Carbon-Supported Nickel Nanoparticles from a Wood Sample of the Tree Sebertia acuminata Pierre ex. Baillon
A wood sample of the nickel hyperaccumulator tree Sebertia acuminata Pierre ex. Baillon was pyrolyzed in an inert atmosphere to produce a charcoal-like material containing nanoparticulate nickel. Its overall nickel content was determined to be ~7 wt-% by wet chemical analysis (acid digestion, inductively coupled plasma optical emission spectroscopy). Depending on the conditions of pyrolysis (5 h at 800°C; or 5 h at 800°C followed by 7 h at 900°C), the average crystallite sizes were ~7 and 42 nm, respectively, as determined by X-ray powder diffraction (XRD) and electron microscopy (scanning, scanning transmission, and transmission). Furthermore, high resolution transmission electron microscopy images reveal that the Ni particles are, in some cases, encapsulated with graphitic carbon layers of varying thickness. Scanning electron microscopy results indicate for the most part, a preservation of the wood framework and a remarkably uniform distribution of the nickel nanoparticles in the vessels of the xylem. XRD and X-ray absorption fine structure analysis reveal the presence of NiO besides Ni.