Dynamics of diffusion-limited photocatalytic degradation of dye by polymeric hydrogel with embedded TiO2 nanoparticles

Theoretical model has been developed for the diffusion-limited photocatalytic degradation of organic dye in aqueous solution by composite hydrogel filament with embedded photocatalyst nanoparticles. The model included transition of dye molecules from the supernatant solution into the composite hydrogel, diffusion of the dye inside and pseudo first-order reaction of dye photocatalytic degradation. Theoretical model was verified by the experimental studies of the methyl orange dye photocatalytic degradation in aqueous solution by composite polyacrylamide hydrogel different degrees of crosslinking with embedded commercial TiO2 nanoparticles Degussa/Evonik P25. The integral rate of the dye concentration diminishing of the supernatant solution can be nicely fitted by a single exponential decay function with an apparent kinetic constant of dye photocatalytic degradation reaction. The dependence of the apparent kinetic reaction constant, the diffusion coefficient of dye through hydrogel and the value of the "true" kinetic reaction constant has been discussed.