Unusual and Highly Tunable Missing-Linker Defects in Zirconium Metal鈥揙rganic Framework UiO-66 and Their Important Effects on Gas Adsorption

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• 作者：Hui Wu ; Yong Shen Chua ; Vaiva Krungleviciute ; Madhusudan Tyagi ; Ping Chen ; Taner Yildirim ; Wei Zhou
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：July 17, 2013
• 年：2013
• 卷：135
• 期：28
• 页码：10525-10532
• 全文大小：504K
• 年卷期：v.135,no.28(July 17, 2013)
• ISSN：1520-5126

文摘

UiO-66 is a highly important prototypical zirconium metal鈥搊rganic framework (MOF) compound because of its excellent stabilities not typically found in common porous MOFs. In its perfect crystal structure, each Zr metal center is fully coordinated by 12 organic linkers to form a highly connected framework. Using high-resolution neutron power diffraction technique, we found the first direct structural evidence showing that real UiO-66 material contains significant amount of missing-linker defects, an unusual phenomenon for MOFs. The concentration of the missing-linker defects is surprisingly high, 10% in our sample, effectively reducing the framework connection from 12 to 11. We show that by varying the concentration of the acetic acid modulator and the synthesis time, the linker vacancies can be tuned systematically, leading to dramatically enhanced porosity. We obtained samples with pore volumes ranging from 0.44 to 1.0 cm³/g and Brunauer鈥揈mmett鈥揟eller surface areas ranging from 1000 to 1600 m²/g, the largest values of which are 150% and 60% higher than the theoretical values of defect-free UiO-66 crystal, respectively. The linker vacancies also have profound effects on the gas adsorption behaviors of UiO-66, in particular CO₂. Finally, comparing the gas adsorption of hydroxylated and dehydroxylated UiO-66, we found that the former performs systematically better than the latter (particularly for CO₂) suggesting the beneficial effect of the 鈭扥H groups. This finding is of great importance because hydroxylated UiO-66 is the practically more relevant, non-air-sensitive form of this MOF. The preferred gas adsorption on the metal center was confirmed by neutron diffraction measurements, and the gas binding strength enhancement by the 鈭扥H group was further supported by our first-principles calculations.