Covalent organic framework (COF)-based membranes are burgeoning candidates for separation technologies owing to their well-ordered channel structures. However, it is still a significant challenge to obtain high-quality COF membranes with a mild and convenient preparation strategy. In this paper, we adopted a simple liquid-liquid interfacial polymerization method to manufacture a self-standing COF membrane with decent crystallinity at room temperature. Aldehyde monomer and catalyst were dissolved in water as the bottom layer and the amine monomer was dissolved in ethyl acetate as the top layer, and new COF membranes were subsequently obtained by interfacial polymerization in the two-phase interface. The synthetic conditions including precursor and catalyst dosage were further optimized, and thus-synthesized PDA-TAPB-ABC membrane displayed a stable rejection to MB of 97.57% with a high water permeance of up to 101. 32 L m −2 h −1 bar −1 . Its dyes separation performance was much better than their AA-stacking counterpart. Moreover, the prepared membrane endowed favorable chemical stability and long-term durability.
It is well known that alkali metals can intercalate into graphite to form graphite intercalation compounds but the structural change of graphite induced by alkali metals has been paid less attention. Herein, we report that alkali metals (Li, Na, K) induce the phase transition from ABC-stacking (or 3R phase) to AB-stacking (or 2H phase) of graphite. Specifically, for the graphite powder containing ∼45% 3R phase in a mixed phase, the temperature needed to ensure a complete stacking phase transition is 600 °C, 500 °C or 350 °C, for Li, Na or K, respectively, much lower than that needed in bare annealing (1800 °C) while without these alkali metals. Simulations based on density functional theory (DFT) suggest that the charge transfer from alkali metals to graphene distinctly lowers the energy barrier of transition, explaining the different phase transition temperatures for these alkali metals.
Covalent organic frameworks (COFs) with designable structure and well-defined aperture are highly desired as novel adsorbents for elimination of dye pollution. Herein, a new carboxyl-functionalized covalent organic framework (TzDABA COF) with clover-like topology was synthesized by the condensation of 1,3,5-tris(4-formyl-phenyl) triazine (Tz) and 3,5-diaminobenzoic acid (DABA) under solvothermal conditions. The obtained TzDABA COF exhibited rapid adsorption kinetics and excellent adsorption capacities toward multiple cationic organic dyes including methylene blue (MB, 315 mg g −1 ), crystal violet (CV, 533 mg g −1 ) and malachite green (MG, 1168 mg g −1 ) owing to the formation of strong electrostatic interaction and π-π interaction between COF framework and organic dye molecules. Remarkably, with particular ABC stacking mode and an abundant of carboxyl functional groups integrated in the clover-like architecture, the anionic TzDABA COF could effectively separate organic dyes in different modes, representing the first case of carboxyl-functionalized clover-like COF for dye separation based on charge effect and size effect. This study paves a new pathway toward construction of carboxyl-functionalized clover-like COFs and reveals their desiring prospect in field of dyes separation and purification.
危险品化学品经营许可证（带存储）