Theoretical study of NO2 adsorption on SiCNT and P-doped SiCNT

The release of NO2 into atmosphere, mainly coming from the combustion of fuel, has brought serious pollution on the environment. In order to detect and remove it, the adsorptions of NO2 on pristine silicon carbon nanotube (SiCNT) and phosphorus-doped silicon carbon nanotube (P-SiCNT) were investigated theoretically based on density functional theory (DFT) and grand-canonical Monte Carlo (GCMC) method, including the geometrical structures, adsorption energies, electronic structures, sensitivities, recovery time and the selectivity for the adsorption of NO2 in high humidity environment. To dope the SiCNT, a carbon or silicon atom was replaced with a phosphorus atom to build P-C-SiCNT and P-Si-SiCNT. It is found that when NO2 is adsorbed on the surface or inside SiCNT, P-C-SiCNT and P-Si-SiCNT, respectively, the largest adsorption energies are -34.53 kcal/mol for M1-NO2-SiCNT, -64.41 kcal/mol for -NO2-P-C-SiCNT, -57.04 kcal/mol for M1-NO2-P-Si-SiCNT, respectively, which are all belong to chemical adsorption. For the adsorption NO2 on SiCNT to form M1-NO2-SiCNT and NO2 SiCNT, the adsorption systems keep p-type semiconductor properties with a slight decrease of band gap. While for the adsorption NO2 on P-C-SiCNT and P-Si-SiCNT to form M1-NO2-P-C-SiCNT, NO2-P-C-SiCNT, -NO2-P-Si-SiCNT and NO2-P-Si-SiCNT, the adsorption systems are converted to p-type semiconductor from metal. Furthermore, the sensitivities were also calculated based on the band gap, and it is found that P-C-SiCNT and P-Si-SiCNT have superior sensing performance in detecting NO2. Therefore, P-SiCNTs may have potential application not only adsorbent but also gas sensors of NO2. For the adsorption configurations with the largest adsorption energies, the suitable desorption temperatures within 1 min are 553 K for M1-NO2-SiCNT, 1023 K for M1-NO2-P-C-SiCNT and 913 K for M1-NO2-P-Si-SiCNT, respectively, which makes the recycle of SiCNT, P-C-SiCNT and P-Si-SiCNT possible. Meanwhile, the effect of the humidity was also explored, and it is found that the humidity has slight effect on the adsorption of NO2 for above nanotubes.