Crystal Growth of Metal–Organic Framework‑5 around Cellulose-Based Fibers Having a Necklace Morphology

Herein, metal-organic framework (MOF)-5 crystals were grown on cellulose-based substrates including paper and cotton. Dopamine was used as a surface modification agent to improve the compatibility between MOF-5 crystals and the used substrates. The formed polydopamine film promoted the growth of MOF-5 crystals, which were bonded to the substrates. Besides dopamine, the structure of the substrate also played a major role in the crystal growth. In the case of paper, which had a structure with fibers closely packed to each other, MOF-5 crystals grew only on the surface of fibers (one side) and could easily fall off. Unlike paper, the cotton bulb had a looser structure and MOF-5 crystals grew around the fibers, forming a stable "necklace" morphology. The effects of dopamine modification on the crystal growth and the formation of "necklace" morphology were investigated using scanning electron microscopy analysis. The crystalline structure of MOF-5 was confirmed using X-ray diffraction. To determine how firmly crystals were attached to the cotton fibers, the substrates were exposed to a constant and strong air flow. It was found that the dopamine-modified cotton increased the strength of MOF-5 crystals attached to fibers. This work demonstrated the firm attachment of MOF-5 crystals onto the substrate, facilitating various potential applications.