In Situ Nanoscale Infrared Spectroscopy of Water Adsorption on Nano-Islands of Surface-Anchored Metal-Organic Frameworks

Abstract

Despite technological advancements, probing gas-solid interfaces at the nanoscale is still a formidable challenge. New nano-spectroscopic methods are needed to understand the guest–host interactions of functional materials during gas sorption, separation, and conversion. Herein, we introduce in situ Photoinduced Force Microscopy (PiFM) to evidence site-specific interaction between Metal-Organic Frameworks (MOFs) and water. To this end, we developed amphiphilic Surface-anchored MOF (SURMOF) model systems using self-assembly for the side-by-side hetero-growth of nanodomains of hydrophilic HKUST-1 and hydrophobic ZIF-8. PiFM was used to probe local uptake kinetics and to show D 2O sorption isotherms on (defective) HKUST-1 paddlewheels. By monitoring defect vibrations, we visualized in real-time the saturation of existing defects and the creation of D 2O-induced defects. This work shows the potential of in situ PiFM to unravel gas sorption mechanisms and map active sites on functional (MOF) materials.