2.2.3. Hydrothermal Procedure

HNT/Fe3O4-H sample was synthesized following the procedure of Tian et al. [30], with some modifications. The procedure consists of two hydrothermal steps: the former to prepare HNT enriched with a carbonaceous component, and the latter to decorate it with magnetite. An amount of 0.5 g of HNT was added to a glucose solution (10 g <sup>L</sup>−1) and magnetically stirred. The dispersion was poured into a Teflon-lined stainless-steel autoclave and heated for 48 h at 160 ◦C. The obtained product was washed 5 times in ethanol, centrifuged, and dried for 18 h at 60 ◦C under vacuum. An amount of 0.5 g of the final product was added to a solution containing 3 mmol of FeCl3·6H2O in ethylene glycol. After stirring for 24 h, 1.8 g of sodium acetate and 0.5 g of ethylene glycol were added, and the dispersion was poured into a Teflon-lined stainless-steel autoclave and heated for 8 h at 200 ◦C. The obtained magnetic composite was washed with distilled water and dried for 12 h at 80 ◦C. The procedure of the second step was also applied to synthesize the Fe3O4 alone (sample Fe3O4-H), by omitting the addition of HNTs.
