Low-temperature catalytic synthesis of graphite aerogels from polyacrylonitrile-crosslinked iron oxide and cobalt oxide xerogel powders

We demonstrate the Fe- or Co-catalyzed preparation of graphitic carbon aerogels that bypasses the typical use of supercritical fluid drying, and takes place at much lower temperatures (800-1500 degrees C) than conventional graphitization (2500-3300 degrees C). The process starts with preparation of polyacrylonitrile (PAN)-crosslinked iron and cobalt oxide xerogel powders via surface-initiated free-radical polymerization of acrylonitrile on the porous solid networks of sol-gel-derived particle suspensions of the oxides. The resulting wet-gel oxide/polymer composite powders were dried under vacuum at 50 degrees C to xerogel powders, which were compressed into desirable form factors, e.g., discs or cylinders. These compacts were then aromatized (300 degrees C, O2), and subsequently carbonized in the range of 800 degrees C to 1500 degrees C under Ar. In situ carbothermal reduction of the oxide networks by the newly produced carbon yielded catalytictoward-graphitization Fe(0) or Co(0) nanoparticles embedded within the carbons. Post-pyrolysis, those metallic nanoparticles were removed with aqua regia leaving behind pure graphitic carbon aerogels. Chemical characterization of materials up to aromatization was carried out with solid-state 13C NMR; characterization of the terminal graphite aerogels was based on powder-XRD, Raman, TEM, SEM, XPS and N2-sorption. Porosities in the range of 63%-78% v/v were created during aromatization, and mainly during pyrolytic carbonization. The best quality graphite aerogels were obtained with iron at 1500 degrees C. These materials consisted of 99.8% w/w graphitic carbon, the crystallite domain size along the (002) plane reached 170 angstrom, and the crystallite width along the a-axis was 70 nm. (c) 2022 Elsevier Ltd. All rights reserved.