Unidirectional diffusion synthesis of stabilized triphenylamine-based organic frameworks (COFs) composite membranes for dye separation

Abstract

The synthesis of high-quality two-dimensional covalent organic frameworks (2D COFs) under mild conditions is crucial for their wide scale industrial application. Therefore, the advancement of the unidirectional diffusion synthesis (UDS) method has garnered significant attention. A comprehensive understanding of the diffusion dynamic occurring between the two phases is vital for optimizing reaction times and enhancing the growth conditions of highly crystalline COF films. In this work, we employed the UDS method, explored through various characterization tests, to fabricate 2D COFs on commercial PAN ultrafiltration membranes. Our study shows that the COF layer forms on one side contacting with the organic phase, regardless of whether the front side of the PAN-based film is exposed to the aqueous or organic phase. Through the different reaction times, it was found that the 2-min treatment yielded the optimal performance, with a pure water permeability coefficient of approximately 98 L·m⁻²·h⁻¹·bar⁻¹, along with a retention rate of exceeding 95 % for both CR and AR 120. Furthermore, it surpassed the interfacial polymerization method in terms of both stability and retention capacity for EBF molecules with molecular weights under 500 g·mol⁻¹.