Physico-Chemical nanomaterials science

Bromination of carbon surface as a toolkit for the preparation of N-, S-, and O- containing sorbents and catalyst carriers
Diyuk V.E.1, Zaderko A.N.1, Grishchenko L.M.1, 
Vakaliuk A.V.1, and Lisnyak V.V.1
1Taras Shevchenko National University of Kyiv, Volodymyrska Street 64/13, Kyiv 01601, Ukraine.
E-mail: vdiyuk@gmail.com

Carbon materials are components of sensors and electronic devices; they are traditional sorbents, catalyst carriers, and catalysts. This universality is related to carbon atoms being in different hybridized states, and there are many carbons forms, e.g., granules, powders, foams, monoliths, fibers and textile, thin films, and nanostructures. But all of them found an application in the modified form mainly. Bromination and subsequent substitution of bromine is one of the most common synthetic approaches used in organic synthesis for preparing amines, mercaptans, oxygen-containing compounds, and their derivatives. In this work, we report on the bromination of carbon granular and fibrous nanostructured materials with liquid Br2 and KBr3 solutions. Physicochemical and functional properties of them were studied by N2 adsorption, TG/DTG, TPDIR, TPD MS, FTIR, and Boehm titration. Chemically active forms of bromine, in amounts up to 1 mmol/g, can be obtained by direct bromination. TPD IR and TPD MS showed the staged desorption of bromine. We found this regardless of the nature of the used carbons, bromination method, and the content of bromine. In contrast, increasing the acidity has an impact on the grafted bromine content which reached values from 0.76 to 1.94 mmol bromine per 1 g of carbon. Thermal treatment and thermal decomposition of oxygen-containing surface groups significantly improves the bromination efficiency. As a result, the surface concentration of active bromine is increased by 20-50%. We proposed a reaction model that describes the interaction of bromine with the system of surface isolated and conjugated double C=C bonds. Part of them binds bromine and breaks the conjugation. However, the C=C bonds can renew through the thermal desorption when eliminating HBr. It is shown that synthesized brominated carbon materials are convenient precursors with a high content of reactive bromine. This surface bromine plays the role of an active site for further substitution by N-, S-, and O-containing groups. In fact, we have obtained the brominated carbons as valuable precursors for making new surface functions for the nanostructured carbon materials.