Influence of different stalks on the metallization degree of FeCl₃-derived magnetic biochar through pyrolysis...

To investigate the effect of stalk type on the metallization degrees in FeCl₃-derived magnetic biochar (MBC), MBC was synthesized via an impregnation-pyrolysis method using six different stalks. The Fe⁰ content in MBC significantly influenced its magnetic properties and ostensibly governed its catalytic capabilities. Analysis of the interaction between stalks and FeCl₃ revealed that the variation in metallization degrees, resulting from FeCl₂ decomposition (6.1%) and stalk-mediated reduction (20.7%), was directly responsible for the observed differences in MBC metallization. The presence of oxygen-containing functional groups and fixed carbon appeared to promote metallization in MBC induced by reduction. A series of statistical analyses indicated that the cellulose, lignin, and hemicellulose content of the stalks were key factors contributing to differences in MBC metallization degrees. Further exploration revealed that hemicellulose and cellulose were more effective than lignin in enhancing metallization through FeCl₂ decomposition and reduction. Constructing stalk models demonstrated that the variance in the content of these three biomass components across the six stalk types could lead to differences in the metallization degree attributable to reduction and FeCl₂ decomposition, thereby affecting the overall metallization degree of MBC. A prediction model for MBC metallization degree was developed based on these findings. Moreover, the elevated Si content in some stalks facilitated the formation of Fe₂(SiO₄), which subsequently impeded the reduction process. This study provides a theoretical foundation for the informed selection of stalk feedstocks in the production of FeCl₃-derived MBC.