Metal-free Conjugated Polyphenothiazine Nanostructures as Visible Light Active Photocatalysts for the Removal of Organic Pollutants and Selective Aerobic Oxidation of Sulfides

Phenothiazine (PTZ) and its derivatives have traditionally been used for photocatalytic molecular oxygen activation in a variety of chemical transformation processes. Despite having a high reduction potential, phenothiazine is transparent under visible light and thus has limited photocatalytic activity at low energies of incidence. We have synthesized highly conjugated polyphenothiazine (PPTZ) nanomaterials via Chemical oxidative polymerization (COP) of PTZ in a one-pot reaction. Polymerization with metal-free oxidizing agents converted PTZ from being a UV-active material to visible light active via π-conjugation extension. Thus, PPTZ was found to be a highly active metal-free photocatalyst for the selective aerobic oxidation of alkyl arylthiosulfide to the corresponding sulfoxide under visible light. This is the first example of metal-free, conjugated PPTZ nanoparticles as a visible light-active photocatalyst for the activation of triplet molecular oxygen. The reduction potential of PPTZ was found to be suitable for the activation of triplet oxygen to produce a moderately reactive superoxide radical anion (O2⋅−) for selective oxidation reactions. PPTZ also exhibited highly active photocatalytic decomposition of organic pollutants under aerobic conditions.