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In this study, a kind of thin film composite (TFC) membrane with two-dimensional (2D) covalent organic frameworks (COFs) as interlayer, termed as iTFC, which has integrally covalent bonding structure, ultra-thin and ultra-smooth surface, as well as high separation performance was fabricated via interfacial polymerization (IP) and subsequent chemical cross-linking and solvent activation for organic solvent nanofiltration (OSN). The COFs interlayer was in situ constructed using 1,3,5-triformylphloroglucinol (Tp) and hydrazine (Hz) on polyimide (PI) substrate prior to the IP. The optimization of the membrane fabrication process shows that very low concentration for both the COFs aqueous monomer Hz and the IP aqueous monomer m-phenylenediamine (MPD) was conducive to the formation of very smooth (roughness of 2.4 nm), very thin and defect-free cortex, thus improving the organic solvent permeation while remaining the dye rejection. Under optimal conditions, the prepared iTFC OSN membrane has an ethanol permeance of 63.4 L m−2 h−1 MPa−1, a Rhodamine B (RDB) rejection of greater than 99 %, and a molecular weight cut-off (MWCO) of as low as 380 Da. In addition, after filtration of 100 mg L−1 RB/DMF solution for 408 h, the optimized iTFC OSN membrane remained Rose Bengal (RB) rejection above 97 %, which proves its excellent solvent resistance performance. [Display omitted] • Ultra-low content Tp and Hz monomers are used for in situ construction of ultra-thin TpHz COFs interlayer. • Ultra-low content MPD, TMC monomer are used during the interfacial polymerization process. • Integrally covalent bonding forms between the adjacent layers of substrate, COFs interlayer and skin layer. • The iTFC OSN membrane achieves a much higher ethanol permeance of 63 L m−2 h−1 MPa−1 and 99 % high RDB rejection. • The integrally covalent bonding TFN OSN membrane achieves superior solvent resistance. [ABSTRACT FROM AUTHOR]

The separation performance of current organic solvent nanofiltration (OSN) membranes are still not satisfied. In this work, an ultra-thin TpHz covalent organic frameworks (COFs) interlayer was in situ constructed in advance on polyimide substrate, then an ultra-thin polyamide separation layer incorporated with amino-functionalized graphene quantum dots (af-GQDs) was constructed via interfacial polymerization (IP). A high performance interlayered thin-film nanocomposite (iTFN) OSN membrane with integrally covalent bonding structure, ultra-thin and ultra-smooth surface was obtained after post crosslinking and activation. The effect of ultra-low concentrations for the polyamide reaction monomers, the COFs monomer Tp and the doped af-GQDs nanoparticle reveals that they could help to form a very thin (7–8 nm in thickness) and defect-free skin layer with very smooth surface (about 2.7 nm in roughness). The iTFN OSN membrane shows excellent solvent permeance and solute selectivity, with an ethanol permeance reaching 97.6 L m−2 h−1 MPa−1 and an RDB rejection higher than 99%. After a 180 h long-term filtration with 100 mg L−1 RB/DMF solution, it remained an RB rejection of higher than 99%, demonstrating its superior resistance to strong polar solvent. Our work paves a unique way for the fabrication of novel OSN membrane with both in situ constructed nanomaterials interlayer and nanomaterials incorporated in skin layer. [Display omitted] • Integrally covalent iTFN OSN membrane has COFs interlayer and af-GQDs incorporated. • Ultra-thin TpHz COFs layer constructed in situ with ultra-low content of Tp and Hz. • Ultra-thin polyamide skin formed using ultra-low content for MPD, TMC and af-GQDs. • Ethanol permeance reaches 97.6 L m−2 h−1 MPa−1 with RDB rejection of above 99%. • The integrally covalent iTFN OSN membrane achieves superior solvent resistance. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) have emerged as promising candidate for the construction of advanced separation membranes due to their well-defined pore structure and highly ordered porous channels. Nevertheless, the implementation of high-efficient COFs-incorporated membranes still suffers from harsh synthetic conditions and possible agglomeration of COFs. Herein, a kind of sandwich-like thin film composite reverse osmosis (RO) membranes was fabricated to overcome such challenges via interfacial assembly of a COFs interlayer on polysulfone substrate, then followed by the formation of a polyamide skin layer via traditional interfacial polymerization (IP) process. The COFs interlayer not only tailored the pore structure and interfacial properties of the substrate, but also manipulated the uptake and release of the amine monomer during the IP process, which would contribute to forming a more ordered polyamide separation layer. The resultant COFs-interlayered RO membrane exhibited a nearly 33.8% higher water permeance (16.78 L m−2 h−1 MPa−1) along with a slightly increased NaCl rejection (99.2%) compared with the pristine RO membrane. More importantly, the emerging RO membrane presented a superior chemical (critic acid and NaOH) resistance and desirable long-term filtration stability, which paved a new pathway to construct high-performance RO membranes for desalination. Image 1 • The RO membranes were prepared on interfacial assembled COFs interlayer. • COFs interlayer optimized physicochemical and interfacial properties of substrate. • The COFs-modulated IP procedure enabled a thinner, denser and smoother PA layer. • The PA/COFs/PSf membrane enhanced the optimal water permeance by up to 33.8%. • The COFs-interlayered RO membrane exhibited a satisfying long-term stability. [ABSTRACT FROM AUTHOR]