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 [small micro]m and some larger voids with an average diameter of 49 [small micro]m. 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

One‐pot emulsion templating for simultaneous hydrothermal carbonization and hydrogel synthesis: porous structures, nitrogen contents and activation

“…Surprisingly, the macroporous morphologies of the carbon monoliths are often strikingly similar to those of the original polyHIPEs, in spite of the extensive reductions in mass and volume. The polyHIPEs used for generating carbons have been based on styrenics, 59,66–70 acrylonitrile, 71–73 tannin, 74 phenolics, 75,76 furfuryl alcohol, 77 Kraft black liquor, 78 polycarbosilane 79 and urea‐based precursors 80 . Porous carbons combining macroporosity with microporosity and mesoporosity ( S BET as high as 900 m 2 g −1 ) were generated by combining several types of templating, often including the use of hybrid or silica frameworks 81–85 ; oxygen and nitrogen functionalities in polyHIPE‐derived carbons have been obtained using oxygen‐ or nitrogen‐containing monomers 5,57,86 ; and chemical activation has been used to generate microporosity ( S BET as high as 2000 m 2 g −1 ) in carbonized polyHIPEs 63,87 .…”

Recent advances in separation applications of polymerized high internal phase emulsions

“…The modification was focused on the functionalization of reactive groups (amino, carboxylic acid, epoxy, thiol) present on polyHIPE surfaces with functional species, such as galactose [33], cyclo‐RGDfK‐maleimide [34], and enzyme [35], or the incorporation of reactive groups including iminodiacetic acid (IDA) [13], pentafluorophenyl acrylate [33], 3‐mercaptopropionate (or 1,9‐nonanedithiol) [36], piperazine [37], and 2‐bromo‐2‐methylpropionyl bromide [38]. Furthermore, the carbonization strategy was also used to functionalize polyHIPEs, and the resulting carbonized polyHIPEs (carbo‐polyHIPEs) markedly enhanced the original polyHIPEs performance including physical and chemical stability, porosity, surface area, adsorption, extraction, and so on [39–42].…”

“…For polyHIPEs, their surface areas are generally lower than 100 m 2 /g owing to their inherent macroporosity, and thus, the higher surface areas are desired for separation applications. At present, many methods, including the addition of suitable inert porogenic solvents to the continuous phase [49], the introduction of novel hypercrosslinking techniques [50, 51], and the carbonization approach [39–42], have been developed to increase the surface area of polyHIPE up to 2392 m 2 /g. However, as the surface areas of polyHIPEs reach a certain level, their mechanical performance, brittleness in particular, are extremely compromised, resulting in the collapse and loss of the materials when subjected to the flow through of liquids.…”

“…Therefore, it is a great challenge to improve the mechanical properties of polyHIPEs while maintaining their high porosity and interconnectivity. As a result, much efforts were dedicated to solving this issue, and several approaches, including selection of the appropriate monomers [52, 53], crosslinkers [44, 54, 55], and surfactants [48, 56], incorporation of organic/inorganic components [16–20, 28, 54–57], introduction of novel polymerization methods [6–8, 58, 59], and postcarbonization of polyHIPEs [40–42], have been developed, which make polyHIPEs fascinating candidate porous materials for a variety of applications including cell culture [33, 34], tissue engineering [60–62], energy storage [63, 64], enzyme immobilization [35, 65, 66], protein purification [67–69], separation, and enrichment [9, 23–26, 70–74].…”

Ring-Opening Metathesis Polymerization Derived Hierarchically Porous Carbon-Foams

“…15 Key for their success was to produce a foam, which does not lose or change its macroporous morphology at the high temperature needed for the carbonization process. Nowadays several synthetic strategies for the preparation of macroporous carbon foams from poly(styrene) and poly(divinylbenzene), 16 poly(acrylonitrile), 17 furfural-phloroglucinol, 18 tannin, 19 Kraft black liquor, 20 2,5-dihydroxy-1,4-benzoquinone and urea 21 or resorcinol-formaldehyde resin based 22 templates are available. Emulsion templating is a more sustainable alternative to the so-called hard templating route for preparing similar carbon foam architectures.…”