Graphene as a promising additive to hierarchically porous carbon monoliths for enhanced H2 and CO2 sorption

Abstract

This study aimed to examine a synthesis of hierarchically porous carbon monoliths (HPCM) doped with graphene oxide (GO) for H2 and CO2 sorption applications. The synthesis procedure combining the sol-gel process with soft-templating was tuned by adding different quantities of GO (0.5; 2 and 10 wt% of the total amount of polycondensation mixture), as well as different carbonization temperatures (500 °C, 900 °C) of the composite materials during which the reduction of GO to graphene occurs. The degree of GO reduction to graphene and its incorporation into the HPCM matrix of prepared materials were characterized by Raman, FTIR, SEM, TEM, and elemental analysis. Although incorporation was successful, the higher pyrolysis temperature of 900 °C promotes the reduction of GO to graphene, which enhances the (ultra)microporosity (proven by gas physisorption experiments) of the samples, especially of the one with 10% GO addition. The effectivity of materials towards H2 and CO2 sorption was examined by sorption of H2 (77 K, up 1 bar) and CO2 (273 K, up 1 bar), respectively. Addition of any amount of GO together with the used lower pyrolysis temperature of 500 °C reduced the adsorption capacity of the samples for CO2 (from 2.4 to 1.8 mmol g−1) and H2 (from 5.8 to 3.6 mmol g−1) compared to the original HPCM. On the bright side, a 10% addition of GO in combination with a pyrolysis temperature of 900 °C results in industrially perspective material with an H2 and CO2 adsorption capacity of 9.6 mmol g−1 and 4.6 mmol g−1, respectively.