C6N7 monolayer as an innovative sensor and scavenger for NO, H2S and SO2: A first-principles study

Abstract

The adsorption, electronic, gas-sensing and capture properties of molecules (NO, H2S, SO2, NO2, NH3, N2, CO, CH4, CO2, and H2O) on the C6N7 monolayer were systematically studied to explore the possibilities of C6N7-based toxic gas sensor and scavenger by using first-principles methods. We found only NO, H2S, and SO2 are adsorbed on the monolayer with large adsorption energy (ranging of -0.853∼-0.931 eV), meanwhile the other molecules are all weakly physisorbed on the monolayer with Ead of -0.193∼-0.547 eV. The NO and H2S adsorption could remarkably affect the electronic properties and work function (Φ) of the C6N7 monolayer, indicating it is highly sensitive and selective towards NO and H2S. The recovery time (τ) of NO and H2S was predicted respectively to be 25 and 1.9 s at 350 K, while the τ of the other molecules was too short to make the sensor device be difficult to measure these gases. The C6N7 monolayer can be promising resistance-type (Φ-type) gas sensors for H2S and NO detection at 350 K. However, the presence of humidity effects the gas sensing of C6N7-based resistance-type sensor, so that it should operate in a dry environment, but as Φ-type sensor can operate regardless of the existence of humidity and concentrations. In addition, the high adsorption capacity and desired recovery time of the C6N7 monolayer make it be an optimal scavenger for toxic gases.