Boron nitride - One of the hot spots in the field of materials
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Update time : 2019-07-30 15:53:31
As a new porous non-oxide material, porous boron nitride has attracted increasing interests due to its plenty of unique properties such as large specific surface area, tunable pore size, excellent chemical inertness and thermal stability, which are useful in catalysis, hydrogen storage, gas adsorption and separation.
Porous boron nitride is a new type of non-oxide porous material. The interior consists of interpenetrating or closed pores. It has a high specific surface area and a rich pore structure. The pore size can be adjusted according to the actual application, and the chemical properties are stable and thermally conductive. High rate, good insulation performance and hydrophobic properties.
In addition, porous boron nitride materials have special hydrogenation properties and selective adsorption properties, and have great application potential in the fields of hydrogen storage, gas adsorption and separation. According to the definition of the International Union of Pure and Applied Chemistry (IUPAC), porous materials can be classified into three categories according to their pore size: micropores (pore size less than 2 nm), mesopores (pore size 2-50 nm) and macropores (apertures) More than 50 nm).
Preparation
Template method
The templating method is to use the space restriction function of the template, control the pore structure, and prepare a method of orderly structure and relatively uniform porous material.
Soft template method
The soft template method is the first method to prepare ordered mesoporous materials. The supramolecular aggregate composed of the amphiphilic surfactant segment copolymerization is used as a template, and the boron nitride precursor is self-assembled by the interaction of non-covalent bond forces, and then pyrolyzed to obtain a porous nitrogen boron material(Fig. 1a).
Hard template method
The hard template method is the most common method for preparing ordered mesoporous boron nitride materials. Using a porous solid as a template, a boron nitride precursor is introduced into the pores by impregnation, and boron nitride is synthesized by pyrolysis, and the hard template is removed to obtain a porous boron nitride material having a corresponding pore structure (Fig. 1b).
Element replacement
Under high temperature conditions, a porous boron nitride material and a porous boron carbon nitride material are obtained by a displacement reaction between boron, nitrogen and a carbon template. The carbon content of the product can be adjusted by controlling the reaction temperature, and the higher the reaction temperature, the lower the carbon content. The preparation of the boron nitride porous material by this method is simple, has little environmental pollution, but requires a high reaction temperature and high energy consumption.
Microporous boron nitride material
The microporous boron nitride material has a small and relatively uniform pore size, which can be obtained by directly pyrolyzing a suitable precursor, has a large specific surface area, a narrow pore size distribution, and has good chemical stability, and can be used for gas adsorption and separation. And other fields.
Mesoporous boron nitride material
Mesoporous boron nitride is one of the most studied porous boron nitride materials. It has a moderate pore size, large specific surface area and stable chemical properties. It has broad application prospects in gas adsorption and catalysis.
Ordered mesoporous boron nitride material
The ordered mesoporous boron nitride material has a periodic arrangement of pore structure and a large specific surface area, and the pore size distribution is narrow, and the application prospect is broad. The synthetic ordered mesoporous boron nitride material mainly adopts a template method, especially a hard template method. The hard templating method generally uses mesoporous silicon or mesoporous carbon as a template, and then impregnates the pores with a boron nitride precursor to be pyrolyzed to obtain an ordered mesoporous boron nitride material. The pore structure of the template and the degree of impregnation of the template by the precursor directly affect the morphology of the mesoporous boron nitride.
Disordered mesoporous boron nitride material
The pores of the disordered mesoporous boron nitride material are disorderly arranged, and the pore size distribution is relatively wide. The material can be prepared by a template method, a high pressure reaction method or a direct pyrolytic boron nitride precursor.
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