Photocatalytic reactions of 2,4-dichlorophenoxyacetic acid using a microwave-assisted photocatalysis system

To use an advanced oxidation process system for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D), a series of experiments were performed in which the effects of microwave and UV irradiation were evaluated. The decomposition rate of 2,4-D increased with increasing microwave intensity, UV intensity, and the auxiliary oxidant dosage. Excessive addition of some oxidants (H₂O₂ and O₂), however, resulted in the reduction of the decomposition rate. The effect of addition of microwave irradiation was not significant unless the ozone addition was applied together. The decomposition rate constant obtained with microwave irradiation combined with ozone addition was considerably higher than those obtained with the combinations of UV and O₃, of UV and photocatalyst, or of microwave, UV and photocatalyst. The rate constant obtained with the combination of microwave, UV, photocatalyst, and ozone was the highest, being 4.5 times that obtained with the microwave, UV and photocatalyst combination and more than 6 times that obtained injection of ozone only. This result suggests that there is a synergy effect when the constituent techniques, i.e., microwave irradiation, UV irradiation, ozone, and photocatalysis are applied together and that the irradiation of microwave can play an important role in the O₃-assisted photocatalysis of organic pollutants in water.