Characterization and photocatalytic activity of TiO2 by sol–gel in acid and basic environments

The sol–gel synthesis of water-based sols of nanocrystalline TiO2 in a large pH range (1.3–10.6) was carried out by acid hydrolysis of titanium(IV) isopropoxide with acetic acid or malonic acid acting also as complexing agents. Subsequent peptization was achieved in acid medium, in the case of acetic acid, and in basic medium (through triethylamine), in the case of malonic acid. The TiO2 particles were characterized using X-ray diffraction, Raman, high-resolution transmission electron microscopy and dynamic light scattering–electrophoretic light scattering. Methyl orange (MeO) and methylene blue (MB) were used as model contaminants to investigate the degradation activity of the different sols under UV irradiation. MB molecules adsorbed on the TiO2 surface of the basic sol were found as trimeric species. The basic TiO2 sol was effective for the degradation of both dyes, whereas the acid sols gave satisfactory results only for MeO.