A series of P2O5 catalyzed covalent triazine-based framework (pCTF) were constructed. The pCTF polymerized
from terephthalamide at 400 °C exhibited excellent NH3 gas sensing ability with high response value, sensitivity
and selectivity at room temperature. Nitrogen atoms from triazine rings served as the active sites for NH3 adsorption,
and then lead to electronic structure changing of pCTF, which resulted in a resistance decreasing of the
sensor prepared by pCTF. In control experiments, the NH3 sensing response value increased with the increasing
of pyridinic nitrogen contents of the CTFs, which confirmed again that nitrogen atoms from triazine rings played
the key role for the excellent NH3 sensing ability. The density functional theory (DFT) calculations were employed
to study the adsorptions of NH3 and CO on a model molecule of pCTF fragment which contained six
benzene rings and six triazine rings. The computational results indicated that the band gap of the model molecule
of pCTF fragment narrowed slightly after NH3 adsorption and 0.024 of electrons transferred from NH3 to
the model molecule of pCTF fragment according to the Mulliken charge distribution at 298.15 K. This results
agreed well with the experimental results in which the sensor resistance decreased after NH3 molecule absorbed
on.