## 3 Results
### Thermal Analyses  
The thermal analyses (DTA, TG, and DTG) of the sample Co-Si LDHs are shown in Figure 5. The total weight loss of Co-Si LDHs was more than 26.8%. The TG diagram illustrated that the removal of surface and intercalated water occurred through two stages. The surface water was 7.6 wt % and easily lost at 100 \({}^{\circ}\)C, indicating an endothermic peak in the DTA curve and a clear peak in the DTG curve. Meanwhile, 3.3 wt% of the interlayered water was gradually lost up to 222 \({}^{\circ}\)C, indicating that the water molecules strongly bonded with the interlayered anions. The decomposition of the interlayered anions happened through two stages, indicating dual interlayered anions. The first anion (8.7 wt%) was sharply lost, exhibiting an endothermic peak in the DTA curve and a sharp peak in the DTG curve at 256 \({}^{\circ}\)C. Meanwhile, the second anion was gradually lost with the dehydroxylation process of the nanolayers. This loss continued up to 800 \({}^{\circ}\)C and was more than 7.2 wt%. These results concluded that the Co-Si LDHs have dual intercalated anions and a large amount of water inside the interlayered space.  
Figure 4: X-ray diffraction of Co–Si LDHs: (**a**) pure, (**b**) after zirconium inclusion, and (**c**) after zirconium and titanium inclusion.  
The thermal analyses (DTA, TG, and DTG) of Co-Si LDHs after the insertion of zirconium are shown in Figure 6. The TG diagram showed similar behavior for Co-Si LDHs before and after the inclusion of zirconium where the total weight loss occurred through four stages. The decomposition of the interlayered anions was observed as two weight losses in the TG diagram and two clear peaks in the DTG diagram. In addition, the DTA diagram showed two endothermic peaks at 250 \({}^{\circ}\)C and 295 \({}^{\circ}\)C, agreeing with the decomposition of the interlayered anions. Two clear peaks mean that there are two different kinds of anions inside the LDH structure, confirming the dual anion intercalation process. These results indicated that there is similarity between the structures of Co-Si LDH before and after the insertion of zirconium.  
The thermal analyses (DTG, DTA, and TG) of Co-Si LDHs after the insertion of zirconium and titanium were recorded as shown in Figure 7. The TG diagram showed only three weight losses. The first two weight losses belong to the adsorbed and the interlayered water, while the decomposition of the intercalated anions occurred through only one step, indicating that the LDH has one kind of the  
Figure 5: Thermal analyses of Co–Si LDHs (**a**) Differential Thermal Analysis; DTA, (**b**) Differential Thermal gravimetric; DTG, and (**c**) Thermal gravimetric; TG.  
Figure 6: Thermal analyses of Co–Si LDHs after zirconium inclusion: (**a**) DTA, (**b**) DTG, and (**c**) TG.  
interlayered anions. The total weight loss is composed of 14.6% surface water, 3.4% interlayered water, and 12% interlayered anions. The DTG diagram showed only one peak at 258 \({}^{\circ}\)C, confirming the presence of one kind of the interlayered anions. The DTA curve revealed one endothermic peak at 261 \({}^{\circ}\)C agreeing with the TG results. These results concluded that the insertion of titanium and zirconium inside the Co-Si LDH structure led to the intercalation of only one kind of anion inside its structure.