A Humidity-Induced Large Electronic Conductivity Change of 107 on a Metal-Organic Framework for Highly Sensitive Water Detection.

The electronic conductivity (EC) of metal-organic frameworks (MOFs) is sensitive to strongly oxidizing guest molecules. Water is a relatively mild species, however, the effect of H2 O on the EC of MOFs is rarely reported. We explored the effect of H2 O on the EC in the MOFs (NH2 )2 -MIL-125 and its derivatives with experimental and theoretical investigations. Unexpectedly, a large EC increase of 107 on H2 SO4 @(NH2 )2 -MIL-125 by H2 O was observed. Brønsted acid-base pairs formed with the -NH2 groups, and H2 SO4 played an important role in promoting the charge transfer from H2 O to the MOF. Based on H2 SO4 @(NH2 )2 -MIL-125, a high-performance chemiresistive humidity sensor was developed with the highest sensitivity, broadest detection range, and lowest limit of detection amongst all reported sensing materials to date. This work not only demonstrated that H2 O can remarkably influence the EC of MOFs, but it also revealed that post-modification of the structure of MOFs could enhance the influence of the guest molecule on their EC to design high-performance sensing materials.

Pore Size Modulation in Flexible Metal-Organic Framework Enabling High Performance Gas Sensing.

Pore size plays a critical role in determining the performance of metal-organic frameworks (MOFs) in catalysis, sensing, and gas storage or separation. However, revealing the pore-size/property relationship remains extremely challenging because ideal structure models possessing different pore sizes but having the same components are lacking. In this work, a solvent-coordination directed structure swelling method was developed for modulating the ratio between the large and narrow pore phases of a flexible MOF, MIL-88B. Pore-size-dependent gas sensitivity and selectivity were studied for the first time in the MIL-88B samples. The optimized MIL-88B-20 % sample showed one of the best sensing performances among all the reported MOF-based H2 S-sensing materials. This work not only provides a method to synthesize ideal structure models for revealing the relationship between pore-size and properties, but also may inspire the development of high-performance gas sensing materials.