Abstract
Considering that metal–organic framework (MOF)-polymer mixed-matrix membranes (MMMs) can overcome the drawbacks of intrinsic fragility and poor processability of pure-MOF membranes, we designed MOF-based MMMs for efficient removal and fast fluorescence sensing of heavily toxic ions within water systems simultaneously. In this work, a series of MOF-based MMMs are prepared by mixing a hydrolytically stable cationic [Eu7 (mtb)5(H2O)16]·NO3 8DMA·18H2O (denoted as Eu-mtb) MOF material into poly (vinylidene fluoride) with high loadings up to 70%. The free volume at the interface between the polymer and Eu-mtb particles, combined with the permanent porosity and uniform distribution of Eu-mtb particles, enables these MMMs to show fast enrichment of Cr2O7 2- from solutions and consequently have a full contact between the analyte and MOFs. The developed Eu-mtb MMM (70wt% loading) thus shows both efficient removal and exceptional fluorescence sensing of Cr2O7 2- in aqueous media. The overall adsorption capacity of the Eu-mtb MMM (70 wt% loading) for Cr2O7 2- reaches up to 33.34 mg/g, which is 3.4 times that of powder-form Eu-mtb. The detection limit of the Eu-mtb MMM (70 wt% loading) for Cr2O7 2- is around 5.73 nM, which is lower than that of the reported powder-form Eu-mtb. This work demonstrates that it is feasible to develop flexible luminescent MOF-based MMMs as a significant platform for efficient removal and sensitive sensing of pollutants from water systems simultaneously.
Highlights
Eu-mtb matrix membranes (MMMs) were prepared according to the published literature with some modifications (Zhang et al, 2018)
The electrostatic interaction between the cationic framework and Cr2O72− is of great benefit for achieving efficient removal and sensitive fluorescence sensing of Cr2O72− within water simultaneously
It is reported that MOFs with micro- or nanoparticles are often preferred to fabricate MOF-based mixed-matrix membranes (MMMs) because they can provide larger interfacial areas at the MOF-polymer boundary to allow closer integration (Dechnik et al, 2017)
Summary
Heavy metal pollution has become a severe environment threat around the world. Hexavalent chromium ions, especially Cr2O72−, has been widely employed in various industrial applications, such as metallurgy, pigment production, leather tanning, electroplating, and other relevant fields (Desai et al, 2016; Lai et al, 2018; Li et al, 2018). Comparing to the harsh growth conditions and intrinsic fragility of pure MOF membranes, the incorporation of MOF particles into the polymer matrix to fabricate MOF-based mixed-matrix membranes (MMMs) is proved to be more competitive for realistic contaminant removal and sensing applications (Zhang et al, 2012; Dong J. et al, 2020; Wu T. et al, 2020). The integration of these two components has the ability to combine the flexibility and processability of polymers with the excellent properties of MOFs (Zhang et al, 2017; Li et al, 2019; Sousaraei et al, 2019; Chen et al, 2020; Muthukumaraswamy Rangaraj et al, 2020). The combination of the enhanced removal and sensing properties with its processability and flexibility makes Eu-mtb MMMs (70 wt%) a promising candidate for practical applications
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