Before discussing any problem, we must clearly explain the meaning of each term and how it is measured. What is the "own life time" and how to measure it?

A photocatalysis includes several process: a formation of excited sate, a charge separation, followed by reactions of an electron and a hole.

Your second question is in bad English. I don't understand what are you asking.

Prof Yurii V Geletii, in his second question which is related to his first question, means "will the photogeneration of charge carriers will cease after a particular time?"

Before discussing the lifetime of photocatalyst, which I mean "the total time for which the material will show a (good) photocatalytic activity", we need to understand and you need to clarify exactly which reaction are we talking about. Hydrogen evolution reaction, oxygen evolution reaction, carbon dioxide reduction reaction, nitrogen reduction reaction, oxygen reduction reaction, and dye degradation are the processes that could take place on the surface of a photocatalyst. In brief, we consider two reactions "reduction" and "oxidation" that takes place over the surface, and they could take place simultaneously also. Now, for each process and every reaction the charge carriers are different, a major factor governing the photogenerated charge carrier is "solution" which could be acidic, alkaline, or neutral.

Therefore, the prediction of lifetime of any photocatalyst is dependent on the reaction which is taking place over its surface along with the condition to which it has been subjected. Although, researchers report the efficiency of photocatalyst on basis of its reusability too.

Dear Brajesh Rajesh Bhagat

Do I understand correctly that your definition of the catalyst lifetime is related to its stability? If yes, I accept it.

Commonly, the life-time is associated with kinetics of certain reactions in the course of photocatalysis.

Prof Yurii V Geletii yes my definition of the catalyst lifetime is related to stability. Can you describe the role of reaction kinetics in the measurement of a photocatalyst's lifetime.

Brajesh Rajesh Bhagat

If you know the reaction rate constants of side reactions, you might be able to calculate the rate of catalyst decomposition

Prof. there are numerous techniques to determine the reaction rate constants when working on the experimental methods. Is there any way to determine the rate constants using theoretical simulation methods

Surely yes, but it depends much on the complexity of the system.