Schlumberger Carola, Sandner Lukas, Michalowski Alexander, Thommes Matthias
Institute of Separation Science and Technology, Department of Chemical and Biological Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 3, 91058 Erlangen, Germany.
Langmuir. 2023 Apr 4;39(13):4611-4621. doi: 10.1021/acs.langmuir.2c03337. Epub 2023 Mar 21.
The reliable assessment of surface area is extremely important for many applications, e.g., catalysis, separation, and energy storage/conversion. Within this context, major progress has been made concerning the textural characterization of porous materials in the gas/dry state, e.g., gas physisorption and mercury porosimetry. However, these methods are not sufficient for the characterization of wet materials utilized in liquid-phase processes. For this, the application of nuclear magnetic resonance (NMR) relaxometry has been considered, but a systematic and rigorous assessment of the applicability of NMR relaxometry for reliable surface and pore size characterization of nanoporous materials is missing. Hence, we present a systematic study in which we assess the applicability of NMR relaxometry for reliable surface area assessment utilizing for the first time true surface area benchmark data based on argon 87 K adsorption on nonporous particles (silica and carbon black) coupled with the development of an advanced methodology including the investigation of the choice of the probe molecule and the effect of its accessibility to the pore network. Our results show that the method provides a fast (a few minutes per measurement) and reliable surface area of silica and carbon black model materials immersed in a liquid phase. In addition, our work clearly demonstrates the potential of NMR relaxometry for the targeted surface area assessment of defined pore classes (here ultramicropores) and suggests a new methodology for the characterization of pore entrances (pore window size). Furthermore, we investigate the effect of wettability and suggest that NMR relaxometry could be developed into a unique tool for assessing the wetting characteristics of adsorbate phases on pore surfaces. This fundamental study can be considered a first major step in enabling NMR relaxometry for reliable surface area assessment for wet materials, particularly relevant for materials used in processes occurring in a liquid phase.
对于许多应用，如催化、分离和能量存储/转换而言，可靠地评估表面积极其重要。在此背景下，在气体/干燥状态下多孔材料的结构表征方面已取得重大进展，例如气体物理吸附和压汞法。然而，这些方法不足以表征液相过程中使用的湿材料。为此，人们考虑应用核磁共振（NMR）弛豫测量法，但缺少对NMR弛豫测量法用于可靠地表征纳米多孔材料的表面和孔径的适用性进行系统且严格的评估。因此，我们开展了一项系统研究，在该研究中，我们首次利用基于氩在87 K下在无孔颗粒（二氧化硅和炭黑）上吸附的真实表面积基准数据，评估NMR弛豫测量法用于可靠地评估表面积的适用性，并开发了一种先进的方法，包括研究探针分子的选择及其对孔网络可及性的影响。我们的结果表明，该方法能快速（每次测量只需几分钟）且可靠地测定浸没在液相中的二氧化硅和炭黑模型材料的表面积。此外，我们的工作清楚地证明了NMR弛豫测量法在针对特定孔类（此处为超微孔）进行表面积评估方面的潜力，并提出了一种用于表征孔入口（孔窗尺寸）的新方法。此外，我们研究了润湿性的影响，并表明NMR弛豫测量法可发展成为一种用于评估吸附质相在孔表面润湿性特征的独特工具。这项基础研究可被视为使NMR弛豫测量法能够可靠地评估湿材料表面积的首要重要步骤，这对于在液相中发生的过程中使用的材料尤为重要。
