In Situ Multicolor Imaging of Photocatalytic Degradation Process of Permanganate on Single Bismuth-Based Metal-Organic Frameworks.

Bismuth-based metal-organic frameworks (Bi-MOFs) have emerged as important photocatalysts for pollutant degradation applications. Understanding the photocatalytic degradation mechanism is key to achieving technological advantage. Herein, we apply dark-field optical microscopy (DFM) to realize in situ multicolor imaging of the photocatalytic degradation process of permanganate (MnO 4 - ) on single CAU-17 Bi-MOFs. Three reaction kinetic processes such as surface adsorption, photocatalytic reduction, and disproportionation are revealed by combining the time-lapsed DFM images with optical absorption spectra, indicating that the photocatalytic reduction of purple MnO 4 - first produces beige red MnO 4 2- through a one-electron pathway, and then MnO 4 2- disproportionates into yellow MnO 2 on CAU-17. Meanwhile, we observe that the deposition of MnO 2 cocatalysts enhances the surface adsorption reaction and the photocatalytic reduction of MnO 4 - to MnO 4 2- . Unexpectedly, it is found that isopropanol as a typical hole scavenger can stabilize MnO 4 2- , avoiding disproportionation and causing the alteration of the photocatalytic reaction pathway from a one-electron avenue to a three-electron (1 + 2) process for producing MnO 2 on CAU-17. This research opens up the possibility of comprehensively tracking and understanding the photocatalytic degradation reaction at the single MOF particle level.