Aminoguanidine Derived N‐Rich Mesoporous Carbon Nitrides with Tunable Nitrogen Contents for Knoevenagel Condensation

Abstract

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.

Sulfoxide-Functional Nanoarchitectonics of Mesoporous Sulfur-Doped C3N5 for Photocatalytic Hydrogen Evolution

“…The diffraction peaks at the low angle region (i.e., 2θ ∼ 0.9 and ∼1.5°) were found for both MSCN-K and MSCN-S, which is typically indicative of ordered periodicity of mesoporous structures, further confirming the previous electron microscopy results. 12,13 However, the bulk SCN, in contrast, did not show any peak in this region due to the lack of any ordered structure. Notably, all three samples exhibited two intense peaks at 2θ ∼ 13 and 27°, corresponding to the (100) and (002) crystallographic planes of the layered CN structure.…”

“…However, despite these advantages, the intrinsic features of CNs, such as poor light absorption limited to <460 nm, rampant exciton recombination, low electrical conductivity, and marginal quantum efficiency, significantly restrict their photocatalytic capabilities. , To address these limitations, the last two decades have seen the development of innovative strategies for morphological manipulation and electronic structure modulation of CNs. Notably, the use of hard-templating methods for morphologically manipulating CN employing mesoporous silica with different nanoarchitectures, pioneered by Vinu et al in 2005 with the development of MCN-1 to the latest development of advanced materials like MCN-12 and MCN-13, have set a foundational precedent for creating well-ordered mesoporous CN architectures with considerably enhanced specific surface areas. − Over the past two decades, our research group has been at the forefront of developing a series of mesoporous carbon and CN materials, leveraging different nanoarchitectures to achieve significant advancements in the CN morphology. These developments have been instrumental in providing a plethora of photocatalytically active sites and in facilitating the rapid diffusion kinetics of reactant molecules across the catalytic surfaces .…”