Nano N-TiO2 mediated selective photocatalytic synthesis of quinaldines from nitrobenzenes

Abstract

N-Doped TiO₂ using a new nitrogen precursor hydrazine hydrate was synthesized by a simple wet method. This photocatalyst was characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, high resolution transmission electron microscopy (HR-TEM), UV-Vis diffused reflectance spectra (DRS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). N-Doping does not change the phase of TiO₂. It is found that the size of N-TiO₂ is 15.6 nm with 134.72 m² g⁻¹ surface area. XPS analysis reveals the presence of anionic nitrogen in TiO₂ as O–Ti–N. Substitution of N in place of oxygen in the TiO₂ lattice causes a decrease in oxygen vacancies which inhibits the recombination of electron–hole pairs. This catalyst was used for the selective one-pot synthesis of quinaldines from nitrobenzenes in ethanol under UV and visible light. N-TiO₂ on irradiation induces a combined redox reaction with nitrobenzene and alcohol and this is followed by condensation-cyclization of aniline with oxidation products to give quinaldines. N-Doped TiO₂ is found to be more efficient than metal doped TiO₂ in quinaldine synthesis under visible light. Higher activity of the N-TiO₂ could be attributed to its stronger absorbance of visible light.