Poly Tri-s-triazines as Visible Light Sensitizers in Titania-Based Composite Photocatalysts: Promotion of Melon Development from Urea over Acid Titanates

Abstract

Photocatalysis has become increasingly popular for applications in the energy and environmental fields. However, in its conventional form as a pristine (white) semiconductor oxide, e.g., titania (TiO2), the photocatalyst has a wide band gap and does not respond to a large fraction of the solar power available across the visible region. Recently, some success has been reported in the in situ synthesis and deposition of melon [poly (tri-s-triazine) with an empirical formulation of H3C6N9] onto TiO2 to act as a visible sensitizer. In the present contribution, we report the interesting finding that composites based on hydrogen titanate cores bearing shells of melon and the related graphitic carbon nitride (g-C3N4) as sensitizers are far superior in simulated solar (visible) light-driven photodegradation of methyl orange (MO) dye and ethanol photo-oxidation as compared to the individual components. These layered titanate nanotubes/nanobelts also offer a practical advantage by promoting the build-up of melon from urea as compared to anatase TiO2. This is believed to be linked to the higher density coverage of titanates by surface OH groups and their Brønsted acidic properties, which promote polymerization. Development of the melon structure was verified by diffuse reflectance infrared spectroscopy (DRIFTS) and solid-state nuclear magnetic resonance (13C NMR). The melon layer was found to be fully developed after thermal activation at ∼400 °C and photostable under open beam irradiation. More severe heat treatment led to melon degradation, as confirmed by TGA, and loss of visible-responsive photocatalytic activity.