Titanate nanotube confined merger of organic photocatalysis and TEMPO catalysis for highly selective aerobic oxidation of sulfides

Abstract

1D titanate (H₂Ti₃O₇) nanotubes were prepared by a hydrothermal treatment of TiO₂ under 10 M NaOH and ensuing acid exchange process. Here, it is discovered that H₂Ti₃O₇ nanotubes can facilitate the merger of organic photocatalysis and TEMPO catalysis. Confined within H₂Ti₃O₇ nanotubes, the organic photocatalyst erythrosin B (ErB) could drive the highly selective aerobic oxidation of sulfides under irradiation of green light-emitting diodes (LEDs), when 0.5 mol% of TEMPO was added as a co-catalyst. The turnover number (TON) for photocatalytic selective aerobic oxidation of thioanisole in terms of ErB is 2450, which is hitherto the best reported TON. Apart from confining the successful merger of ErB photocatalysis and TEMPO catalysis, H₂Ti₃O₇ nanotubes not only activate O₂ to generate superoxide anion radical (O₂˙⁻), but also ensure high selectivity of sulfoxides with their abundant surface hydroxyl groups. This work represents a crucial step forward in selective oxidation reactions by materials design of dye-semiconductor assembly photocatalysts.