2.2.1. Co-Precipitation Procedure

The HNT/Fe3O4-C sample was synthesized following the procedure of Xie et al. [27]. An amount of 0.5 g of HNT was added to an aqueous solution of 4.32 mmol of FeCl3·6H2O and 2.16 mmol of FeSO4·7H2O. The suspension was heated at 60 ◦C under N2 flux, and an 8 M ammonia solution was added dropwise to reach pH 9–10. The suspension was further heated for 4 h at 70 ◦C, then the solid was magnetically recovered, washed three times, and dried for 3 h at 100 ◦C. The same procedure was applied to synthesize the Fe3O4 alone (sample Fe3O4-C), by omitting the addition of HNTs.
