MCM-41: a versatile platform to support organic and inorganic phases

NICOLÁS FELLENZ

Pucón

Congreso; VII Congreso Nacional de Nanotecnología CNN7; 2023

Pontificia Universidad Católica de Chile, la Universidad de Chile, la Universidad Federico Santa María, la Universidad Austral y la Universidad de Valparaíso

Using the sol-gel synthesis route, an ordered mesoporous silica with MCM-41 type structure was synthesized. Then, different post-synthesis treatments were carried out to incorporate species of different nature into the mesoporous matrix. A first modification sought the incorporation of Fe atoms inside the pores of the MCM-41: using incipient wetness impregnation method, the MCM-41 was treated with an aqueous solution of Fe(NO3)3.9H2O followed by calcination in N2 flow (60 cm3.min-1) at 350°C to obtain the composite material called MCM-41-Fe. A second modification with the aim of incorporating terminal amino functions was carried out, for this MCM-41 was treated with a solution of 3-aminopropyl-triethoxysilane (APTES) in toluene under magnetic stirring (6 h, 80°C), the resulting sample was designated as MCM-41-N. Low angle XRD results confirm the existence of a long-range hexagonal mesoporous ordering typical of MCM-41 in both synthesized composites. Besides the nitrogen sorption measurements at -196°C with the application of the BET model allowed us to determine that both samples have a monomodal pore distribution, with mean pore diameter values of 3.0 and 2.5 nm and specific surfaces areas of 691 and 774 m2.g-1 for MCM-41-Fe and MCM-41-N, respectively. Taking as a starting point the values of 1143 m2.g-1 and 3.0 nm recorded for MCM-41, this indicates that both post-synthesis treatments performed affect the available specific surface area of the original platform, while the average pore diameter only changes when incorporating organic functions. The values of the C constant of the BET model were 107, 108 and 41 for MCM-41, MCM-41-Fe and MCM-41-N, respectively, indicating that the treatment with APTES in toluene generates an increase in the surface hydrophobicity degree, something that does not happen when incorporating iron1. Images from scanning transmission electron microscopy high-angle annular dark-field (STEM-HAADF) allowed a direct observation of iron oxide nanocrystals of average length size of 3-4 nm inside the mesoporous channels on MCM-41-Fe. Using Mössbauer spectroscopy it was determined that these crystals present superparamagnetic behavior at room temperature and are made up of the iron oxide phases hematite and maghemite2. Regarding MCM-41-N, FT-IR, XPS and thermogravimetric analysis measurements confirmed the covalent anchoring of NH2/NH3+ groups onto the mesoporous surface with an estimated organic content of 1.9 mmol per gram of sample3. The registered experimental data allow us to affirm that the MCM-41 system is capable of acting as a highly porous and stable platform to host phases of varied composition and chemical nature, thus giving rise to nanostructured composite materials with potential applications in fields as catalysis, electronics devices, separation process and nanomedicine, among others. (por los cambios económicos sucedidos no se puedo asistir al evento aunque el trabajo fue realizado y aceptado para su presentación oral)