Synthesis and comparative study of the photocatalytic performance of hierarchically porous polymeric carbon nitrides

• Different crystalline and porous hierarchical carbon nitrides were prepared.
• Photocatalytic activity in H2 evolution and dye degradation was compared.
• Photo luminescence of carbon nitrides was studied in the picosecond range.
• Catalytic activity correlates with crystallinity and the fluorescence intensity.
• Low crystalline CN materials with large crystal size are not active!

Graphitic carbon nitride materials with tri-s-triazine and s-triazine based structures were prepared by thermal condensation of melamine (CNT) and by solution reaction of cyanuric chloride with lithium nitride (CNS), respectively. An amphiphilic block copolymer-F68 was used as a soft template for the synthesis of mesoporous carbon nitride. The structural and photophysical properties of the as-prepared catalysts were characterized by X-ray powder diffraction, elemental analysis, N2-adsorption measurement, transmission electron microscopy, X-ray photoelectron spectroscopy, differential scanning calorimeter and UV–Vis absorption as well as time-resolved picosecond emission spectroscopy. The photocatalytic activity of the samples was evaluated by H2 evolution from water under visible light irradiation and the degradation of rose bengal (RB). The mesoporous CNT materials prepared with Pluronic F68 as template showed markedly higher activity compared to bulk carbon nitride, which can be attributed to its crystallinity, hierarchical porous structure and the enlarged surface area. The catalyst was relatively stable as proven by recycling experiments. Besides, the addition of H2O2 promoted the formation of active ·OH radicals and increased the activity of carbon nitride for photodegradation of rose bengal. The carbon nitrides prepared by solution reactions were of very poor activity both in photocatalytic water splitting and rose bengal degradation.

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