Facile synthesis and basic catalytic application of 3D mesoporous carbon nitride with a controllable bimodal distribution

Abstract

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 NH2 groups which are originated from ethylenediamine and can offer the basic sites. The temperature programmed desorption of CO2 confirms that the samples are highly basic and the basicity of the sample is 0.195 mmol of CO2 per g which is higher than that of MCN-1 (0.14 mmol of CO2 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 α,β-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.