Metal-organic framework (MOF) membranes, by virtue of their high selectivity and low diffusion resistance, make a significant contribution to energy conservation and CO 2 emission reduction via separation technology. Despite possessing substantial potential for propelling the production of high-performance membranes, hurdles persist in the process of constructing MOF membranes that are both highly integrated and structurally sound on flexible polymer substrates. We propose a strategy for constructing highly stable cobalt zeolitic imidazolate framework (ZIF-67) composite membranes on seeded polyacrylonitrile (PAN) substrate. Through a timed-interrupted in-situ growth process, the amino-modified polycrystalline ZIF-67 as a CO 2 affinity layer is precisely and completely confined within the “top sites” and partial “face sites” of the vertical layered double hydroxide (LDH) precursor layer, creating a barrier-low passage for CO 2 as a fast diffusion layer. The substrate and the hybrid ZIF-67@LDH layer were robustly anchored together by the pre-embedded LDH seeds, thereby producing an appealing membrane-multilayer interlocked-support (MMIS) composite architecture. This fast diffusion-CO 2 affinity Pebax/ZIF-67@LDH/PAN membranes with MMIS architecture show average CO 2 permeability of 1487 Barrer and CO 2 /N 2 selectivity of above 55.1 after the surface repair coating of polyether-block-amide (Pebax), maintaining stable performance over 150 h, surpassing the Robeson upper bound. The Pebax/ZIF-67@LDH/PAN membranes also exhibit the durability and mechanical robustness, because of the highly inducible activity of LDH precursor layer serving as a linker between the membrane and substrate. These results promote the development of MOF-based membranes in practical separation applications.
Alkynyl carbon material (ACM) is a type of graphite derivative that is mainly composed of sp 2 and sp 1 hybrid carbons. It has a uniform distribution pore of 3–5 nm. Given its extreme thinness, high porosity and superhydrophilic surface, it is ideal for highly permeable and selective membranes. In this paper, a novel alkynyl carbon composite nanofiltration membrane was first prepared based on the coprecipitation of PDA, PEI and ACM. XPS, FTIR, SEM confirmed that the ACM was effectively compounded on the surface of the PAN substrate. CA and Zeta potential analyses show that the membrane surface is superhydrophilic due to itself superhydrophility and pore structures. The nanofiltration experiments showed that the water flux of the membrane is as high as 366 L m −2 h −1 MPa −1 , which also provides a good rejetion of organic dyes and natural organic matter (NOM) in water. For example, the permeation flux and rejection of methyl blue and humic acid are 360 L m −2 h −1 MPa −1 and 96% and 285 L m −2 h −1 MPa −1 and 94%, respectively. In addition, the membrane also showed strong running stability. This new membrane separation material has great potential application prospects in water purification and wastewater treatment.
Qihang Wang,Hongyang Ma,Madani Khan,Benjamin S. Hsiao
Novel reverse osmosis (RO) membranes with a hydrazine-based polyamide barrier layer were fabricated by interfacial polymerization (IP) on an electrospun PAN substrate. The membranes were made with a non-aromatic monomer hydrazine and trimesoyl chloride (TMC), which substantially increased the permeability and separation ability for desalination performances. The chemical structure, composition, and top/cross-sectional morphologies of the hydrazine-based RO membranes were investigated and compared with the conventional aromatic RO membranes. The kinetics of the IP process was analyzed to further comprehend the formation of hydrazine-based polyamide barrier, while the surface charge nature and the free volume radius and distribution of the resultant polyamide barrier were measured by ζ-potential and positron annihilation (PALS), respectively. The barrier layer crosslinking degree, free volume distribution, free volume radius distribution, and radial distribution function (RDF) of the hydrazine, as well as other aliphatic amine monomers (i.e., 1,2-ethylenediamine, 1,4-butanediamine, and 1,6-hexanediamine)-based polyamides were analyzed by molecular dynamic (MD) simulation, to explore the unique molecular structure of the hydrazine-based polyamide different from others and to propose an innovative desalination mechanism. The desalination performances of the hydrazine-based RO membrane against NaCl, BSA/NaCl, and boron, respectively, were demonstrated and compared with the that of a conventional and a commercial RO membrane in brackish water treatment, where 2-times higher permeation flux and higher rejection ratio of 98.7 % than that of the conventional and commercial membranes against NaCl were achieved, indicating that the non-aromatic hydrazine monomer opens a new pathway to breakthrough via the trade-off between the permeation flux and rejection ratio.
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