducing photocatalytic reactivity. If the Ag NPs were too small, l...

Addressing the Effects of Size‐dependent Absorption, Scattering, and Near‐field Enhancements in Plasmonic Catalysis

“…It can be anticipated that higher E‐field enhancements (as a result of stronger LSPR excitation) may lead to improved performances in LSPR‐mediated transformations ,. For example, near‐field at the metal‐adsorbate interface can increase the rates of photoexcitation of metal‐adsorbate bonds . In addition, absorption should play a very important role over the activities in LSPR‐mediated transformations involving charge transfer.…”

“…In general, it has been established that nanoparticle size plays a fundamental role over activities in nanocatalysis . In addition to changes in surface area, size is expected to strongly influence absorption and scattering efficiencies as well as the intensity of the near‐field enhancements in plasmonic nanoparticles . Surprisingly, the importance of size in plasmonic catalysis remains overlooked, and several studies employ relatively large nanoparticles (>50 nm in size) as catalysts .…”

Quantum‐Sized Metal Catalysts for Hot‐Electron‐Driven Chemical Transformation

“…The amplified optical absorption in the QSMNPs supported on the plasmonic metal nanoantennae leads to an improved photocatalytic activity compared to the freestanding QSMNPs. Li and co‐workers demonstrated that loading Pt QSMNPs with a size of ≈5 nm on silica coated Ag nanoantennae (Ag@SiO 2 ) increased the photocatalytic activity toward CO oxidation in comparison with the freestanding Pt QSMNPs . However, the design of the hybrid structures consisting of QSMNPs supported on plasmonic nanoantennae has some obvious downsides to fully benefit photocatalytic chemical transformations.…”

“…These two examples highlight the great promise of photoexcited hot‐electron‐driven chemical transformations on QSMNPs with regard to improve reaction rate and selectivity. A broad range of chemical reactions including dissociation, partial oxidation,[20b,27] and full oxidation[18b,25] can also benefit from the use of photocatalysis on the QSMNPs. It is worth to point out that chemical transformation of adsorbate molecules on the QSMNPs is usually a nonadiabatic process.…”

Engineering Colloidal Lithography and Nanoskiving to Fabricate Rows of Opposing Crescent Nanogaps

“…[ 10–12 ] A currently fast developing area in plasmonics is metal nanoparticles. They have great applications in sensing, [ 13 ] imaging, [ 14 ] catalysis, [ 14–17 ] biomedicine, [ 18,19 ] etc. In particular, asymmetric nanoparticles have unique optical properties, which are different from their normal symmetrical nanostructures.…”