Molecular adsorption study of nicotine and caffeine on single-walled carbon nanotubes from first principles

•We study physical properties of nicotine and caffeine molecules on carbon nanotubes.•Caffeine adsorbs on the nanotube with a higher binding energy than nicotine.•The caffeine-adsorbed CNT exhibits electron donation and back-donation together.•The influence of caffeine is stronger than nicotine on the conductance of the CNT.