title: Characterization of citrates on gold and silver nanoparticles.
abstract: In this paper, we report different coordinations of citrates on gold (AuNP) and silver (AgNP) nanoparticles, as determined using Fourier transform infrared spectroscopy (FTIR) and molecular orbital (MO) calculations. AuNPs and AgNPs are found to have completely different interactions with the carboxylate anchoring groups, as indicated by their unique asymmetric stretching vibrations in the FTIR spectra. The ν(as) (COO(-)) of citrate exhibits a high-frequency shift resulting from the formation of a unidentate coordination on AuNPs, whereas this vibration exhibits a low-frequency shift as a result of ionic bond formation on AgNPs, as predicted from the MO calculations of the corresponding metal complex salts. The enhancement in the IR signals when their vibration direction was perpendicular to the nanoparticle surface revealed the influence of localized surface plasmons excited on the metal nanoparticles.
authors.affiliation: Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan; Department of Physics, Institut Teknologi Bandung, Jalan Ganesha 10, Bandung 40132, Indonesia.
authors.forename: Priastuti
authors.initials: P
authors.lastname: Wulandari
authors.affiliation: Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nagahiro
authors.affiliation: Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, Tsukuba 305-8561, Japan.
authors.forename: Nobuko
authors.initials: N
authors.lastname: Fukada
authors.affiliation: Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Kimura
authors.affiliation: Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Michio
authors.initials: M
authors.lastname: Niwano
authors.affiliation: Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan; Institute for Materials Chemistry and Engineering, Kyushu University, 6-10-1 Hakozaki, Higashiku, Fukuoka 812-8581, Japan. Electronic address: tamada@ms.ifoc.kyushu-u.ac.jp.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Tamada
keywords: Carboxylate; Infrared spectroscopy; Metal nanoparticles; Vibration of adsorbed molecules