Monolithic resorcinol–formaldehyde alcogels and their corresponding nitrogen-doped activated carbons

Abstract

Here we report the adaptation of formaldehyde crosslinked phenolic resin-based aerogel and xerogel synthesis to ethanolbased solvent systems. Three specific formulations, namely one resorcinol-formaldehyde (RF) and two resorcinolmelamine-formaldehyde (RMF) systems were studied. As-prepared resins were characterized in terms of envelope and skeletal density. Furthermore, resin samples were pyrolyzed and activated in a CO 2 gas atmosphere using a single-step protocol. The corresponding carbon materials featured high surface areas, moderate water uptake capacity and thermal conductivities in the 0.1 W.m −1 K −1 range, in line with comparable activated carbons. The amount of formaldehyde in the synthesis of the RMF derived carbons proved to be a critical parameter in terms of both structural features and amount of N dopant in the carbonaceous matrix. Furthermore, a high formaldehyde concentration also has a drastic effect on the pore structure of the corresponding RMF carbons, leading primarily to mesopore formation without almost any macropore formation. Perhaps more importantly, the effect of the ammonia curing catalyst concentration on the material microstructure showed the opposite effect as observed in classical, water-based phenolic resin preparations. The ethanol-based synthesis clearly affects the pore structure of the resulting materials but also opens up the possibility to create inorganic/organic hybrid materials by simple combination with classical alkoxide-based silica sol-gel chemistry.

Silica–Resorcinol–Melamine–Formaldehyde Composite Aerogels as High-Performance Thermal Insulators

“…Mixing two chemical systems requires finding compatible conditions for them to interact. Silica sols and RMF resins 41 can both form wet gels in ethanol when catalyzed by ammonia. By finding the optimum NH 3 catalyst concentration, composite silica–RMF alcogels of homogeneous appearance were obtained for nominal silica precursor contents spanning the entire range from 0 to 100% nom ( Table 1 ).…”

“…The preparation of the RMF ethanolic precursor sol, with a known solid-to-liquid ratio (0.379 g·mL –1 ), is described in detail in our previous publication. 41 Briefly, melamine is dissolved in a water–ethanol–formaldehyde solution at 55 °C, and resorcinol is dissolved in ethanol also at 55 °C. The two sols are brought together and catalyzed by the addition of ammonia.…”

Hybrid Proton-Exchange Membrane Based on Perfluorosulfonated Polymers and Resorcinol–Formaldehyde Hydrogel

“…Regarding the solvents, one can note that alcohol opens up membrane pores better than water, facilitating the gelation process. The downside of ethanol is that it may react with formaldehyde, generating hemiacetal and acetal molecules that do not react with resorcinol [ 32 , 33 , 34 ].…”

Nanoporous Sponges as Carbon-Based Sorbents for Atmospheric Water Generation

“…With those considerations in mind, a carbon-based adsorbent is discussed in the present work: nanoporous sponges (NPSs) are heat-treated resorcinol-formaldehyde (RF) resins, preferably with oxygen (O) and/or nitrogen (N) functionalities added on their surface. Carbonized RF resins have already been reported in the literature for supercapacitor and CO 2 adsorption applications. − Pyrolyzed RF resins, , with the presence of melamine , or urea, have also been investigated as water sorbents, but mostly under the form of monoliths for adsorption heat pump applications. We have performed physical characterization of the NPS sorbent, determined its water harvesting capabilities, and have applied a theoretical model to better grasp underlying fundamental mechanisms.…”

“…Carbonized RF resins have already been reported in the literature for supercapacitor and CO 2 adsorption applications. 20−22 Pyrolyzed RF resins, 23,24 with the presence of melamine 25,26 or urea, 27 have also been investigated as water sorbents, but mostly under the form of monoliths for adsorption heat pump applications. We have performed physical characterization of the NPS sorbent, determined its water harvesting capabilities, and have applied a theoretical model to better grasp underlying fundamental mechanisms.…”