Monolithic nanocarbon-based
CO2 solid sorbents offer fast mass transport, easy handling,
minor pressure
drop, and cycle operation stability because of the interconnected
three-dimensional network of pores that provides a unique porous structure.
In this work, following a one-step water-based method, graphene-based
monoliths were produced by a spontaneous reduction-induced self-assembly
of graphene oxide nanoplatelets under mild conditions (45–90
°C). By varying the reaction temperature and amount of reducing
agent (ascorbic acid, AsA), the engineering of the porous structure
of the monoliths was performed and resulted in a portfolio of different
monoliths with different capacities for CO2 adsorption.
It was found that the monolith produced at the highest temperature
and with the lowest AsA amount possessed the highest specific surface
area and porosity as well as a high level of functionalization. As
a result, this monolith presented an excellent CO2 capture
performance of 2.1 mmol/g at T = 25 °C and P = 1 atm. This value is between the highest achieved in
CO2 sorption in comparison to that of similar and nontreated
materials. The selectivity of this monolith for CO2 capture
over that for N2 at 25 °C and atmospheric pressure
is 53, presenting a high viability for practical applications. The
monolith was shown to lose capacity in cycle operations, probably
because of the collapse of the smallest pores, which was solved by
the addition of a small amount of polymer particles during the one-step
synthesis of the monolithic structures. This modification provides
for an excellent stability over five adsorption/desorption cycles.