As we all know, C6H6 and HCO are two indoor harmful gases that seriously threaten human health, and are classified as carcinogens and teratogens by the World Health Organization. Long-term inhalation of low concentrations of C6H6 may lead to chronic C6H6 poisoning, which can manifest as bleeding tendency, blood pressure drop, coma, convulsions, respiratory and circulatory failure, and even DNA changes.
In light of this,Gui Yingang et al., Southwest UniversityBased on first-principles calculations, Ag2O- and Cuo-modified MoSe2 nanosheets were selected as gas-sensitive materials to study their adsorption and sensitivity to C6H6 and HCOs.
Models and calculation methods
Figure 1C6H6, HCHO and MOSE2 structural models
In order to obtain the adsorption characteristics of the TMO MOSE2 sensor for C6H6 and HCO2, the established C6H6 molecule, HCho molecule and MOSE2 structure models are shown in Figure 1. For mose2, a supercellular structure of 5 5 is adopted, and a vacuum layer of 25 is set up for shielding periodic action.
And the optimization of the structure is based on:DMOL3 module in Materials Studio, the PBE functional under the Generalized Gradient Approximation (GGA) is used, and the computational basis set of DNP is also adopted. The Brillouin zone was sampled using a 5 5 1 k-point grid, and the convergence criteria for the corresponding energy, force field, and displacement were set to 1 10-5 ha, 2 10-3ha, and 5 10-3, respectively.
Results & Discussion
Figure 2Optimized TMO-MOSE2 structure
As can be seen in Figure 2, in the TMO-MOSE2 structure, the Cu and Ag atoms are relatively close to the MoSe2 substrate, while the O atoms are far away from the MoSe2 substrate. The corresponding adsorption energies of Ag2O and CuO on MoSe2 are 7., respectively489 and 6301 ev。
And according to the mulliken theory analysis, the metal atom acts as an acceptor for electrons in metal oxides, and the matrix is the donor of electrons. This results in electron transfer, which achieves an adequate distribution of charge, which changes its conductivity.
Figure 3Tmo-MOSE2 band structure and density of states
As can be seen from Figure 3, impurity energy levels are introduced into the conduction and valence bands after the Ag2O and Cuo modifications, thereby increasing the probability of electrons reaching the conduction bands and increasing their conductivity. As shown in Figure 3a-c, the bandgaps of the original MoSe2, Cuo-MoSe2, and Ag2O-MoSe2 are 1., respectively657，0.194 and 0963 ev。Through the analysis of the DOS in Figure 3D-G, the modification causes the Fermi level to shift to the left, resulting in the enhancement of the conductivity of the system. And from PDOS, it can be found that there is a strong hybridization between the 4D of Ag, the 4D of Cu and the 4P orbital of Se, which is conducive to maintaining the chemical stability of the modified structure.
Figure 4The most stable adsorption structure of gas molecules on TMO-MOSE2Table 1Adsorption parameters of gas molecules on TMO-MOSE2
Figure 4a shows the adsorption structure of HCOs on Ag2O-Mose2, and the gas molecules do not change significantly after adsorption. For the variation parameters of the other three adsorption configurations (distance between the gas molecule and the substrate, adsorption energy and charge distribution) as shown in Table 1, it can be found that the shorter the distance between the gas molecule and the substrate, the more the electron cloud overlaps, the stronger the interaction, and the more negative the adsorption energy.
Figure 5The band structure of a gas molecule after adsorption
After adsorption of gas molecules, a decrease in the band gap means that the conductivity of the whole system increases to some extent and the conductivity becomes better. Through the comparison of the band changes before and after (Fig. 3 and Fig. 5), it is found that the changes of the bands and conductivity of the four adsorption configurations follow the following rules, namely, Ag2O-Mose2 Hcho > Ag2O-Mose2 C6H6 > Cuo-Mose2 Hcho > Cuo-Mose2 C6H6.
Figure 6DoS after adsorption of gas molecules
After HCO adsorption (Figure 6A), the 4D peak of Ag and the 2P peak of O are at -125 EV and -3There is overlap around 50 EV because there is a significant change in the electron orbit near this energy, which causes a change in the TDoS curve. The same is true for Figure 6b. For C6H6 adsorption, the TDOS near the Fermi level decreases slightly, which means that the conductivity of the structure is also slightly reduced, as is the case in Figure 6d.
Fig7.Changes in homo and lumo before and after adsorption of gas molecules
As shown in Figure 7a, due to the strong chemical properties of the Ag atoms, Homo and Lumo are mainly distributed around the Ag atoms before adsorption, and the Eg values gradually increase after the adsorption of gas molecules. For Ag2O-Mose2, conductivity changes Hcho > C6H6. The same is true for cuo-mose2. In summary, it can be attributed to the following rules, namely, ag2o-mose2 hcho > ag2o-mose2 c6h6 > cuo-mose2 hcho > cuo-mose2 c6h6.
Conclusions and prospects
The results show that Ag2O and CuO exhibit stable modified structures on MOSE2 nanosheets, which improves the gas adsorption activity on MOSE2 surface. Based on density functional theory, the adsorption structure, adsorption energy, charge transfer, energy band and density of states were analyzed. The gas molecules formed a stable configuration on the surface of the Ag2O Mose2 nanosheet by chemical adsorption, and formed a stable configuration on the Cuo Mose2 nanosheet by physical adsorption. The adsorption capacities of the Ag2O and Cuo-modified MOSE2 nanosheets were HCO>C6H6, and the adsorption of both gases was an exothermic spontaneous process. In contrast, gas adsorption on Ag2O MoSe2 nanosheets is more stable than Cuo MoSe2 nanosheets.
Bibliographic information
gui yingang et.al first-principles study of the gas sensing of benzene and formaldehyde by ag2o- and cuo-modified mose2 nanosheets acs applied nano material 2022, 5, 9, 12907–12914