Synthesis of nitrogen-rich mesoporous carbon nitride with tunable pores, band gaps and nitrogen content from a single aminoguanidine precursor

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 CN 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

Immobilization of chiral amide derived from (1R,2S)-(-)-norephedrine over 3D nanoporous silica for the enantioselective addition of diethylzinc to aldehydes

Chiral amide synthesized from (1R,2S)-(-)-norephedrine has been successfully immobilized onto three dimensional Ia3d cubic nanoporous material. The immobilization of the chiral amide has been confirmed by using various physiochemical techniques. The immobilized ligand has been screened for its catalytic activity in the enantioselective addition of diethylzinc to aromatic aldehydes. The immobilized catalyst was found to be highly active and selective, affording the final product chiral alcohols in 92% yield with a 95% ee at room temperature. The enantioselectivity of the immobilized catalyst is much higher than that of the homogenous catalyst (40% ee) at room temperature. In addition, the catalyst was stable and found to be purely heterogeneous and recyclable. The activity of the immobilized catalyst has been also investigated for the aromatic aldehydes with different electron donating and withdrawing groups. In addition, the electronic and steric effects of the substrates affecting the activity and the enantioselectivity of the catalysts were discussed in detail

Microwave-assisted synthesis of highly crystalline mesoporous hydroxyapatite with a rod-shaped morphology

Mesoporous hydroxyapatite (MHA) with a rod-shaped morphology has been successfully synthesized for the first time employing cetyltrimethylammonium bromide (CTAB) as a template and CaCl 2 and K 2HPO 4 as the precursors for hydroxyapatite under alkaline medium at the reaction temperature of 120°C via microwave method. The obtained material exhibits a disordered mesoporous structure with a high crystallinity and highly uniform rod-like morphology with an average size of ca. 25 nm in width and 100 nm in length

Direct synthesis and characterization of highly ordered cobalt substituted KIT-5 with 3D nanocages for cyclohexene epoxidation

Highly ordered cobalt incorporated KIT-5 silica (Co-KIT-5) with different Co contents and a well-ordered three-dimensional cage type porous structure were prepared for the first time by using Pluronic F127 as structure directing agent at different molar water to hydrochloric acid (nHO/) ratio. The amount of Co content in the silica framework of KIT-5 can be finely controlled with a simple adjustment of the nHO/ ratio as it controls the concentration of the H ions in the synthesis gel. It has been found that the nHO/ ratio of 463 is the best condition to obtain Co-KIT-5 with a high Co content. The obtained materials were characterized by various techniques such as powder X-ray diffraction (XRD), N adsorption studies, field emission high resolution scanning electron microscopy (FE-HRSEM), high resolution transmission electron microscopy (HRTEM), ultraviolet-visible diffused reflectance (UV-Vis DRS), electron spin resonance (ESR) and X-ray photoelectron spectroscopy (XPS). Characterization results revealed that Co atom can be introduced in the silica framework without affecting the structural order and the textural parameters of the samples. ESR, XPS and UV-Vis DR spectra confirmed that the Co atoms are indeed occupy the tetrahedral coordination with the silica framework of KIT-5. The catalytic performance of Co-KIT-5 with different Co contents in the cyclohexene epoxidation has been investigated using TBHP/HO as oxidants and acetonitrile as a solvent. Co-KIT-5 exhibited a high catalytic performance with TBHP as oxidant and remained inactive when HO was used. The effect of various reaction parameters such as reaction time, reaction temperature, and reactant feed ratio and oxidant, affecting the catalytic activity of Co-KIT-5 has also been studied. Among the catalysts studied, Co-KIT-5-0.90 was found to be the best catalyst, affording a high conversion of cyclohexene. In addition, the catalyst was found to be highly stable and can be reused several times without affecting its catalytic activity under the optimized reaction conditions

Cobalt oxide functionalized nanoporous carbon electrodes and their excellent supercapacitive performance

Nanoporous carbon (CMK-3-150) functionalized with different amounts of cobalt oxide (CoO) nanoparticles was synthesized by an incipient wetness impregnation technique for supercapacitor application. The characterization results reveal that the specific surface area and pore volume of the CoO functionalized CMK-3-150 marginally decrease upon increasing the amount of the CoO whereas the pore diameter and the structure of the CMK-3-150 were not affected even after the functionalization. The electrochemical measurements show that the specific capacitance of the electrodes was enhanced after the functionalization with CoO. Among the electrodes studied, CMK-3-150 functionalized with 15 wt% CoO shows an excellent cycling stability and specific capacitance of 331 F g, which is ca. two times higher than that of the pure nanoporous carbon. This enhanced performance is due to the combined contribution of electrical double layer capacitance and pseudocapacitance. A symmetric supercapacitor device based on the CMK-3-150-15Co electrode gives the maximum energy density of 29.67 W h kg at a power density of 0.07 kW kg. This journal i

Preparation of mesoporous titanosilicate molecular sieves with a cage type 3D porous structure for cyclohexene epoxidation

We report on the preparation of mesoporous titanosilicate with a 3D porous structure and Fm3m symmetry using Pluronic F127 as structure directing agent and titanium isopropoxide as a titanium source. The amount of titanium in the silica framework of the materials is controlled by a simple adjustment of the molar water to hydrochloric acid (n/n) ratio. The materials with different n/n ratios are also prepared by varying the amount of titanium source in the synthesis gel at an optimized n/n of 463. The structural order, the textural parameters, morphology, the nature and co-ordination of Ti species, and the amount of Ti content in the samples are analyzed by various techniques including X-ray diffraction (XRD), N adsorption, high resolution scanning electron microscopy (HRSEM), UV-vis diffused reflectance spectroscopy (UV-vis DRS), and inductively coupled plasma emission spectroscopy (ICP), respectively. All the materials prepared with various n/n ratios exhibit well-ordered porous structure and possess high BET surface areas (673-941 m g) and large pore volumes (0.46-0.71 cm g). The pore diameter of the samples also increases with increasing the Ti content in the samples. UV-vis results confirm that most of the Ti atoms are in the tetrahedral co-ordination. Finally, the materials are subjected to cyclohexene epoxidation using TBHP/HO as oxidant and acetonitrile as solvent in order to investigate their catalytic activity. Ti-KIT-5 samples display a high catalytic activity with TBHP as oxidant and remain inactive when HO was used. The amount of Ti plays a crucial role in controlling the catalytic activity of the samples. Of the catalysts studied, Ti-KIT-5(5) where the number in the parenthesis indicates the Si/Ti ratio shows the best activity, affording a high conversion to cyclohexene. Among the catalysts studied, Ti-KIT-5-5 exhibited better catalytic activity with respect to reaction time, reaction temperature, conversion and epoxide selectivity