Chiu Nan Chieh, Loughran Ryan P, Gładysiak Andrzej, Vismara Rebecca, Park Ah-Hyung Alissa, Stylianou Kyriakos C
Materials Discovery Laboratory (MaD Lab), Department of Chemistry, Oregon State University, Corvallis, Oregon, USA.
Department of Earth and Environmental Engineering, Department of Chemical Engineering, Lenfest Center for Sustainable Energy, Columbia University, New York, USA.
Nanoscale. 2022 Oct 21;14(40):14962-14969. doi: 10.1039/d2nr04156a.
Herein, we describe the use of an ultramicroporous metal-organic framework (MOF) with a composition of [Ni(pzdc)(ade)(HO)]·(HO) (pzdc: 3,5-pyrazole dicarboxylic acid; ade: adenine), for the selective capture of carbon dioxide (CO) from wet flue gas followed by its conversion to value-added products. This MOF is comprised of one-dimensional Ni(II)-pyrazole dicarboxylate-adenine chains; through pi-pi stacking and H-bonding interactions, these one-dimensional chains stack into a three-dimensional supramolecular structure with a one-dimensional pore network. Upon heating, our MOF undergoes a color change from light blue to lavender, indicating a change in the coordination geometry of Ni(II). Variable temperature ultraviolet-visible (UV/vis) spectroscopy data revealed a blue shift of the d-d transitions, suggesting a change in the Ni-coordination geometry from octahedral to a mixture of square planar and square pyramidal. The removal of the water molecules coordinated to Ni(II) leads to the generation of a MOF with open Ni(II) sites. Nitrogen isotherms collected at 77 K and 1 bar revealed that this MOF is microporous with a pore volume of 0.130 cm g. Carbon dioxide isotherms show a step in the uptake at low pressure, after which the CO uptake is saturated. The step in the CO uptake is likely attributable to the rearrangement of the three-dimensional supramolecular structure to accommodate CO within its pores. The affinity of this MOF for CO is 35.5 kJ mol at low loadings, and it increases to 41.9 kJ mol at high loadings. While our MOF is porous to CO and water (HO) at 298 K, it is not porous to N, and the CO/N selectivity increases from 28.5 to 31.5 as a function of pressure. Breakthrough experiments reveal that this MOF can capture CO from dry and wet flue gas with uptake capacities of 1.48 ± 0.01 and 1.14 ± 0.06 mmol g, respectively. The MOF can be regenerated and reused at least three times, demonstrating consistent CO uptake capacities. Upon understanding the sorption behavior of this MOF, catalysis experiments show that the MOF is catalytically active in the fixation of CO into an epoxide ring for the formation of a cyclic carbonate. The turnover frequency for this reaction is 21.95 ± 0.03 h. The MOF showed no catalytic deterioration after two cycles and maintained comparable catalytic activity when dry and wet CO/N mixtures were used. This highlights that both N and HO do not dramatically affect the catalytic activity of our MOF toward CO fixation.
在此，我们描述了一种超微孔金属有机框架（MOF），其组成为[Ni(pzdc)(ade)(H₂O)]·(H₂O)（pzdc：3,5-吡唑二甲酸；ade：腺嘌呤），用于从湿烟道气中选择性捕获二氧化碳（CO₂），随后将其转化为高附加值产品。这种MOF由一维Ni(II)-吡唑二甲酸酯-腺嘌呤链组成；通过π-π堆积和氢键相互作用，这些一维链堆积成具有一维孔网络的三维超分子结构。加热时，我们的MOF会从浅蓝色变为淡紫色，表明Ni(II)的配位几何结构发生了变化。变温紫外-可见（UV/vis）光谱数据显示d-d跃迁发生蓝移，表明Ni配位几何结构从八面体变为平面正方形和正方锥的混合结构。去除与Ni(II)配位的水分子会导致产生具有开放Ni(II)位点的MOF。在77 K和1 bar下收集的氮气等温线表明，这种MOF是微孔的，孔体积为0.130 cm³ g⁻¹。二氧化碳等温线显示在低压下吸收有一个台阶，之后CO₂吸收饱和。CO₂吸收的台阶可能归因于三维超分子结构的重排，以在其孔中容纳CO₂。在低负载量下，这种MOF对CO₂的亲和力为35.5 kJ mol⁻¹，在高负载量下增加到41.9 kJ mol⁻¹。虽然我们的MOF在298 K时对CO₂和水（H₂O）是多孔的，但对N₂不是多孔的，并且CO₂/N₂选择性随压力从28.5增加到31.5。突破实验表明，这种MOF可以从干、湿烟道气中捕获CO₂，吸收容量分别为1.48 ± 0.01和1.14 ± 0.06 mmol g⁻¹。该MOF可以再生并重复使用至少三次，显示出一致的CO₂吸收容量。在了解这种MOF的吸附行为后，催化实验表明，该MOF在将CO₂固定到环氧环中以形成环状碳酸酯方面具有催化活性。该反应的周转频率为21.95 ± 0.03 h⁻¹。在两个循环后，该MOF没有显示出催化劣化，并且当使用干、湿CO₂/N₂混合物时保持了相当的催化活性。这突出表明N₂和H₂O都不会显著影响我们的MOF对CO₂固定的催化活性。
