Covalent organic frameworks (COFs) functionalized with boronate and triazole moieties for selective adsorption of d-fructose

Abstract

Development of efficient downstream processes presents one of the central issues in biorefining. In this respect, synthesis of tailored adsorbents for separation of saccharides from product streams is a major challenge. In this study, separation of D-fructose and D-glucose over covalent organic frameworks functionalized with boronate moieties is proposed. Two-dimensional COFs were synthesized via condensation of a tripodal amine linker with dipodal aldehyde linkers to obtain scaffolds bearing propargyl moieties, which were post-synthetically modified via an azide click reaction. The materials obtained were characterized by N₂> physisorption, ¹H, ¹³C and ⁻¹¹B MAS NMR spectroscopy, SAXS, FTIR spectroscopy, and SEM. The COFs functionalized with boronate moieties exhibit outstanding Langmuir D-fructose adsorption capacity up to 560 mg g⁻¹. D-fructose can be efficiently desorbed by washing with sulfuric acid solution, and the adsorbent can be recycled four times. Adsorption tests over COFs bearing different functionalities suggest formation of covalent bonds with boronates as well as non-covalent interactions with triazole moieties as driving forces of the adsorption of D-fructose and D-glucose. The results of adsorption under batch and continuous conditions evidence the high potential of the synthesized COFs for adsorptive separation of D-glucose and D-fructose.