Hong-Jie Zhang,Xue-Bin Shang,Xu-Ran Wang,Chen-Xi Zhang,Qing-Lun Wang
SCPEEK@MOF proton exchange membranes, where SCPEEK is sulfinyl chloride polyether ether ketone and MOF is a metal–organic framework, were prepared by doping Fe-MIL-101-NH2 into polymers. The amino group in the MOF and the -SOCl2 group in thionyl chloride polyether ether ketone cross-link to form a covalent bond through the Hinsberg reaction, and the prepared composite membrane has stronger stability than other electrostatic interactions and simple physical doping composite membranes. The formation of covalent bonds improves the water absorption of the composite membrane, which makes it easy for water molecules to form hydrogen bonds. Moreover, SPEEK as a proton conductive polymer and the synergy of MOFs improve the proton conductivity of composite membranes. The composite membranes were characterized by Fourier transform infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The swelling rate, water absorption, mechanical stability, ion exchange capacity, and proton conductivity of the pure sulfonated polyether ether ketone (SPEEK) membrane were compared with those of the mechanically doped SPEEK/MOF membrane and the composite membrane SCPEEK@MOF doped with different ratios of Fe-MIL-101-NH2, and all of the SCPEEK@MOF showed superior performance. When the Fe-MIL-101-NH2 loading rate of the composite membrane is 2%, the proton conductivity of the composite membrane can reach 0.202 S cm–1 at 363 K and a 98% relative humidity, which is much higher than that of the SPEEK/MOF membrane obtained by simple physical doping under the same conditions.
The pollution of aromatic organophosphorus flame retardants (aromatic OPFRs) in aquatic environments has drawn great attention over the last few years. Two MIL-101-based metal–organic frameworks (Cr-MIL-101 and Fe-MIL-101-NH2) which possess ordered mesoporous cavities (2.9 and 3.4 nm) and aromatic structures were chosen and prepared to selectively adsorb a typical aromatic OPFR [triphenyl phosphate (TPhP)] from aqueous solution. Pore distribution analysis showed that Cr-MIL-101 and Fe-MIL-101-NH2 had both a mesoporous structure (2–3.5 nm) and microporous structure (1–2 nm), conducive to diffusion and adsorption of TPhP molecules. Compared with Fe-MIL-101-NH2 as well as commercial activated carbon, Cr-MIL-101 showed rapid and efficient adsorption for TPhP, and its initial sorption velocity (v0) calculated from the pseudo-second-order model was up to 568.18 μmol g−1 h−1. The adsorption equilibrium of TPhP on the Cr-MIL-101 was almost achieved within 12 h, while the equilibrium time of other adsorbents required more than 48 h. The study of selective adsorption found that Cr-MIL-101 had a higher sorption amount for aromatic OPFRs than alkyl-OPFRs and other aromatic compounds with different chemical structures. Cr-MIL-101 was able to keep a steady selective adsorption for TPhP in the presence of co-existing aromatic compounds. Based on the analysis of Kow, molecular structure and further density functional theory calculations, hydrophobic interactions may play a dominant role in the selective adsorption process of TPhP, and π–π interactions may be also involved. Cr-MIL-101 exhibits reusability and promising potential to rapidly and selectively remove aromatic OPFR in environmental remediation.
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