Synthesis of CoNi nanowires by heterogeneous nucleation in polyol

doi:10.1016/j.matlet.2010.03.006

Materials Letters

Volume 64, Issue 11, 15 June 2010, Pages 1271-1274

https://doi.org/10.1016/j.matlet.2010.03.006 Get rights and content

Abstract

CoNi nanorwires/nanorods, depending on the loading of Ni, were prepared by heterogeneous nucleation in polyol. CoNi nanowires with the length up to 1000 nm and the diameter of about 10 nm were obtained when the loading of Ni was no more than 30%, whereas nanorods with the length of about 500 nm and the diameter of 20 nm were produced with further increasing the loading of Ni. It was revealed that the nanowires might be a core-shell structure where the core was formed by the fast reduction of Co²⁺ and the shell was constructed by the combined reduction of Co²⁺ and Ni²⁺. When used for hydrogenolysis of glycerol, the CoNi nanowires showed significantly enhanced glycerol conversion and propanediol selectivity as compared to the pure Co nanowires.

Introduction

Bimetallic nanomaterials have attracted wide attention because of their unique properties which are largely different from their mono-metal counterparts [1], [2]. Doping a second metal in transition metals could adjust the d-band filling of electron, and thus greatly alter the surface properties as well as the catalytic performance [3], [4]. For example, NiAu alloy showed excellent activity and stability in steam reforming of n-butane, where the doping of Au decreased the activation energy for C–H bond and thus impeded coke deposition [5]. CuPt alloy exhibited exceptionally high activity in low-temperature water–gas-shift reaction because of the facile activation of H₂O and the weak adsorption of CO [6]. CoNi alloy was also found to be highly active for methane drying reforming, and the alloyed structure significantly promoted the stability by inhibiting coke formation [7], [8]. These investigations were mainly focused on the conventional spherical particles without particular geometries; however, examination of bimetallic alloyed structures with varied shape/morphology that favors to expose specific crystal facets is rarely concerned.

Recently, novel structured Co-based bimetallic materials such as CoPt nanorods [9], CoFe nanocubes [10], CoNi urchins [11], and CoNi nanowires and nanodumbbells [12] have been fabricated in liquid phase by effectively controlling the reduction rate of the metallic ions. In particular, Co₈₀Ni₂₀ urchins which were consisted of radiant nanowires have been synthesized by heterogeneous nucleation in polyol, but the length of the wires was limited to about 500 nm [11], [12]. We have recently synthesized Co nanowires with a diameter of 10 nm and a length up to 1000 nm by chemical reduction of cobalt acetate using Ru as heterogeneous agent and stearic acid as structure-directing agent [13]. In this work, we have extended to fabricate alloyed CoNi nanowires with this heterogeneous nucleation technique. By varying the basicity of the solution and the loading of Ni in proper ranges, alloyed CoNi nanowires with the diameter of about 10 nm and the length up to 1000 nm were obtained.

Section snippets

Materials synthesis

1.0 g of a solid mixture of cobalt and nickel acetate tetrahydrates with desired Ni/Co molar ratios and 0.2 g of sodium hydroxide were dissolved into 80 ml of 1, 2-propanediol. Then, 0.267 g of stearic acid and 0.02 g of RuCl₃·xH₂O (35 wt% Ru) dissolved in 5 ml of 1, 2-propanediol were added to the solution. The mixture was transferred into a teflon-lined autoclave (100 ml) and gradually heated to 413 K and maintained at this temperature for 12 h. The product was centrifuged, thoroughly washed with

Results and discussion

Fig. 1 shows the TEM images of the CoNi materials with varied Ni loading. For Co alone, nanowires with a length of 500–1000 nm and a diameter of about 12 nm were obtained. When 10% Ni was added, the wire-like morphology was maintained, but the diameter decreased to about 7 nm and the length shortened to 200–1000 nm with a cone head of about 50 nm on each tip. It is noted that agglomeration which was mainly composed of the short nanorods with the length of 200–500 nm was also produced. This might be

Conclusion

Alloyed CoNi nanowires were obtained as the loading of Ni was less than 30%. Co²⁺ was initially reduced to Co crystals as the core and the remaining Co²⁺ and Ni²⁺ were slowly and simultaneously reduced to form CoNi alloyed shell. Basicity of the synthetic solution varied the shape of the CoNi nanomaterials considerably through adjusting the reduction rates of the two metal ions. Catalytic test for hydrogenolysis of glycerol revealed that the alloyed CoNi nanowires greatly promoted the catalytic

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Synthesis of CoNi nanowires by heterogeneous nucleation in polyol

Abstract

Introduction

Section snippets

Materials synthesis

Results and discussion

Conclusion

Surf Sci Rep

Appl Catal A

Catal

Nanotechnology

Prog Solid State Chem

J Mol Catal

Vacuum

New J Chem

Chem Rev

Surf Sci Rep