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 disulfonic acids enhancing simultaneously its hydrophilicity and water stability without sacrificing its uptake capacity of � 30 mmol g À 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.
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.
It has been reported that the rate of the direct acylation of 2methylfuran (2-MF) by acetic acid (AcOH) in H-ZSM5 and H-BEA zeolites is controlled by the dehydration of the acid and the formation of the acyl intermediate, which raises the reasonable question of whether it could be accelerated by an acidic catalyst stronger than an aluminosilicate. We report on a comprehensive computational study of the reaction over the Keggin-type phosphotungstic acid (HPW), widely considered a superacid, and in H-BEA. We find that HPW can catalyze the acylation of 2-MF 1.5 times as fast as H-BEA but not because it is more efficient in catalyzing the dehydration of the acidneither on HPW nor on H-BEA is the acylation reaction rate determined by the dehydration of AcOH. On HPW, the turnover frequency is limited by the dissociation of an acylium−water complex and the desorption of the water molecule; the subsequent electrophilic attack at the furan is non-activated and proceeds spontaneously. On H-BEA, on the other hand, the reaction rate is limited by the deprotonation of the Wheland intermediate after the electrophilic addition of the acylium, which itself is an activated step. Although in light of these findings the need to accelerate the dehydration of AcOH becomes rather moot, our study reveals that confinement and enthalpic stabilization of a transition state can trump sheer Brønsted acidity. Owing to extra enthalpic stabilization of the respective transition state by the zeolite framework and by the furan co-adsorbate, H-BEA is more active than HPW for the dehydration of the organic acid, presenting both the lowest intrinsic free energy barrier, by 3 kcal/mol, and the lowest free energy span, by 6 kcal/mol. By investigating a number of pathways, we find that a mechanistically similar pathway on HPW turns out to be kinetically irrelevant due to significant entropic losses related to the binding of the furan co-adsorbate; on H-BEA, these losses are compensated by the strong enthalpic gains.
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