Core-Shell Metal-Organic Frameworks with Improving Cyclic Stability for Water Adsorption

抄録

MIL-100(Fe) is a metal-organic framework (MOF) with high water adsorption capacity but poor stability under continuous adsorption–desorption cycling. This paper reports on a novel method for improving the cyclic adsorption stability of MIL-100(Fe) by coating it with ZIF-7 or ZIF-8 to form MOF–MOF composites. This process is meant to prevent the direct exposure of MIL-100(Fe) to moisture, and thereby extend its lifespan. The structure of resulting MIL-100(Fe)@ZIF-7 and MIL-100(Fe)@ZIF-8 was characterized using a number of solid-state techniques, including scanning electron microscopy, energy dispersive spectroscopy, FT-IR spectroscopy, and powder X-ray diffraction with synchrotron source. Pure MIL-100(Fe) and the two composites were subjected to cyclic water adsorption–desorption tests at 25°C under 80% relative humidity. After 25 cycles, the water adsorption capacity of pure MIL-100(Fe) dropped by approximately 30%. The adsorption uptake of the MOFs remained almost unchanged; however, their overall adsorption capacity is slightly lower than that of pure MIL-100(Fe).