报告题目：Gap mode induced photocatalytic reactions of p-alkyl thiophenol and related molecules
报告人：Prof. Masayuki Futamata, Graduate School of Science and Engineering, Saitama University,Japan
时间：2019-10-25 10:00
地点：卢嘉锡楼202报告厅
报告摘要：
Metal nanoparticles (MNPs) are utilized mostly after immobilization on metal oxides like SiO2 or TiO2 for catalyzing chemical transformation of organic molecules typically at the temperatures lower than ~370 K. Photocatalytic reactions can also be implemented solely by MNPs, which are driven by hot carriers, electrons and holes excited during dephasing process of surface plasmons (SP). Although the role of the lifetime of hot carriers is still a matter for debate, crucial reactions have been reported for plasmon induced oxidation of ethylene [1] or dissociation of hydrogen [2]. Inherently, a localized surface plasmon (LSP), which generates high density of hot carriers and enormously enhanced electric field available for highly-sensitive spectroscopy, is quite suitable for in-situ elucidation of photocatalytic reactions on MNPs. Among various surface enhanced Raman scattering (SERS) probes such as roughened metal surfaces, MNPs and arrays of metal nanostructures, the gap mode plasmon generating markedly enhanced electric field by a factor of 104-105 at a nanogap between MNPs on various transition metal substrates [3] plays a salient role for this purpose. Indeed, Al, Ni, Zn as well as Ag, Au and Cu substrates provide promising SERS enhancement factors of 107-109 for adsorbed thiophenol (TP) molecules using AuNPs [4].
Under the gap mode geometry, we recently found that various p-alkyl thiophenol (p-AlTP) molecules, such as methyl, ethyl, iso-propyl, or tertiary butyl groups, irrespective of their normal or branched alkyl groups, in AgNP/p-AlTP/Ag film (t=45 nm)/Ge film (t=1 nm)/Si substrates are oxidized into p-mercaptobenzoic acid (p-MBA) by irradiating laser light at 532 nm (<~1 μW/μm2). In contrast, o- and m-methyl TP (o-, m-MeTP) do not show such reactions [5]. We investigated here detailed properties of the photocatalytic reaction specific to p-AlTP in terms of the following contrasting observations [6]. (1) The oxidation of p-MeTP was not induced by thermal heating of the samples up to 373 K. Subtle temperature increase during the oxidation under the laser irradiation was also corroborated by the measurements of the Stokes and anti-Stokes scattering intensity. (2) The oxidation of p-MeTP was accelerated by oxygen atmosphere at room temperature, whereas nitrogen atmosphere yielded an intermediate species, presumably attributed to p-mercaptobenzyl radical. (3) Ortho-, m-, and p-mercaptobenzyl alcohol molecules were oxidized to corresponding o-, m- and p-mercaptobenzoic acid (MBA) with no definite site selectivity.
References
1.P. Christopher, H. Xin, S. Linic, Nature Chem. 2011, 3, 467-472.
2.S. Mukherjee, F. Libisch, N. Large, O. Neumann, L. V. Brown, J. Cheng, J. B. Lassiter, E. A. Carter, P. Nordlander and N. J. Halas, Nano. Lett. 2013, 13, 240-247.
3.K. Ikeda, J. Sato, N. Fujimoto, N. Hayazawa, S. Kawata, K. Uosaki, J. Phys. Chem. C 2009, 113, 11816–11821.
4.M. Futamata, M. Ishikura, C. Iida, S. Handa, Faraday Discuss. 2015, 178, 203-220.
5.K. Akai, M. Futamata, Chem. Phys. Lett. 2017, 675, 63-68.
6.K. Tabei, K. Akai, M. Futamata, Chem. Phys. Lett. 2019, 730, 568-574.
报告人简介：
Masayuki Futamata
PhD, Prof.
Graduate School of Science and Engineering, Saitama University
(Born in April 08, 1956 at Hiroshima pref., Japan)
1985 PhD at Tohoku University (Department of Chemistry, Faculty of Science) (Sendai, Japan)
1985-1991 Osaka National Research Institute, AIST-MITI (Osaka, Japan)
1991-1992 Visiting research scientist, Institute of Solid State Physics, Heinrich-Heine-Universitaet Duesseldorf (Germany)
1993-2000 Senior Research Scientist, Atom Technology Group, National Institute for Advanced Interdisciplinary Research (NAIR)-AIST-MITI (Tsukuba, Japan)
2001-2008 Senior Research Scientist, National Institute of Advanced Industrial Science and Technology (AIST, Tsukuba, Japan)
2008- present Prof., Saitama University (Saitama, Japan)
