Comparing the effects of different oxygen-containing functional groups on sulfonamides adsorption by carbon nanotubes: Experiments and theoretical calculation

Abstract

Combined with batch adsorption experiments of sulfadimethoxine (SDM), sulfamethizole (SMZ), sulfamethazine (SMT), sulfamethoxazole (SMX) by carbon nanotubes (CNTs) with different oxidation degree, this study investigated the effect of different oxygen-containing functional groups (COC, OH, CO, COO−) on sulfonamides (SAs) adsorption by CNTs using density functional theory (DFT) calculation. The experimental results showed that the SAs adsorption decreased with increasing oxidation degree of CNTs, and followed the order of SDM>SMZ>SMT>SMX. The π-π interactions of the benzene and heterocyclic rings in SAs with the benzene-type rings of CNTs were the predominant adsorption mechanisms. DFT calculation showed that the oxygen-containing functional groups inhibited SAs adsorption, and the inhibitory effects declined in the order of COO−>CO>OH>COC. The COO− and CO groups could damage the ring structure of CNTs while OH and COC only damaged the conjugated structure of benzene-type rings of CNTs if they were located on the basal plane of CNTs. This disabled the π-π interactions of the damaged benzene-type ring and weakened the π-π interactions of the adjacent rings with SAs. However, the functional groups could only weaken the π-π interactions between CNTs and SAs if they were located on the edge of CNTs. The extension degree of V-shaped SAs and the type of heteroatoms in heterocyclic groups of SAs led to their different adsorption by CNTs. The results highlight the type of oxygen-containing functional groups is great importance in their effects on pollutants adsorption by CNTs.