title: An in situ quick XAFS spectroscopy study on the formation mechanism of small gold nanoparticles supported by porphyrin-cored tetradentate passivants.
abstract: We previously reported that a porphyrin-cored tetradentate passivant, which has two disulfide straps over one face of the porphyrin plane, can produce monolayer-protected gold nanoparticles, 2-4 nm in size, by the one-pot reduction of HAuCl(4) in DMF. The resulting nanoparticles are smaller than those prepared using the same S/Au molar ratio of a monodentate passivant. To examine the formation mechanism of small gold nanoparticles, the formation of gold nanoparticles in the presence of porphyrin-cored tetradentate passivants or a structurally related monodentate passivant was studied by time-resolved quick X-ray absorption fine structure spectroscopy. The results demonstrated that all of Au ions in solution are reduced to compose small Au clusters, i.e. nuclei, just after the NaBH(4) reduction of HAuCl(4) in both cases, but their size varied with the initial S/Au molar ratios and structure of the passivants. Thus, the size of Au nuclei was kinetically controlled by the passivants. Interestingly, the porphyrin-cored tetradentate passivant could stabilize smaller gold nanoparticles, 2-4 nm in size, but it was less efficient in trapping the Au nuclei formed at a very early stage, in comparison to the monodentate passivant.
authors.affiliation: Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Kyoto, Japan.
authors.forename: Junya
authors.initials: J
authors.lastname: Ohyama
authors.forename: Kentaro
authors.initials: K
authors.lastname: Teramura
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Higuchi
authors.forename: Tetsuya
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authors.lastname: Shishido
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Hitomi
authors.forename: Kazuki
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authors.lastname: Aoki
authors.forename: Takuzo
authors.initials: T
authors.lastname: Funabiki
authors.forename: Masahito
authors.initials: M
authors.lastname: Kodera
authors.forename: Kazuo
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authors.lastname: Kato
authors.forename: Hajime
authors.initials: H
authors.lastname: Tanida
authors.forename: Tomoya
authors.initials: T
authors.lastname: Uruga
authors.forename: Tsunehiro
authors.initials: T
authors.lastname: Tanaka