Crystalline imine-based covalent organic frameworks (COFs) have attracted great interest as next-generation water treatment materials owning to their numerous merits. The construction of COF layers with tunable pore sizes ranging from meso- to micropores, which can significantly broaden the membrane selectivity from ultra- (UF) to nanofiltration (NF), has remained unexplored. Herein, we demonstrate the controllable solvothermal synthesis of COF layers with adjustable pore sizes on anodic aluminum oxide (AAO) substrates. With rising synthesis duration the modulation on pore sizes of AAO supports can be achieved till the formation of continuous COF layers, leading to a gradually enhanced selectivity. Importantly, the synthesized microporous COFs shrink the pore sizes of AAO substrates and provide additional nanochannels for water transporting, eventuating in a ~2–9 times higher permeance than other reported UF membranes with comparable rejections. Once forming continuous COF layers, more rigid selectivities based on COF inherent nanochannels (~1.83 nm) can be realized with capacities of removing dyes from water or organic solvent . This work provides a facile methodology to construct COF-based membranes with broadly tunable separation performance, recommending the membranes for removing targeted molecules including proteins, nanoparticles , and dyes.
The increase in the discharge of industrial oily wastewater poses a threat to the environment and human health. Thus, the treatment of oily wastewater has become a focus of current research. The superhydrophobic surface derived from the lotus effect provides an effective direction for oil-water separation. Based on this, the authors reported a tunable superhydrophobic stainless steel separation mesh with a water contact angle of 155° through simple electrodeposition and modification with a fluorine-free modifier. The separation mesh with different surface morphology, by controlling different electrodeposition time and current, is able to achieve oil-water separation with super flux up to 51561 L/(m 2 ·h) in heavy oil/water mixture and high-efficiency over 99.5% in water-in-oil emulsion. This controllable process constructs superhydrophobic membrane with tunable pore size, which is capable of separating heavy oil/water mixtures and water-in-oil emulsions depending on the process. This proposal is suggestive in the field of oil-water separation.
Hui Zhang,Yinkun Sun,Junjie Yang,Zhiyu Sun,Yanxin Zhao,Xin Li,Wei Wang,Dongwei Lu,Jun Ma
Precise adjustment of the pore size, damage repair, and efficient cleaning is all challenges for the wider application of inorganic membranes. This study reports a simple strategy of combining dry-wet spinning and electrosynthesis to fabricate stainless-steel metal–organic framework composite membranes characterized by customizable pore sizes, targeted reparability, and high catalytic activity for membrane cleaning. The membrane pore size can be precisely customized in the range of 14–212 nm at nanoscale, and damaged membranes can be repaired by targeted treatment in 120 s. In addition, advanced oxidation processes can be used to quickly clean the membrane and achieve 98% flux recovery. The synergistic actions of the membrane matrix and the selective layer increase the adsorption energy of active sites to oxidant, shorten the electron transfer cycle, and enhance the overall catalytic performance. This study can provide a new direction for the development of advanced membranes for water purification and high-efficiency membrane cleaning methods.
Ting Wang,Hongyu Wu,Song Zhao,Wen Zhang,Muhammad Tahir,Zhi Wang,Jixiao Wang
Covalent organic frameworks (COFs) with crystalline imide structure achieved remarkable application in the field of water treatment membrane. In this work, 1,3,5-triformylphloroglucinol (Tp) and benzidine (Bd) or melamine (Me) monomers as the assemble units were firstly in-situ interfacial polymerized upon polysulfone (PSf) porous substrate to form COFs composite membrane with a thin and stable COFs selective layer. Furthermore, adding melamine monomer during interfacial polymerization between Tp and Bd monomers could further introduce a triazine ring type-keto-enol tautomeric type into COFs selective layer, and adjust the molecular network structure and crystallinity of the COFs layer with variable pore aperture. The results indicated that the as-prepared TpBd/PSf and TpBdMe/PSf membranes could be efficiently applied for dye separation process with congo red rejection above 99.0%. Compared with TpBd/PSf membrane, water permeability of TpBdMe/PSf membrane increased from 33.6 L·m −2 ·h −1 ·bar −1 to 62.2 L·m −2 ·h −1 ·bar −1 . Moreover, both TpBd/PSf and TpBdMe/PSf membranes exhibited excellent anti-fouling property, chemical and thermal stability. This work develops a facile method to prepare the imine-linked COFs membrane with variable pore aperture by changing reaction parameters and selecting appropriate amine monomers.
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