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Polymeric carbon nitride (PCN) can be prepared by heating of nitrogen rich precursors and is used as a photocatalyst for hydrogen evolution and transformation of organic molecules. This work gives a deeper understanding of the different properties of PCN and the observed intermediates when melamine or urea are chosen as precursors and heated to temperatures in the range of 350–575 °C. Melem or a melem-tetramer are the main intermediates when melamine is used as starting material, while urea-based PCN is formed via a supramolecular assembly of melamine and cyanuric acid. This leads to crucial differences in properties such as surface area, amount of NH2-groups and photocatalytic activity. PCN from urea, loaded with Pt nanoparticles, shows higher activities for photocatalytic hydrogen evolution due to more NH2-groups. The melem-tetramer shows nanosheetlike structure combined with a high amount of NH2-groups and has the highest activity of all prepared catalysts for the photocatalytic reduction of 5-(hydroxymethyl)furfural (HMF) to 2,5-bis(hydroxymethyl)furan (BHMF). Thus, this research demonstrates the formation mechanism and the design of PCN based catalysts with a large amount of NH2-groups and a high photocatalytic reduction ability.
Weers et al. (Wed,) studied this question.