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

• Published in: Journal of physical chemistry. C Vol. 118; no. 13; pp. 6866 - 6872
• Main Authors: Ogino, Isao, Kazuki, Sakai, Mukai, Shin R
• Format: Journal Article
• Language: English
• Published: American Chemical Society 03.04.2014
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp412781d

Monolithic carbon cryogels having a honeycomb structure with pore openings a few tens of micrometers in diameter (Carbon MicroHoneycomb, CMH) were synthesized by directional freezing of precursor resorcinol–formaldehyde (RF) hydrogels and subsequent carbonization at temperatures ≥ 674 K. Aging of precursor RF monoliths with 1 N HCl aq. was found to markedly increase the hydrophobicity of the corresponding CMHs as characterized by water vapor adsorption experiments conducted at 298 K. Analysis of the water vapor adsorption data indicates that levels of hydrophobicity of CMHs are similar to those exhibited by other types of highly hydrophobic adsorbents, such as a coal-derived activated carbon and a defect-free pure silica zeolite Beta. HCl aging also drastically changes the porous structure of CMHs from microporous to micro/mesoporous as characterized by nitrogen adsorption/desorption experiments. Because of significantly enhanced hydrophobicity of CMHs as well as hierarchical pore structure (straight macropores connected with micro/mesopores), CMHs can readily separate 1-butanol molecules from a diluted aqueous solution at 310 K and demonstrate high capacities (up to ≈3.13 mol kg–1 at a 1-butanol concentration of 135 mM). The unique morphology of CMHs, consisting of straight macropores coupled with micro/mesopores embedded within honeycomb walls, and the highly hydrophobic surface properties offer future prospects of CMHs in various applications that require fast separation of hydrophobic molecules from a large volume of aqueous solutions.