Layer‐by‐Layer Assembled Conductive Metal–Organic Framework Nanofilms for Room‐Temperature Chemiresistive Sensing

The utility of electronically conductive metal–organic frameworks (EC‐MOFs) in high‐performance devices has been limited to date by a lack of high‐quality thin film. The controllable thin‐film fabrication of an EC‐MOF, Cu₃(HHTP)₂, (HHTP=2,3,6,7,10,11‐hexahydroxytriphenylene), by a spray layer‐by‐layer liquid‐phase epitaxial method is reported. The Cu₃(HHTP)₂ thin film can not only be precisely prepared with thickness increment of about 2 nm per growing cycle, but also shows a smooth surface, good crystallinity, and high orientation. The chemiresistor gas sensor based on this high‐quality thin film is one of the best room‐temperature sensors for NH₃ among all reported sensors based on various materials.     

Surface Modification of Two‐Dimensional Metal–Organic Layers Creates Biomimetic Catalytic Microenvironments for Selective Oxidation

Microenvironments in enzymes play crucial roles in controlling the activities and selectivities of reaction centers. Herein we report the tuning of the catalytic microenvironments of metal–organic layers (MOLs), a two‐dimensional version of metal–organic frameworks (MOFs) with thickness down to a monolayer, to control product selectivities. By modifying the secondary building units (SBUs) of MOLs with monocarboxylic acids, such as gluconic acid, we changed the hydrophobicity/hydrophilicity around the active sites and fine‐tuned the selectivity in photocatalytic oxidation of tetrahydrofuran (THF) to exclusively afford butyrolactone (BTL), likely a result of prolonging the residence time of reaction intermediates in the hydrophilic microenvironment of catalytic centers. Our work highlights new opportunities in using functional MOLs as highly tunable and selective two‐dimensional catalytic materials.     

Expanding the Toolbox of Metal–Phenolic Networks via Enzyme-Mediated Assembly

Functional coatings are of considerable interest because of their fundamental implications for interfacial assembly and promise for numerous applications. Universally adherent materials have recently emerged as versatile functional coatings; however, such coatings are generally limited to catechol, (ortho-diphenol)-containing molecules, as building blocks. Here, we report a facile, biofriendly enzyme-mediated strategy for assembling a wide range of molecules (e.g., 14 representative molecules in this study) that do not natively have catechol moieties, including small molecules, peptides, and proteins, on various surfaces, while preserving the molecule's inherent function, such as catalysis (≈80 % retention of enzymatic activity for trypsin). Assembly is achieved by in situ conversion of monophenols into catechols via tyrosinase, where films form on surfaces via covalent and coordination cross-linking. The resulting coatings are robust, functional (e.g., in protective coatings, biological imaging, and enzymatic catalysis), and versatile for diverse secondary surface-confined reactions (e.g., biomineralization, metal ion chelation, and N-hydroxysuccinimide conjugation).