Kinetic modeling of photocatalytic degradation reactions: Effect of charge trapping

This study investigates the important role of charge trapping in a photocatalytic degradation kinetic model. Different charge trapping reactions were coupled with photocatalytic degradation reaction schemes. The resulting kinetic models were applied to formate and trichloroethylene (TCE) in aqueous and gas phase, respectively. In both cases addition of charge trapping improved the reliability of the kinetic models. Hence, two dissipative charge reactions are considered in the new model: electron–hole recombination with second-order kinetics and charge trapping with first-order kinetics. For the formate system, it was shown that accounting for UV irradiance effects on a mechanistic basis requires the incorporation of charge trapping effects in the kinetic model. The improved model fitted literature data to within experimental error. A reasonable mechanism was suggested for degradation of TCE which involves three electron–hole pairs for the complete mineralization of one molecule of TCE. A kinetic model of TCE degradation via three main steps, along with considering charge trapping can explain the kinetic data with the same accuracy as an existing model of Demeestere et al., but with a more realistic electron–hole pair requirement, and added flexibility to account for light intensity effects.