Tuning the Properties of Iron-Doped Porous Graphitic Carbon Synthesized by Hydrothermal Carbonization of Cellulose and Subsequent Pyrolysis

The applied pyrolysis temperature was found to strongly affect composition, structure, and oxidation behavior of pure and iron oxide nanoparticle (NP)-loaded carbon materials originating from hydrothermal carbonization (HTC) of cellulose. A strong loss of functional groups during pyrolysis at temperatures beyond 300 degrees C of the HTC-derived hydrochars was observed, resulting in an increase of the carbon content up to 95 wt% for the carbon materials pyrolyzed at 800 degrees C and an increase of the specific surface area with a maximum of 520 m(2) g(-1) at a pyrolysis temperature of 600 degrees C. Devolatilization mainly took place in the range from 300 to 500 degrees C, releasing light pyrolysis gases such as CO, CO2, H2O and larger oxygen-containing molecules up to C-11. The presence of iron oxide NPs lowered the specific surface areas by about 200 m(2) g(-1) and resulted in the formation of mesopores. For the iron oxide-containing composites pyrolyzed up to 500 degrees C, the oxidation temperature was decreased by about 100 degrees C, indicating tight contact between the iron oxide NPs and the carbon matrix. For higher pyrolysis temperatures, this catalytic effect of iron oxide on carbon oxidation vanished due to carbothermal reduction to iron and iron carbide, which, however, catalyzed the graphitization of the carbon matrix. Thus, the well-controlled two-step synthesis based on a biomass-derived precursor yielded stably embedded iron NPs in a corrosion-resistant graphitic carbon matrix.