Hydrothermal Treatment of Tannin: A Route to Porous Metal Oxides and Metal/Carbon Hybrid Materials

In the present paper, porous materials were prepared from the hydrothermal treatment of aqueous solutions of tannin, a renewable phenolic resource extracted from tree barks, containing dissolved salts of transition metals: V, Cr, Ni and Fe. Hydrothermal treatment produced carbonaceous particles doped with the aforementioned metals, and such materials were treated according to two different routes: (i) calcination in air in order to burn the carbon and to recover porous oxides; (ii) pyrolysis in inert atmosphere so as to recover porous metal/carbon hybrid materials. The nature of the metal salt was found to have a dramatic impact on the structure of the materials recovered by the first route, leading either to nano-powders (V, Cr) or to hollow microspheres (Ni, Fe). The second route was only investigated with iron, leading to magnetic Fe-loaded micro/mesoporous carbons whose texture, pore volumes and surface areas gradually changed with the iron content.