Sol-Gel hydrothermal synthesis and visible light photocatalytic degradation performance of Fe/N codoped TiO₂ catalysts

Using Ti(OC₄H₉)₄ as a precursor, Fe(NO₃)₃.9H₂O as the source of iron, and NH4NO₃ as the source of nitrogen, an Fe/N codoped TiO₂ catalyst was prepared using a sol-gel hydrothermal method. The as-prepared powders were characterized using X-ray powder diffraction, electron spectroscopy for chemical analysis, Fourier-transform infrared spectroscopy, and ultraviolet-visible spectrophotometry. Fe and N codoping resulted in decreased crystallite size and increased specific surface area. Results of the photocatalytic degradation of acid orange 7 (AO7) in a continuous-flow fluidized-bed reactor indicated that the maximum decolorization (more than 90%) of AO7 occurred with the Fe/N-TiO₂ catalyst (dosage of 20 g/L) when a combination of visible light irradiation for 10 h HRT (hydraulic retention time), and a heterogeneous system was used. The AO7 degradation efficiency was considerably improved by increasing the hydraulic retention time from 2.5 to 10 h or by reducing the initial AO7 concentration from 300 to 100 mg/L. The reaction rate increased with the light intensity and the maximum value occurred at 35 mW/cm²; moreover, the efficiency of the AO7 degradation increased when the pH decreased with maximum efficiency at pH 3.