A Metal-Organic Framework with Optimized Open Metal Sites and Pore Spaces for High Methane Storage at Room Temperature
A Metal-Organic Framework with Optimized Open Metal Sites and Pore Spaces for High Methane Storage at Room Temperature
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DOI：
10.1002/anie.201007583
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Chen, Banglin
中科院分区：
文献类型：
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作者：
Guo, Zhiyong;Wu, Hui;Chen, Banglin
实现高容量储气材料是未来利用氢、甲烷（天然气）、乙炔等清洁能源的必要条件。虽然已经对气体存储材料进行了广泛的研究，但是迄今为止还没有实现满足在室温和中等压力下所需的存储容量的可行的储氢材料，而乙炔的爆炸性质使其不能作为最优先考虑的;因此甲烷（天然气）被认为是最有前途的替代能源，特别是对于移动的应用。[1]事实上，MOF（金属有机框架）甲烷燃料箱已经在测试车辆中实施。[2]具有大孔隙空间和高表面积的高度多孔的M0 F显然有利于高气体储存容量;然而，与气体分子的相对弱的相互作用将其高气体储存容量限制在低温（例如，对于H2为77 K）或高压（高达100巴）以充分利用孔隙空间。[3-11]此外，一些极多孔的MOF的低骨架密度也限制了它们的体积气体储存能力，这是在移动的应用中实际实施这种材料的另一个重要参数。因此，用于高体积气体储存的理想的MOF材料是具有中等孔隙率的那些，其中孔隙空间和功能位点通过与气体分子的强相互作用而被有效地利用;因此它们的储存容量可以在室温和35巴的较低压力下被最大化。我们的设计原则，以最大限度地提高高密度甲烷储存是1）高密度开放的金属网站和2）构建合适的孔隙空间内的金属有机框架。我们在此报告其在[Cu 3（BHB）]中的实施。（我们称之为UTSA-20; UTSA=德克萨斯大学圣安东尼奥分校），其结构基于zyg拓扑的新型三结点（3，3，4）网（图1c），[12]由六羧酸有机连接体H6 BHB自组装形成（H6 BHB = 3，3 '，3“，5，5'，5”-苯-1，3，5-三基六苯甲酸，图1a）与桨轮Cu 2-（COO）4 SBU（图1 B）。[13]开放的铜网站的密度已被固定的六个羧酸盐，而孔隙空间已被优化的m-benzenedicarboxylate部分和中央苯骨架。UTSA-20中开放铜位点的高密度和最佳孔隙空间使其能够充分用于甲烷储存，突出显示UTSA-20是在300 K和35 bar下微孔中具有最高甲烷储存密度（0.222 gcm 3）的材料。195 cm 3/cm 3的总绝对体积甲烷储存导致UTSA-20成为在室温和35巴下超过180 cm 3/cm 3/cm 3的DOE甲烷储存目标的极少数M0 F之一。[14]通过H6 BHB的溶剂热反应合成了UTSA-20（10 mg，0.018 mmol）和Cu（NO3）2· 2.5 H2O（20 mg，0.086 mmol）在N，N-二甲基甲酰胺（DMF，1.5 mL）中的混合物，加入两滴HBF 4，在65 ℃下反应48小时，得到小的绿色块状晶体（15.8 mg，基于H6 BHB的产率为69%）。通过元素分析确定了配合物的化学式为[Cu 3（BHB）-（H2O）3]·（DMF）6（H2O）2.5。[15]丙酮交换的UTSA-20在高真空下于120 ℃活化24小时，用于粉末X射线衍射和气体吸附研究。如支持信息中的图S1所示，活化的UTSA-20显示出分辨率良好的PXRD图谱，这使我们能够通过粉末X射线Rietveld细化来细化结构。不出所料，桨轮……
Realization of high-capacity gas storage materials is essential to make use of clean energy resouces such as hydrogen, methane (natural gas), and acetylene in the future. Although there has been extensive research on gas storage materials, no feasible hydrogen storage materials have been achieved to date that meet the storage capacity needed at room temperature and moderate pressure, while the explosive nature of acetylene has excluded it as top priority; thus methane (natural gas) is considered to be the most promising alternative energy source, especially for mobile applications.[1] In fact, a MOF (metal–organic framework) methane fuel tank has already been implemented in test vehicles.[2] Highly porous MOFs with large pore space and high surface areas apparently favor high gas storage capacities; however, the relatively weak interactions with gas molecules have limited their high gas storage capacities to low temperature (for example, 77 K for H2) or high pressure (up to 100 bar) to fully utilize the pore space.[3–11] Furthermore, the low framework densities of some extremely porous MOFs have also limited their volumetric gas storage capacities, another important parameter for the practical implementation of such materials in mobile applications. Accordingly, the ideal MOF materials for high volumetric gas storage are those with moderate porosities in which the pore spaces and functional sites are efficiently utilized through strong interactions with gas molecules; thus their storage capacities can be maximized at room temperature and lower pressures of 35 bar. Our design principle to maximize high-density methane storage is to 1) immobilize high-density open metal sites and to 2) construct suitable pore spaces within a metal–organic framework. We report herein its implementation in [Cu3 (BHB)](which we term UTSA-20; UTSA= University of Texas at San Antonio) with a structure based on the novel trinodal (3, 3, 4) net of zyg topology (Figure 1c),[12] which is formed by the self-assembly of a hexacarboxylate organic linker H6BHB (H6BHB= 3, 3’, 3’’, 5, 5’, 5’’-benzene-1, 3, 5-triylhexabenzoic acid, Figure1a) with the paddle-wheel Cu2-(COO) 4 SBU (Figure 1 b).[13] The density of open copper sites has been secured by the six carboxylates, while the pore spaces have been optimized by the m-benzenedicarboxylate moieties and the central benzene backbone. The high density of open copper sites and optimal pore spaces within UTSA-20 has enabled them to be fully utilized for methane storage, highlighting UTSA-20 as the material with the highest methane storage density (0.222 gcmÀ3) in micropores at 300 K and 35 bar. The overall absolute volumetric methane storage of 195 cm3 cmÀ3 has resulted in UTSA-20 being one of the very few MOFs surpassing the DOE methane storage target of 180 cm3 cmÀ3 at room temperature and 35 bar.[14] UTSA-20 was synthesized by the solvothermal reaction of H6BHB (10 mg, 0.018 mmol) and Cu (NO3) 2· 2.5 H2O (20 mg, 0.086 mmol) in N, N-dimethylformamide (DMF, 1.5 mL) with addition of two drops of HBF4 at 658C for 48 hours to give small green block-shaped crystals (15.8 mg, 69% yield based on H6BHB). The compound was formulated as [Cu3 (BHB)-(H2O) 3]·(DMF) 6 (H2O) 2.5 on the basis of elemental microanalysis.[15]Acetone-exchanged UTSA-20 was activated at 1208C for 24 hours under high vacuum for powder X-ray diffraction and gas sorption studies. As shown in Figure S1 in the Supporting Information, the activated UTSA-20 exhibits a well-resolved PXRD pattern, which has allowed us to refine the structure by powder X-ray Rietveld refinement. As expected, the paddle-wheel …