Synthesis and optical properties of gold/silver nanocomposites prepared on multi-walled carbon nanotubes via galvanic replacement of silver nanoparticles
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We report in this article a simple route for synthesizing small-sized silver/gold core–shell (Ag/Au) on multi-walled carbon nanotube (MWCNT) surfaces via galvanic replacement of Ag nanoparticles (Ag NPs). The Raman response of MWCNT decorated with Ag/Au was investigated under surface-enhanced Raman scattering. A relatively weak Raman signal enhancement of the tube was observed due to the large interparticle distance between neighboring small-sized nanostructures. Ag/Au gives better enhancing capability than the starting Ag because of the synergistic effect between the localized electric field of the Ag core, and the Au shell separated with a hollow space formed during the galvanic replacement reaction. Furthermore, the Ag/Au was removed from the CNT surfaces via sonication with 1-octanethiol (OT), releasing unreplaced Ag NPs and Au nanobowls (Au NBs) with 1.3 and 7.6 nm of mean diameter sizes, respectively. The production of these fine-sized nanocomposites (Au/Ag NCs) allowed us to investigate their luminescent property. Interestingly, the separated Au/Ag NCs (i.e., the mixture of Au NBs and unreplaced Ag NPs) exhibit fluorescence behavior that may be useful for single-molecule detection. Our technique provides the synthesis of smallest dimension of Au NBs so far simply achieved by wet-chemical process using MWCNTs as templates.
KeywordsGalvanic replacement reaction Gold nanobowls Gold/silver nanocomposites Multi-walled carbon nanotubes Fluorescence Core-shell Synthesis
The authors thank Te-Yu Liu for the assistance in Raman analysis, Shuo-Cheng Tsai for the help in TEM analysis, and Chun-Hong Kuo for the technical discussions. The authors acknowledge the financial support received from the Taiwan International Graduate Program (TIGP) and from the National Science Council (NSC) of Taiwan (grant numbers: 100-2120-M-007-006, 99-2113-M-007-017, 98-2113-M-007-017, 99-2113-M-007-013, and 100-2113-M-007-014).
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