A general approach to the synthesis of second-order nonlinear optical (NLO) polyimides exhibiting high thermal stability has been developed. Several selected NLO chromophores have been incorporated into the polyimide backbone. Detailed physical studies showed that these polymers are very promising for practical applications. Three of these polyimides are soluble in common organic solvents, offering the ease of processing. High glass temperatures, around 230 °C, assure a long-term NLO stability at elevated temperatures, such as 150 °C. Low optical loss was observed for those soluble polymers. The synthetic approach is also versatile and will allow the syntheses of many other functional polymers.
Highly cation permselective metal–organic framework (MOF) membranes are desirable for the extraction of valuable metal cations. However, fabrication of defect‐free and stable permselective MOF membranes is technically challenging, owing to their arduous self‐assembly and poor water resistance, respectively. A simple and readily scalable method has been developed for the controlled in situ smart growth of UiO‐66‐NH2 into leaf‐like nanostructures with tunable density of the leaves and the surface layer thickness. The self‐assembly approach reproducibly fabricates seamless, ultrathin (<500 nm) UiO‐66‐NH2 membranes at the surface of anodic aluminum oxide. The membranes contain nanosized interstices among the MOF leaves, which enable maximum admission of ions within the membrane, and angstrom‐sized inherent pores in every single UiO‐66‐NH2 crystal, which efficiently regulate the cation permselectivity. Consequently, the highest ever reported cation separations (Na+/Mg2+>200 and Li+/Mg2+>60) and excellent membrane stability during five sequential electrodialysis cycles are achieved. These characteristics position the fabricated MOF membranes as potential candidates for efficient extraction of pure lithium and sodium ions from salt lakes and seawater, respectively.
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