Microwave assisted synthesis of MCM-41 type mesoporous materials and diffusion of organic vapors in porous media: MCM-41 and carbon nanotubes

Official URL: http://192.168.1.20/record=b1306618 (Table of Contents)

In this study a novel synthesis technique of MCM-41 has been successfully applied for the production of pure and metal incorporated MCM-41 type mesoporous molecular sieves under microwave radiation by using a household microwave oven operated at several different combinations of power and time. High quality MCM-41 hexagonal mesoporous materials of good thermal stability were obtained in 30 minutes at 120 Watt by microwave assisted hydrothermal autoclave heating with specific surface area value of 1438 m²/g and average pore diameter of 3.49 nm. The effect of metal incorporation into the MCM-41 mesoporous molecular sieves was studied in detail with transition metals such as copper, nickel, cobalt and iron. Impregnation and microwave assisted direct synthesis techniques were used in the production of MCM-41 type catalytic materials and the physical and structural properties of these were investigated. The incorporation of metal into MCM-41 structure was investigated using different Si/Metal mol ratios as 25, 50, 75 and 100. Development of the hexagonal mesoporous structure was confirmed by X-ray diffraction (XRD) and N₂ [Nitrogen] physisorption and Fourier transform infrared (FT-IR), while the metal dispersion were characterized by energy dispersion spectroscopy (EDS) and transmission electron microscopy (TEM). Thermal stabilities of the samples were characterized by thermal gravimetric analyzer (TGA). Diffusion of organic volatile chemicals in pure MCM-41, metal incorporated MCM-41 (Si/Metal mol ratio: 25) and carbon nanotubes were investigated. Diffusion coefficients, mode of transport and activation energies of diffusion of alcohols (methanol, ethanol, n-propanol, n-butanol) and aromatic solvents (benzene, toluene, ethylbenzene, propylbenzene, o-xylene, m-xylene, p-xylene) into the porous media were measured in 26-32 ºC [degrees Celsius] temperature range with a macroscopic measurement technique. As the molecular weight of the alcohols and aromatics increased, diffusion coefficients into MCM-41 and CNTs decreased, activation energy for diffusion increased, and the time necessary to reach equilibrium increased. The diffusion of alcohols and aromatics into MCM-41 and CNTs obeyed the anomalous transport mechanism. Diffusion rate constants slightly increased with increasing temperature. The diffusion coefficients of volatile molecules into the CNTs were at least 10 times higher than that of diffusion coefficients into MCM-41.