Multi-walled carbon nanotubes/carbon foam nanocomposites derived from biomass for CO2 capture and supercapacitor applications

Abstract

Biomass-based carbon foams (CFs) exhibit improved performance relative to traditional porous carbons in many applications. However, the more extensive use of these materials is significantly impeded by their inferior mechanical properties, including poor compressive strength. In this work, we prepared hierarchically porous multi-walled carbon nanotubes (MWCNTs)/CF (MCF) nanocomposites using liquefied larch sawdust as the carbon precursor by in-situ polymerization, foaming and carbonization. MWCNTs incorporated in foam increased the compressive strength of the CF significantly (by 113%) and also improved the thermal stability and degree of graphitization. The MCF nanocomposites possessed more developed hierarchical porosities than the pure CF, in particular ultra-microporosity with pore sizes from 0.50 to 0.80 nm and mesopores with an average size of approximately 3.70–3.90 nm. Micropores with pore diameters less than 0.80 nm were found to play an especially major role in CO2 adsorption by these materials. The MCF nanocomposites were determined to have large isosteric heats of adsorption from 23.32 to 36.48 kJ mol−1, and the MCF-2 specimen (the addition of 2 wt%) showed high CO2 adsorption capacities of 4.58 and 3.19 mmol g−1 at 0 and 25 °C, respectively. This sample also demonstrated an excellent CO2/N2 selectivity ratio of 23.71 at 25 °C and was readily recycled. The MCF-2 displayed a specific capacitance of 157.07 F g−1 at a current density of 1 A g−1 in a 6 M KOH electrolyte together with a superior rate retention of 71% at 15 A g−1 and so has potential applications in supercapacitors.