New strategy for forming and recovering poorly soluble, pyrolyzable single crystal coordination polymers

On June 1, 2023, Hu Ming et al. of East China Normal University published a research result entitled “Casting and recycling of insoluble, labile single-crystal coordination polymer through reversible solid-liquid-solid transition” in the journal Matter.

This achievement breaks through the long-term difficulties of forming and recycling of Prussian blue materials that are difficult to solubilize and easy to pyrolyze, and reversibly triggers the solid-liquid phase transformation of Prussian blue materials under the action of volatile hydrochloric acid, and establishes the solidification forming and recycling principle of Prussian blue materials. The technical solution based on this principle has successfully realized the manufacture of Prussian blue micro-single crystal particles and their composite materials with various structures, regulated the material properties, and has potential application value in potassium-ion batteries, seawater batteries, catalytic degradation and other fields, and provides new ideas for the forming and recycling of other poorly soluble and pyrolytic materials (such as coordination polymers).

The corresponding author of the paper is Professor Hu Ming of East China Normal University, and the first authors are Zhang Wei and Xia Lingling.

Reversible solid-liquid two-phase transitions play a key role in material forming. Temperature or solvent control enables solid-fluid reversible changes in important materials such as metals, thermoplastics and glass. Therefore, casting and other processes can be established to realize the solidification forming and compounding of materials, and the development of recycling treatment processes to recycle materials. However, for some materials that are insoluble or have poor thermal stability, such as coordination polymers, although they show great potential in many applications, their industrial manufacturing and recycling are still difficult.

In this work, the authors chose a coordination polymer (Prussian blue) with very low solubility (Ksp, 1x.10–43) and easy decomposition. As early as the eighteenth century, Prussian blue was known as a blue dye. After hundreds of years of development, Prussian blue has become a functional material with a wide range of applications. However, due to the characteristics of Prussian blue that is easy to decompose and has very low solubility, its forming processing and recycling have faced long-term challenges, which seriously restrict the actual production and utilization. In this paper, the authors introduce volatile hydrochloric acid to successfully achieve reversible solid-liquid two-phase transition in the Prussian blue system. Prussian blue in solid powder form can be decomposed into Fe3+ and in concentrated hydrochloric acid[Fe(CN)6]4+ ions, and dissolve to form a solution. After that, accompanied by the volatilization of hydrogen chloride molecules in hydrochloric acid, Fe3+ and[Fe(CN)6]The 4+ ions will combine again to form solid Prussian blue. Based on the above solid-liquid transformation, the authors cast single-crystal granular materials with a variety of morphological structures (macroporous anti-protein structure, mesoporous structure and columnar pore structure) and single crystal matrix composites embedded with a variety of reinforcements (silicon nanoparticles, conductive carbon particles, titanium dioxide particles and carbon nanotubes), and successfully established a recycling scheme to realize the effective recovery and regeneration of single crystal particles and composite structures. The results show that structural regulation can significantly change the gas adsorption, ion intercalation, decentralization and conductivity of materials, and reproduce them in the process of multiple recycling. This technology narrows the gap between chemical synthesis and industrial processing and recycling of Prussian blue materials, and is expected to be extended to other coordination polymer molding and recycling in the future.

Figure 1: Schematic diagram of the casting and recycling of Prussian blue.

Figure 2: Single crystal Prussian blue particles with different morphological structures.

Figure 3: Single-crystal base Prussian blue composite.

Figure 4: Recycling of single crystal Prussian blue and its composites.

This work was supported by the National Natural Science Foundation of China (52173252). (Source: Science Network)

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