The design of heterojunctions based on boron-/phosphorus-doped graphene and ZnO monolayer to enhance adsorption properties for toxic gases

Boron-/phosphorus-doped graphene and ZnO monolayer (B-G/ZnO and P-G/ZnO) heterojunctions are modeled. The density functional theory is performed to investigate the optimal adsorption configurations, electronic and adsorption properties of oxycarbide (CO, CO2), oxynitride (NO, NO2), and sulfide (SO2, H2S) gas molecules adsorbed on the heterojunctions. Results indicate that the adsorption characteristics of both B-G/ZnO and P-G/ZnO heterojunctions are better than those of G/ZnO heterojunction. Specifically, NO2 and SO2 gas molecules are chemisorbed on doped heterojunctions, and the adsorption energies are almost three times more than that on the G/ZnO heterojunction. Then, the two gas molecules are simultaneously adsorbed on the two opposite terminals of the doped G/ZnO heterojunctions to evaluate the influence of gas concentration on electronic and adsorption properties of the G/ZnO heterojunction. It is found that the adsorption energy almost doubles compared with adsorbing a gas molecule, which provides a new idea to regulate the electronic and adsorption properties of the G/ZnO heterojunction. In addition, the bandgap of graphene can be opened by B and P atom doping and the p-n junction and n-n junction can be formed with the ZnO monolayer, respectively. The theoretical investigation helps us to better understand the mechanism of G/ZnO heterojunctions as gas sensors and offers the guidance for future p-n and n-n junction designs used in advanced gas sensor devices.