In situ preparation of nitrogen-rich and functional ultramicroporous carbonaceous COFs by “segregated” microwave irradiation

The present research developed a strategy for in situ synthesizing functionalized ultra-microporous carbons by “segregated” microwave irradiation using covalent organic frameworks as simultaneous C and N source. The products have high N-doping concentration (>30   wt%), narrow pore size distribution, and the surface area of 507 and 243   m 2 /g at the pore size of 0.4 and 0.6   nm, which are much larger than the specific area (2 and 117   m 2 /g) of samples prepared by conventional heating. They exhibit outstanding chemical, irradiation and thermal stabilities. Meanwhile, the carbonaceous COFs could retain the bulk morphology of the precursors and possess a unique functional group (cyano) which is helpful in material characters or in further modification. The findings support the potential use of “segregated” microwave irradiation in preparation of functional microporous carbons without any other additional process, and this method can also overcome the drawbacks of conventional heating and expand the range of microwave irradiation. The thus-prepared carbons were used as adsorbents for uranium recovery from a simulated nuclear effluent containing 12 co-existent cations with different pH value (4.5, 2.5 and 1.0). Results from batch experiments showed the amount of uranium adsorbed accounts for unreported 80% of the total adsorption amount at pH 1.0 with uranium sorption capacity of 50   mg/g. In addition, the carbonaceous COFs could be applicable to various fields, such as heavy metal removal, gas storage, and could be beneficial for exploration of the behaviors of ions in sub-nanometer pore (<1   nm) in the fields of carbon super-capacitors.