Enhancing the CO2 capture capacity of natural macroporous carbonized fibers by growing carbon nanotubes on their surface

Abstract

In this study, a new hybrid material with superior CO2 sorption capacity was prepared by the growth of carbon nanotubes (CNT) into the macroporous structure of acid carbonized fibers (ACF). The growth of CNT was carried out by chemical vapor deposition using acetylene as a carbon source for 3.5 min at 700 °C. Selected materials were characterized by N2 physisorption, FTIR, potentiometric titrations, acid digestions, Raman spectroscopy, scanning and transmission electron microscopy. The CO2 capture was measured in static mode at pressure up to 10 atm in a sorptometer and in dynamic mode in a thermogravimetric analyzer at pressure of 1 atm. CNTs were homogeneously grown on the entire surface of ACF. The surface area of carbonized fibers increased from 2 to 452 m2/g after CNT growth and treatment at 300 °C for 1 min in air. The CO2 capture capacity of the ACF increased from 2.30 to 3.51 mmol/g at 25 °C and 10 atm after CNTs growth and air treatment (ACF3-CNT-AT1). The CO2 capture rate was also higher, from 0.023 to 0.032 mmol/g·min for ACF and ACF3-CNT-AT1 at 25 °C and 1 atm, respectively. These results were mainly attributed to the increase in basic groups and highly reactive edge sites. In addition, regeneration capacities of 99% and 95% were obtained for the first 3 sorption-desorption cycles and an apparent selectivity (QCO2/QN2) of 1.65 and 2.48 for ACF and ACF3-CNT-AT1, respectively. The rapid sorption-desorption kinetics, coupled with the high reversibility of CNT-modified ACFs, makes this hybrid material viable for use in CO2 capture systems.