Hierarchically porous carbons from an emulsion-templated, urea-based deep eutectic

Abstract

A hierarchically porous carbon monolith with a density of 0.059 g cm⁻³ (97% porosity) was generated through the carbonization of an emulsion-templated monolith formed from a deep-eutectic polymer based on the polycondensation of 2,5-dihydroxy-1,4-benzoquinone with excess urea. The mechanical integrity and thermal stability of the monolith were successfully enhanced through a chain extension reaction with terephthaloyl chloride (TCL) that occurred during/following the formation of a high internal phase emulsion (HIPE). The bimodal, open-cell macroporous structure of the monolith consisted of many smaller voids with an average diameter of 15 μm and some larger voids with an average diameter of 49 μm. Carbonization of the monolith introduced microporosity and meso/macro-porosity, yielding a high specific surface area (812 m² g⁻¹, largely from micropores), a micropore volume of 0.266 cm³ g⁻¹ (an average diameter of 0.67 nm), and a meso/macro-pore volume of 0.238 cm³ g⁻¹ (an average diameter of 8.1 nm). The elemental composition of the chain-extended polymeric monolith was similar to that predicted from the HIPE components except for a relatively low nitrogen content which may indicate the loss of some urea groups during the chain extension reaction with TCL. The nitrogen–carbon bonds in the carbon monolith from the chain-extended polymer were around 47% pyridinic, 20% pyrrolic, and 33% graphitic. While chain-extension reduced the nitrogen content, the mechanical integrity and thermal stability were enhanced, which was key to generating a highly microporous carbon monolith with a hierarchical porous structure. The carbon monolith exhibited promising results for aqueous solution sorption applications, in both batch and flow modes, owing to its advantageous combination of properties.