Effect of Synthesis Duration on the Physicochemical Properties of Siliceous Mesoporous Molecular Sieve (Si-MMS)

Pure silica mesoporous molecular sieve (MMS) solid has been synthesized at 100oC by hydrothermal process. The effect of synthesis duration from 2 to 10 days has been investigated on the physicochemical properties of mesoporous molecular sieve. Samples were characterized by low angle XRD, N2 adsorption-desorption and HRTEM analysis. XRD patterns of the as-synthesized samples showed four well-defined diffraction peaks corresponding to 100, 110, 200 and 210 planes. These peaks are the fingerprint characteristics of MCM-41 mesoporous material. The high intensity diffraction peaks were observed in 8-days sample that define the high ordering of the pores and long range order. N2 adsorption-desorption results showed that all samples possessed a type IV isotherm having hysteresis loop of type H1 which is an identification of mesoporous material. Calcined samples exhibited high surface area i.e., 984-1036 m2 g-1, pore volume i.e., 1.00-1.13 cm3 g-1 and average pore diameter i.e., 3.04-3.30 nm. A hexagonal pore structure was found in the synthesized materials by HRTEM analysis, which confirms that the synthesized materials are MCM-41. HRTEM analysis showed the effect of synthesis duration on the materials and found that 8-days sample exhibited highly ordered hexagonal pore structure like honeycomb structure. All the
samples were calcined at 550oC to remove the template and to study the changes in the mesoporous framework. The results showed that the mesoporous structure remained intact after calcination at 550oC, indicating that the mesoporous materials exhibit high thermal stability.