Morphological control of porous SiC templated by As-synthesized form of mesoporous silica.

Porous silicon carbide with fiber like morphology was successfully prepared via a hard templating approach using as-synthesized form of mesoporous silica SBA-15 as template and sucrose as carbon precursor. The obtained materials have been characterized by various sophisticated techniques such as XRD, nitrogen adsorption, HRTEM, HRSEM, FT-IR and TGA. The XRD and the nitrogen adsorption results revealed that the materials are highly crystalline and exhibit porous structure with excellent textural characteristics. It has been demonstrated that the morphology of the materials can be finely controlled from rod shaped morphology to fiber like nanostructures by the simple adjustment of the reaction time from 5 to 12 h at the reaction temperature of 1300 degrees C. The reaction time of 12 h at 1300 degrees C was found to be the best condition to obtain highly crystalline nanofiber like morphology. The obtained materials display beautiful nanofiber morphology which has the diameter of 20 to 60 nm and a length of 7 to 10 microm which is much longer than the previously reported SiC nanofibers.

Ultrafast microwave assisted synthesis of mesoporous SnO2 and its characterization.

Mesoporous SnO2 was prepared by a high temperature microwave assisted process using a low cost polymeric surfactant, poly(ethylene glycol). The obtained material has been characterized by several sophisticated techniques such as XRD, nitrogen adsorption, HRTEM, UV-Vis DRS, HRSEM and photoluminescence. The characterization results reveal that the obtained material exhibits a high surface area with a spherical morphology, crystalline walls and narrow mesopores. In addition, microwave process requires only a short time for the formation of mesoporous SnO2. SnO2 with no porous structure was obtained when hydrothermal technique was used. We also found that the band gap of the mesoporous SnO2 is much smaller than that of the nonporous bulk SnO2 and showed excellent photoluminescent properties.

Synthesis of superacid-functionalized mesoporous nanocages with tunable pore diameters and their application in the synthesis of coumarins.

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.