A rapid and scalable synthesis of six new imine-linked highly porous and crystalline COFs is presented that feature exceptionally high chemical stability in harsh environments including conc. H SO (18 m), conc. HCl (12 m), and NaOH (9 m). This is because of the presence of strong interlayer C-H⋅⋅⋅N hydrogen bonding among the individual layers, which provides significant steric hindrance and a hydrophobic environment around the imine (-C=N-) bonds, thus preventing their hydrolysis in such an abrasive environment. These COFs were further converted into porous, crystalline, self-standing, and crack-free COF membranes (COFMs) with extremely high chemical stability for their potential applications for sulfuric acid recovery. The as-synthesized COFMs exhibit unprecedented permeance for acetonitrile (280 Lm h bar ) and acetone (260 Lm h bar ).

Covalent Organic Frameworks (COFs) have convened inordinate scientific attention from last few years because of their unique tunable porosity and long range ordered structures with high atomic precisions. Although the high crystalline nature with considerable porosity fashioned these novel materials as an eligible candidate for diverse applications, the ordered nanochannels with controllable pore aperture, especially regarding membrane separations in extreme conditions, have been poorly explored. Herein, we have demonstrated rapid and scalable synthesis of six new imine-linked highly crystalline and porous COFs via salt (p-toluenesulfonic acid) mediated solid state crystallization approach. These as-synthesized materials show exceptionally high chemical stability in harsh environments including conc. H2SO4 (36 N), conc. HCl (12 N) and NaOH (9N). This is exclusivly because of the presence of strong interlayer C-H•••N H-bonding interactions among the individual layers. This H-bonding reinforce interlayer stacking interaction and provides a steric hindrance and hydrophobic environment around the imine (-C=N) bonds making it safe from hydrolysis, as confirmed by the Density Functional Theory (DFT) calculations. By taking advantage of processability of COF powders in salt mediated synthesis approach, the continuous, porous, crystalline, self-standing and crack-free COF membranes (COFMs) with high chemical stability have been transmuted, for their potential applications to separate various environmentally toxic materials from drinking water with high water flux. Moreover, owing to its highly robust backbone, the COFM have showed the unprecedented Sulfuric acid (12 N) permeance reflecting its potential applications for sulfuric acid purification. Also, the as-synthesized COFMs exhibit exceptionally high permeance of acetonitrile (380 Lm -2 h -1 bar -1 ) and acetone (340 Lm -2 h -1 bar -1 ).

No abstract

No abstract

In this study, composites of HKUST‐1 MOF with nanocellulose, HKUST‐1@NCs, have been prepared and explored for CO2/N2 gas‐separation and dye‐sorption based applications. Our biopolymer‐MOF composites are prepared via a copper ion pre‐seeding method, in which, the HKUST‐1 crystallites are grown in situ on the Cu‐seeded and carboxylate anchored NC fibers for a better interfacial integration between the MOF and the polymer matrices. Static gas sorption studies show the capability of one of our HKUST‐1@NC composites to reach ∼300 % enhancement in the CO2/N2 sorption selectivity compared to the corresponding MOF alone ‐ blank reference sample prepared at similar conditions. The same composite, C100, in the bulk powder form, shows a remarkable IAST sorption selectivity of 298 (CO2/N2) at 298 K and 1 bar for the CO2/N2 (15/85, v/v) gas mixture. The relative position of the C100, in the bound plot visualizations of the CO2/N2 separation trade‐off factors indicate a significant potential. The HKUST‐1@NC composites have also been processed along with a polymeric cellulose acetate (CA) matrix as HKUST‐1@NC@CA films to study them as free‐standing mixed‐matrix membranes. The CO2/N2 sorption selectivity, at 298 K and 1 bar is 600 for one such membrane, C‐120@CA, as bulk sample studied by the static gas sorption. The composite, C120, exhibits a good uptake with an enhancement of 11 % for alizarin and 70 % for Congo red in comparison to the uptakes of the corresponding blank reference HKUST‐1 sample, B120.