Probing into the relationship between charge carrier dynamics and photocatalytic reactions is central to the understanding and therefore the design of photocatalysts. We have studied the charge carrier lifetime of Pt/CN and compared it to that of CN alone using femtosecond pump-probe transient absorption spectroscopy in the 500-900 nm signal range. Parallel photocatalytic reactions were also conducted to link the extracted lifetime to the corresponding rates of hydrogen production from water. The presence of Pt (with a mean particle size of ca. 2.5 nm) on CN decreased the lifetime of excited electrons in the conduction band (CB). This has occurred in pure water as well as in the presence of the organic sacrificial agent used. These results suggest that Pt particles on this n-type semiconductor act as electron trap centers (either by pumping away CB electrons or by creating trap centers at the interface). The corresponding increase in reaction rates can be linked to this electron transfer.