Design of high sensitivity graphite carbon nitride/zinc oxide humidity sensor for breath detection

Abstract

In this work, a high-performance graphite carbon nitride/zinc oxide (g-C3N4/ZnO) humidity sensor for respiratory monitoring was designed for the first time. The humidity sensing mechanism for g-C3N4/ZnO was analysized by the first principles of density functional theory (DFT). It is found that compared to ZnO, oxygen vacancy defects and hydroxyl groups on g-C3N4/ZnO surface have higher adsorption energy for water molecules to make more water molecules to be adsorbed on surface of g-C3N4/ZnO. Experiments showed that the combination of g-C3N4 and ZnO increases the number of oxygen vacancy defects and hydroxyl groups on the surface of g-C3N4/ZnO, which makes a large number of water molecules adsorb on surface and accelerates the decomposition of water molecules into conductive ions to improve the performance of g-C3N4/ZnO humidity sensor. Such a g-C3N4/ZnO humidity sensor shows high response ((1.05±0.07)×104), small hysteresis (2.4%), good linearity, fast response/recovery speed (22/5 s) and higher stability in the range of 11 % RH to 95 % RH when the mass ratio of g-C3N4 and ZnO is 5%. In addition, the g-C3N4/ZnO sensor is effectively used to detect different respiratory states of the human, which shows strong application potential in the diagnosis of respiratory diseases.