2.2.2. Element Analysis of SeCS

To determine chemical compositions of SeCS samples, scanning electron microscopy equipped with an energy dispersion spectrum detector (SEM-EDS) was employed. The results were shown in Figure 3. It was found that C (44.16%), O (37.74%), and Na (18.1%) were the chemical compositions of CS (Figure 3A). Furthermore, an SEM-EDS investigation of SeNPs showed the percentages of Se, C and O atoms were 92.27%, 7.43% and 0.30% (Figure 3B), which were similar to previous findings of Ye et al. [21]. An EDS investigation of SeCS (Figure 3C) showed that the presence of a strong Se atoms signal (65.73%). The existence of the Na atom (1.27%), C atom (25.55%) and O atom (7.44%) in SeCS suggested that CS successfully combined to the surface of the SeNPs.

**Figure 3.** SEM-EDS element analysis of CS (**A**), SeNPs (**B**) and SeCS (**C**). The SeNPs were obtained in the same procedure of SeCS without CS.

2.2.3. Fourier Transform Infrared Spectroscopy (FT-IR) Analysis

To confirm the chemical binding of CS to the surface of the SeNPs, FTIR spectroscopy is used to ascertain the formation of SeCS. The FTIR spectra of CS and SeCS were shown in Figure 4. The typical IR spectrum of CS was presented in Figure 4 which was in good agreement with the literature [23]. The FTIR spectrum of CS exhibited an absorption band at 3402 cm<sup>−</sup>1, indicating the overlapping of –OH and –NH stretching vibrations. Additionally, the absorption peaks of CS were 1070 cm−<sup>1</sup> and 1128 cm−1, 1224 cm−1, 1419 cm−1, and 1635 cm−1, which corresponded to the characteristic asymmetric stretching vibrations of the C–O–C bridge (β-1,4 glycosidic bonds), asymmetric stretching vibrations of –S=O, stretching vibrations of the -COOH and stretching vibrations of the –C=O of –NHCO–. By comparing the FTIR spectra of CS, SeCS resembled that of CS and there were no new absorption peaks in the FTIR spectrum of SeCS, indicating that the reaction between CS and SeNPs did not generate any new covalent bonds. However, an obvious change occurred in the peak locations of SeCS, indicating that the main interaction between CS and SeNPs was physical adsorption.

**Figure 4.** FT-IR spectra of CS, SeNPs and SeCS. The SeNPs were obtained in the same procedure of SeCS without CS.

2.2.4. Powder X-ray Diffractometry (XRD) Analysis

On this basis of FT-IR analysis, XRD was used to characterize the formation of SeCS. XRD analysis could detect phase identification of crystalline materials. The intensity and sharpness of XRD peaks reflected the crystalline nature of the sample. The XRD spectra of CS, SeNPs and SeCS were shown in Figure 5. As shown in Figure 5, the X-ray diffractogram of SeNPs showed two broad peaks in the ranges of 20–40◦ and 40–60◦ (2θ), indicating that SeNPs existed in an amorphous form. This result was in good agreement with the literature [21]. No sharp peaks were found in the XRD pattern of CS and SeCS, confirming their amorphous characteristic in nature. Compared with the XRD diffraction patterns of

CS and SeNPs, both the peak positions and intensity of SeCS shifted, suggesting that the formation of SeCS.

**Figure 5.** XRD patterns of CS, SeNPs and SeCS. The SeNPs were obtained in the same procedure of SeCS without CS.
