Detection of CO2 using CNT-based sensors: Role of Fe catalyst on sensitivity and selectivity

Abstract

The adsorption of CO2 on surfaces of graphene and carbon nanotubes (CNTs), decorated with Fe atoms, are investigated using the self-consistent-charge density-functional tight-binding (SCC-DFTB) method, neglecting the heat effects. Fe ad-atoms are more stable when they are dispersed on hollow sites. They introduce a large density of states at the Fermi level (NF); where keeping such density low would help in gas sensing. Furthermore, the Fe ad-atom can weaken the CO double bonds of the chemisorbed CO2 molecule, paving the way for oxygen atoms to drain more charges from Fe. Consequently, chemisorption of CO2 molecules reduces both NF and the conductance while it enhances the sensitivity with the increasing gas dose. Conducting armchair CNTs (ac-CNTs) have higher sensitivity than graphene and semiconducting zigzag CNTs (zz-CNTs). Comparative study of sensitivity of ac-CNT-Fe composite towards various gases (e.g., O2, N2, H2, H2O, CO and CO2) has shown high sensitivity and selectivity towards CO, CO2 and H2O gases.