| Surface-enhanced Raman scattering (SERS) has greatly improved the detection limits of surface species, which has a unique advantages to study molecular absorption, desorption and orientations in real time. In order to discuss the SERS mechanism furtherly, extend variety of SERS substrates and widen application area of SERS technique, the design and fabrication of a variety of nanoparticles and nanostructures as new SERS substrates are hot topics. Recently, high-quality SERS signals have been observed in composite systems such as metal core/shell nanoparticles and metal-semiconductor composite.Single-walled carbon nanotubes (SWNTs) can be classified into metallic ones (met-SWNTs) and semiconducting ones (sem-SWNTs). The Ag/SWNTs with different ratio of C: Ag was synthesized by a facile one-step approach using the sodium citrate as reducing agent, developing the classical preparing method of silver-sol system. The effect of interfacial action between Ag and SWNTs on SERS activity of Ag/SWNTs was analyzed. It was concluded that the charge-transfer between Ag and SWNTs enhanced SERS activity of Ag/SWNTs. To deepen the study of the effect of charge-transfer between Ag and SWNTs on SERS activity, Ag/sem-SWNTs and Ag/met-SWNTs were fabricated, respectively. The effect of charge-transfer between Ag and SWNTs on SERS activity of composite was verified via the contrastive studies of them.Ag dendrites, size-controlled Pd nanocubes, hexagonal prism and Pd dendrites nanostructures were synthesized by a simple galvanic displacement process between Ag (Pd) ion and Cu. The sizes and morphology of Pd nanostructures could be controlled by simply regulating the reaction parameters, such as concentration of palladium dichloride, reaction time and types of surfactant. A possible formation mechanism of Pd nanocubes was also briefly discussed. Furtherly, SERS investigation demonstrated the nanostructures on copper foils were SERS-active. The SERS enhancement factor (EF) values for PATP on Pd nanocubes was about 3.4×107. Based on the excellent dispersion of the graphene obtained by"in situ self-generating template"route and the previous studies of fabrication of Ag dendrites, Pd nanocubes and Pd dendrites were obtained on Cu plate. Ag (Pd) was supported on graphene via Sacrifice Cu templet. Firstly, Cu was supported on graphene sheets, and it was negligible, whether the CuNPs shall be aggregated or not. Then, Ag (Pd) NPs supported on graphene sheet were fabricated via galvanic displacement process between Ag (Pd) ion and the Cu. In his way, though Cu nanoparticles (Cu NPs) on graphene sheets were aggregated in the first step, the obtained Ag (Pd) NPs on graphene sheets should be in good dispersions via a moderate replacement reaction. Successfully, something expected and unexpected has turned up, that the big-sized Cu NPs have magically been transformed into small-sized and high-dispersed Ag(Pd)NPs supported on graphene nanosheets in the absence of stabilizers. The study showed the small-sized Ag (Pd) NPs possess SERS activity which is different from Ag nanostucture. The electromagnetic field of small-sized Ag NPs is different from big-sized Ag (Pd) NPs, for the small-sized Ag NPs would lead to the change of dielectric constant of Ag (Pd) NPs. Moreover, the SERS activity of Ag (Pd)/graphene hybrid is relevant to the charge-transfer between Ag (Pd) and graphene. The obtained Pd/graphene hybrid exhibited more significant catalytic activity for formic acids oxidation than Pd/graphene and Pd/Vulcan obtained by one-step procedure that Pd ions were reduced with NaBH4 directly. Thus, the Pd/graphene hybrid should be applied to in-situ electrochemical SERS promisingly. |
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