Physico-Chemical nanomaterials science

Surface functionalization of nanoporous carbons with sulfur- and halogen-containing groups
Pryhunova O.1, Grishchenko L.M.1, Zaderko A.N.1, Diyuk V.E.1,
Mariychuk R.2, Boldyrieva O.Yu.1, Lisnyak V.V.1,2
1 Taras Shevchenko National University of Kyiv, 62a, Volodymyrska Str., Kyiv 01601, Ukraine, E-mail: lisnyak@univ.kiev.ua
2 Prešov University in Prešov, Ul. 17 Novembra, 1, 080 01, Prešov, Slovakia

The introduction of two types of heteroatoms in the structure of carbon materials allows to change of the properties of the surface layer in a wide range and to obtain materials much better adapted to the specific application. Dual-doped carbons where one of the heteroatoms is fluorine are used mainly as electrode materials. Dual-doped carbons with S, N, Cl, and P heteroatoms are widely used in electrocatalytic processes, sensory, and catalysis. They are also integrated into the production of lithium-ion and sodium-ion batteries, and in supercapacitors.
In this work, the surface of nanoporous carbon (NC) was modified with C2F4Br2 or CF2Cl2 freons in the gas phase process, which provides the introduction into the surface layer of 0.7–1.9 mmol of fluorine, 1.3–2.1 mmol of bromine, and 2.4–2.9 mmol of chlorine per gram of NC, as evidenced by elemental analysis and confirmed by NMR spectroscopy. The TGA method showed that the halogenated NCs have high thermal stability, and the thermal decomposition of surface groups is observed at temperatures above 500 °C. Modification with C2F4Br2, compared with that of CF2Cl2, leads to the formation of a more active surface layer.
Acid-base catalysts obtained by sulfonation of halogen-containing NC have two temperature intervals of the thermal decomposition of the surface layer: 140–310 °C and 320–510 °C. It is shown that the determining effects of weight loss in these temperature ranges correlate with the catalytic activity of the obtained sulfonated NCs. The sulfonated NCs have been shown to have high catalytic activity in the isopropanol dehydration reaction. The temperature of 100% conversion of isopropanol to propylene for the most active sulfonated samples is 170–180 °C.