Covalent organic framework (COF) membranes have uniform pores and excellent chemical stability, making them promising for water treatment. However, conventional solvothermal synthesis requires harsh conditions (typically 120 °C for 48–72 h) and corrosive solvents, severely hindering practical development. In a study published in ENG. Chem. Eng., researchers at Beijing University of Chemical Technology report a dynamic interfacial polymerization (IP) strategy that fabricates TpPa‑1 COF membranes in only 3 minutes.
The method uses a polyacrylonitrile (PAN) ultrafiltration membrane as the substrate. The aqueous phase monomer (p‑phenylenediamine, Pa‑1) is pre‑impregnated into the substrate voids, providing reactive sites. The substrate is then immersed in an organic phase containing the Tp monomer (2,4,6‑triformylchloroglucinol). Pa‑1 and Tp rapidly condense at the oil–water interface, forming a reversible imine structure that subsequently undergoes keto–enol tautomerism to produce a stable β‑ketoenamine structure. Confining the reaction zone shortens monomer diffusion paths, while the high intrinsic reactivity of TpPa‑1 monomers enables rapid and efficient membrane formation.
The resulting TpPa‑1 membrane (TpPa‑1‑M2, prepared with 2 min aqueous impregnation and 1 min IP time) was characterized by FTIR, XRD, and XPS. The FTIR spectrum showed C–N stretching at 1287 cm⁻¹ and C=C absorption at 1579 cm⁻¹, confirming successful TpPa‑1 formation. XRD revealed characteristic (100), (110) and (001) diffraction peaks at 4.8°, 8.3° and 26.8°, respectively, indicating good crystallinity. XPS detected only C, N and O, consistent with TpPa‑1 composition, and the absence of a N=C peak confirmed the irreversible keto–enol tautomerism. SEM showed that the TpPa‑1‑M2 membrane surface was uniformly covered without defects, and the selective layer thickness was approximately 251 nm – much thinner than COF membranes prepared by conventional solvothermal methods, which reduces mass transfer resistance and enhances permeance.
The membrane pore size distribution was fitted using polyethylene glycol rejection data. The molecular weight cut‑off was about 950 Da, and the average pore size was 5.97 Å. Zeta potential measurements showed the membrane surface was negatively charged across pH 3–10, reaching −52.8 mV at pH 7, which aids rejection of anionic dyes via Donnan exclusion. The water contact angle of the TpPa‑1‑M2 membrane was only 38.8°, demonstrating excellent hydrophilicity.
In methyl blue/Na₂SO₄ nanofiltration tests (0.1 g·L⁻¹ MB, 1 g·L⁻¹ Na₂SO₄, 0.4 MPa), the TpPa‑1‑M2 membrane achieved a permeance of 865 L·m⁻²·h⁻¹·MPa⁻¹ and a separation factor of 212. During a 40‑h stability test, permeance decreased by only 13 % while MB rejection remained above 99 %. The membrane also maintained its crystal structure after treatment with 1 mol·L⁻¹ hydrochloric acid for 48 h, demonstrating excellent acid resistance. An 18 cm‑diameter membrane was successfully fabricated using the same dynamic IP method, showing potential for scale‑up.
Compared with previously reported dye desalination membranes, the TpPa‑1‑M2 membrane shows more than 100 % higher permeance at similar separation factors. This study provides a simple, rapid and scalable approach for manufacturing high‑performance COF nanofiltration membranes.
ENGINEERING Chemical Engineering
Experimental study
Not applicable
Minute-level interfacial polymerization of covalent organic framework membranes for high-flux nanofiltration
1-May-2026