Tuning the Properties of Iron-Doped Porous GraphiticCarbon Synthesized by Hydrothermal Carbonization of Cellulose andSubsequent Pyrolysis

摘要

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 °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 °C and an increase of the specific surface area with a maximum of 520 m² g^–1 at a pyrolysis temperature of 600 °C. Devolatilization mainly took place in the range from 300 to 500 °C, releasing light pyrolysis gases such as CO, CO2, H2O and larger oxygen-containing molecules up to C11. The presence of iron oxide NPs lowered the specific surface areas by about 200 m² g^–1 and resulted in the formation of mesopores. For the iron oxide-containing composites pyrolyzed up to 500 °C, the oxidation temperature was decreased by about 100 °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 carbothermalreduction to iron and iron carbide, which, however, catalyzed thegraphitization of the carbon matrix. Thus, the well-controlled two-stepsynthesis based on a biomass-derived precursor yielded stably embeddediron NPs in a corrosion-resistant graphitic carbon matrix.