Gas adsorption by nanoporous materials: Future applications and experimental challenges
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Introduction Over the last century or so, the use of synthetic adsorbents in industrial gas separation and purification has become widespread.1–6 As a result, pressure swing adsorption (PSA), the most common separation method, is now a mature technology. The materials used traditionally in these applications include activated carbons, activated aluminas, silica gels, and zeolites.4,5,7 In recent years, the number of available adsorbents has increased significantly and now includes ordered mesoporous silicas,8,9 permanently microporous metal-organic frameworks,10–14 covalent organic frameworks,15 and amorphous microporous organic polymers.16–18 The dramatic growth in the range of materials and our ability to control their properties and characterize them at the nanometer scale, combined with a technological focus on the development of clean energy sources, has led to worldwide research efforts aimed at new gas storage, separation, and purification applications. Characterizing the adsorption properties of a material under practical conditions is crucial both to assess its suitability for a specific task and to improve our understanding of the processes involved. Gas storage requires elevated pressures due to volumetric capacity considerations and the need to deliver gas at ambient pressure or above. Separation and purification, meanwhile, involve the selective adsorption of particular species from gas mixtures. However, both high
pressures and multicomponent adsorption pose significant experimental challenges. In this article, following an introduction to nanoporous materials, we cover some emerging gas adsorption applications and discuss the associated measurement challenges.
Nanoporous materials and their gas adsorption properties The term nanoporous refers to any material with a pore size below ~100 nm. This encompasses both the microporous (
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