Metal-Free Conjugated Polyphenothiazine Nanostructures as Visible Light Active Photocatalyst for Selective Aerobic Oxidation of Sulfides

Phenothiazine (PTZ) and its derivatives have been widely explored for photocatalytic molecular oxygen activation in various chemical transformations due to their high reduction potential. However, their photocatalytic activity is restricted to UV light irradiation because of a wide band gap (~3.56 eV). In this work, we report a single-step polymerization of PTZ to synthesize nanostructured polyphenothiazene (PPTZ). The resulting PPTZ exhibits a significantly reduced band gap (~2 eV), enabling efficient visible-light absorption. Furthermore, polymerization using different oxidizing agents modulates the morphology of PPTZ nanoparticles, leading to distinct photocatalytic performances. As a metal-free photocatalyst, PPTZ nanoparticles demonstrate excellent activity toward the selective aerobic oxidation of sulfides (SAOS) under visible-light irradiation. High sulfide conversions of up to 99% with selectivity exceeding 99% were achieved. Moreover, the photocatalyst is recyclable for at least three consecutive cycles without any significant loss in performance, highlighting PPTZ-based nanomaterials as promising visible-light-active photocatalysts for SAOS reactions.