LED-Based Photocatalytic Treatment of Pesticides and Chlorophenols

In this paper, light-emitting diodes (LEDs), a novel light source, is reported for the photocatalytic degradation of four known pesticides [2,4-dichlorophenoxyacetic acid (2,4-D), 2-methyl-4-chlorophenoxyacetic acid (MCPA), 4-chlorophenol (4-CP), and 2,4-dichlorophenol (2,4-DCP)] in aqueous solution. 2,4-Dichlorophenoxyacetic acid was further chosen to evaluate the impact of photocatalyst loading and light intensity on the degradation rate. The degradation of 2,4-D under LED irradiation (365 nm) was compared with that using mercury discharge lamp irradiation (350 nm). Irradiation of the different pesticides with a 365-nm LED light source led to their complete mineralization upon prolonged exposure. The degradation rate was slower when mixtures of pesticides were used because of competition between pesticide molecules for adsorption sites, hydroxyl radicals, and holes. A suitable photocatalyst loading was determined to be 2 g/L of TiO2; a linear relationship between the first-order kinetic rate and light intensity (2.7 to approximately 46.5 mW) was observed. A comparison between LEDs and conventional mercury discharge lamps indicated that the former was more energy-efficient.