Metal-organic frameworks (MOFs) that contain M6O4(OH)4 [M = Zr or Hf] secondary building units (SBUs) have been shown to facilitate organophosphate hydrolysis, however, they often necessitate buffers or basic amine moieties to facilitate high activity and turnover. The buffer increases the pH around the SBUs and facilitates removal of metal bound mono carboxylic modulators which generate “missing-linker” sites that provide active site binding for organophosphate hydrolysis. While non-volatile buffers can be integrated into the MOF through the use of amine polymers, all solid-state formulations with MOFs ultimately suffer from SBU active site poisoning due the strong binding of hydrolyzed organophosphate hydrolysis products to the Zr-OH,-H2O sites which inhibit further catalytic turnover. Herein, we demonstrate that a simple soaking procedure with a basic aqueous solution reactivates the active sites of spent MOF organophosphate catalysts through the efficient removal of byproducts from the poisoned SBU sites. We demonstrate that varied SBU activation procedures significantly alter the catalytic properties within a MOF scaffold. Moreover, we developed functionalized MOF-808 derivatives through de novo synthesis and post-synthetic modification (PSM) that are highly active for organophosphate hydrolysis under non-buffered aqueous conditions compared to their non-functionalized analogs. We believe that our newly synthesized highly active catalysts along with our regenerative basic post-treatment activation technique are critical advancements for the practical and recyclable utilization of MOFs as organophosphate hydrolysis catalyst within fibers or composites for nerve agent protection.

Enhancing catalytic activity and mitigating poisoning of active sites within metal-organic frameworks in organophosphate hydrolysis through post-synthesis modification

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ACS Fall 2022

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