Platinum Metals Rev., 2005, 49, (4), 189
Anisotropic Growth of Platinum Nano-Multipods
Nanometer-sized branched nanocrystals (multipods) of metal, metal oxide and semiconducting materials have intrinsic electronic, magnetic, photonic and catalytic properties that make them suitable as building blocks for complex nanostructures. Such multipods, such as 3D tetrapod nanocrystals, may find use in the generation of hierarchical nanostructured networks. Tetrapods of CdSe and CdS have already been developed, and multipods and hyperbranched nanostructures are being investigated. However, the anisotropic growth needed to produce branched nanocrystals for other metals has not been achieved, perhaps because the metals are not polymorphic. Only platinum (Pt), rhodium and gold are known to form branched nanocrystals.
Now, scientists at the University of Rochester, New York, U.S.A., report an induced anisotropic growth process for making Pt multipods from Pt acetylacetonate ((Pt(acac)2) at temperatures below that at which Pt nanoparticles are nucleated and grown (X. Teng and H. Yang, Nano Lett., 2005, 5, (5), 885–891 http://dx.doi.org/10.1021/nl0503072).
To induce nucleation and branched Pt nanocrystal growth, 3 mg of silver acetylacetonate was added to 200 mg of Pt(acac)2 in diphenyl ether with complexing agents, at temperatures from 160 to 210°C, and reaction times of 4.5 to 60 min. Three distinct temperature-dependent regimes, were observed:
Without the Ag, no Pt particles formed for the entire reaction period of 60 min, at temperatures 160 to 175°C.
Multipods were formed at 2.5 to 4.5 min after the Ag addition for reactions at 180 to 200°C.
The multipods turned into spheres after reaction for a further 10 to 15 min (at 180 to 200°C).
Injecting more Pt(acac)2 into the reaction mixture of three equal aliquots at 7, 9 and 12 min after Ag addition extended the multipod growth process. The transition time from multipods to spherical particles increased to 30 min and some multipods could still be seen at 60 min.
The morphologies of Pt multipods made include I- and V-shaped bipods, various types of tripods, and planar and 3D tetrapods. It is concluded that using this method, multipods of different metals could be produced, and be nanoscale building blocks for complex functional nanostructures through self-assembly.