2.2.2. Sol-Gel Procedure

The HNT/Fe3O4-SG sample was synthesized as reported by He et al. [29]. An amount of 1 g of HNT was dispersed in an ethanol solution containing 1.98 mmol of Fe(NO3)3·9H2O. The dispersion was sonicated, stirred 24 h at room temperature and dried for 24 h at 35 ◦C. An amount of 2 mL of ethylene glycol was added, and the sample was heated for 2 h at 400 ◦C under N2 flux (N2 99.999%; flow rate: 3 L <sup>h</sup>−1; heating and cooling rate: 5 ◦C min−1). The same procedure was applied to synthesize the Fe3O4 alone (sample Fe3O4-SG), by omitting the addition of HNTs.
