Effect of ionic liquid on sugar-aromatic separation selectivity by metal-organic framework NU-1000 in aqueous solution

Leveraging on previously observed selectivity in separating sugars from aromatics in aqueous solution via adsorption to metal-organic framework NU-1000, we investigate the effect of ionic liquid (IL) cosolvent on this separation. Four ILs (cholinium lysinate, cholinium phosphate, ethanolamine acetate, and ethanolamine phosphate) were investigated at concentrations of 0.4, 10, and 20 vol%. When treated with an aqueous IL mixture containing glucose, xylose, coumaric acid, and ferulic acid, highly selective sugar-aromatic separations were observed for NU-1000 at 0.4 vol% for both cholinium lysinate and ethanolamine acetate. In contrast, amorphous carbon under similar conditions lacked selectivity, adsorbing similar amounts of aromatics to NU-1000 while also adsorbing ≥96 mg gadsorbent−1 of sugars. These results parallel those previously observed in pure aqueous solution. At higher concentrations of IL, however, NU-1000 displayed ≥56 mg gadsorbent−1 of sugar uptakes for all ILs, with the largest sugar uptakes being observed for ethanolamine acetate. This mirrored results when treating NU-1000 with sugars and IL in aqueous solution, in the absence of aromatics, in a way that depended non-monotonically on the IL concentration. We implicate coadsorption of IL onto NU-1000 as the reason why selectivity in the presence of IL is lower than the selectivity in pure aqueous solution.