An investigation of the role of pH in the rapid photocatalytic degradation of MCPA and its primary intermediate by low-power UV LED irradiation

The rapid and efficient removal of pollutants from water is of vital importance. The removal of such compounds is often achieved by adsorption techniques, however the deployment of advanced oxidation processes can present a method for complete degradation. 2-methyl-4-chlorophenoxyacetic acid (MCPA) has been shown to be present in high concentrations in waterways, especially in Northern Ireland. Reported here is the rapid removal of MCPA and its primary degradation intermediate, 4-chloro-2-methylphenol (CMP), in a novel propeller fluidised photo reactor under low-power LED UV irradiation (1.05 W). Under optimum conditions (pH=3.8) MCPA was completely degraded within 30 min and CMP within 90 min of UV exposure with a high reaction rate and photonic efficiency of 9.74 molMCPA photon-1 min-1. The mechanism of degradation and contaminant-TiO2 surface interaction are elucidated through investigation of the impact of pH on photocatalytic activity.