Degradation of the herbicide isoproturon by a photocatalytic process

In this study, the adsorption and photocatalytic degradation of isoproturon (one of the most widely used herbicides in agriculture) was investigated in an annular photoreactor packed with a TiO₂ photocatalyst. The results highlighted that the monolayer Langmuir adsorption isotherm model was well obeyed. The isoproturon adsorption equilibrium constant was determined experimentally. The codegradation of isoproturon and of other copollutants such as salicylic acid and phenol occurred, demonstrating that within the catalyst, the same type of sites can be involved in the adsorption of the two pollutants. The heat of adsorption fell in the range of 20 to 50 °C and was found to be ∼43 kJ/mol. As expected, the adsorption constant K_a decreased with increasing the fluid flow due to the temperature rise. The kinetics of the photocatalytic degradation of isoproturon revealed a first-order reaction for initial concentrations between 3 and 43 ppm. In our experimental conditions, no by-products were detected and total disappearance of isoproturon was observed.