表面基团对Ti_(3)C_(2)T_(x)吸附NO性能影响的第一性原理研究

First-principle Study on the Effect of Surface Groups on the Adsorption of NO by Ti_(3)C_(2)T_(x)

本工作基于密度泛函理论的第一性原理方法,构建了Ti_(3)C_(2)O_(2)、Ti_(3)C_(2)O1.5(OH)0.5、Ti_(3)C_(2)O(OH)、Ti_(3)C_(2)O1.5F0.5和Ti_(3)C_(2)OF五种模型,从几何结构、电荷转移以及电子性质等方面研究了基团种类和比例对Ti_(3)C_(2)T_(x)吸附NO的影响。结果表明:相较于Ti_(3)C_(2)O_(2),含低比例-OH和-F基团的Ti_(3)C_(2)T_(x)对NO的吸附能更大,电荷转移更弱,不利于其探测NO,与实验结果一致;但随着-OH和-F比例的提高,吸附能分别减小和增大,电荷转移分别增强和减弱,表明高比例的-OH有利于Ti_(3)C_(2)T_(x)探测NO,而高比例的-F是不利的;同时,在吸附NO后,Ti_(3)C_(2)O_(2)在费米能级附近的能带极值曲率变小,电子有效质量增大,表明-O基团有利于Ti_(3)C_(2)T_(x)探测NO。在几何弛豫过程中NO分子总是以N原子靠近衬底,吸附距离均较小,而且最近邻原子的电子轨道出现杂化,电子的聚集和消散位于两端,表明最近邻原子间成键较弱且偏离子性。此计算结果可以为Ti_(3)C_(2)T_(x)探测和屏蔽NO提供理论指导,同时为Ti_(3)C_(2)T_(x)的表面改性提供思路。

In this work,based on the first-principles method of density functional theory,five models of Ti_(3)C_(2)O_(2),Ti_(3)C_(2)O 1.5(OH)0.5,Ti_(3)C_(2)O(OH),Ti_(3)C_(2)O 1.5 F 0.5 and Ti_(3)C_(2)OF were constructed.The effect of different groups on the adsorption of NO on Ti_(3)C_(2)T_(x) were studied from the geometric structure,charge transfer and electronic properties.The results show that:compared with the-O group,Ti_(3)C_(2)T_(x) with low proportion of-OH and-F groups have higher adsorption energy and weaker charge transfer for NO,which is not conducive to the detection of NO and consis-tent with the experimental results.However,with the increase of the-OH and-F proportion,the adsorption energy decreases and increases respectively,the charge transfer is enhanced and weakened respectively.This indicates that-OH groups of high proportion are favorable for Ti_(3)C_(2)T_(x) to detect NO,while a high proportion of-F is unfavorable.At the same time,the curvature of Ti_(3)C_(2)O_(2) becomes smaller at the extreme value of the band near the Fermi level,and the effective mass of the electron increases after NO adsorption.The result indicates that the-O group is beneficial for Ti_(3)C_(2)T_(x) to sense NO.In the process of geometric relaxation,NO molecule always uses N atom close to the substrate,and the adsorption distance is small.Moreover,the electron orbital of the nearest neighbor atom is hybridized,and the electron accumulation and dissipation are located at its two ends.The result indicates the bonds between the adsorbed nearest neighbor atoms are weak,and biased towards ions.The calculation results can provide theoretical guidance for Ti_(3)C_(2)T_(x) detection or shielding to NO,and also provide ideas for the surface modification of Ti_(3)C_(2)T_(x).