Xiaoming Xu,Guoyan Hua,Yuxuan Chen,Yanhong Zhang,Zepeng Zhang,Weiben Yang,Fuqiang Liu,Aimin Li
Traditional polyamide nanofiltration membranes suffer from permeability-selectivity trade-off limitation and unsatisfactory rejection for divalent cations. Herein, a novel dually charged membrane was constructed by incorporating positively charged UiO-66-(NH 2 ) 2 into the negatively charged polyamide layer. Thanks to the customizable nanochannels of metal-organic frameworks, the amino-rich nanochannels of UiO-66-(NH 2 ) 2 could be fabricated through a ligand replacement strategy. UiO-66-(NH 2 ) 2 played a crucial role in the enhanced rejection of divalent cations, meanwhile negatively charged polyamide surface guaranteed the efficient Na 2 SO 4 rejection. Satisfactory rejections of CaCl 2 (96.07 %) and Na 2 SO 4 (90.62 %) were achieved simultaneously by optimal TFN-D5. Meanwhile, TFN-D5 owned the greatly-improved water permeance of 19.44 LMH/bar, which was about 1.5 times better than that of the TFC-control. Calculations based on density functional theory further confirmed UiO-66-(NH 2 ) 2 rejected Ca 2+ efficiently since the migration energy barrier across UiO-66-(NH 2 ) 2 was an order of magnitude higher than that of UiO-66-NH 2 and UiO-66. Moreover, the desirable rejections were beyond 94 % towards many divalent cation salts including MgCl 2 , NiCl 2 , PbCl 2 , MnCl 2 , CdCl 2 and ZnCl 2 . Thus, this work provided an efficient way to realize the synergistic removal of both divalent cations and anions.
Zhenggang Wang,Jing Yin,Yuanhang Jin,Feifan Yang,Haipeng Zhu,Siyuan Huang,Boqun Cao,Gongping Liu,Wanqin Jin
Pervaporation membrane process is promising for separation of organic-organic azeotropic systems, while a trade-off relationship restricts the performance of widely-studied polymeric membranes. In this work, we proposed a MOF ligand engineering strategy to boost the molecular-sieving property of mixed-matrix membrane (MMM) by synergistically manipulating the channel size, affinity and interfacial morphology. Specially, we designed UiO-66-(NH 2 ) 2 /polyvinyl alcohol (PVA) mixed-matrix membranes to separate methanol (MeOH)/methyl acetate (MeOAc) azeotropic mixture via pervaporation process. By comparing the incorporation of UiO-66-(NH 2 ) 2 , UiO-66 and p-phenylenediamine (PPD), the MOF pore size and chemistry were systematically investigated on the influence of microstructures and separation performance of the MMMs. The results demonstrated that the rationally introduced para-position –NH 2 groups on the terephthalic acid (BDC) ligands not only finely reduce the MOF pore size of UiO-66 filler, but also improve the interfacial compatibility via hydrogen bonding between UiO-66 and PVA chain, as well as enhance the MeOH affinity in the MMM. The optimized 7.5 wt% UiO-66-(NH 2 ) 2 /PVA MMM exhibited a total flux of 1554.6 g/m 2 h and a separation factor of 70.9 in 20 wt% MeOH/MeOAc azeotropic mixture at 30 °C, which is superior to the state-of-the-art membranes. The ligand engineering strategy offers a route for regulating the morphology and molecular transport property of mixed-matrix membranes.
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