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 degrees 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.