Energy-Converting Metal-Organic Nanomaterials for Biomedical and Photocatalytic Applications

Metal-organic frameworks (MOFs), an emerging class of crystalline inorganic-organic hybrid materials constructed from metal or metal-oxo secondary building units (SBUs) and organic or metal-containing bridging ligands, have been intensively explored over the past two decades. Characterized by structural regularity and tunability, compositional diversity, and intrinsic porosity, MOFs have shown tremendous potential in gas storage and separation, catalysis and photocatalysis, and biomedical imaging and therapy, among other areas. Particularly, these structural advantages of MOFs present a unique opportunity for energy-converting photoreactions, in which MOFs can hierarchically incorporate both sensitizers to capture the photons, including X-ray photons and visible-light photons, and catalysts to convert the energy of these captured photons into high-energy molecules, such as reactive oxygen species (ROSs) and solar fuels. The proximity of these incorporated components (<2 nm) within MOFs allows for facile energy transfer, in the form of electromagnetic waves or moving particles (electrons or reactive intermediates), leading to efficient energy-converting reactions and, in certain instances, unparalleled synergy between these functional subunits. By carefully modifying synthetic conditions, two evolved classes of MOFs are achieved either by scaling down the size of MOFs to the nanoscale regime, affording nanoscale metal-organic frameworks (nMOFs), or by reducing the dimensionality of MOFs to a single layer (<2 nm in thickness), affording metal-organic layers (MOLs). nMOFs, while inheriting all aforementioned merits of conventional MOFs, also possess advantageous characteristics of nanomaterials, such as the enhanced permeability and retention (EPR) effect and strong biocompatibility, which engender nMOFs as promising candidates for biomedical applications. On the other hand, MOLs are two-dimensional with high specific surface areas, which not only eliminates diffusion constraints of MOFs, but also allows for post-synthetic surface functionalization through carboxylate-exchange modifications. In my research, I designed and synthesized a series of MOFs, nMOFs, and MOLs, systematically studied their growth mechanisms, and investigated their interactions with photons, including X-ray and visible-light photons, leading to unique energy-converting applications.