Amorphous sol-gel titania modified with heteropolyacids

Samples of amorphous sol-gel titania were prepared at 50%wt with tungstophosphoric or molybdophosphoric acid. The resulting gels were dried and annealed at 100, 150 and 200°C and studied by FT-IR, UV-Vis, EPR, TGA and Raman spectroscopy. By FT-IR the evolution of the stretching vibration of the OH groups (3450–3700 cm⁻¹) was followed. The intensity of this band decreased as the annealing temperature increased. With UV-Vis spectroscopy the band gap was determined for each sample, and the Eg was found between 2.72 and 3.38 eV. Raman spectroscopy revealed the formation of Mo—O—Ti and W—O—Ti—O bonds. An intense EPR signal at g = 1.998 was observed during annealing of the samples. Amorphous solids with a significant number of vacancies and promising photocatalytic properties were obtained.