Aminoguanidine derived N-rich mesoporous carbon nitrides with tunable nitrogen contents for Knoevenagel condensation

Nitrogen-rich carbon nitrides are desired materials for base-catalysed transformations; however, their synthesis is challenging due to the volatile nature of N at high temperatures. Herein, we report on the temperature-controlled synthesis of ordered N-rich mesoporous carbon nitrides (MCNs) via pyrolysis of aminoguanidine by using SBA-15 as a hard template. The properties and the nitrogen content of the materials were tuned by varying the carbonization temperature in the range of 350–500 °C. At 350 and 400 °C, higher amounts of N could be retained in the MCN framework with the predominant formation of C₃N₆ having a six-membered aromatic ring with diamino-s-tetrazine moiety, whereas C₃N₅ with 1-amino/imino-1,2,4-triazole moieties was produced at 450 and 500 °C. The base catalytic activity of MCNs in Knoevenagel condensation of benzaldehyde with malononitrile revealed that the MCN-400 exhibited the highest catalytic performance by displaying a 96.4 % product yield with toluene as a solvent. The superior catalytic activity of MCN-400 is attributed to high N content (62.6 wt%), high surface area (235 m² g⁻¹), and large pore volume (0.74 cm³ g⁻¹). The optimum temperature for obtaining the highest yield of the products is 80 °C, and the catalyst showed good cycling stability for 5 consecutive cycles.