Adsorption-/desorption-limited diffusion of porphyrin molecules in nano-porous TiO2 networks

The adsorption of porphyrin molecules out of ethanol solution onto TiO2 particles of nano-porous TiO2 films was studied by means of optical absorption (UV–Vis) spectroscopy. The process was found to be limited by aggregation of dye molecules. From the temperature dependence of the process, an activation energy of 0.18 ± 0.02 eV was deduced. It is correlated to the interaction energy of π-stacked porphyrin molecules. Aggregation-breaking additives change the up-take kinetics in a way that it becomes similar to the kinetics of non-aggregating molecules.