Structural evolution and stability studies of heterostructures comprised of carbon nanotubes decorated with nickel/nickel oxide core/shell nanoparticles

The single-step synthesis of heterostructures, denoted as CNC heterostructures, comprised of carbon nanotubes (CNTs) decorated with nickel (Ni)/nickel oxide (NiO) core/shell nanoparticles through a direct nucleation approach is reported. This approach allowed for a single-parameter and well-controlled structural evolution of Ni/NiO core/shell nanoparticles on CNTs. It was possible to control the size (similar to 12-52 nm), shape, spatial density, and chemical composition of nanoparticles formed on CNTs by changing the nanoparticle growth time (15 min to 15 h). It was observed that growth time of 15 h led to the reaction between phosphine-based stabilizers and Ni core forming solid and hollow Ni12P5 nanoparticles directly on CNTs. Thermal stability of CNC heterostructures (in N-2-rich atmosphere) dispersed on a silicon wafer as well as subsequent surface migration of nanoparticles were studied by annealing heterostructures at different temperatures (125-750 degrees C). In comparison to as-produced CNTs, the surface characteristics, oxidative resistance or thermal stability, and changes in heterostructure compositions were studied using electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The heterostructures showed greater oxidative resistance as compared to as-produced CNTs. (C) 2011 Elsevier Ltd. All rights reserved.