Please check the photocatalytic mechanism of TiO2. Hydroxyl radicals are generated through positive holes and superoxide with electrons.TiO2 plates gets deactivated once the excitation process comes to an end?

Dear Prof. Feroz

To the extent of my knowledge, after receiving UV light, electrons jump to the conduction band and participate in the reactions, however the rate of recombination soon after is very high, so only a few electrons can Join the reaction, TiO2 itself then lost some electrons, but that number is very small. That could explain the gradual decrease in efficiency over the next times.

Best wish.

Quan-Doan Mai