The adsorption of CO, CO ₂ , CH ₄ , H ₂ , N ₂ and N ₂ O on armchair (5,5) boron nitride nanotube (BNNT) with and without the doping of transition metals (TM), i.e. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu or Zn, was investigated using the density functional theory calculation. The results indicate all the considered gases are physically adsorbed by weak interaction on the pure BNNT, revealing that pure BNNT has poor sensing performance for these gases. TM are then doped in the B or N vacancy of BNNT to improve the sensitivity and selectivity. As a result, it was found that the gas adsorption performance of BNNT is obviously enhanced due to the introduction of TM dopant atom. In particularly, according to the results of adsorption energy, Cu doped BNNT (Cu-BNNT) system shows a high selectivity toward CO molecule compared with other metal doped systems. This is further confirmed by the density of state, energy gap and charge transfer analyses. Furthermore, based on the sensor performance analysis, it was found that Cu-BNNT also has favorable desorption characteristics for CO. Therefore, this study concluded that Cu-BNNT can be used as a superior sensor material with high sensitivity, selectivity and favorable recycle time for CO gas.

In this research, the potential application of borophene as gas sensor device is explored. The first-principles theory is employed to investigate the sensing performance of pristine and Li-doped borophene for SO ₂ and five main atmospheric gases (including CH ₄ , CO ₂ , N ₂ , CO and H ₂ ). All gases are found to be adsorbed weakly on pristine borophene, which shows weak physical interaction between the pristine borophene and gases. The gas adsorption performance of borophene is improved by the doping of Li atom. The results of adsorption energy suggest that Li-borophene exhibits high selectivity to SO ₂ molecule. Moreover, analyses of the charge transfer, density of states and work function also confirm the introduction of Li adatom on borophene significantly enhances the selectivity and sensitivity to SO ₂ . In addition, desorption time of gas from pristine and Li doped borophene indicates the Li-borophene has good desorption characteristics for SO ₂ molecule at high temperatures. This research would be helpful for understanding the influence of Li doping on borophene and presents the potential application of Li-borophene as a SO ₂ gas sensor or scavenger.