J. Phys. Chem. C 2009, 113, 16921–16926
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Structural and Magnetic Properties of PdxNi1-x (x ) 0 and 0.54) Metallic Nanoparticles in an Ordered Mesoporous Carbon Template R. Campesi,† V. Paul-Boncour,† F. Cuevas,† E. Leroy,† R. Gadiou,‡ C. Vix-Guterl,‡ and M. Latroche*,† CMTR-ICMPE-UMR 7182-CNRS, 2-8 rue Henri Dunant, 94320 Thiais Cedex, France, and IS2M-LRC 7228-CNRS, 15 rue Jean Starcky, 68057 Mulhouse Cedex, France ReceiVed: May 13, 2009; ReVised Manuscript ReceiVed: July 30, 2009
In the frame of developing nanocomposites, the confinement of nanosized metals or alloys in nanostructured porous materials is a key point. Using a wetness method starting from metal salt precursors [PdCl2, Ni(NO)3], we have succeeded in the synthesis of two nanocomposites in which nanoclusters of either Pd54Ni46 alloy or Ni have been dispersed in a carbon template (CT). For the CT-PdNi nanocomposite, XRD and TEM analyses show the dispersion of 5 nm nanoparticles inside the pores of the CT. For the CT-Ni nanocomposite, the metal particles are close to 10 nm and are mostly located at the CT surface and are partly oxidized. XRD, EDX, and EELS analysis as well as magnetic measurements have demonstrated that Pd and Ni elements have fully reacted in the CT-PdNi nanocomposite to form the Pd54Ni46 alloy. The magnetic properties of the CT-PdNi composite are compared with those of the CT-Ni one. The CT-PdNi has a lower blocking temperature TB than CT-Ni, confirming the smaller size of the nanoparticles. For CT-Ni nanocomposite, the coexistence of both Ni and NiO phases leads to a slight asymmetry of the hysteresis loop, and the M-H curve does not reach the saturation magnetization. In contrast, the CT-PdNi composite displays a larger hysteresis loop without asymmetry, confirming that alloying Pd with Ni prevents Ni from oxidation. Introduction In the past decades, the interest toward the development of nanocomposites resulting from the dispersion of metal or alloy-intermetallic nanoparticles in nanostructured porous materials has continuously increased. Nanocomposites can be applied in numerous technical applications such as catalysis. The dispersion of metal clusters (Ni, Pd, Pt, etc.) supported on porous materials like alumina,1 silica,2,3 or carbon compounds4-6 increases the yield of many reactions involving organic compounds. Another interesting aspect is related to the possibility of synthesizing hard or soft nanomagnets for either technological7 or medical applications.8-11 It has been found that when the particle size is reduced to the nanoscale range (∼10 nm), the magnetic properties of metals or alloys change dramatically with respect to the crystalline counterparts.12 The main target in the design of nanocomposites is to get highly dispersed nanoparticles with a narrow size distribution.13 This goal is facilitated by using a hard matrix with a well-defined pore structure avoiding agglomeration of the nanoparticles which can be confined during their growth. To this aim, silica mesoporous compounds,14 zeolites,15 and metal organic frameworks16 as well as carbon nanotubes,17 nanofibers,18 or carbon replica19-21 were used as host materials for the insertion of metal or alloy nanoparticles. Recently, we report on the synthesis and hydrogen sorption properties of a composite made of carbon and PdNi alloy nanoparticles20 for which an accurate determination of the Pd/Ni alloy composition as well as the magnetic properties are of prime importance in the frame of the potential applications mentioned above. Moreover, regarding magnetic properties, the * Corresponding author: Tel +33 1 49 78 12 01; Fax +33 1 49 78 12 03; e-mail
[email protected]. † CMTR-ICMPE-UMR 7182-CNRS. ‡ IS2M-LRC 7228-CNRS.
development of material constituted of nanosized Ni particles embedded in a carbon matrix is very relevant. In the present paper, we report on the synthesis and characterization of two nanocomposites obtained by dispersion of Ni and PdNi nanoparticles in a carbon template (CT). The materials were characterized by conventional techniques (XRD, ICP, BET) but also by more specific techniques such as electron energy loss spectroscopy (EELS) and magnetic measurements. The combination of these techniques allows to correlate the chemical composition and the microstructure of CT containing Ni and PdNi nanoparticles with their physical properties. Information about the oxidation state of the metallic species is also reported. Experimental Section The nanostructured carbon materials are of the CMK-3 type.22 They were prepared by a templating procedure using SBA-15 as silica template and propylene as carbon precursor. The SBA15 was prepared according to the synthesis already presented in the literature.23 The temperature used for the silica synthesis was 110 °C. For such experimental conditions, the obtained silica displays cylindrical pores with a diameter close to 7 nm and a mean wall width around 4 nm. Carbon was deposited into the SBA-15 by chemical vapor deposition (CVD) of propylene at 750 °C. The CVD was done in a fixed bed reactor at atmospheric pressure with a flow of 3% of propylene in argon. Then, to remove the silica template, the mixed material (silica/ carbon) was stirred overnight with a HF solution (40 vol % concentration), before being filtered and washed with distilled water. It was finally dried overnight under air at 80 °C in a muffle furnace.24-26 The resulting material is a hexagonal arrangement of carbon nanorods which have a size close to 6 nm. The cell parameter is 11 nm, and the porous volume is mainly composed of interconnected small mesopores with a mean size of 5 nm.25,27
10.1021/jp904453k CCC: $40.75 2009 American Chemical Society Published on Web 09/02/2009
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J. Phys. Chem. C, Vol. 113, No. 39, 2009
Campesi et al.
TABLE 1: Chemical Compositions of CT-Ni and CT-PdNi Composites Obtained by ICP-OES sample
C (wt %)
Ni (wt %)
Pd (wt %)
Si (wt %)
CT-Ni CT-PdNi
88.0 85.9
11.7 ( 0.3 4.88 ( 0.43
9.15 ( 0.47
