Controlling Photocatalytic Reactions and Hot Electron Transfer by Rationally Designing Pore Sizes and Encapsulated Plasmonic Nanoparticle Numbers

Controlled self-assembly of different numbers of gold nanoparticles (AuNPs) in the highly ordered cylindrical anodic aluminum oxide nanopores was achieved by a facile ultrasonication method. The surface plasmon resonance bands became red-shifted by increasing the number of nanoparticles (N), in the top view, from monomer M1 (N = 1) to multimers of M2 (N = 3 ± 1), M3 (N = 5 ± 1), and M4 (N = 7 ± 1). The numerical calculations of the M2 model showed the best match of 2 nm nanogap among 28 nm diameter AuNPs in 53 nm diameter nanopores. When the number of AuNPs inside the nanopores increased, more hotspots were generated, which induced the plasmon-driven photocatalysis on AuNP clusters at the incident visible light of 633 nm. The enhanced photocatalytic reaction of 4-nitrobenzenethiol was observed after sequentially increasing the number of AuNPs, which began at M3 and was maximum for M4. The M3 configuration could be a magical number of AuNP clusters for the nanogap-induced photocatalysis under 633 nm irradiation (∼0.2 mW) for 12 min. Our methods should be helpful in adjusting photocatalysis by varying the numbers of nanoparticles inside the tunable nanopores.