The effect of Pt cocatalyst on the performance and transient IR spectrum of photocatalytic g-C3N4 nanospheres

Graphitic carbon nitride (g-C3N4) is a fascinating visible-light-responsive conjugated polymer with appealing characteristics for applications in the solar to fuel conversion arena. Specifically, the morphology of hollow nanoscale spheres decorated with metal cocatalyst attracts attention for the water splitting reaction. Here, we reveal general challenges relating to proper conjugation of this layered material with Pt, with regards to both efficiency of charge separation and long-term stability. We correlate photocatalytic activity towards water splitting and the oxidation half-reaction with transient IR measurements, which provide indirect information on the whereabouts of photoinduced charge carriers. These transient spectral changes were found to be as long as 100 ns in g-C3N4 hollow spheres. The addition of Pt nanoparticles as cocatalysts resulted in nearly 3-fold improvement in activity towards water oxidation half-reaction. Yet, this improvement was short lived. It seems that the Pt domains, which likely grow on primary and secondary amino sites, provide an avenue for trapping holes in shallow traps for a time that is sufficient for them to participate in redox reactions, while still maintaining enough oxidative power. The benevolent effect of platinum was found to be hampered by insufficient stability of the Pt attachment to the surface of the g-C3N4.