Matter Fabian, Niederberger Markus
Laboratory for Multifunctional Materials, Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 5, 8093 Zurich, Switzerland.
Chem Mater. 2023 Sep 20;35(19):7995-8008. doi: 10.1021/acs.chemmater.3c01218. eCollection 2023 Oct 10.
Aerogels composed of preformed titania nanocrystals exhibit a large surface area, open porosity, and high crystallinity, making these materials appealing for applications in gas-phase photocatalysis. Recent studies on nanoparticle-based titania aerogels have mainly focused on optimizing their composition to improve photocatalytic performance. Little attention has been paid to modification at the microstructural level to control fundamental properties such as gas permeability and light transmittance, although these features are of fundamental importance, especially for photocatalysts of macroscopic size. In this study, we systematically control the porosity and transparency of titania gels and aerogels by adjusting the particle loading and nonsolvent fraction during the gelation step. Mass transport and light transport were assessed by gas permeability and light attenuation measurements, and the results were related to the microstructure determined by gas sorption analysis and scanning electron microscopy. Mass transport through the aerogel network was found to proceed primarily via Knudsen diffusion leading to relatively low permeabilities in the range of 10-10 m/s, despite very high porosities of 96-99%. While permeability was found to depend mainly on particle loading, the optical properties are predominantly affected by the amount of nonsolvent during gelation, allowing independent tuning of mass and light transport.
由预制二氧化钛纳米晶体组成的气凝胶具有大表面积、开孔率和高结晶度，这使得这些材料在气相光催化应用中颇具吸引力。最近关于基于纳米颗粒的二氧化钛气凝胶的研究主要集中在优化其组成以提高光催化性能。尽管微观结构层面的特性对于宏观尺寸的光催化剂至关重要，尤其是气体渗透性和透光率等特性，但在控制这些基本特性方面，对微观结构层面的改性关注较少。在本研究中，我们通过在凝胶化步骤中调整颗粒负载量和非溶剂比例，系统地控制了二氧化钛凝胶和气凝胶的孔隙率和透明度。通过气体渗透性和光衰减测量评估了质量传输和光传输，并将结果与通过气体吸附分析和扫描电子显微镜确定的微观结构相关联。尽管气凝胶孔隙率高达96% - 99%，但发现通过气凝胶网络的质量传输主要通过克努森扩散进行，导致渗透率相对较低，在10^-10 m/s范围内。虽然发现渗透率主要取决于颗粒负载量，但光学性质主要受凝胶化过程中非溶剂用量的影响，从而可以独立调节质量传输和光传输。
