Physico-Chemical nanomaterials science

Surface functionalization of nanoporous carbons with fluoralkyl groups
Zaderko A. N.1, Diyuk V. E.1, Chernenko S. I. 1, Afonin S.2, Mariychuk R.3, Grishchenko L. M.1, Boldyrieva O. Yu.1, Lisnyak V. V.1,3
1 Faculty of Chemistry, Taras Shevchenko National University of Kyiv, Volodymyrska Street, 64/13, Kyiv 01601, Ukraine.
E-mail: sofiiachernenko@ukr.net; lisnyak@chem.univ.kiev.ua
2 Institute of Biological Interfaces (IBG-2), Karlsruhe Institute of Technology, POB 3640, Karlsruhe, 76021, Germany.
3 Preљov Universirty in Preљov, Ul. 17 novembra, 1, Preљov 15 080 01, Slovakia.

In recent years, fluorine-containing carbons have been of considerable interest. The most promising fields of their applications are lithium battery electrodes and supercapacitors. Fluorination can also significantly affect the properties of the surface layer of the material, increasing its hydrophobicity and conductivity, which are important. Known methods of fluorination operate with potentially dangerous and toxic compounds: elemental fluorine, BrF3, ClF3, XeF2, and the plasma of CF4, CF3I, and SF6. Fluorination of carbon materials at high temperatures by fluorine-containing hydrocarbons is a promising alternative as it requires no special treatment conditions, chemically aggressive and toxic substances and can be carried out using standard chemical equipment. Modification of nanoporous activated carbon BAU with 1,1,1,2-tetrafluoroethane and pentafluoroethane was carried out and reported here. Fluoroalkylation was carried out at 400, 500, 600, 700, and 800 °C in a stream of fluorinating agent diluted in argon. The obtained samples were examined by TGA, ATR, XPS, N2 adsorption, and 19F MAS NMR methods. Fluoroalkylation at 400 and 500 °C caused the formation of a small concentration (up to 0.5 mmol/g) of fluoroalkyl groups on the surface. The optimal temperatures are in the range of 600–700 °C, at which of the maximum fluorine content of 2–3 mmol/g, was obtained. The fluorine content decreases when the treatment temperature is increased to 800 °C. XPS spectra show that all attached fluorine is in the semi-ionic form. 19F NMR spectroscopy showed the presence of CF3, CF2, CH2F, and –CF2–CF2 groups. The fluoroalkylation at high temperatures slightly decreases microporous structure. Therefore, the most favorable for fluorine chemisorption is the use of 1,1,1,2-tetrafluoroethane, which is more effective than pentafluoroethane.