From ultra-large micropores to mesopores
This is another leap in the development history of molecular sieves and porous materials. Mesoporous materials generally refer to materials with ordered pore structures with pore sizes ranging from 2 to 50 nm. In fact, the synthesis of ordered mesoporous materials started as early as 1971, and Japanese scientists T. Yanagisawa and KKuroda also started the synthesis of mesoporous materials before 1990. It was only in 1992 that the report of C. Gong. Kresge of Mobil Corporation attracted people's attention and was considered to be the real beginning of the synthesis of mesoporous materials. The M41S series of mesoporous materials synthesized by Mobil scientists using surfactants as templates include MCM-41 (hexagonal phase), MCM-48 (cubic phase), and MCM-50 (layered structure). This is comparable to the successful synthesis of ZSM-5, another major achievement by Mobil scientists in the 1970s. The micropores of zeolite limit the development of the size of reactants and related functions to less than about 10A. Even through pore modification and modification, it is limited by the original pore size and cannot be specially changed. The emergence of mesoporous materials with pore sizes in the range of 2–50 nm offers broad opportunities for these efforts.
Mesoporous materials have regular mesoporous (2-50 nm) channels, large specific surface area and pore volume, and a framework with diverse components, which are the characteristics and structural advantages of mesoporous materials. In addition, mesoporous channels are constructed by amorphous pore walls. From the atomic level, the mesoporous framework structure is usually long-range disordered, which is different from long-range ordered microporous compounds. Therefore, compared with microporous molecular sieves , the mesoporous material has low thermal stability and hydrothermal stability. In recent years, the emergence of SBA-15, MAS-7 and MAS9 has improved this weakness to some extent. However, ordered mesoporous materials have their special advantages, which is the limitation of their framework atoms and species types. At present, there are mesoporous metal oxides, mesoporous oxo-acid salts, mesoporous metals, mesoporous silicon-based high-temperature ceramics, mesoporous non-metallic nitrides, and mesoporous metal sulfides, nitrides, carbides, fluorides, etc. . Generally speaking, the current mesoporous materials with periodic structure can be generally divided into the following types according to their composition, structure and function.
(1) Mesoporous silica materials: ① have different pore network structures, pore sizes and pore volumes; ② can be
Surface modification; ③ containing organic components; ④ mesoporous silica materials containing other metals (heteroatoms) in the pore walls, etc.,
(2) Non-silica mesoporous materials.
(3) Chiral mesoporous materials.
(4) Mesoporous carbon materials.
(5) Large pore size mesoporous materials, etc.
As for mesoporous materials with special shapes, there are many kinds. The rapid development and continuous improvement of mesoporous materials have provided a broad field for its application, and the research in related fields is also constantly deepening and expanding.
