Ali Usman, Meinusch Rafael, Turke Kevin, Schreiner Peter R, Smarsly Bernd M
Institute of Physical Chemistry, Justus Liebig University Giessen, Heinrich-Buff-Ring 17, 35392 Giessen, Germany.
Center for Materials Research, Heinrich-Buff-Ring 16, 35392 Giessen, Germany.
Langmuir. 2025 Jun 10;41(22):13845-13859. doi: 10.1021/acs.langmuir.5c00572. Epub 2025 May 27.
Macro-mesoporous silica monolith columns, prepared by a sol-gel procedure developed by K. Nakanishi, show beneficial flow and separation properties due to their 3D-interconnected macropores in combination with mesopores, providing a high surface area. Building on this, they are routinely used in analytical liquid chromatography. Within the synthetic process, fine-tuning of the mesopore dimension and interconnection is achieved by an etching step involving hydrothermal treatment under basic conditions, typically in the range of 80 °C-100 °C. The present study aims to unravel details of this harsh procedure by a comprehensive analysis of the resulting mesoporous network. Thus, a series of silica monoliths was prepared across a range of hydrothermal treatment temperatures (HTT) between 80 and 110 °C, thereby tuning the mesoporosity. Mercury intrusion porosimetry confirmed that enhanced HTT does not alter the macropore dimension and only affects the mesopore space. The study employed state-of-the-art physisorption analysis applying two adsorptives, Ar (87 K) and N (77 K), to identify changes in the mesopore size and network connectivity as a function of HTT. Also, advanced hysteresis scanning was performed on the same materials, providing independent insights into pore network effects. These analyses indicate that increasing HTT systematically enhances the average mesopore size from 8 nm (80 °C) to approximately 25 nm (110 °C) and widens the pore size distribution, pointing to pronounced dissolution of SiO at higher HTT. Surprisingly, the total mesopore volume remains constant upon increasing the HTT, implying a dissolution-reprecipitation mechanism for SiO, rather than mere etching. Importantly, the in-depth porosity analysis reveals an increase in the size of necks, which reduces restrictions in the mesopore network connectivity. Furthermore, the data are in line with a recently proposed spatial mesopore size gradient in monoliths, which we find to be relevant at lower HTT and to systematically diminish toward higher HTT.
由K. 中谷开发的溶胶 - 凝胶法制备的宏观 - 介孔二氧化硅整体柱，由于其三维互连的大孔与介孔相结合，具有高表面积，因而展现出良好的流动和分离性能。基于此，它们在分析液相色谱中得到了常规应用。在合成过程中，通过在碱性条件下（通常在80°C - 100°C范围内）进行水热处理的蚀刻步骤，实现对介孔尺寸和互连性的微调。本研究旨在通过对所得介孔网络的全面分析来揭示这一苛刻过程的细节。因此，制备了一系列在80至110°C范围内不同水热处理温度（HTT）的二氧化硅整体柱，从而调节介孔率。压汞法证实，提高HTT不会改变大孔尺寸，只会影响介孔空间。该研究采用先进的物理吸附分析方法，应用两种吸附剂Ar（87 K）和N（77 K），以确定介孔尺寸和网络连通性随HTT的变化。此外，对相同材料进行了先进的滞后扫描，提供了关于孔网络效应的独立见解。这些分析表明，增加HTT会系统地将平均介孔尺寸从8 nm（80°C）提高到约25 nm（110°C），并拓宽孔径分布，这表明在较高HTT下SiO有明显溶解。令人惊讶的是，增加HTT时总介孔体积保持不变，这意味着SiO存在溶解 - 再沉淀机制，而不仅仅是蚀刻。重要的是，深入的孔隙率分析表明颈部尺寸增加，这减少了介孔网络连通性的限制。此外，数据与最近提出的整体柱中空间介孔尺寸梯度一致，我们发现该梯度在较低HTT时相关，并随着HTT升高而系统地减小。
