Photocatalytic activity of ascorbic acid-modified TiO2 sol prepared by the peroxo sol–gel method

A TiO2 neutral sol has been successfully prepared by a peroxo sol–gel method using TiCl4 as the precursor and H2O2 as the peptizing agent. However, the particle size of TiO2 is varied, with a wide range of size distribution. Moreover, the sol becomes unstable after a long period of time. Therefore, the purpose of this study was to apply the peroxo sol–gel method to prepare an ascorbic acid-modified TiO2 to ensure enhancement of sol stability, good dispersion of TiO2 nanoparticles with a narrow size distribution, and improvement of photocatalytic activity under UV light and visible light irradiation. The presence of the ascorbic acid sol caused the formation of a charge-transfer complex, resulting in a red shift for TiO2 in the visible light spectrum region through the specific Ti–O–C linkage of ascorbic acid and TiO2 which can extend the limitation to applications of TiO2. It was demonstrated that AA-modified TiO2 particles with different concentrations of ascorbic acid addition were dispersed in a relatively stable, well-dispersed colloidal suspension with a narrow size distribution, as confirmed by DLS result. The optimum observed ascorbic acid/TiO2 molar ratio of 0.75 represents the highest photocatalytic activities under both UV light and visible light irradiation. Thus, it can be seen that the addition of ascorbic acid as a surface modifier improves the photocatalytic activity, prevents particle agglomeration, and provides a very stable TiO2 colloidal system with individual dispersion of titania particles.