Nanoporous Magnetic Carbon Nanofiber Aerogels with Embedded α-Fe/γ-Fe Core–Shell Nanoparticles for Oil Sorption and Recovery

Biomass-based carbon aerogels have received a lot of attention as oil sorbents or oil/water separators due to their effectiveness, low cost, and vast availability of natural resources as their precursors. Magnetically functionalizing the carbon aerogel improves its reusability by magnetic recovery after oil sorption. This work fabricated magnetic carbon nanofibers (MCF) aerogels from the pyrolysis of magnetic bacterial cellulose (MBC) aerogels. The effect of the pyrolysis temperature on the phase transformation and functionalities of the MCF aerogel was investigated. The combined characterization techniques concluded that the MBC aerogel consists of the BC nanofiber matrix decorated with nonmagnetic FeC4H2O4 and magnetic Fe3O4 nanoparticles, which transformed into amorphous carbon nanofibers anchored with the α-Fe/Fe3O4 core–shell structured nanoparticles after pyrolysis at 700 °C. Increasing the pyrolysis temperature to 800–900 °C led to the formation of purer amorphous carbon nanofibers, whereas the nanoparticles turned into the α-Fe/γ-Fe core–shell structure. At 1000 °C, the amorphous carbon structure is better developed and coated on the α-Fe/γ-Fe core–shell nanoparticles. The interpretation explains the results from the magnetic measurement very well and fits perfectly on the Fe–C phase diagram. Furthermore, the MCF aerogels show excellent properties as an efficient oil sorbent, such as large surface area, low density, and hydrophobic properties. Among the samples, the MCF aerogel pyrolyzed at 700 °C (MCF700) exhibits the most desirable properties while requiring the lowest pyrolysis temperature. It could adsorb various oils and organic solvents with high sorption capacity and could be recycled several times. With its magnetic attraction ability, the MCF700 could be magnetically manipulated toward oil, and it could be retrieved after use without direct human contact. These synergistic functionalities make it practically helpful for oil-spill remedies over a large-scale area.