## 3 Results and Discussion  
### Scanning Electron Microscopy  
The prepared samples were coated with a thin film of platinum to increase the resolution of the images obtained through scanning electron microscopy (SEM). Figure 1 shows SEM images of CSHDS. It indicated that CSHDS has platelike morphology, agreeing with the literature on HDS (2018, 2019). The perpendicular orientations of the plates formed a porous structure, as shown in Figure 1a. The plates of the sample CSHDS were observed to have fine edges, indicating that it is in the nanoscale. Their plates' thickness is less than 100 nm, as shown in Figure 1c. The HDS structure was formed through decomposition of urea, as shown in the following equation:  
\[\text{NH}_{2}\text{CONH}_{2}\rightarrow\text{NH}_{4}{}^{+}+\text{CNO}{}^{-}+ \text{H}{}^{+}+\text{OH}{}^{-} \tag{1}\]  
According to this equation, the concentration of cyanate gradually increased and the medium of the reaction converted to alkaline with high pH. These conditions are suitable for building a hydroxyl double salt structure. The presence of cyanate anions was confirmed by FT-IR results and EDS spectrum, which will be discussed below.  
In the case of CSLDH-1, nanofibers were observed as shown in Figure 2. Figure 2a,b reveal bundles of nanofibers. In addition, individual fibers with diameters of 50 nm are displayed in Figure 2c. However, the plate morphology is the most famous morphology for the natural samples of layered double hydroxides, which consist of di- and trivalent cations ([PERSON] et al., 2019). Figure 2d confirms this speculation through displaying the conversion of Sn/Co plates to nanofibers. It shows that the major part of one plate has already transformed to nanofibers and the remaining part of the plate did not convert to nanofibers.  
Figure 1: SEM images of CSHDS: (**a**) First location, (**b**) second location, and (**c**) after magnification \(\times\)10,000.  
Energy dispersive X-ray spectrum analysis (EDS) of CSLDH-1 provides local information of the concentrations of the different elements in the outermost layers of the nanofibers. Cobalt and tin were observed in the EDS spectrum with similar percentages for the starting salts. In addition, carbon, oxygen and nitrogen are clearly identified in the nanofibers, as shown in Figure 3. It means that EDS spectrum of CSLDH-1 confirmed the presence of cyanate anions as interlayered anions in addition to traces of nitrate anions because the ratio between carbon and nitrogen in the cyanate anions equal one.  
The nanofibrous morphology of the sample CSLDH-1 could be explained through presence of tetravalent cations of Sn beside divalent cations of Co inside the nanolayers which created positive charges (+2). During the decomposition of urea, the concentration of cyanate anions increased and the medium of the reaction became rich in cyanate anions. Therefore, dual cyanate anions intercalated among the cationic layers through one side to neutralize the positive charges. The steric hindrance and repulsion between the bulk cyanate anions caused the distortion or curvature of the nanolayers of Sn/Co LDHs. This distortion or curvature led to the formation of nanofibers.  
Figure 3: Energy dispersive X-ray spectrum of CSLDH-1.  
Figure 2: SEM images of CSLDH-1 at different locations.  
By increasing the content of tin in the sample CSLDH-2, the positive charges increased in the nanolayers and the amount of interlayered anions accordingly increased, causing more distortion and strong curvature for the layers and producing clear nanofibers because of the repulsion forces among the dual anions. Figure 4 shows that the sample CSLDH-2 has clear nanofibers, confirming this speculation. The diameter of these nanofibers was less than 100 nm, as shown in Figure 4b,c.