We can find some information about Fe-C interaction in Chen et al., where a "facile fabrication of 3D biochar absorbers dual-loaded with Fe3O4 nanoparticles for enhanced microwave absorption" is proposed. The Raman spectra are given for the Fe3O4@SP[spirulina]-BC and SP-BC composites (Fig. [of Chen et al.]). Chen and coworkers are not showing the Raman shift below 300 cm -1 . "All the samples exhibited two characteristic peaks at approximately 1340 cm -1 and 1585 cm -1 , which represented effective carbonization in the form of D and G bands, respectively" . "Generally, the ID/IG ratio [I intensity] is commonly utilized to assess the defects and disorder degree in carbonized composites. In this case, the ID/IG value of Fe3O4@SP-BCs was higher than that of SP-BC-700, indicating that more defects and disordered carbon components were formed due to the loading of Fe3O4 NPs" .