N-p heterojunction composites Bi₂₀TiO₃₂-Bi₂S₃: Fabrication and efficient photocatalytic NO removal

To efficiently remove nitrogen oxides at ppb level, a series of Bi₂₀TiO₃₂-Bi₂S₃ (BBS) composites were successfully crafted for the first time through a one-pot anion-exchange protocol and systematically characterized. It was confirmed that the in-situ grown Bi₂S₃ phase was anchored on surface of Bi₂₀TiO₃₂ and n-p heterojunction structures were established. The combination of high visible-adsorption Bi₂S₃ and formation of n-p heterojunction composites simultaneously strengthened the visible light harvesting, accelerated transfer and spatial segregation of charge carriers, and enriched the generation of oxidative species ·O₂^- and ¹O₂. Under visible irradiation, these as-synthesized BBS composites exhibited the significantly improved NO removal efficiency. In particular, the best candidate BBS-6 exhibited the highest NO removal efficiency of 35.4 % and the largest apparent rate constant (K_app) of around 0.42 min^-1, which were 2.36 and 2.64 times those of pristine Bi₂₀TiO₃₂, respectively. Besides, it possessed the lowest NO₂ selectivity of 4.83 % and delivered the highest DeNO_x index of 81.91 among all tested samples. This study provides valuable insights into the design and development of vulcanized Bi₂₀TiO₃₂ composites for effective NO removal at ppb levels under visible light irradiation.