Abstract: A nitrogen-modified TiO₂ (N-TiO₂) catalyst with different nitrogen content was prepared by a modified sol-gel method, using tetrabutyl titanate as the precursor and urea as the nitrogen source. The catalyst samples were used in the photocatalytic reduction of Cr(Ⅵ) under visible light, using formic acid as a hole scavenger to enhance the photocatalytic reduction reaction. The results demonstrated that the N-TiO₂ catalyst had higher photocatalytic activity than bare TiO₂, and the N-TiO₂ sample with 10% (molar ratio) nitrogen calcined at 400 ^oC held the highest photocatalytic efficiency. The N-TiO₂ samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and ultraviolet visible diffuse reflectance spectroscopy. The results showed that the higher photocatalytic activity of the N-TiO₂ sample calcined at 400 ^oC was mostly attributed to the melon condensation products, which acted as visible-light sensitizers.

Key words: nitrogen-modification, urea, titania, sol-gel method, melon, potassium dichromate