Covalent organic frameworks (COFs), with ordered pores and well-defined topology, are ideal materials for nanofiltration (NF) membranes because of their capacity of transcending the permeance/selectivity trade-off predicament. However, most reported COF-based membranes are focused on separating molecules with different sizes, resulting in low selectivity to similar molecules with different charges. Here, the negatively charged COF layer was fabricated in situ on a microporous support for the separation of molecules with different sizes and charges. Ultrahigh water permeance (216.56 L m–2 h–1 bar–1) was obtained because of the ordered pores and excellent hydrophilicity, which exceeds that of most membranes with similar rejections. For the first time, we used multifarious dyes with different sizes and charges, for the investigation of the selectivity behavior caused by the Donnan effect and size exclusion. The obtained membranes represent superior rejections to negatively and neutrally charged dyes larger than 1.3 nm, while positively charged dyes with a size of 1.6 nm can pass through the membrane, resulting in the separation of negative/positive mixed dyes with similar molecular sizes. This strategy of combining the Donnan effect and size exclusion in nanoporous materials may evolve into a generic platform for sophisticated separation.
Traditional thin film composite polyamide nanofiltration (NF) membranes are difficult to simultaneously achieve high rejection for salts that are divalent anionic and cationic, and their separation selectivity for mono-/di-valent salt separation is usually poor. Herein, novel polyesteramide NF membranes were developed by interfacial polymerization on modified poly(vinylidene fluoride) (PVDF) substrates containing tannic acid (TA) self-assembled coating (TC@PVDF). TC@PVDF substrates were firstly fabricated via non-solvent induced phase separation technology using amphiphilic hyperbranched poly(methyl methacrylate- co -N-methylacrylamide) (HPMH) copolymers as in situ modifiers and TA aqueous solution as coagulation bath. The self-assembly behavior between TA and HPMH results in the increase of substrate surface hydrophilicity, electronegativity and pore size, which would facilitate the storage and uniform distribution of aqueous monomer piperazine on the substrate surface. For these reasons, TA coating interlayered NF (TCi-NF) membrane exhibits a thick polyesteramide layer with crisscrossing ridge surface morphology, a low molecular weight and a small pore size. The TCi-NF membrane not only demonstrates high rejection toward Na 2 SO 4 (99.3 %) and MgCl 2 (95.7 %), but also displays exceptional separation selectivity for both mono-/di-valent anions [α(Cl − /SO 4 2− ) = 49] and mono-/di-valent cations [α(Na + /Mg 2+ ) = 52]. Since the surface charge property of TCi-NF membrane is close to weak negativity, electrostatic effect between charged ions and membrane surface would be weakened, so the separation mechanism mainly depends on the size exclusion effect. Specifically, the TCi-NF membrane displays stable long-term separation performance and high salt concentration resistance. Therefore, this research provides a new preparation strategy for improving the precise desalination performance of thin film composite NF membranes.
The removal of organic pollutants in complex aqueous environments is often hindered by the presence of natural organic matter (NOM), such as humic acid (HA), which can interfere with pollutant degradation processes. Peroxymonosulfate (PMS) activation has emerged as a promising strategy for pollutant degradation; however, its efficiency is typically compromised by NOM interference. To address this challenge, this study develops a metal–organic framework (MOF)-derived Co-N@C hollow multi-shell nanoreactor (HoMS) that effectively isolates NOMs while targeting organic pollutants. The Co-N@C HoMS, synthesized via a “hierarchical temperature control, one-step pyrolysis” strategy, demonstrated superior catalytic performance in selectively degrading carbamazepine (CBZ) in the presence of HA. Over 99% of CBZ was removed within 10 min, even with HA present. Mechanistic studies revealed that PMS activation by Co-N@C HoMS for CBZ degradation involves both radical oxidation and electron transfer pathways. The unique size-exclusion effect of the Co-N@C HoMS selectively allows small molecules (CBZ) to pass through while blocking larger ones (HA), enabling rapid and selective pollutant degradation in complex environments. This work provides a novel solution for the efficient and selective removal of multi-component pollutants in complex environmental systems.
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