  We use ab intio density functional theory to investigate the adsorption
properties of acetylsalicylic acid or aspirin on a (10, 0) carbon nanotube
(CNT) and a (8, 0) triazine-based graphitic carbon nitride nanotube (CNNT). It
is found that an aspirin molecule binds stronger to the CNNT with its
adsorption energy of 0.67 eV than to the CNT with 0.51 eV. The stronger
adsorption energy on the CNNT is ascribed to the high reactivity of its N atoms
with high electron affinity. The CNNT exhibits local electric dipole moments,
which cause strong charge redistribution in the aspirin molecule adsorbed on
the CNNT than on the CNT. We also explore the influence of an external electric
field on the adsorption properties of aspirin on these nanotubes by examining
the modifications in their electronic band structures, partial densities of
states, and charge distributions. It is found that an electric field applied
along a particular direction induces aspirin molecular states in the in-gap
region of the CNNT implying a potential application of aspirin detection.
