UiO-66-(OH)2-mediated transition layer for ultra-thin homogeneous defect-free polyamide membrane

Abstract

The synthesis of ultra-thin, uniform and continuous polyamide (PA) membranes is a crucial prerequisite for enhancing their desalination performance. Research has indicated that effectively slowing down the interfacial polymerization (IP) reaction and promoting the interface stability are key strategies for achieving ultra-thin, uniformly nano-structured membranes with excellent performance. Herein, we have demonstrated the successful design of a continuous and uniform PA membrane, ranging from 10 to 20 nm, by utilizing the UiO-66-(OH)2 n-hexane dispersion as a transition layer to regulate IP reaction and enable efficient water-salt separation. The results showed that the presence of the transition layer facilitated a bidirectional diffusion-contact reaction between the two monomers, resulting in improved interface stability and alleviating the occurrence of severe IP that may lead to heterogeneous membrane structures. As a result, the PA active layers formed through this approach exhibited superior thinness and uniformity compared to those produced via traditional IP methods. Moreover, the transition layer enabled uniform pre-polymerization of UiO-66-(OH)2 at the reaction interface by pre-exposing it to down-diffusing acyl chloride monomers. This ensured the continuity of membrane structure while creating additional free volume within the membrane. This work presented a scalable method for manufacturing ultra-thin, defect-free, homogeneous, and high-performance nanofiltration membranes.