Organocatalytic Keratin Sponges for the Chemical Fixation\nof CO<sub>2</sub> into Cyclic Carbonates

The\nfabrication of a novel macroporous organic material from keratin\nwool fiber waste is herein described together with its utilization\nas a heterogeneous matrix for the immobilization of organocatalysts,\nnamely, methyl imidazolium iodide, TBD, and a combination thereof.\nApplication of the freeze-drying method and utilization of the cross-linking\nagent hexamethylene diisocyanate (HDI) allow for the preparation of\nkeratin sponges suitably shaped in the form of cylindrical pellets\nwith an interconnected three-dimensional porous structure (main pore\nsize, 72 μm; porosity, 68%). Additional features of the cross-linked\nkeratin sponges include their insolubility in water and common organic\nsolvents, as well as their exposure to the surface of isocyanate groups\nfor organocatalyst immobilization. The anchoring step is effectively\nperformed in anhydrous acetone-DMSO with either 1-hydroxyethyl-3-methyl\nimidazolium iodide (HO-EtMImI; 50 °C) or TBD (room temperature)\nto produce the corresponding heterogeneous catalysts with a satisfactory\nloading of active units (0.47 and 1.80 mmol g<sup>–1</sup>,\nrespectively). The unprecedented monofunctionalization of HDI with\nHO-EtMImI affords a novel monoisocyanate imidazolium iodide derivative,\nwhich, in turn, is grafted on the immobilized TBD catalyst to form\na one-component multifunctional keratin sponge bearing hydrogen bond\ndonor, nucleophilic, and CO<sub>2</sub> activating sites. This heterogeneous\ncatalyst can effectively function in the cycloaddition of CO<sub>2</sub> to epoxides free of solvent and cocatalysts, producing five-membered\ncyclic carbonates in high yields (79–94%) at moderate temperature\n(35 °C) and pressure (10 atm), with satisfactory recyclability\n(five runs) and the possibility of complete biodegradation in 2 days\nby enzymatic treatment (protease XIV).