Unraveling the molecular mechanism for enhanced gas adsorption in mixed-metal MOFs via solid-state NMR spectroscopy

• 成果类型: Article
• 署名作者: Yan, Tao; Hou, Huaming; Wu, Changzong; Cai, Yuhang; Yin, Anping; Cao, Zhi; Liu, Zhong; He, Peng; Xu, Jun
• 署名单位: Nankai University; Nankai University; Chinese Academy of Sciences; Institute of Coal Chemistry, CAS; Chinese Academy of Sciences; University of Chinese Academy of Sciences, CAS; Chinese Academy of Sciences; Qinghai Institute of Salt Lakes, CAS
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-8664
• DOI: 10.1073/pnas.2312959121
• 发表日期: 2024-02-06
• 关键词: frameworks m-2(dobdc) m; organic frameworks; carbon-dioxide; co; cu3-xznx(btc)(2); reduction; mg; mn; fe; ni

摘要

The incorporation of multiple metal ions in metal-organic frameworks (MOFs) through one - pot synthesis can induce unique properties originating from specific atomic-scale spatial apportionment, but the extraction of this crucial information poses challenges. Herein, nondestructive solid-state NMR spectroscopy was used to discern the atomic-scale metal apportionment in a series of bulk Mg1-xCox-MOF-74 samples via identification and quantification of eight distinct arrangements of Mg/Co ions labeled with a 13C- carboxylate, relative to Co content. Due to the structural characteristics of metal- oxygen chains, the number of metal permutations is infinite for Mg1-xCox-MOF-74, making the resolution of atomic-scale metal apportionment particularly challenging. The results were then employed in density functional theory calculations to unravel the molecular mechanism underlying the macroscopic adsorption properties of several industrially significant gases. It is found that the incorporation of weak adsorption sites (Mg2+ for CO and Co2+for CO2 adsorption) into the MOF structure counterintuitively boosts the gas adsorption energy on strong sites (Co2+ for CO and Mg2+ for CO2 adsorption). Such effect is significant even for Co2+ remote from Mg2+ in the metal- oxygen chain, resulting in a greater enhancement of CO adsorption across a broad composition range, while the enhancement of CO2 adsorption is restricted to Mg2+ with adjacent Co2+. Dynamic breakthrough measurements unambiguously verified the trend in gas adsorption as a function of metal composition. This research thus illuminates the interplay between atomic-scale structures and macroscopic gas adsorption properties in mixed-metal MOFs and derived materials, paving the way for developing superior functional materials.