두 가지 합성법(전구체 방법, 방법-P; 기존 방법, 방법-C)으로, 화학식은 [Zn(Im)2-x(mIm)x] (Im = imidazolate, mIm = 2-methylimidazolate; x = 0 ∼ 2)로 같지만, 구조형태가 다른 견고한 골격의 SOD 형태 ZIF-8x와 유연한 골격의 MER 형태 ZIF-mer를 구분하여 합성하였다. 동시에, ZIF-8x와 ZIF-mer 골격 각각의 경직 특성을 고려하여 화학적 조성 또는 이미다졸들의 존재 비율 (Im/mIm 또는 화학식 [Zn(Im)2-x(mIm)x]에서의 x 값)을 조절하여 두 경우 모두 비표면적을 증가시킬 수 있었다. 방법-C에서는, 고정된 양의 Zn(NO3)2·6H2O (0.67 mmol)과 반응하는 이미다졸 (Im-H) 및 2-메틸이미다졸 (mIm-H)의 양을 조절하여 ZIF-8x(C)와 ZIF-mer(C)를 각각 구분하여 합성할 수 있었다. 생성된 결정들의 구조형태는 분말 X-선 회절법으로 확인하였고, 골격에서의 이미다졸들의 존재 비율은 핵자기 공명 분광법으로 결정하였다. ZIF-8x(C)의 경우 [Zn(Im)2-x(mIm)x]에서 x = 0.96 또는 1.34인 두 종류 생성물이 얻어지며, ZIF-mer(C)는 x = 0.45인 생성물만이 얻어졌다.전구체 방법(방법-P)에서는 전구체와 외부의 이미다졸을 반응시켜 구조형태의 변화를 유도하였다. 미리 합성한 일정량의 준안정성의 ZIF-pcb [Zn(Im)2]를 mIm-H (2 ∼ 10 mmol)와 반응시켜 일련의 SOD ZIF-8x(P) (x = 0.93 ∼ 1.36)를 생성시켰다. 이 중에서 x = 0.96인 ZIF-8x(P)를 1,1’-carbonyldiimidazole(CDI)과 반응시켜 ZIF-mer(P) (x = 0.14)를 얻었다. 만일 방법-C로 합성한 ZIF-8x(C) (x = 1.34)를 전구체로 이용하면 ZIF-mer(P) (x = 0.14)를 얻을 수 있었다.77K에서 측정된 질소 흡착 등온선으로 계산된 ZIF-8x(C)의 BET 표면적은 x = 0.96, 1.34에 대하여 각각 1881, 1828 m2/g이었고, ZIF-8x(P)은 x = 0.93, 1.17, 1.36에 대하여 각각 1379, 1590, 1658 m2/g이었다. 별도로 합성한 순수한 ZIF-8 (x = 2, Zn(mIm)2)의 비표면적 1568 m2/g과 비교할 때, ZIF-8x(C)는 약 1.2배 증가한 비표면적을 가진다. ZIF-8과 ZIF-8x(C) (x = 0.96)에 대한 각각의 CH4 기체 흡착(상온, 70 bar) 실험은 ZIF-8x(C)는 ZIF-8보다 1.4배 더 많은 총 저장량(172 cm3/cm3)을 가짐을 보여주었다.ZIF-mer(C) (x = 0.45)의 BET 비표면적은 1114 m2/g로서, ZIF-mer(P) (x = 0.14)의 74 m2/g보다 월등하게 크게 측정되었다. 하지만 ZIF-mer(C)도 흡·탈착 과정을 2회 반복하면, 비표면적이 48 m2/g로 매우 감소하였다. 이에 ZIF-mer(C) (x = 0.45)와 mIm-H를 반응시켜, 골격 내에 mIm의 비율이 증가한 ZIF-mer (x = 0.96)을 얻었다. 이 ZIF-mer는 반복된 흡·탈착 과정에도 비표면적의 감소가 없었다.
With two synthetic methods (Precursor method or Method-P, Conventional method or Method-C), rigid SOD-type ZIF-8x and flexible MER-type ZIF-mer were respectively synthesized, where both ZIFs have the same formula of [Zn(Im)2-x(mIm)x] (Im = imidazolate, mIm = 2-methylimidazolate; x = 0 to 2) although their topologies are different. At the same time, their chemical compositions (or the value of x in the formula) could be adjusted by taking into account the rigidity characteristics of each framework, leading to a significant increase in their specific surface areas.In Method-C, the phase-pure ZIF-8x(C) and ZIF-mer(C) could be respectively obtained by adjusting the amount of imidazole (Im-H) and 2-methylimidazole (mIm-H) reacting with a fixed amount of Zn(NO3)2·6H2O (0.67 mmol). The structural types of the resulting crystals were confirmed by powder X-ray diffraction methods, and the ratios of imidazoles in the frameworks were determined by nuclear magnetic resonance spectroscopy. Two ZIF-8x(C) products had x = 0.96 or 1.34 in the formula [Zn(Im)2-x(mIm)x], while ZIF-mer(C) was produced only with x = 0.45.In Method-P, a precursor ZIF was reacted with exogenous imidazole to induce a change in framework structures. A predetermined amount of metastable ZIF-pcb formulated as Zn(Im)2 was reacted with mIm-H (2 ∼ 10 mmol) to produce a series of SOD ZIF-8x(P) crystals with x = 0.93 ∼ 1.36. In turn, a ZIF-8x(P) sample having x = 0.96 was selected and reacted with 1,1’-carbonyldiimidazole (CDI), resulting ZIF-mer(P) having x = 0.14. If ZIF-8x(C) (x = 1.34) instead of ZIF-8x(P) was used as a precursor, ZIF-mer(P) having x = 0.14 was produced.The BET surface areas of ZIF-8x(C) calculated by N2 adsorption isotherms measured at 77K were 1881 and 1828 m2/g respectively for x = 0.96 and 1.34, and those of ZIF-8x(P) were 1379, 1590, and 1658 m2/g respectively for x = 0.93, 1.17, and 1.36. The ZIF-8x(C) products have 1.2 times greater specific surface areas than 1568 m2/g of pristine ZIF-8 (Zn(mIm)2). The CH4 gas adsorption isotherms measured at 298 K and 70 bar showed that ZIF-8x(C) (x = 0.96) had 1.4 times more total uptake capacity (172 cm3/cm3) than ZIF-8. The BET surface area of ZIF-mer(C) (x = 0.45) was 1114 m2/g, which was significantly larger than 74 m2/g of ZIF-mer(P) (x = 0.14). However, the specific surface area of ZIF-mer(C) was greatly reduced to 48 m2/g after two adsorption/desorption cycles. Therefore, ZIF-mer(C) (x = 0.45) was further reacted with mIm-H to obtain ZIF-mer (x = 0.96) with an increased amount of mIm in the framework, which maintained the initial surface area after a repeated measurement.