(Invited) Site-Selective Introduction of MnO2 Co-Catalyst to Gold Nanocubes for Enhanced Plasmonic Photocatalysis

Abstract

Plasmon-induced charge separation (PICS) is known to take place at the interface between a nanoparticle exhibiting localized surface plasmon resonance (LSPR) and a semiconductor such as titanium oxide.1 PICS has been applied to photovoltaics, photocatalysis, and so on.2 For energy harvesting based on plasmonic photocatalysis, it is important to optimize geometrical arrangements of the plasmonic nanoparticles, semiconductor, and co-catalyst if any, to enhance the charge separation efficiency and minimize charge recombination probability.Since LSPR confines light to a nanoscale region smaller than visible light wavelength, PICS allows one to fabricate plasmonic materials in nanoscale beyond the diffraction limit.3-7 We have reported fabrication of wide variety of plasmonic nanostructures via site-selective reactions such as oxidative dissolution of silver and oxidative deposition of lead oxide.In the present work, gold nanocubes were adsorbed onto a thin film of titanium oxide to obtain a plasmonic photocatalyst. Then, lead oxide was deposited on the top or bottom part of the gold nanocube via the site-selective oxidation of lead ions based on PICS. Lead ions in the deposited lead oxide were replaced with manganese ions by galvanic replacement and the lead oxide was transformed to manganese oxide. The manganese oxide moieties on the gold nanocubes serve as co-catalyst of the plasmonic photocatalyst.We examined photocatalytic currents for ethanol oxidation by PICS. As a result, the photocurrents were enhanced by introducing manganese oxide to the top part of the gold nanocubes. In marked contrast, the photocurrents were suppressed when the manganese oxide was introduced to the bottom part of the nanocubes. In the latter case, charge recombination occurs between the holes injected to manganese oxide and the electrons injected to titanium oxide. On the other hand, the charge recombination is suppressed in the former case, because manganese oxide is not directly contact with titanium oxide. Thus we found that the position of a co-catalyst greatly affect the activity of plasmonic photocatalysts.8 1. Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005).2. T. Tatsuma, H. Nishi, and T. Ishida, Chem. Sci., 8, 3325 (2017) [review].3. I. Tanabe and T. Tatsuma, Nano Lett., 12, 5418 (2012).4. K. Saito, I. Tanabe, and T. Tatsuma, J. Phys. Chem. Lett., 7, 4363 (2016).5. H. Nishi, M. Sakamoto, and T. Tatsuma, Chem. Commun., 54, 11741 (2018).6. K. Saito and T. Tatsuma, Nano Lett., 18, 3209 (2018).7. T. Tatsuma and H. Nishi, Nanoscale Horiz., 5, 597 (2020) [review].8. K. Kim, H. Nishi, and T. Tatsuma, J. Chem. Phys., 157, 111101 (2022).