Mesoporous Carbon Materials with Ultra-Thin Pore Walls and Highly Dispersed Nickel Nanoparticles

Abstract

Mesoporous carbon materials with ultra-thin carbon pore walls and highly dispersed Ni nanoparticles have been successfully prepared by using two different SBA-15 silicas as hard templates and 2,3-dihydroxynaphthalene (DHN) as a carbon precursor. The nickel precursor was a concentrated nickel nitrate hexahydrate [Ni(NO₃)₂·6H₂O] solution in 2-propanol, which was added to the carbon–silica nanocomposite prior to thermal treatment. The samples studied were analyzed by thermogravimetry (TG), nitrogen adsorption at –196 °C, powder X-ray diffraction (XRD), Raman spectroscopy, scanning and transmission electron microscopy (STEM), and in situ electron diffraction X-ray spectroscopy (EDX). While TG analysis revealed carbon contents lower than 30 wt.-%, nitrogen adsorption provided information about the homogeneity of the carbon thin film deposited onto the mesopore walls of the ordered silica templates SBA-15. The templates, carbon–silica nanocomposites, and carbon inverse replicas with nickel nanoparticles exhibit uniform pores, high surface areas, and large pore volumes. Partially graphitic carbon was identified by the presence of a characteristic G band in the Raman spectra, whereas the diffraction peak attributed to the stacking of graphene planes was not observed by powder XRD. The presence of ordered domains in the carbon materials studied was confirmed by small angle XRD and STEM imaging. In addition, the STEM images revealed that the nickel nanoparticles are uniform in size, ca. 3 nm, and are homogeneously dispersed on the tubular carbon walls. A few larger clusters of nickel, ca. 60 nm, present on the external surface, were identified by powder XRD as metallic Ni. The in situ EDX revealed that the small nanoparticles are largely composed of Ni with traces of NiO. Similar nanoparticle dispersions have been reported only for Ni-containing multiwalled carbon nanotubes (CNTs), whereas previously reported ordered mesoporous carbon materials, CMK-3, possess larger Ni/NiO nanoparticles.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)