The SiP nanotubes as potential metal-free photocatalyst: a density functional theory study.

Hydrogen generation via photocatalytic water splitting holds significant potential as a strategy to tackle energy crises and environmental degradation. We investigated the electronic and photocatalytic properties of silicon phosphide (SiP) single-walled nanotubes as potential photocatalysts employing HSE06 hybrid density functional along with all-electron Gaussian basis sets. Relative to the monolayer, the band gap of nanotube is reduced (e.g. 1.99 eV for (55, 0)), and the nature of electron transfer in nanotube changes to direct which can extend the visible light absorption range. Moreover, the hydrogen production rate for SiP (55, 0) nanotube increases from 9.97% to 12.41%. Calculations of the band edge positions under various pH conditions indicate that nanotubes exhibit strong reduction capabilities. Within the pH value between 0 and 7 nanotubes with a radius exceeding 40 Å can split water into H₂and O₂simultaneously under sunlight irradiation. Applying tensile and compressible strain can effectively enhance the oxidation ability for overall water splitting due to downward valance band edge. Furthermore, the difference in mobility between the (50, 0) nanotube electrons (140.68 cm²v^-1s^-1) and hole (4.26 cm²v^-1s^-1) suggests that electron-hole recombination can be mitigated. Based on the above findings, we hypothesize that SiP nanotubes should be a potential metal-free photocatalyst.