Bimetallic nanowires

This chapter deals with the selective preparation, TEM/EXAFS/XPS characterization and catalysis of mono- and bimetallic nanowires and nanoparticles highly ordered in silica FSM-16, organosilica HMM-1 and mesoporous silica thin films. The mechanism of nanowire formation is discussed with the specific surface-mediated reactions of metal precursors in the restraint of nanoscale void space of mesoporous silica templates. The unique catalytic performances of nanowires and particles occluded in mesoporous cavities are also reviewed in terms of their shape and size dependency in catalysis as well as their unique electronic and magnetic properties for the device application. 

Figure 15.6 (a) TEM image of a PtPd bimetallic nanowire/HMM-1 prepared by UV-irradiation of an (H2PtCl6 -r H2PdCl4)/ HMM-1 sample with MeOH and H2O vapor (b) high-resolution TEM image of a PtRh nanowire/HMM-1 prepared by UV-irradiation... 

Walter EC, Murray BJ, Favier F, Penner RM (2003) Beaded bimetallic nanowires wiring nanoparticles of metal 1 using nanowires of metal 2. Adv Mater 15 396-399... 

Template synthesis of tremsition metal nanowires in mesoporous materials is presented. Pt, Rh, Pt-Rh, ind Pt-Pd neuiowires tu"e synthesized in HMM-1 and FSM-16 by the photoreduction method. The bimetallic nanowires in HMM-1 are alloy crystallite with a necklace-like structure. The Pt-Pd wire/HMM-1 shows higher magnetic susceptibility at low temperature than the Pt wire. In butane hydrogenolysis, Pt-Rh wire/FSM-16 shows high selectivity to isobutane. 

In an interesting study, Sankaranarayanan et compared bimetallic nanowires with clusters and the macroscopic crystals. They performed molecular-dynamics simulations using the Sutton-Chen potential for an approximate description of the interatomic interactions. They considered two systems, Pd-Rh and Pd-Cu. As initial structures, they considered cut-outs of the infinite, crystalline fee or hep structures. Subsequently, the two types of atoms were distributed at those atomic positions that led to the... 

Fig. 42 The calculated phase diagram of (left part) bimetallic nanowires, (middle part) bimetallic clusters, and (right part) bimetallic crystals for (a) Pd-Rh and (b) Pd-Cu. Reproduced with permission of American Chemical Society from ref. 127.

The wire surface energy o, defined according to Equation 1.10, was redefined in order to study the stability of bimetallic nanowires. In a similar way, the surface energy was calculated in reference with the bulk systems ... 

Figure 1.3 shows the variation of the surface energy as a function of the fractional composition y. We have considered Au p nanowires, where p=Ag or Cu, due to the fact that they were obtained experimentally [20]. For the same fractional composition, we have evaluated different systems by changing the order of the atoms in the unit cell. Compositions with the highest degree of intercalation or mixing are connected with a line in each case. For all the compositions, the bimetallic nanowires with the higher intercalation are the most stable ones. 

According to Figure 1.3, most of the bimetallic nanowires studied have a thermodynamic stability in between the corresponding pure wires. Nevertheless, in both cases, there is a local minimum at x=0.5 in the surface energy that corresponds to wires with the largest entropy possible for a bimetallic compound. The existence of this local minimum emerges from the increase of the intermetal interactions that stabilize the bimetallic wires. 

Soldano, G., Santos, E., and Schmickler, W. 2011. Intrinsic stability and hydrogen affinity of pure and bimetallic nanowires. 7. Chem. Phys. 134 174106 1-174106 8. 

Kim YS, Nam SH, Shim HS, Ahn HJ, Anand M, Kim WB (2008) Electrospun bimetallic nanowires of PtRh and PtRu with compositional variation for methanol electrooxidation. Electrochem Commun 10(7) 1016-1019... 

Fig. 16.13 SEM images of as-spun (a) Pt-Rh precursor/PVP and (b) Pt-Ru precursor/PVP and bimetallic nanowires of (c) PtlRhl and (d) PtlRul insets of (c) and (d) show the diameter of bimetallic NWs (Reprinted from Ref [104]. Copyright 2(X)8, with permission from Elsevier)...

Mayorga-Martinez CC, Guix M, Madrid RE, Merkoci A (2012) Bimetallic nanowires as electrocatalysts for nonenzymatic real-time impedancimetric detection of glucose. Chem Commun 48 1686-1688... 

Attention has been given to the synthesis of bimetallic silver-gold clusters [71] due to their effective catalytic properties, resistance to poisoning, and selectivity [72]. Recently molecular materials with gold and silver nanoclusters and nanowires have been synthesized. These materials are considered to be good candidates for electronic nanodevices and biosensors [73]. 

Similarly, monometallic Rh, Pd, and Au and bimetallic Pt-Rh and Pt-Pd nanowires were prepared in FSM-16 or HMM-1 by the photoreduction method [30,33,34]. The bimetallic wires gave lattice fringes in the HRTEM images, and the EDX analysis indicated the homogeneous composition of the two metals. These results show that the wires are alloys of Pt-Rh and Pt-Pd. Mesoporous silica films were also used as a template for the synthesis of uniform metal particles and wires in the channels [35,36]. Recently, highly ordered Pt nanodot arrays were synthesized in a mesoporous silica thin film with cubic symmetry by the photoreduction method [37]. The... 

Hunyadi SE, Murphy CJ (2006) Bimetallic silver-gold nanowires fabrication and use in surface-enhanced Raman scattering. J Mater Chem 16(40) 3929-3935... 

Gunawidjaja R, Peleshanko S, Ko H, Tsukruk W (2008) Bimetallic nanocobs decorating silver nanowires with gold nanoparticles. Adv Mater 20 1544-1549... 

Template synthesis and catalysis of bimetallic platinum-rhodium and -palladium nanowires in mesoporous materials... 

PtML/Pd interlayer/IrCo Pt hollow spheres (from dealloying PtML/Ag) Pd-Pt bimetallic nanodendrites Pt-Pd core-shell nanowires ... 

The copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction [1] (Fig. lA) has been extensively employed for the site-specific labeling of oligonucleotides with various reporter groups [3,4, 7, 9,12-16], ligating DNA strands [17, 18], cross-linking complementary strands [19], for surface functionalization [20] and for the formation of bimetallic Ag-Au nanowires from DNA templates [21], Selected examples are described in the following section. 

Fischler M, Simon U, Nir H, Eichen Y, Burley GA, Gierlich J, Gramlich PM, Carell T (2007) Formation of bimetallic Ag-Au nanowires by metallization of artificial DNA duplexes. Small 3(6) 1049-1055. doi 10.1002/smll.200600534... 

N content and exhibited better resistance to oxidation and hence a much higher activity than reduced iron catalyst [81]. PtCo and PtFe NPs and nanowires have been selectively confined in CNTs (Fig. 5.7). A marked confinement effect has been evidenced, both on bimetallic nano-object shape and composition. Large diameter nanotubes favor the confinanent of small Co- or Fe-rich NPs (Fig. 5.7a), while in small-diameter CNTs Pt-rich nanowires are formed (Fig. 5.7b). 

In addition, surfactants as capping agents are indispensable for preparing bimetallic nanorods and nanowires. In the synthesis of Pt-Ag alloy nanowires in a... 

So far, we have only discussed the reactivity of monometallic wires further. Because of the wide range of possibilities for the adsorption, the study of hydrogen interaction with bimetallic wires is much more complicated. However, it is interesting to examine some aspects that give us a better understanding of the nature of the bond between hydrogen and nanowires. Due to their stability, the most important and illustrative cases are the gold bimetallic wires Au p2 and Au ,P5, where p correspond to copper or silver atoms. 

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