Influence of post-pyrolysis treatment on physicochemical properties and acid medium stability of magnetic carbon nanocomposites

BURBANO, A. A.; MEDINA, G. A. MUÑOZ; SÁNCHEZ, F. H.; LASSALLE, V. L.; HORST, M. F.; GASCÓ, G.; MÉNDEZ, A.

Biomass Conversion and Biorefinery

Springer

Año: 2022

2190-6815

This study presents the preparation of magnetic carbon nanocomposites (MCNCs) through a two-step procedure: (i) in situco-precipitation of magnetite (Fe3O4) nanoparticles into four different carbonaceous matrixes and (ii) post-pyrolysis treatmentto coat the magnetic core. Four post-pyrolysis MCNCs were obtained: MACP (post-pyrolyzed magnetic activatedcarbon), MCCP (post-pyrolyzed magnetic charcoal), MHCPOR(post-pyrolyzed magnetic hydrochar from orange residue),and MBCPSFH(post-pyrolyzed magnetic biochar from sunflower husk). These four samples were compared with the startingMCNCs prepared without post-pyrolysis treatment: MAC, MCC, MHCOR,and MBCSFH,respectively. After post-pyrolysistreatment, a thin carbon layer surrounding some of the magnetite nanoparticles was identified by transmission electronmicroscopy. Post-pyrolysis modified the porous structure and chemical composition of MCNCs. Furthermore, a leachingtest with acid sulfuric solution at 90 °C was carried out. The results suggested that the MHCPORand MBCPSFHwere morestable in an acidic medium than MACP and MCCP, indicating that the coat generated during post-pyrolysis of hydrocharand biochar could partially protect the magnetic core by reducing Fe leaching into the aqueous solution. Biochar and thehydrochar-based MCNCs before and after post-pyrolysis treatment exhibit superparamagnetic properties; however, theirsaturation magnetization (Ms) decreased considerably. These results open the potential application fields of MCNCs obtainedby post-pyrolysis of biochar and hydrochar-based materials in acidic mediums.