Modulating the structural and band-structure properties of double-walled silicon nanotubes for possible photocatalytic applications

Silicon nanotubes (SiNTs) exhibit carbon nanotube-like structures and hold great potential for application in microelectronics and photocatalysis. However, their practical implementation is limited by structural instability and excessively narrow band gaps. In particular, their extremely narrow band gaps coupled with negligible built-in electric fields for charge separation, result in sub-picosecond carrier lifetimes. Additionally, the recombination of photogenerated charge carriers causes low quantum efficiency. Interestingly, due to their tunable electronic structures, SiNTs can induce a transition from metal to semiconductor, which suggests a potential solution to the aforementioned limitations. This study employs molecular dynamics (MD) and density functional theory (DFT) simulations to investigate the structural stability and photocatalytic performance of small-sized double-walled SiNTs (DWSiNTs), addressing the limitations of single-walled SiNTs such as structural instability and narrow band gaps. The main findings indicate that DWSiNTs possess smaller per-atom cohesive binding energies and therefore exhibit better structural stability than single-walled nanotubes, owing to the enhanced interlayer interactions. Although quantum confinement induces minimal or zero band gaps in DWSiNTs, the introduction of defects effectively opens the band gap. Narrower interlayer spacing and smaller radii yield wider band gaps and superior catalytic performance. These findings elucidate the unique structural and electronic properties of DWSiNTs, providing critical insights for their controlled synthesis and practical photocatalytic applications.