Triazinane-based thin-film composite membrane fabrication via heterocycle network formation from formaldehyde and amines for organic solvent nanofiltration

Thin film composite (TFC) membranes are generally used in organic solvent nanofiltration (OSN). However, most of the studies that have explored the chemistry of TFC membranes have focused on polyamide and polyester network polymers. This study focuses on the fabrication of a novel polytriazinane network polymer for TFC membranes via interfacial polymerization (IP) using formaldehyde and a primary amine such as priamine or 1,3,5-tris(4-aminophenyl)benzene. This approach enables the formation of a solvent-stable network polymer using only bis-functionalized amines. Along with small-molecular model reactions, the membranes were characterized using Fourier transform infrared spectroscopy, solid-state nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy to confirm the proposed triazinane structure. The membranes demonstrated high stability in a wide range of organic solvents, but they were susceptible to acidic hydrolysis. The molecular weight cutoff and methanol permeance of the TFC membranes were 555–698 g mol−1 and 7.5–131 L m−2 h−1 bar−1, respectively. A polyimide aerogel support was used in TFC fabrication to achieve high solvent permeance. The three-dimensional structure of the aerogel support was visualized using electron tomography to demonstrate its high porosity and pore interconnectivity. The stability of the TFC membranes was confirmed through long-term cross-flow filtration tests showing no significant change in solute rejection or methanol permeance over three days at 10 bar. A carcinogenic impurity from a semi-synthetic macrolide antibiotic was successfully removed using these membranes. To summarize, heterocyclization resulting in triazinane structures during IP opens new options for TFC membrane fabrication.