Chemical modifications of Polyheptazine-imides : carbon-nitride-based semiconductors with improved structure and electronic properties for full photochemical water splitting and novel photocatalytic reactions

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The direct splitting of water into H2 and O2 on semiconductor-based photocatalysts is an ideal methodology for the sustainable utilization of solar energy. Coupling water splitting photocatalysis with organic transformations expands applications beyond fuel generation to organic synthesis providing reduction or oxidation equivalents without consumption of fossil resources. Recently, the class of graphitic carbon nitride polymers with their semiconductive, Pi-conjugated electronic features has attracted intense research interests, due to its metal-free, low-cost, stable, and sustainable properties for artificial photosynthesis. This effect was discovered by two of the contributors of this joint proposal. Although significant progress on water half-splitting reactions has been made ever since, the direct water splitting releasing H2 and O2 stoichiometrically has however been rarely realized. This is mainly limited by the large activation barrier to evolve O2 and a still non-optimal semiconductor band structure with insufficient overpotentials. To address the above issues achieving overall water splitting on graphitic carbon nitride, optimizations on both thermodynamic and kinetic aspects are addressed. To achieve this goal, a joint project composed by a Chinese part and a German part is proposed, in which the Chinese group (Wang) focuses on the kinetic control of photocatalytic reactions to facilitate gas release, and one of the German groups (Antonietti) majors in the thermodynamic issues to facilitate water splitting. The thermodynamically and kinetically optimized catalysts are in addition applied to advanced organic photocatalysis, which will be performed by the second German group (König) having a broad expertise in this area. The ideal complementary expertise will allow to improving the overall water splitting to produce hydrogen fuel by graphitic carbon nitride photocatalysts and utilize the added-value of the developed catalysts for photoredox organic synthesis coupled with the water splitting reaction.