Casting and recycling of insoluble, labile single-crystal coordination polymer through reversible solid-liquid-solid transition

Reversible solid-liquid-solid transition controlled by temperature or solvent plays a vital role in manufacturing and recycling many important materials. However, this kind of transition is hard to be realized for insoluble and labile materials, for instance coordination polymers. In this work, we introduce a volatile dissociating agent to realize reversible liquification and solidification of a kind of coordination polymer, Prussian blue. The Prussian blue powders are disassociated into electrolytic solution by hydrochloride acid (the volatile dissociating agent) and transformed back to solids via volatilization of the hydrochloride vapor. Using this solid-liquid-solid transition, Prussian blue powders are cast into single crystals with various shapes (i.e., inverse opal, mesoporous) or single-crystal matrix composites with functional networks encapsulated (i.e., carbon, silicon, TiO₂). Significant improvements of the performance of Prussian blue in secondary battery, seawater battery, water treatment, etc., are observed after casting. Moreover, all of the cast Prussian blue materials can be recycled.