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General scheme showing the entrapment process
Source:    Published:2011/6/10 11:28:04

   General scheme showing the entrapment process of unprotected noble metal nanoclusters within the matrix of metal oxide nanoparticles. (Reprinted from Ref. [18],⑥ 2004, with permission from Elsevier. Results Synthesis of Metal Nanoclusters Stab17ized by Ethylene Glycol and Simple Ions The unprotected Pt, Rh and Ru nanoclusters prepared according to the alkaline EG synthesis method in EG with metal concentrations of 0.3-3.7g/l have small average particle sizes of l.1-1.3 nm and narrow size distributions from 0.7 t0 2.2nm, as measured by TEM (Figure l and Table l) [11]. The Os nanoclusters (3.7g/l) prepared by this method have an average diameter of 0.9 nm and a size distribution of 0.6-1.8 nm (Figure 2) [12].

  

   The reduction of metal hydroxides or oxides powder by polyol was first reported by Figlarz and co-workers, which gave rise to fine powders of Cu, Ni, Co and some noble

   metals with micrometer sizes (polyol process) [32,33]. The polyol process was first modified for the preparation of PVP-protected bimetallic and monometallic nanoclusters such as Pt/Cu, Pd/Pd, Pt/Co, Pt, Pd, etc. [34-38]. The previous results definitely revealed that Pt, Pd, Cu and Co in

   these PVP-protected metal or alloy nanoclusters were in a zero-valent metallic state.

  

   In the XRD patterns of the unprotected metal nanoclusters prepared by the alkaline EG synthesis method, no signals derived from their corresponding oxides could be

   detected, XPS measurements also revealed that the prepared metals nanoparticles had the binding energies close to those of their corresponding zero valence species, 70.9 eV for Pt 4f7j2, 280.0 eV for Ru 3d5/2, 307.1 eV for Rh 3d5/2 and 50.0 eV for Os 4f7/2, respectively, indicating that the

   metal species were in a metallic state The alkaline EG synthesis method has been successfully applied to the preparation of unprotected bimetallic nanocluster colloids with controllable composition. Figure 3 shows the TEM image of bimetallic Pt/Ru nanoclusters (Pt/Ru molar ratio - 1:1.9, total metal

  

   concentration: 1.85g/l) with an average particle size of 1.9 nm and a size distribution from l.4 t0 2.4nm. XRD pattern of the bimetallic nanoclusters is shown in Figure In addition to the wide peak centered at ~400 containing the signals of (1 1 1) and (200) reflections, there is another weak peak at 20 = 670 assignable to the (220) diffraction line of fcc Pt/Ru alloy Pt/Rh bimetallic nanoclusters were similarly prepared by this alkaline EG method [12]. The particle sizes of bimetallic Pt/Rh nanoclusters (0.37 g/l in total metal concentration) ranged from 0.9 t0 2.lnm with an average diameter of l.3 nm. A combined EDX analysis, using an electron beam of l.Onm in diameter, revealed that both signals of Pt and Rh existed in each individual particle

   and the average ratio of Pt to Rh (1.4:1) was close to the

  

  

CAS NO.200116-81-0
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