A study on the adsorptions of SO2 on pristine and phosphorus-doped silicon carbide nanotubes as potential gas sensors

In this work, the adsorptions of one of important gas pollutant, i.e., SO2 on pristine silicon carbon nanotube (SiCNT) and phosphorus-doped SiCNT (P-SiCNT) are investigated theoretically, including the adsorption configurations, energetics, electronic structures, the sensitivity and the recovery time of desorption based on density functional theory (DFT). 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 SO2 can be chemisorbed on the surfaces of SiCNT, P-c-SiCNT and P-s(i); -SiCNT with monodentate and cycloaddition configurations. For the encapsulations, SO2 can be formed chemisorption inside P-c-SiCNT, and physisorption inside SiCNT and P-si; -SiCNT. For the adsorption of SO2 on the surface or inside of P-c-SiCNT, the configurations of M1-SO2-P-c-SiCNT and SO2-P-c-SiCNT are converted from metal for P-c-SiCNT to semiconductor. For the adsorptions of SO2 on the surfaces of P-s(i); -SiCNT, M1-SO2-P-si; SiCNT, M2-SO2-P-si; -SiCNT and C1-SO2-P-si; -SiCNT are converted from metal for P-s(i); -SiCNT to semiconductors with the significant decrease of conductivity, while after encapsulation of SO2 inside P-si; -SiCNT, SO2-P-si; -SiCNT still maintains metallicity. In addition, P-c-SiCNT and P-s(i); -SiCNT have superior sensing performance to SO2 compared with SiCNT. And SO2 can be desorbed from SiCNT, P-c-SiCNT and P-si; --SiCNT under 673 K with the recovery time of 9.63, 33.6 and 16.4 s, respectively. Furthermore, the selectivity and of SO2 based on GCMC in the mixtures of SO2-CO2, SO2-N-2 and SO2-CO2-N-2 on P-c-SiCNT and P-si-SiCNT are much larger and better than that on SiCNT. Based on MD simulation, we found that SO2 has the ideal diffusion ability on SiCNT and P-si-SiCNT. In summary, P-si;-SiCNT may have potential application as SO2 gas sensor.