The development of high-performance gas sensing materials is one of the development trends of new gas sensor technology. In this work, in order to predict the gas-sensitive characteristics of HfSe2 and its potential as a gas-sensitive material, the interactions of nonmetallic element (O, S, Te) doped HfSe2 monolayer and small molecules (NH3 and O3) have been studied by first-principles based on density functional theory. The results show that the adsorption of NH3 and O3 on pristine HfSe2 monolayer is weak, and the adsorption strength can be significantly improved by doping O. And O-HfSe2 is chemical adsorption to O3 with large adsorption energy and transfer charge, and the band gap of O[sbnd]HfSe2 disappears after adsorbing O3, indicating that the adsorption of O3 has a significant effect on the electrical properties of the substrate. These mean that O3 is difficult to recover from the substrate surface, thus preventing O-HfSe2 from developing into a sensitive material for O3 detection. After doping S, the charge transfers and adsorption strength to NH3 are the largest, but it is still small. So, the strain effect on the S-HfSe2/NH3 adsorption system is also studied. The results indicate that the adsorption strength of S-HfSe2 to NH3 can be enhanced by stretching S-HfSe2 along x-axis. After absorbing NH3, the conductivity of x-axis strained S-HfSe2 changes, which suggest its sensitivity. And the predicted recovery times of S-HfSe2 surfaces with εx=4%, 6% and 8% are 0.027 s, 1.153 s and 102.467 s, respectively, which suggests that the S-HfSe2 monolayer has the potential to be developed as a sensitive material for NH3 detection. These adsorption mechanism studies can also serve as a theoretical foundation for the experimental design of gas-sensing materials.@en

Sensitivity and selectivity are important factors for Tl2O monolayer to be the sensitive material. In this work, the sensing performance of NO2 on pure and X-Tl2O (X = In, Cd, Y, Pb, Ga, Si) sheets has been detailed investigated by means of DFT. The results show that the doped systems have a better sensing performance for NO2 and it is most evident in the In-Tl2O substrate. And In-Tl2O has a unique response to NO2 with appropriate adsorption energy (−1.79 eV) and charge transfer (−0.51 e) which are far more than B-C3N (−1.15 eV, 0.44 e). Besides, although In-Tl2O monolayer and SO2 have formed the chemical bond, the adsorption effect of NO2 on the substrate hardly changes when the co-adsorption of SO2 and NO2 occurs on it. In addition, the reflectivity and optical absorption of the gas/In-Tl2O (gas = NO, NO2 and SO2) adsorption system are calculated, and the results indicate optical absorption and reflectivity of NO2/In-Tl2O system are all far greater than that of other systems in the visible and near infrared regions. So it is easy to be distinguished by infrared detection. These all show that the In-Tl2O is an excellent sensing material for NO2 detection.@en

As the concentration of acetone (C3H6O) in exhaled gas of diabetics is significantly higher than that of healthy people. Here, the sensing performance of X doped MoSe2 (X–MoSe2, X = Ti, Ni and Cu) for acetone is studied theoretically. It is found that Ti–MoSe2 shows absolute advantages in both adsorption energy and charge transfer. Additionally, the changes of bandgap for C3H6O/Ti–MoSe2 in the adsorption process are the largest in all adsorption systems, indicating it will produce the largest electrical signal that can be detected. Besides, the co-adsorption system (consisting of C3H6O, H2O, CO2, N2 and O2) will be more stable after O2 is removed and the adsorption site occupied by acetone restricts the contact of other disturbing gases with Ti–MoSe2. Importantly, comparing with the reported acetone sensing materials ((110) face of SnO2, (MgO)12-graphene and oxygen-plasma-treated ZnO (ZnO–O)), Ti–MoSe2 demonstrates its superiority in terms of the absolute value of charge transfer (0.37 e) and adsorption energy (2.42 eV). All these results show that Ti–MoSe2 is expected to become the reliable sensing material for acetone and has enormous potential for the application in noninvasive and rapid detection of type-1 diabetes.@en

As the concentration of acetone (C3H6O) in exhaled gas of diabetics is significantly higher than that of healthy people. Here, the sensing performance of X doped MoSe2 (X–MoSe2, X = Ti, Ni and Cu) for acetone is studied theoretically. It is found that Ti–MoSe2 shows absolute advantages in both adsorption energy and charge transfer. Additionally, the changes of bandgap for C3H6O/Ti–MoSe2 in the adsorption process are the largest in all adsorption systems, indicating it will produce the largest electrical signal that can be detected. Besides, the co-adsorption system (consisting of C3H6O, H2O, CO2, N2 and O2) will be more stable after O2 is removed and the adsorption site occupied by acetone restricts the contact of other disturbing gases with Ti–MoSe2. Importantly, comparing with the reported acetone sensing materials ((110) face of SnO2, (MgO)12-graphene and oxygen-plasma-treated ZnO (ZnO–O)), Ti–MoSe2 demonstrates its superiority in terms of the absolute value of charge transfer (0.37 e) and adsorption energy (2.42 eV). All these results show that Ti–MoSe2 is expected to become the reliable sensing material for acetone and has enormous potential for the application in noninvasive and rapid detection of type-1 diabetes.@en

Recently, the application of phosphorene structure analogues in gas sensors has been a hot research topic since the appearance of phosphorene. SnSe monolayer as one of them has been proved to be much more stable properties than phosphorene. Based on the density-functional theory, the interaction between gas molecules (CO, CO 2 , O 2 , NO, NH 3 , SO 2 and NO 2 ) and SnSe monolayer are theoretically investigated by first-principles calculation. Macroscopically, gas molecules selective adsorption of SnSe monolayer is analyzed by molecular dynamics. Compared to CO, CO 2 , O 2 , SnSe monolayer performs stronger affinity for SO 2 and NO 2 , which possesses appropriate adsorption energies (−6.000 eV and −0.759 eV) and elevated charge transfers (−0.239 e and −0.328 e). SnSe monolayer chemical adsorption of NO 2 , while physically adsorbing SO 2 , is more suitable for the adsorption mode of SO 2 sensors. Surprisingly, the adsorption amount of SO 2 is 6 times that of NO 2 . Therefore, the adsorption of SO 2 is more likely to occur compared to other gas molecules. For a mixed environment of SO 2 and NO 2 , the adsorption quantity of SO 2 is not significantly affected, while the adsorption of NO 2 is inhibited. Therefore, the SnSe monolayer could be a promising candidate as SO 2 sensors with high selectivity and sensitivity. @en

Recently, the application of phosphorene structure analogues in gas sensors has been a hot research topic since the appearance of phosphorene. SnSe monolayer as one of them has been proved to be much more stable properties than phosphorene. Based on the density-functional theory, the interaction between gas molecules (CO, CO 2 , O 2 , NO, NH 3 , SO 2 and NO 2 ) and SnSe monolayer are theoretically investigated by first-principles calculation. Macroscopically, gas molecules selective adsorption of SnSe monolayer is analyzed by molecular dynamics. Compared to CO, CO 2 , O 2 , SnSe monolayer performs stronger affinity for SO 2 and NO 2 , which possesses appropriate adsorption energies (−6.000 eV and −0.759 eV) and elevated charge transfers (−0.239 e and −0.328 e). SnSe monolayer chemical adsorption of NO 2 , while physically adsorbing SO 2 , is more suitable for the adsorption mode of SO 2 sensors. Surprisingly, the adsorption amount of SO 2 is 6 times that of NO 2 . Therefore, the adsorption of SO 2 is more likely to occur compared to other gas molecules. For a mixed environment of SO 2 and NO 2 , the adsorption quantity of SO 2 is not significantly affected, while the adsorption of NO 2 is inhibited. Therefore, the SnSe monolayer could be a promising candidate as SO 2 sensors with high selectivity and sensitivity. @en

Recently, the application of phosphorene structure analogues in gas sensors has been a hot research topic since the appearance of phosphorene. SnSe monolayer as one of them has been proved to be much more stable properties than phosphorene. Based on the density-functional theory, the interaction between gas molecules (CO, CO 2 , O 2 , NO, NH 3 , SO 2 and NO 2 ) and SnSe monolayer are theoretically investigated by first-principles calculation. Macroscopically, gas molecules selective adsorption of SnSe monolayer is analyzed by molecular dynamics. Compared to CO, CO 2 , O 2 , SnSe monolayer performs stronger affinity for SO 2 and NO 2 , which possesses appropriate adsorption energies (−6.000 eV and −0.759 eV) and elevated charge transfers (−0.239 e and −0.328 e). SnSe monolayer chemical adsorption of NO 2 , while physically adsorbing SO 2 , is more suitable for the adsorption mode of SO 2 sensors. Surprisingly, the adsorption amount of SO 2 is 6 times that of NO 2 . Therefore, the adsorption of SO 2 is more likely to occur compared to other gas molecules. For a mixed environment of SO 2 and NO 2 , the adsorption quantity of SO 2 is not significantly affected, while the adsorption of NO 2 is inhibited. Therefore, the SnSe monolayer could be a promising candidate as SO 2 sensors with high selectivity and sensitivity. @en

For the relevant properties of pristine and doped (Si, P, Se, Te, As) monolayer WS2 before and after the adsorption of CO, CO2, N2, NO, NO2 and O2, density functional theory (DFT) calculations are made. Calculation results reveal that the monolayer WS2 doped with P and As atoms can be substrate materials for NO and NO2 gas sensors. However, after the subsequent CDD and ELF calculations, it is found that P-doped monolayer WS2 adsorbs NO and NO2 in a chemical way, while As-doped monolayer WS2 adsorbs NO and NO2 in a physical way. Also, the charge transfer between As-doped monolayer WS2 and NO is relatively small and not easily detected. Besides, As-doped monolayer WS2 system exhibits greater differences in optical properties (the imaginary part of reflectivity and dielectric function) before and after the adsorption of NO2 gas than before and after adsorption of NO gas. These differences in optical properties assist sensor devices in making gas adsorption-related judgments. Through the analysis of the recovery time, DOS and PDOS, As-doped monolayer WS2 is also verified to be a promising NO2 sensing material, whose recovery time is calculated to be as short as 0.169 ms at 300 K.@en