Deep eutectic solvents-assisted cost-effective synthesis of nitrogen-doped hierarchical porous carbon xerogels from phenol-formaldehyde by two-stage polymerization

Abstract

The cost-effective synthesis of nitrogen-doped hierarchical porous carbons has been demonstrated. Phenol and formaldehyde based polymers were used as the carbon precursor, deep eutectic solvents (DES) synthesized from choline chloride (CCl) and urea (U) in a molar ratio of 1:2 served as solvent as well as structure-directing agent, and also, the source of nitrogen of the carbons. A designed two-stage synthesis was applied for the polymerization. Carbon xerogels were derived via ambient drying followed by thermal treatment at 800 °C using N2 flow. The obtained carbons exhibit a hierarchical porous structure with modest macropores and well-developed micropores. The homogeneous incorporation of nitrogen from the urea-type DES at the solution stage, in combination with the two-stage synthesis process, allowed an excellent nitrogen-doping efficiency (ca. 5–9% for samples aged at 50 °C and ca. 3% for that at 90 °C) in the carbons even after thermal treatment at 800 °C. The unique carbons with nitrogen-rich hierarchical porous architecture are highly desirable for CO2 capture at both 0 °C and 25 °C and ~1 bar.