Nano-Metal-Organic Frameworks Isolated in Mesoporous Structures

As an alternative to bulk counterparts, metal-organic framework (MOF) nanoparticles isolated within conductive mesoporous carbon matrices are of increasing interest for electrochemical applications. Although promising, a "clean" carbon surface is generally associated with poor compatibility and weak interactions with metal/ligand precursors, which leads to the growth of MOFs with inhomogeneous particle sizes on outer pore walls. Here, a general methodology for in situ synthesis of eight nanoMOF composites within mesochannels with high dispersity and stability are reported. Mesoporous polydopamine (mesoPDA)-F127 nanospheres with unique surface chemistry, e.g., nanoconfined spaces, catechol functional groups, pyrrolic N doping, and hydrophilic PEO blocks, are found to be a suitable molecular platform. Sliced cross-sectional TEM, HAADF-STEM, and corresponding EDS elemental mapping, as well as nitrogen adsorption characterizations, are utilized to visualize the in situ growth process of ZIF-8 nanoparticles. These careful analyses provides direct evidence that the highly dispersed ZIF-8 is exclusively located inside the internal mesochannels. After moderate carbonization of the mesoPDA-F127/ZIF-8 nanocomposites, a prototype for a mesoporous carbon-isolated ZIF-8 nanostructure is achieved, which can regulate Zn²⁺ plating electrochemistry toward stable aqueous Zn batteries. This is the first report of the complete impregnation and even dispersion of nanoscale MOFs within the interior channels of mesoporous carbons.