Distinguishing Three Colorations: A Designed Experiment for Chemistry Laboratory

The mechanisms and appearances of coloration are captivating aspects of optical science. Although university courses touch upon relevant knowledge, including pigment-based, physical, and luminescent colorations, it remains challenging for most students to distinguish between these types. This paper presents an innovative teaching experiment that combines these three types of colorations into a single substrate designed to enhance the understanding of distinct coloration mechanisms and their applications. MAF-4 (ZIF-8; chemical formula Zn(mim)2), a prototypical zinc-based metal–organic framework constructed from Zn2+ nodes and 2-methylimidazole (Hmim) linkers, is employed as the substrate of these colorations by leveraging its high porosity and crystallinity. The synthesis and characterization of submicrometer MAF-4 crystals are introduced in this course. MAF-4 photonic crystals are prepared via drop-coating. Three types of colorations can be observed in MAF-4 simultaneously. The entire experimental process is environmentally friendly and easy to operate. Designed to explore an effective pedagogical method, it demystifies confusing concepts, helping students both distinguish colorations of diverse origins and analyze problems from the appearance to the essence.