Because of very high potential barrier for thermionic emission and
trap-assisted charge recombination, photocatalytic reaction rate that
determined by semiconductor-cocatalyst interfacial electron transfer
severely deviates from linearity to the photocatalyst dosage or to the
light intensity. This makes it challenging to maximize utilization of
practical irradiation by referring the parameters evaluated from method
used in conventional catalysis. We here develop a model and predict that
photocatalytic reaction rate positively correlates to photocatalyst
concentration under weak illumination while the correlation becomes
negative under intense irradiation. The theoretical simulation that
matches the experimental values can be used to guide maximizing
photocatalytic photon utilization under various intensity of
irradiation. The strong correlation can rationalize photocatalytic
evaluation instead of obtaining a numerically high value by excessively
lowering the denominators. To realize efficient utilization of real-time
changing sunlight, we propose a reactor configuration that can optimize
the amount of photocatalyst participating into the reaction.