It's known that the rate of photocatalytic reaction increases with the concentration of dissolved oxygen. I noticed this effect in my previous work but recently i prepared a new photocatalyst and i found that the rate of photocatalytic reaction (Under UV light) decreases in the presence of oxygen gas flow! I could not understand and explain this effect. Can any one help me?
Oxygen richness is one of the major factor in inducing remarkable photocatalysis. But oxygen deficiency also has found impetus in the same area. In addition band gap, surface area, phase purity(crystallinity) are all important factors for photoactivity. So better you try to check the environment (extent of oxygen richness) and find a suitable organic pollutant to degrade. U didn't mention your material. So the explanations that I have given in a general perspective.
It could be related to an accelerated poisoning of the catalyst by the degradation products. The hypothesis could be tested by increasing concentration of a substrate yet maintaining the same concentration of oxygen. Will it reduce the rate of photocatalysis?
molecular oxygen itself must be reactive when it adsorb a surface electron from TiO2.
the case now is not the logical result. therefor, on can expect a retardation step prevent
oxygen from electron adsorption. Therefore, search for the composition of the new catalyst could a new phase formed on the surface be inert towards the enhancing step for oxygen. I recommend you to characterize the surface and find the new phase formed and do an experiment determine the amount of surface active oxygen.
Dear Osama,
pay attention, the solubility of oxygen in water is limited. Only soluble oxygen can interact with the catalyzer surface. If you are using too high oxygen flow it can form microbubbles on the catalyst surface and reduce its reactivity.
Best wishes
Sabino
Dear Osama
There is n surprise. We found similar behavior in photodegradation of organic dyes. As we closed the system from oxygen the reaction ceased (which is expected).
As we used a flow of oxygen or even air, the reaction slowed down as well. There are many explanations (as shown above by friends) but the your observation is credible.
You may just look ate the known mechanisms for photdegradation processes and you get the answer.
Good luck