**3. Results and Discussion**

*3.1. Characterization of Nanoparticles*

TEM images of the pristine HNTs and the treated HNTs nanoparticles are shown in Figure 1. Both HNTs and T-HNTs are cylindrical, with a central transparent region extending lengthwise along the nanotubes, indicating that the HNTs are hollow and open. No significant changes are observed in the tube length of HNTs and T-HNTs. Interestingly, after HNTs were treated with sulfuric acid, the inner lumen was clearly etched, and their inner diameters were significantly increased by about 10–20 nm. This indicated that sulfuric acid treatment resulted in an increase in the inner diameter of HNTs.

**Figure 1.** TEM images of HNTs and T-HNTs.

The porous structure parameters of HNTs, T-HNTs, and T-HNTs-CIN are shown in Table 1. After HNT was etched by sulfuric acid, its specific surface area increased from 25.50 to 76.61 m2/g, and its pore volume increased from 0.30 to 0.39 m3/g, which were consistent with the TEM observation results. The same trend was found for average pore size of HNTs. The selective dissolution of the AlO6 octahedral layer in the inner cavity of HNTs and the decomposition of silica would cause the increase of the specific surface area and pore volume of HNTs [27]. Garcia-Garcia et al. found the same trend when treating halloysite nanotubes with acid [28]. CIN itself is volatile, and samples need to be degassed before measurement, which will cause a certain error between the actual measurement result and the theoretical value (the actual measurement result is less than the theoretical value). If the CIN was not successfully loaded onto the T-HNTs, the specific surface area of the T-HNTs-CIN did not change significantly. The actual results showed that the specific surface area and pore volume of the T-HNTs-CIN increased compared with the HNT, but decreased compared with the T-HNTs, indicating that the CIN was successfully loaded onto the T-HNTs.

**Table 1.** The surface area, pore volume, and average pore size of samples.


#### *3.2. Surface Morphology of Composite Film*

Figure 2 illustrates the surface morphology of four different formulations of SA film. Figure 2a is the SA film, the surface of which is uniform and smooth. The presence of CIN in the SA matrix did not significantly affect the surface of the matrix. However, when T-HNTs were added to the SA matrix, many uniformly distributed white spots appeared on the surface of SA/T-HNTs film. Similarly, SA/T-HNTs-CIN film showed the same phenomenon. This implied that there was no significant difference between T-HNTs and CIN-loaded T-HNTs on the surface morphology of the SA film.

**Figure 2.** SEM micrographs of the surface of the bio-nanocomposite film: (**a**) SA film, (**b**) SA/CIN film, (**c**) SA/T-HNTs film, and (**d**) SA/T-HNTs-CIN film.
