Mesoporous silica MCM-48: Synthesis and application prospects

Abstract

Amorphous silica is an inorganic material with unique properties. It has become a key material in various areas of global industry, medicine, and cosmetology. Amorphous silicon dioxide consists of an arrangement of pores of various size: macro- (d>50 nm), meso- (2 <2 nm). In 1992, Mobil Oil Corporation developed a group of mesoporous materials named M 41S with a sharp pore distribution on the surface and a large pore volume (>1000 m2/g) thus addressing the issue of different-size pores of amorphous silicon dioxide. The key materials in this group are MCM-41 with a hexagonal two-dimensional pore system, MCM-48 with a cubic pore system, and MCM-50 with a layered pore system. The cubic pore structure of MCM-48 creates the conditions for convenient mass transfer of molecules which reduces diffusion restrictions and makes this material resistant to clogging of pores. The paper focuses on the specific features of MCM-48 synthesis, as well as its application prospects. The synthesis of the mesoporous silica MCM-48 can be carried out in two modes: hydrothermal synthesis and room-temperature synthesis. The process itself is determined by a number of factors, including the reaction temperature, the reaction time, the stirring rate, pH, the ratio of the initial components, the nature of the solvent, the nature of the Si precursor, and the length of the surfactant chain. Due to its structure, the mesoporous silica MCM-48 has a wide range of applications: in catalysis processes both as a catalyst (Si-MCM-48) and as a catalyst base (Al-MCM-48, Pt/MCM-48, ZnO-CuO/MCM-48); in sorption and separation processes (MCM-48 modified by 3-mercaptopropyltrimethoxysilane, Al-MCM-48 with a bimodal pore system); in microfluidics as a nanostructured ion-selective membrane (MCM-48 layers deposited on macroporous α-aluminium oxide substrate and silicon nitride microsieves).