Abstract
The Cu-BTC, a widely studied metal-organic framework (MOF), has been applied in various fields such as gas adsorption, separation, storage, and catalysis. However, the Cu-BTC collapses due to the replacement of the organic linker by water molecules under humid conditions, which limits its practical application in industries. In consideration of the undesirable water effect on the framework stability of Cu-BTC, a stable activated carbon (AC) was incorporated into it by the in situ method to yield a composite material AC/Cu-BTC with high water stability. XRD and SEM patterns proved that the AC7%/Cu-BTC successfully retains its crystal structure after being exposed to water molecules. The adsorption amount of n-hexane vapor of the AC7%/Cu-BTC after water vapor adsorption-thermal desorption is 307% of that of the Cu-BTC. The addition of the AC changes the adsorption active sites and reduces the strong affinity of the Cu-BTC to water molecules, resulting in the AC7%/Cu-BTC having a much lower adsorption rate for water vapor than the Cu-BTC. Therefore, the AC7%/Cu-BTC can be protected from a large amount of water molecules and avoid structural collapse caused by the disconnection between the copper center and the organic linker. The composite displays a potential value for stable applications of MOF-based materials under ambient conditions.
Highlights
The continuously increasing amount of volatile organic compounds (VOCs) due to the exploitation, storage, refining, transport, and usage of fossil fuels has severely threatened human health and the ecological environment [1,2,3]
A sufficient amount of the activated carbon (AC) has a nonnegligible effect on the crystallization of the Cu-BTC, such as plugging its pores and introducing mesopores
The n-hexane vapor adsorption capacity of the CuBTC is 3.52 mmol·g-1, which only retains 0.65 mmol·g-1 after adsorbing water vapor, while the AC7%/Cu-BTC preserves 81% of its initial n-hexane vapor adsorption capacity, from 2.47 mmol·g-1 to 2.00 mmol·g-1, which is 307% of that of the Cu-BTC
Summary
The continuously increasing amount of volatile organic compounds (VOCs) due to the exploitation, storage, refining, transport, and usage of fossil fuels has severely threatened human health and the ecological environment [1,2,3]. Yu et al [23] used copper nitrate as the metal ion source and BTC-(n)Br as an organic ligand and successfully synthesized a new type of hydrophobic adsorbent, Cu-BTC-(n)Br, by the hydrothermal method, which shows distinguished hydrophobicity and remarkable adsorption effectivity under aqueous circumstance. All the above-mentioned approaches for improving the water stability of the Cu-BTC need to introduce chemicals, which are generally toxic or unfriendly to the environment and humans. In view of these shortcomings, this study tried to seek other environment-friendly alternatives. The water vapor adsorption and desorption rates were investigated
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