The role of temperature and adsorbate on negative gas adsorption transitions of the mesoporous metal–organic framework DUT-49,Faraday Discussions

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The role of temperature and adsorbate on negative gas adsorption transitions of the mesoporous metal–organic framework DUT-49
Faraday Discussions ( IF 3.3 ) Pub Date : 2020-04-30 , DOI: 10.1039/d0fd00013b
Simon Krause _{1,

2,

3,

4,

5} , Jack D. Evans _{1,

2,

3,

4} , Volodymyr Bon _{1,

2,

3,

4} , Irena Senkovska _{1,

2,

3,

4} , François-Xavier Coudert _{6,

7,

8,

9,

10} , Daniel M. Többens _{4,

11,

12} , Dirk Wallacher _{4,

11,

12} , Nico Grimm _{4,

11,

12} , Stefan Kaskel _{1,

2,

3,

4}

Affiliation

Unusual adsorption phenomena, such as breathing and negative gas adsorption (NGA), are rare and challenge our thermodynamic understanding of adsorption in deformable porous solids. In particular, NGA appears to break the rules of thermodynamics in these materials by exhibiting a spontaneous release of gas accompanying an increase in pressure. This anomaly relies on long-lived metastable states. A fundamental understanding of this process is desperately required for the discovery of new materials with this exotic property. Interestingly, NGA was initially observed upon adsorption of methane at relatively low temperature, close to the respective standard boiling point of the adsorptive, and no NGA was observed at elevated temperatures. In this contribution, we present an extensive investigation of adsorption of an array of gases at various temperatures on DUT-49, a material which features an NGA transition. Experiments, featuring a wide range of gases and vapors at temperatures ranging from 21–308 K, were used to identify for each guest a critical temperature range in which NGA can be detected. The experimental results were complemented by molecular simulations that help to rationalize the absence of NGA at elevated temperatures, and the non-monotonic behavior present upon temperature decrease. Furthermore, this in-depth analysis highlights the crucial thermodynamic and kinetic conditions for NGA, which are unique to each guest and potentially other solids with similar effects. We expect this exploration to provide detailed guidelines for experimentally discovering NGA and related “rule breaking” phenomena in novel and already known materials, and provide the conditions required for the application of this effect, for example as pressure amplifying materials.

中文翻译：

温度和被吸附物对介孔金属-有机骨架DUT-49的负气体吸附转变的作用

罕见的吸附现象（如呼吸和负气体吸附（NGA））很少见，并挑战了我们对可变形多孔固体中吸附的热力学理解。尤其是，NGA似乎随着压力的增加而自发释放气体，从而打破了这些材料中的热力学规则。这种异常依赖于长期存在的亚稳态。迫切需要对这一过程有一个基本的了解，以发现具有这种奇异特性的新材料。有趣的是，最初在相对较低的温度（接近吸附剂各自的标准沸点）吸附甲烷时观察到NGA，而在升高的温度下未观察到NGA。在这项贡献中，我们对DUT-49（一种具有NGA过渡特性的材料）在不同温度下吸附一系列气体进行了广泛的研究。实验采用了温度范围为21–308 K的各种气体和蒸气，用于为每位来宾确定可以检测NGA的临界温度范围。实验结果得到了分子模拟的补充，这有助于合理化在高温下不存在NGA的情况，以及在温度降低时出现的非单调行为。此外，此深入分析突出显示了NGA的关键热力学和动力学条件，这对于每位来宾以及可能具有相似作用的其他固体都是唯一的。

更新日期：2020-04-30

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