Dye-sensitized TiO₂ for enhanced photocatalytic synthesis of hexahydroquinazolinones

Pomegranate-dye-sensitized TiO₂ (POM - TiO₂) is claimed to be a heterogeneous photocatalyst in the multicomponent condensation of hexahydroquinazoline derivatives. As a consequence of a significant increase in the photoresponse of TiO₂ to the visible spectrum, dye significantly shortens the optical band gap of TiO₂ to 2.40 eV, which is compared to 3.20 eV with pristine TiO₂. An outstanding yield (89–97%) of a series of hexahydroquinazolinone derivatives was obtained in 40 min at room temperature under optimized reaction conditions (2 mg/mL catalyst loading, 100 mW cm⁻² visible light irradiation). Photocatalytic reaction systems were observed to be in a pristine and thermocatalytic environment, which promoted a faster reaction rate as well as a higher conversion. Therefore, it was established that POM-TiO₂ was stable and reusable with high activity until four consecutive reactions cycle with slight activity loss. In addition, a detailed catalytic characterization (FT-IR, XRD, XPS, UV–Vis, BET and SEM) is effectively established dye-anchoring and structural integrity of the photocatalyts. This paper demonstrates the possible application of pomegranate in the work of TiO₂ as a sensitizer of natural dye in the visible light to be used in the heterocyclic synthesis in a cost-effective and environmentally friendly protocol.