Simultaneously Enhanced Hydrophilicity and Stability of a Metal-Organic Framework via Post-Synthetic Modification for Water Vapor Sorption/Desorption.

With increasing demands for high-performance water sorption materials, metal-organic frameworks (MOFs) have gained considerable attention due to their high maximum uptake capacities. In many cases, however, high overall capacity is not necessarily accomplishing high working capacity under operating conditions, due to insufficient hydrophilicity and/or water stability. Herein, we present a post-synthetic modification (PSM) of MOF-808, with di-sulfonic acids enhancing simultaneously its hydrophilicity and water stability without sacrificing its uptake capacity of ≈30 mmol g-1 . Di-sulfonic acid PSM enabled a shift of the relative humidity (RH) associated with a sharp step in water vapor sorption from 35-40 % RH in MOF-808 to below 25 % RH. While MOF-808 lost uptake capacity and crystallinity over multiple sorption/desorption cycles, the di-sulfonic acid PSM MOF-808 retained >80 % of the original capacity. PSM MOF-808 exhibited good hydrothermal stability up to 60 °C and high swing capacity.

Phosphonate-Modified UiO-66 Brønsted Acid Catalyst and Its Use in Dehydra-Decyclization of 2-Methyltetrahydrofuran to Pentadienes.

Phosphorus-modified all-silica zeolites exhibit activity and selectivity in certain Brønsted acid catalyzed reactions for biomass conversion. In an effort to achieve similar performance with catalysts having well-defined sites, we report the incorporation of Brønsted acidity to metal-organic frameworks with the UiO-66 topology, achieved by attaching phosphonic acid to the 1,4-benzenedicarboxylate ligand and using it to form UiO-66-PO3 H2 by post-synthesis modification. Characterization reveals that UiO-66-PO3 H2 retains stability similar to UiO-66, and exhibits weak Brønsted acidity, as demonstrated by titrations, alcohol dehydration, and dehydra-decyclization of 2-methyltetrahydrofuran (2-MTHF). For the later reaction, the reported catalyst exhibits site-time yields and selectivity approaching that of phosphoric acid on all-silica zeolites. Using solid-state NMR and deprotonation energy calculations, the chemical environments of P and the corresponding acidities are determined.

Healable and Foldable Carbon Nanotube/Wax Conductive Composite.

In this study, a composite material with healable and foldable features is formulated to print conductive patterns on rough surfaces, such as paper, cloth, and three-dimensional (3D) printed objects. Carbon nanotubes (CNTs) are mixed with wax to formulate a solid composite for pen writing. The composite has a low percolation threshold of 2.5 wt % CNTs and can be written on various rough substrates, such as paper and cloth, to create conductive patterns for electronic conductors. Because of the strong infrared (IR) absorption of CNTs, the printed patterns can be selectively sintered by noncontact IR radiation efficiently to show great electrical conductivity. The electrical resistance of the written patterns on paper also show an insignificant increase after bending, folding, and crumpling. Furthermore, the conductive composite exhibits great healability after destructive damages. The conductivity of the damaged patterns after severe folding or knife cutting recovers to its original value with thermal or IR heating. Several examples, such as conductive tracks on paper, cloth, or 3D printed objects, are also demonstrated to show the potential of this healable conductive composite for electronic applications.