Controllable synthesis of magnetic carbon composites with high porosity and strong acid resistance from hydrochar for efficient removal of organic pollutants: An overlooked influence

Facile fabrication of magnetic carbon composites (MCs) via pyrolysis of hydrochar in the presence of ZnCl2 and an iron salt has been attracting enormous interest to simultaneously realize high-surface area and magnetization. During this synthesis, the interactions between the carbon matrix and iron salts have remained unknown. In this work, a closer look was taken on iron salt interactions and their respective effect on MC characteristics. These newly fabricated MCs can provide guidance for further design of efficient MCs. It was discovered that ferric chloride (FeCl3) promoted the enhancement of MC porosity, largely due to the strong reduction reaction between amorphous carbon and iron oxide (γ-Fe2O3 and Fe3O4). Various other iron salts (including ferrous oxalate (FeC2O4), ferric citrate (FeC6H5O7), and ferric sulfate (Fe2(SO4)3) were also evaluated. These compounds inhibited pore structure development, resulting from decreased carbonization seen in the composite. This phenomenon was observed from complexation reactions between Zn2+ and the corresponding anions of these salts. Also, high Fe content and low γ-Fe2O3:Fe3O4 ratios led to decreased acid resistance of the MC. Finally, higher porosity in resultant MCs resulted in larger adsorption capacity for organic pollutants (roxarsone). This study will aid in further optimization of MCs to ultimately maximum performance.