Thermally controlled growth of carbon onions within porous graphitic carbon-detonation nanodiamond monolithic composites

Abstract

Unique porous carbon monoliths containing thermally annealed carbon onions, were prepared from a resorcinol formaldehyde precursor rod, containing silica gel acting as a hard template, detonation nanodiamond, and Fe³⁺ as a graphitisation catalyst. Detonation nanodiamond was converted to carbon onions during controlled pyrolysis under N₂, where the temperature cycle reached a maximum of 1250 °C. Thermal characterisation and high resolution electron microscopy have confirmed the graphitisation of nanodiamond, and revealed the resulting quasi-spherical carbon onions with an average particle size of 5.24 nm. The bimodal porous composite contains both macropores (5 μm) and mesopores (10 nm), with a BET surface area of 214 m² g⁻¹ for a nanodiamond prepared monolith (0.012 wt% nanodiamond in the precursor mixture), approximately twice that of blank monoliths, formed without the addition of nanodiamond, thus providing a new approach to increase surface area of such porous carbon rods. Raman spectroscopy and X-ray photoelectron spectroscopy also confirmed an enhanced graphitisation of the monolithic carbon skeleton resulting from the elevated thermal conductivity of the added nanodiamond. TEM imaging has confirmed the nanodiamond remains intact following pyrolysis at temperatures up to 900 °C.