Influence of inorganic solids on photocatalytic oxidation of 2,4-dichlorophenoxyacetic acid with UV and TiO2 fiber in aqueous solution

The negative impact of water turbidity on UV transmission and disinfection is well-known in water industries. Reduction in photocatalytic oxidation reaction rate can be expected in turbid water due to shielding (absorption, scattering and/or blocking) of incident UV, but no article on this issue is published till to date. This article aimed for the first time to elucidate UV shielding effect of inorganic solids (kaolin, bentonite and silica gel) on photocatalytic oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D) in water using TiO2 fiber by laboratory batch experiments. Of the three solids, only silica gel exhibited no significant impact on solution pH. But it increased considerably with bentonite and kaolin. As solution pH is a very sensitive parameter for photocatalytic reaction, the latter two were not suitable for the purpose. 2,4-D degradation, TOC removal and dechlorination decreased with increasing silica gel content (0–1.0 g/L). The largest UV shielding effect was observed at 0.5 g/L silica gel, but the effect weakened considerably at 1.0 g/L concentration due to entrapment of solid particles to jagged TiO2 surface and/or their settlement. More tests are required to understand whether solid particle entrapment and/or settlement associated with TiO2 fiber can be avoided by using TiO2 film.