Monolayer CuI: A Promising Sensor for Environmental Toxic Gases with High Sensitivity and Selectivity – A DFT Study

The adsorption behavior of various toxic gas molecules such as HF, CO, CO2, SO2, H2S, NH3, NO, and NO2 on the CuI monolayer (ML) has been investigated using DFT + U calculations with the Grimme scheme (DFT-D2) for an accurate description of van der Waals interactions. The structural and electronic properties of the CuI ML with the adsorbed gas molecules have been calculated to evaluate the sensitivity and selectivity of the CuI ML to these molecules. The results of our calculations demonstrate that the CuI ML is highly sensitive to CO, SO2, H2S, NH3, NO, and NO2 due to strong adsorption energies of −1.221, −0.635, −1.027, −1.264, −0.806, and −1.705 eV, respectively, and notable charge transfer. In contrast, HF and CO2 are weakly adsorbed, with small adsorption energies of −0.302 eV and −0.282 eV, respectively. The charge density difference and Bader charge analysis reveal that gas molecules either act as charge acceptors or charge donors when adsorbed on the CuI ML. The variation in work function and conductivity of CuI after adsorption confirms the high sensitivity of these molecules. Similarly the large band gap changes after adsorption indicate the high selectivity of the molecules. The recovery time for the desorption of HF, CO2, and SO2 is observed to be short at room temperature compared to other gas molecules. The long desorption time is reduced to a small value by increasing the temperature from 300 to 500 K. The results of Ab Initio Molecular Dynamics simulations show the thermal stability of the pristine CuI ML and after the adsorption of gas molecules at room and elevated temperatures. Thus, our theoretical results suggest that the CuI ML is a promising candidate as a gas sensor for sensing applications of HF, CO2, CO, SO2, H2S, NH3, NO, and NO2 with high sensitivity and selectivity.