Diazotization of Nano-Titanium Dioxide; A Novel Approach to obtain Colored Metal Oxides

Abstract

BACKGROUND

Dye sensitization is a promising approach to modify semiconductor photocatalysts. However, the use of synthetic dyes is neither cost-effective nor rational.

RESULTS

This research is the first report on the synthesis of colored nano-titanium dioxides as dye-sensitized photocatalysts via a convenient azo coupling reaction directly on the surface of n-TiO₂-P25. According to their reduced band gap (2.6, 2.5, and 2.35 eV for dye-sensitized n-TiO₂-P25 compared to 3.2 eV for bare n-TiO₂-P25), dye-sensitized TiO₂-P25 nanoparticles showed the absorption edge in the visible region, which expands their application compared to ultraviolet absorption in bare titanium dioxide. Various characterization techniques confirmed the structure and enhanced properties of the as-prepared nanoparticles, which were utilized as photocatalysts for the selective oxidation of benzyl alcohol to benzaldehyde in the presence of nitrate as an oxidant. These reactions were carried out under different wavelengths of visible light (blue LED, λ > 420 nm; green LED, λ > 510 nm; and red LED λ > 620 nm), yielded promising results, with reaction times of 19 h and significantly improved yields ranging from 80% to 20%, in comparison with the bare n-TiO₂-P25. Furthermore, these photocatalysts are properly recyclable and reusable, addressing limitations of dye sensitization methods.

CONCLUSION

This study introduces an effective and straightforward approach for engineering visible light responsive TiO₂ nano-particles via azo coupling reaction. The covalent linkage of dyes not only improves light absorption and photocatalytic efficiency, but also overcomes the drawbacks associated with physical dye absorption, offering outstanding potential for advanced applications and future studies. © 2025 Society of Chemical Industry (SCI).