(350g) A Simple Method for Preparing Metal Nanoparticles Inside Multi-Walled Carbon Nanotubes and Their Transmission Electron Microscopy Image Analysis
Carbon nanotubes (CNTs), including both single-walled and multi-walled carbon nanotubes, have been used as catalyst support and showed several advantages over traditional carbon or oxide supports. The electronic atmosphere inside CNTs can affect the behavior of both reactants and catalytic particles, therefore preparing catalysts with particles selectively deposited inside CNTs are desired. Current methods are either tedious or lack of accurate control of catalyst loading. In this study, a simple and efficient method was developed for the introduction of metal nanoparticles inside multi-walled carbon nanotubes (MWCNTs) with accurate loading control. The method is based on the incipient wetness impregnation using the aqueous solution of a metal salt precursor, followed by the reduction in hydrogen. A hydrophobic MWCNT outer surface is created, which minimizes the wetting of the impregnation solution on the MWCNT outer surface, leading to the highly selective deposition of metal particles inside the MWCNTs. The selectivity toward nanoparticles inside MWCNTs is about 80% based on a particle number average. Also, a new method was developed for the analysis of microscopic images from transmission electron microscope (TEM) so that the fraction of particles inside MWCNTs can be accurately characterized without 3D TEM. This method is based on the measurement of r/R , the ratio of the inside to outside diameters of the MWCNTs.