Highly ordered mesoporous carbon nitride (CN) with an extremely high nitrogen content and tunable pore diameters was synthesized by using a new precursor with a high nitrogen content, aminoguanidine hydrochloride and mesoporous silica SBA-15 with different pore diameters as hard templates. Surprisingly, the N/C ratio of the prepared mesoporous CN (MCN-4: 1.80) was considerably higher than that of the theoretically predicted C(3)N(4) nanostructures (1.33). This is mainly due to the fact that the CN precursor easily undergoes polymerization at high temperature and affords a highly stable polymer composed of a diamino-s-tetrazine moiety with a six-membered aromatic ring containing six nitrogen atoms that are linked trigonally with the nitrogen atoms. The obtained materials were thoroughly characterized by means of XRD, nitrogen adsorption, high resolution TEM, electron energy loss spectra, high resolution SEM, X-ray photoelectron spectroscopy, FTIR, and C, N, O, and S analysis. The results show that the MCN-4 materials possess a well-ordered mesoporous structure similar to SBA-15 with a high specific surface area and tunable band gap in the range of 2.25-2.49 eV. Interestingly, the pore diameter of the materials can be finely tuned from 3.1-5.8 nm by increasing the pore diameter of the hard-template SBA-15. The reaction temperature plays a critical role for the formation of MCN, and we found that 400 °C is the best condition to obtain MCN-4 with a high nitrogen content. We have further investigated the catalytic application of the MCN-4 materials towards Friedel-Crafts hexanoylation of benzene and compared the results with the mesoporous CN with less nitrogen content (MCN-1) and nonporous CN. Among the materials studied, MCN-4 showed the highest activity, affording a high yield of hexanophenone within a few hours, which is mainly due to the presence of free amine groups on the wall structure of MCN-4.

Here we demonstrate a facile synthesis of 3D mesoporous carbon nitride with Ia3d symmetry (MCN-6) using mesoporous silica KIT-6 with 3D porous structure and different pore diameters as hard templates, and ethylenediamine and carbon tetrachloride as the sources for N and C, and C, respectively. The obtained materials possess bimodal pores that can be controlled with a simple adjustment of the pore diameter of the KIT-6 templates. The lower angle powder X-ray diffraction (XRD) patterns and high resolution transmission electron microscope (HRTEM) images confirm that the MCN-6 materials possess a well-ordered mesoporous 3D structure with a highly interwoven and a branched pore structure. The textural parameters such as the specific surface areas and specific pore volumes of the materials can also be controlled by tuning the pore diameter of the hard template. The specific surface area and the specific pore volume of the samples increase with increasing the pore diameter of the hard template. The C/N ratio of the MCN-6 is ca. 4.3 which is similar to that obtained for MCN-1 prepared from SBA-15 as template. FT-IR and XPS spectroscopy results reveal that samples contain a CN network with a lot of free NH 2 groups which are originated from ethylenediamine and can offer the basic sites. The temperature programmed desorption of CO 2 confirms that the samples are highly basic and the basicity of the sample is 0.195 mmol of CO 2 per g which is higher than that of MCN-1 (0.14 mmol of CO 2 per g). We tested the performance of MCN-6 materials in the base-catalyzed Knoevenagel condensation of benzaldehyde and malononitrile. The catalysts exhibit excellent activity and afford a high yield of the corresponding a,b-unsaturated nitrile in a short reaction time even at room temperature. In addition, catalysts are highly stable and can be recyclable several times without affecting their activity.

Here we demonstrate for the first time the preparation of a triflic acid (TFA)-functionalized mesoporous nanocage with tunable pore diameters by the wet impregnation method. The obtained materials have been unambiguously characterized by XRD, N(2) adsorption, FTIR spectroscopy, and NH(3) temperature-programmed desorption (TPD). From the characterization results, it has been found that the TFA molecules are firmly anchored on the surface of the mesoporous supports without affecting their acidity. We also demonstrate the effect of the pore and cage diameter of the KIT-5 supports on the loading of TFA molecules inside the pore channels. It has been found that the total acidity of the materials increases with an increase in the TFA loading on the support, whereas the acidity of the materials decreases with an increase in the pore diameter of the support. The acidity of the TFA-functionalized mesoporous nanocages is much higher than that of the zeolites and metal-substituted mesoporous acidic catalysts. The TFA-functionalized materials have also been employed as the catalysts for the synthesis of 7-hydroxy-4-methylcoumarin by means of the Pechmann reaction under solvent-free conditions. It has been found that the catalytic activity of the TFA-functionalized KIT-5 is much higher than that of zeolites and metal-substituted mesoporous catalytic materials in the synthesis of coumarin derivatives. The stability of the catalyst is extremely good and can be reused several times without much loss of activity in the above reaction.

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