External and internal mass transfer effect on photocatalytic degradation

A rational approach is proposed in determining the effect of internal and e xternal mass transfer, and catalyst layer thick ness during photocatalytic degradation. The reaction occurs at the liquid-catalyst interface and there fore, when the catalyst is immobilized, both external and internal mass tra nsfer plays significant roles in overall photocatalytic processes. Several model parameters, namely, external mass transfer coefficient, dynamic adsor ption equilibrium constant, adsorption rate constant, internal mass transfe r coefficient, and effective diffusivity were determined either experimenta lly or by fitting realistic models to experimental results using benzoic ac id as a model component. The effect of the internal mass transfer on the ph otocatalytic degradation rate over different catalyst layer thickness under two different illuminating configurations was analyzed theoretically and l ater experimentally verified. It was observed that an optimal catalyst laye r thickness exists for SC (substrate-to-catalyst) illumination. (C) 2001 El sevier Science B.V. All rights reserved.