A novel use of TiO2 fiber for photocatalytic ozonation of 2,4-dichlorophenoxyacetic acid in aqueous solution

More efficient oxidation methods are needed to degrade especially newly emerging recalcitrant organic contaminants at low concentrations in the water environment. Reduced photonic efficiency of immobilized TiO2 is a major challenge in TiO2-assisted advanced oxidation processes (AOP). Mineralization of 2,4-dichllorophenoxyacetic acid (2,4-D) in low aqueous solution by O3/UV/TiO2 using the world's first high-strength TiO2 fiber was investigated and compared with O3, UV/TiO2, and O3/TiO2 in laboratory batch experiments. The 2,4-D degradation and total organic carbon (TOC) removal followed pseudo first-order reaction kinetic, while their rates in O3/UV/TiO2 were respectively about 1.5 and 2.4 times larger than the summation of the values in O3 and UV/TiO2. The O3/UV/TiO2 was characterized by few aromatics with very low abundance, fast disappearance of aliphatics and more than 95% dechlorination. The discrepancies in organic carbon mass balance among the intermediates and 2,4-D were attributed mainly to few apparently major unidentified intermediates. The significantly enhanced 2,4-D mineralization in O3/UV/TiO2 was attributed to increased ozone dissolution followed by its decomposition, and reduced electron-hole recombination in presence of dissolved ozone resulting in a large number of hydroxyl radical (·OH) generation from more than one parallel path. The removal efficiencies of the systems can further be enhanced by optimizing design parameters, and O3/UV/TiO2 with the TiO2 fiber is promising to mineralize recalcitrant organic contaminants in water at low concentrations.