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J. Phys. Chem. C 2010, 114, 256–264
Combination of Digestive Ripening and Seeding Growth As a Generalized Route for Precisely Controlling Size of Monodispersed Noble Monometallic, Shell Thickness of Core-Shell and Composition of Alloy Nanoparticles Yun Yang,* Xuezhong Gong, Huanmi Zeng, Lijie Zhang, Xihu Zhang, Chao Zou, and Shaoming Huang* Nanomaterials and Chemistry Key Laboratory, Wenzhou UniVersity, Wenzhou, Zhejiang 325027, P. R. China ReceiVed: September 20, 2009; ReVised Manuscript ReceiVed: NoVember 18, 2009
On the basis of combining the effect of digestive ripening and seeding growth, a generalized route for precisely controlling the size of noble monodisperse (MD) nanoparticles (NPs), the shell thickness of core-shell NPs, and composition of alloy NPs has been reported. First, small NPs are dispersed in high-boiling-point organic solvent as seeds; second, an alkyl amine-containing metal complex is used as the NP precursor; and finally, the metal atoms are reduced by the alkyl amine and grow on the surface of the seeds to form large NPs. The combining effect of seeding growth and digestive ripening render this route the ability to precisely control the size and maintain monodispersity. Through adjusting the reactive conditions, various MD noble NPs (Ag, Au, Pd), core-shell NPs (Ag@Pd, Pd@Au, Pd@Ag, Au@Pd, Au@Ag, Pt@Au, and Pt@Pd), and alloy nanoparticles(Ag/Au) can be prepared. The diameter, shell thickness, and composition of MD NPs can be precisely controlled by adjusting the ratio of the precursor/seed, offering a flexible route to tune surface plasmonic properties. Through increasing the digestive time, the core-shell NPs can be easily transformed to alloy NPs. By adjusting the composition and size of the used core-shell NPs, alloy NPs with tunable composition and size are achievable. Additionally, as-prepared core-shell NPs can be employed as starting materials to build other nanostructured NPs. 1. Introduction Nanoparticles (NPs) that have a diameter of less than 100 nm behave significantly different from their bulk form. For example, 5 nm gold NPs show red, but yellow for the bulk form.1-6 Properties of NPs also have a strong dependence on many parameters, including surface chemistry; for instance, alkyl thiol-, or amine-capped NPs showing oil-solubility but NPs coated with sodium citrate having good solubility in water.7 In terms of solubility and size distribution, NPs always are divided into two types: MD hydrophobic NPs and MD hydrophilic NPs. MD hydrophobic NPs (MHNPs) have received extensive interest due to their applications in fabricating ordered nanostructures.8-12 Among the MHNPs, noble metal NPs (Au, Ag, Pt, and Pd) have attracted much attention for several decades owing to their promising applications in catalysis,13-15 nanoelectronics,1-6 and optics.16 There are several techniques to synthesize noble MHNPs, such as one-step synthesis,17-32 the classic Brust two-phase method,23,24 size-selective precipitation,25 seeding growth,26-29 solid-state heating,30 and digestive ripening.31-38 Among those, digestive ripening involving Ostwald ripening is a popular synthetic strategy. This method is based on the size-dependent solubility and tendency of minimization of the system energy. The size-narrowing effect from digestive ripening has not been understood fully so far, but it has been used to fabricate MHNPs, including magnetic,39-41 semiconductor,42-45 and noble NPs.46-48 Digestive ripening always is used only to generate noble MHNPs with diameters of
