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<p>Co-ZIF-67 (Zeolitic Imidazolate Framework) is a porous material in which cobalt (Co) metal ions are tetrahedrally coordinated with organic ligands. It exhibits unique properties by combining the advantages of both zeolites and metal–organic frameworks (MOFs), including high surface area and structural tunability. Due to these characteristics, Co-ZIF-67 is widely studied for applications such as gas separation, making it an important target for research. A large single crystal of Co-ZIF-67 was successfully synthesized using a simple solvothermal method. Dehydration and demethylation of the 2-methylimidazole in Co-ZIF-67, as well as altering the central metal, change the aperture size and affect the types of gases that can be separated. Therefore, dehydrated, demethylated, and hybrid Co-ZIF-67s containing cobalt (Co) and zinc (Zn) were prepared in this work. These crystal structures were analyzed using single-crystal synchrotron X-ray diffraction techniques. In the untreated Co-ZIF-67 single crystal, water molecules were located at two sites opposite the 6-ring, with eight molecules per unit cell. Heat treatment at 673&#xa0;K completely removed the water molecules without loss of crystallinity, and demethylation began at 683&#xa0;K. As the temperature increased, the number of carbon atoms at C3 per unit cell decreased, indicating the gradual removal of methyl groups. Measurement of the 6-ring aperture size revealed that heat-treated crystals had larger aperture sizes compared to untreated Co-ZIF-67 (crystal 1). However, at 753&#xa0;K, single-crystal X-ray diffraction data could not be obtained due to the loss of Co-ZIF-67 crystallinity. In the case of Co/Zn-ZIF-67 single crystals synthesized with different molar ratios, the structures were similar to those of Co-ZIF-67 single crystals, with Co exhibiting higher occupancy rates compare to Zn. Additionally, the Co/Zn-ZIF-67 demonstrated smaller unit cell parameters compared to Co-ZIF-67 (crystal 1). Consequently, the aperture size of the Co/Zn-ZIF-67 with tuning of the amount of Co and Zn was smaller than that of Co-ZIF-67 (crystal 1).</p>

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Fine-tuning the aperture size of Co-ZIF-67 via dehydration, demethylation, and Co-Zn hybridization

  • 期刊论文

  • 发表日期：

    2025年11月19日

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  • Hu Sik Kim,
  • Ga Eon Song,
  • Hyeon Uk Choo,
  • Woo Taik Lim

摘要

Co-ZIF-67 (Zeolitic Imidazolate Framework) is a porous material in which cobalt (Co) metal ions are tetrahedrally coordinated with organic ligands. It exhibits unique properties by combining the advantages of both zeolites and metal–organic frameworks (MOFs), including high surface area and structural tunability. Due to these characteristics, Co-ZIF-67 is widely studied for applications such as gas separation, making it an important target for research. A large single crystal of Co-ZIF-67 was successfully synthesized using a simple solvothermal method. Dehydration and demethylation of the 2-methylimidazole in Co-ZIF-67, as well as altering the central metal, change the aperture size and affect the types of gases that can be separated. Therefore, dehydrated, demethylated, and hybrid Co-ZIF-67s containing cobalt (Co) and zinc (Zn) were prepared in this work. These crystal structures were analyzed using single-crystal synchrotron X-ray diffraction techniques. In the untreated Co-ZIF-67 single crystal, water molecules were located at two sites opposite the 6-ring, with eight molecules per unit cell. Heat treatment at 673 K completely removed the water molecules without loss of crystallinity, and demethylation began at 683 K. As the temperature increased, the number of carbon atoms at C3 per unit cell decreased, indicating the gradual removal of methyl groups. Measurement of the 6-ring aperture size revealed that heat-treated crystals had larger aperture sizes compared to untreated Co-ZIF-67 (crystal 1). However, at 753 K, single-crystal X-ray diffraction data could not be obtained due to the loss of Co-ZIF-67 crystallinity. In the case of Co/Zn-ZIF-67 single crystals synthesized with different molar ratios, the structures were similar to those of Co-ZIF-67 single crystals, with Co exhibiting higher occupancy rates compare to Zn. Additionally, the Co/Zn-ZIF-67 demonstrated smaller unit cell parameters compared to Co-ZIF-67 (crystal 1). Consequently, the aperture size of the Co/Zn-ZIF-67 with tuning of the amount of Co and Zn was smaller than that of Co-ZIF-67 (crystal 1).