Synthesis of a TiO₂ Photocatalyst for Dehydrogenative Cross-Coupling of (Hetero)Arenes

Abstract—

Nanostructured titanium dioxide (TiO₂) with a particle size from 7 to 50 nm, photocatalytically active for organic reactions under illumination with visible light, has been prepared by sol–gel synthesis at different pH values of the starting solution. X-ray diffraction data demonstrate the formation of a crystalline anatase phase in an acid medium and an amorphous phase in an alkaline medium. Annealing at a temperature of 350°C for 4 h has led to a phase transition from the amorphous structure to anatase in all of the samples. The particle size has been shown to increase from 7 to 50 nm as the solution pH rises from 3 to 9. Further increasing the pH value to 10 reduces the particle size to 23 nm. Diffuse reflection spectra indicate that the band gap of the samples ranges from 2.9 to 3.4 eV and that annealing reduces it to 2.8–3.2 eV. According to comparative testing results, the efficiency of the synthesized TiO₂ as a catalyst for oxidative ${\text{S}}_{{\text{N}}}^{{\text{H}}}$ cross-coupling of acridine with indole is comparable to that of the commercially available catalysts Degussa P25 and Hombifine N, as evidenced by product yields above 50%.