Towards addressing environmental challenges: rational design of metal-organic frameworks-based photocatalysts via a microdroplet approach

Metal-organic frameworks (MOFs) have attracted much attention in the past decades owing to their amazing properties, including rich surface chemistry, flexible structure, superior surface area, and tunable porosity. MOFs are conventionally synthesized via wet-chemistry methods, which, however, are oftentimes plagued by long reaction durations, inhomogeneous mixing, and limited batch processes. This article reviews a rapid microdroplet-based nanomanufacturing process to fabricate MOFs-based functional materials with controlled hierarchical nanostructures to overcome the aforementioned disadvantages of wet-chemistry processes. The general formation pathways of MOFs inside the microdroplets were investigated by both experimental and theoretical approaches. Further, strategies to integrate MOFs with semiconductors to form hybrid photocatalysts are also summarized towards addressing environmental challenges, with a major focus on CO2 photoreduction. The quantitative mechanisms of CO2 adsorption, activation, and charge transfer within the hybrid nanostructures were explored by various in-situ techniques, such as diffuse reflectance infrared Fourier transform spectroscopy, photoluminescence spectroscopy, and x-ray photoelectron spectroscopy. This review provides a new avenue for the rational design of MOFs-based functional materials to tackle a variety of environmental issues, including but not limited to global warming, air pollution, and water contamination.