Novel H2S multifunctional sensing materials: Cu or Ag-decorated (4,4)SWSiC nanotubes

Abstract

Density functional theory employing Grimme's D3 method was used to study the H₂S sensing ability of pristine, as well as Cu or Ag decorated, (4,4)SWSiC nanotubes (NTs). The adsorption energy, most stable geometry and electronic (spin-distinct) structures of the compounds were calculated. The results show that the H₂S adsorption process is exothermic, with energies of −0.391 eV (physical), −0.965 eV (chemical) and −0.618 eV (chemical) for pristine, Cu or Ag-decorated (4,4)SWSiCNTs, respectively. The range of adsorption energies points to the possible use of Cu-decorated (4,4)SWSiCNTs as an effective thermopower-based H₂S sensing material. From a study on electronic structures, moreover, it was concluded that the adsorption of H₂S leads to a considerable change in the corresponding energy band gaps and the carrier effective masses. The compounds under study were then treated as suitable candidates for incorporation into resistance-based schemes. Among the three compounds, the adsorption of H₂S onto a Cu-decorated (4,4)SWSiCNT showed largest change (16.09%) in the true band gap and a change of 57.49% (33.36%) in the effective spin-up (spin-down) electron mass, meaning that this compound may be used with more efficiency in such schemes. Furthermore, the spin-distinct band structures of the compounds, influenced by the presence of H₂S, indicate that the decorated (in contrast to the pristine) (4,4)SWSiCNTs remain magnetically bipolar. It then naturally follows that external potentials (gate potentials), needed to generate spin-polarized current, undergo an observable change when H₂S is adsorbed onto the decorated (4,4)SWSiCNTs. Therefore, the decorated (4,4)SWSiCNTs can be employed in spin-current-based sensing devices. Last but not least, a complete discussion of the magnetization and the nature of the current carriers (electrons or holes), reveals that some of the compounds under investigation can potentially be used in more advanced and accurate schemes, such as magneto-based or Seebeck-effect-based H₂S detection. The recovery time for the detection of H₂S by any of the three compounds and the suggestions to make it shorter are also fully discussed. For completion, the physical reasons behind the electronic behavior in the compounds are given in detail. The materials presented in this article, therefore, provide new insights into the quest for designing high-performance H₂S sensing devices.