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

Abstract

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 PC-SiCNT and PSi-SiCNT. It is found that SO2 can be chemisorbed on the surfaces of SiCNT, PC-SiCNT and PSi-SiCNT with monodentate and cycloaddition configurations. For the encapsulations, SO2 can be formed chemisorption inside PC-SiCNT, and physisorption inside SiCNT and PSi-SiCNT. For the adsorption of SO2 on the surface or inside of PC-SiCNT, the configurations of M1–SO2–PC-SiCNT and SO2–PC-SiCNT are converted from metal for PC-SiCNT to semiconductor. For the adsorptions of SO2 on the surfaces of PSi-SiCNT, M1–SO2–PSi-SiCNT, M2–SO2–PSi-SiCNT and C1–SO2–PSi-SiCNT are converted from metal for PSi-SiCNT to semiconductors with the significant decrease of conductivity, while after encapsulation of SO2 inside PSi-SiCNT, SO2–PSi-SiCNT still maintains metallicity. In addition, PC-SiCNT and PSi-SiCNT have superior sensing performance to SO2 compared with SiCNT. And SO2 can be desorbed from SiCNT, PC-SiCNT and PSi-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–N2 and SO2–CO2–N2 on PC-SiCNT and PSi-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 PSi-SiCNT. In summary, PSi-SiCNT may have potential application as SO2 gas sensor.