External and internal mass transfer effect on photocatalytic degradation

A rational approach is proposed in determining the effect of internal and external mass transfer, and catalyst layer thickness during photocatalytic degradation. The reaction occurs at the liquid–catalyst interface and therefore, when the catalyst is immobilized, both external and internal mass transfer plays significant roles in overall photocatalytic processes. Several model parameters, namely, external mass transfer coefficient, dynamic adsorption equilibrium constant, adsorption rate constant, internal mass transfer coefficient, and effective diffusivity were determined either experimentally or by fitting realistic models to experimental results using benzoic acid as a model component. The effect of the internal mass transfer on the photocatalytic degradation rate over different catalyst layer thickness under two different illuminating configurations was analyzed theoretically and later experimentally verified. It was observed that an optimal catalyst layer thickness exists for SC (substrate-to-catalyst) illumination.