1、Types of substances that can easily achieve mesoporous structures
Experiments have shown that mesoporous structures are easily achieved on materials such as silicon sources, metal salts, carbon sources, and polymer materials, while mesoporous structures are not easily achieved on materials with dense structures, stable chemical bonds, strong intermolecular forces, difficult regulation or poor thermal stability, and easy decomposition during processing.
1. Silicon source: Tetraethyl orthosilicate (TEOS) is one of the most commonly used silicon sources, which forms a silica network structure after hydrolysis and is easy to form mesopores under the action of template agents. Sodium silicate is also a commonly used raw material with low cost. Through appropriate acid-base adjustment and template assistance, high-performance silicon-based mesoporous materials can be prepared.
2. Metal salts: Metal nitrates, metal chlorides, etc. can be used to prepare metal oxide mesoporous materials. For example, aluminum nitrate, titanium nitrate, etc. can form mesoporous oxides such as aluminum oxide and titanium oxide through hydrolysis, polymerization, and subsequent treatment under specific conditions.
3. Carbon sources: Organic carbon sources such as phenolic resin, sucrose, glucose, etc. can be used to prepare mesoporous carbon materials in the presence of hard or soft templates through a series of treatments such as carbonization. These carbon sources come from a wide range of sources and are relatively inexpensive.
4. Polymer: Some amphiphilic block copolymers can self assemble to form ordered structures at the mesoscale, and can also serve as templates to guide inorganic materials to form mesoporous structures.
2、Reasons for easy implementation of mesoporous structure
1. Chemical composition and reactivity: Substances that are prone to chemical reactions such as hydrolysis and condensation, which are conducive to the formation of mesoporous structures. Silicon source materials (such as ethyl orthosilicate) can undergo hydrolysis and condensation reactions under alkaline or acidic conditions, forming a silica network structure. When the template agent is present, these reactions can occur around the template, gradually forming an inorganic skeleton around the template as the reaction progresses, leaving behind a mesoporous structure after removing the template.
2. Self assembly characteristics: Some amphiphilic molecules, such as surfactants and amphiphilic block copolymers, have special molecular structures that include hydrophilic and hydrophobic moieties. In solution, they spontaneously self assemble through intermolecular interactions, forming ordered aggregate structures such as micelles and liquid crystals. These ordered structures can serve as templates to guide the deposition of inorganic materials around them, ultimately forming mesoporous materials.
3. Structural flexibility and controllability: Under certain conditions, certain substances have a certain degree of flexibility in their structure, allowing for adjustments and modifications without compromising the overall structural integrity. For example, some metal organic framework materials (MOFs) are formed by connecting metal ions and organic ligands through coordination bonds. Due to the diversity and designability of organic ligands, the pore size and shape of MOFs can be regulated by changing the structure and length of ligands, thereby preparing mesoporous materials.
3、Types of substances that are difficult to implement mesoporous mechanisms
1. Materials with dense structure and stable chemical bonds, such as diamond, have a three-dimensional network structure formed by extremely strong covalent bonds between carbon atoms. The structure is extremely stable and dense, making it difficult to introduce the pores required for mesoporous structures through conventional methods.
2. Materials with strong intermolecular forces that are difficult to control: Some ionic crystals, such as sodium chloride, have strong ionic bonds and tightly and regularly arranged ions, making it difficult to form the ordered pore structure required for mesopores without damaging the original crystal structure.
3. Materials with poor thermal stability and easy decomposition during processing: Some natural polymer materials are prone to irreversible changes such as decomposition and carbonization during heating or other processing, and cannot maintain a stable structure to form ordered mesopores.
4、Reasons for the difficulty in implementing mesoporous structures
1. Chemical bond characteristics and structural stability: Substances with overly stable and dense structures have strong chemical bonds between atoms or ions, which limit structural changes and the introduction of pores. For example, carbon atoms in diamond form a robust three-dimensional network structure through covalent bonds, which is very stable and difficult to introduce the required pores for mesopores without damaging the overall structure.
2. Lack of appropriate interactions: If there is a lack of forces between material molecules that can guide self-assembly or interact with template agents, it is difficult to form ordered mesoporous structures. Some simple small molecule substances have weak and non-specific interactions with each other, and cannot spontaneously form ordered aggregation structures or effectively cooperate with template agents to construct mesopores.
3. Thermal stability and processing sensitivity: In the preparation process of mesoporous materials, heating, solvent treatment, and other steps are often required. Substances with poor thermal stability may undergo decomposition, phase transition, or other irreversible changes during these processes, resulting in the inability to form or maintain mesoporous structures. For example, certain organic compounds can rapidly decompose at high temperatures and cannot withstand the heat treatment conditions required for preparing mesoporous materials.
