Resorcinol-Formaldehyde Polycondensation in Deep Eutectic Solvents for the Preparation of Carbons and Carbon-Carbon Nanotube Composites

Deep eutectic solvents (DES, a new class of ionic liquids) have been used as solvents to carry out the polycondensation of resorcinol-formaldehyde (RF). RF gels were characterized by FTIR and solid C-13 NMR spectroscopy, and scanning electron microscopy. Solid C-13 NMR spectroscopy demonstrated that the use of DES containing small amounts of water (those required to introduce formaldehyde in the solution) favored RF polycondensation as compared to that carried out in regular aqueous conditions (that is, in absence of DES). RF polycondensation also occurred in DES in its pure state (in this case, after lyophilization) albeit the reaction efficiency was difficult to evaluate given to partial elimination of formaldehyde. Carbonization of any of the RF gels obtained in DES (e.g., with or without water) resulted in the formation of monolithic carbons with conversion rates and carbon contents in range to and even slightly above those obtained in aqueous solutions. Finally, we took advantage of the excellent solvent properties of DES to suspend carbon nanotubes (CNTs) within the starting sol. Polycondensation of resorcinol and formaldehyde in DES also containing CNTs in suspension allowed the preparation of carbon-carbon nanotube RF gels and ultimately (i.e., after thermal treatment) carbon composites, having multiwall CNTs (MWCNTs) homogeneously distributed within the whole monolithic structure.