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.