Time-Efficient Acid-Catalyzed Synthesis of Resorcinol−Formaldehyde Aerogels

Abstract

Resorcinol (R)-formaldehyde (F) aerogels are pursued as precursors of carbon aerogels, which are electrically conducting. They are usually prepared via a week-long base-catalyzed gelation process from an aqueous sol. For this work, we reasoned that because both the reaction of R with F and the condensation of the resulting hydroxymethyl resorcinol with R are electrophilic aromatic substitutions, they should proceed easily by acid catalysis in one pot. Thereby, we have developed and reported an HCl-catalyzed gelation process in CH 3 CN, which is completed in about 2 h at room temperature or in 10 min at 80°C. The final aerogels are chemically indistinguishable (by IR and 13 C CPMAS NMR) from typical basecatalyzed samples. In analogy to phenol-formaldehyde resin formation, the mechanism may involve o-quinone methide intermediates (hence the red color prevailing throughout the process). The effect of aging is discussed in terms of shrinkage and is attributed to further reaction and incorporation of more formaldehyde into wet gels, followed by syneresis (reaction with one another of dangling oligomeric appendices on the skeletal framework).

Marked Increase in Hydrophobicity of Monolithic Carbon Cryogels via HCl Aging of Precursor Resorcinol–Formaldehyde Hydrogels: Application to 1-Butanol Recovery from Dilute Aqueous Solutions

“…The IR spectrum characterizing an RFMH-0 (sample without HCl aging) shows bands that can be assigned to modes typically found for an RF gel ( Figure 1 To further investigate the effects of HCl treatment on the structure of RFMHs, 13 C CP MAS NMR characterization was performed for selected materials: RFMH-0, RFMH-4, and RFMH-20. All of the data show resonances that are consistent with an RF gel: 15,37 (Figure 2). …”

“…One of the most widely used precursor for carbon gels is a resorcinol−formaldehyde (RF) resin 11−13 that is synthesized by the polycondensation of resorcinol and formaldehyde in water using a base 11 or acid 14,15 catalyst. As in the case of sol−gel synthesis of silicate materials, 16 a wide variety of adjustable synthesis conditions, including the concentrations of monomers and a catalyst, 17,18 pH of the synthesis solution, 19 use of an organic template, 20 and drying conditions, 21 allow one to tailor the porous properties of resultant RF resins, 16,22,23 which ultimately determine the pore structure of the final carbonized materials.…”

Nanoporöse Metallschäume

“…[22] Die Nanoverhüttung beginnt mit der Sol-Gel-Synthese eines Hybridgels bestehend aus einem verzahnten nanostrukturierten Netzwerk des RFPolymers und Eisenoxid. Zur Synthese des Gels wurde eine Säure-katalysierte Variante [78] der von Pekala et al entwickelten Sol-Gel-Methode [20,22] mit der Epoxid-unterstützten Gelierung von Metallsalzen (zur Herstellung von MetalloxidGelen nach Gash und Tillotson) [11] kombiniert, wobei das Brönsted-saure Metallsalz (z. B. Nitrat oder Chlorid) sowohl als Quelle für das Metalloxid-Netzwerk als auch als Katalysator für die RF-Polymerisation genutzt wird.…”

An underrated variable essential for tailoring the structure of xerogel: the methanol content of commercial formaldehyde solutions

“…Figure 3a shows the The peak at 132.4 corresponds to carbons in meta position with respect to both phenols, whereas the peak at 120.5 ppm corresponds to mono and bi-substituted aromatic carbons in ortho position relative to the phenol group. The peak at 103.7 ppm corresponds to the carbons between the phenolic OH and the wide peak at 28.3 is assigned to different CH 2 bridges [22].…”