超临界CO_2在多孔材料合成中的应用

Advances of supercritical CO_2 application in porous materials synthesis

超临界流体技术作为一种绿色技术在多孔材料合成领域受到了研究者的广泛关注.与传统方法相比较,利用超临界CO2制备多孔材料的方法具有方法简单、环保、产品性能好等优点,且CO2无毒、价廉、原料易得,具有很好的工业应用前景.本文概述了近年来超临界CO2在分子筛、碳纳米管、金属/复合氧化物纳米粒子、金属有机骨架材料、聚合物等多孔材料的合成方面的应用和研究进展.

Porous materials have attracted more and more attentions for variety of applications, such as gas adsorption and separation, water purification, catalysis, pharmaceutical, solar cells, supercapacitor, and sensors. Current methods for porous materials synthesis mostly use excessive organic solvent which is environmental unfriendly and need further wash or purifications. In contrast to the traditional method, supercritical fluid technology especially supercritical CO2, as a green process, is an attractive method for the synthesis of porous materials. This is because supercritical CO2 as a green solvent has many favorable properties, such as low-cost, abundant, non-toxic, non-flammable and easy to get. Furthermore, the fabrication process using supercritical CO2 is much more convenient as the process pressure and temperature could be easily controlled. In addition, the produced materials have better performance than the ones synthesized by other methods. Therefore, the utilization of supercritical CO2 is a promising method for porous materials synthesis in the future. In this article, the advances in the synthesis of zeolite, carbon nanotube, meta//composite metal oxide, metal organic frameworks and polymers using supercritical CO2 method were reviewed. In the synthesis of zeolite, solvent selection is very important. Conventional organic solvents would block the pores because of high viscosity and prevent further diffusion. Supercritical CO2 has low viscosity and high mass transfer rate and this could facilitate its applications in zeolite synthesis and modification. At the same time, the mild critical conditions and high resolution of supercritical CO2 make it as a suitable medium as the template and cleaner for zeolite and carbon nanotube preparation. For carbon nanotube fabrication, supercritical CO2 could also act as carbon source for the reaction. The metal/composite metal oxide prepared by supercritical CO2 technology has better catalytic performance. In metal-organic frameworks （MOFs） synthesis, traditional vacuum process for desolvation will make the framework collapse. Supercritical CO2 could remove the solvent in the framework under mild conditions while maintain the structure. As a result, the surface area, gas adsorption capacity, and catalytic performance of MOFs could be increased. Lastly, supercritical CO2 as foaming agent for polymers synthesis was reviewed.