Synthesis of sulfur-doped Bi ₅ O ₇ Br nanotubes for efficient photocatalytic degradation of tetracycline hydrochloride

Bismuth-rich Bi₅O₇Br nanotubes demonstrate high efficiency in photocatalytic degradation of organic pollutants due to their reduced diffusion distance from bulk to surface, broadened photo absorption range and abundant active sites associated with surface oxygen vacancies (OVs). However, the inherent OVs in hydrothermally synthesized Bi₅O₇Br nanotubes also act as recombination centers for electron-hole pairs, thereby limiting the ultimate photocatalytic property. In this work, sulfur (S) atoms are intentionally doped in Bi₅O₇Br nanotubes to effectively reduce the detrimental effect of OVs. The experimental results and density functional theory calculation confirm that S atoms fill in partial OVs in Bi₅O₇Br nanotubes, resulting in a narrower band gap and inhibited bulk recombination of photo-generated electron-hole pairs. Consequently, the S-doped Bi₅O₇Br nanotubes (Bi₅O₇Br-S) demonstrate superior performance in the photocatalytic degradation of tetracycline hydrochloride (TC) compared to pristine Bi₅O₇Br nanotubes. The electron paramagnetic resonance analysis and free radical capture experiments further reveal that the photo-generated holes are the primary active species for the TC degradation by Bi₅O₇Br-S. This work demonstrates a novel strategy to enhance the photocatalytic activity of Bi₅O₇Br.