基于定向冷冻技术构建的多孔材料及其应用

Review of Porous Materials Derived from Using the Directional Freeze-casting Technique and Their Applications

定向冷冻技术是将原材料、溶剂及添加剂均匀混合,利用溶剂的“液-固-气”相转变获得多孔材料的一种方法,具有操作简便和绿色环保等优点。与通常的造孔技术不同,定向冷冻技术可实现对物理、化学和力学性能的高度控制,所制备的材料具有定向排列的孔隙和不同层面上的分级结构。这种技术被广泛应用于制备具有各向异性的无机、有机、杂化和碳质多孔材料。此外,该方法还可以扩展到模拟天然结构的仿生材料中,以组装具有优异力学和物理特征的多孔复合材料,在环境、能源、热管理和生物医学等领域具有广阔的应用前景。本文从定向冷冻技术的来源以及原理出发,根据单颗粒及多颗粒的受力模型揭示了定向结构的形成机理,分析了溶质、溶剂、温度梯度和添加剂等对材料结构以及性能的影响。另外,根据前驱体材料掺杂改性的不同手段,介绍了一步法与两步法制备定向结构的特点。同时,总结了定向冷冻技术在污染物吸附、能量储存与转换、结构材料、热管理和生物材料等方面的研究进展,最后指出了当前研究中亟需解决的问题,并展望了其未来的发展方向。

Directional freeze casting is a method that uses the " liquid-solid-gas" phase transformation of solvents to obtain porous materials by uniformly mixing raw materials, solvents and additives. It has the advantages of simple operation and green environmental protection. Different from the usual pore-making technology, it offers a high degree of control over the physical, chemical and mechanical properties of materials, where the materials prepared by this technology have oriented pores and hierarchical structures at different levels. Because of these characteristics, this technique is widely used in anisotropic porous inorganic, organic, hybrid and carbonaceous materials. This method can also be extended to simulate the structures of natural materials to assemble porous composites with excellent mechanical and physical properties. Finally, the method offers wide application prospects in fields such as environmental science, energy, thermal management and biology. In this paper, based on the origins and principles of directional freezing technology, the formation mechanism of a directional structure is revealed based on the force model of single and multiple particles. The effects of the solute, solvent, temperature gradient, and additives on a structure and on the properties of the materials are analyzed. In addition, according to the different means of doping modification of precursor materials, the characteristics of directional structures prepared by one-step and two-step methods are introduced. Simultaneously, the research progress of directional freezing technology in pollutant adsorption, energy storage and conversion, structural materials, thermal management, and biomaterials are summarized. Finally, the problems that must be solved in the current research are briefly described, and future developmental directions are proposed.