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_Si-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_Si-SiCNT, M1–SO₂–P_Si-SiCNT, M2–SO₂–P_Si-SiCNT and C1–SO₂–P_Si-SiCNT are converted from metal for P_Si-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_Si-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–N₂ and SO₂–CO₂–N₂ 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.