## 3 Results and Discussion  
### Structural and Chemical Characterization  
To study the surface morphology of DE and DE-LDH before and after CR adsorption, FESEM with energy-dispersive X-ray spectroscopy (FESEM-EDX) images were obtained and shown in Figure 2a-d. The bare DE shows a well-arranged porous structure, its surface is well purified and there is no contamination on the surface. The chemical composition for DE was analyzed by EDX which showed silicon (Si) and oxygen (O) as major components, which confirms that DE consists of SiO\({}_{2}\). After modification with LDH, the surface of DE showed LDH formation with sheet-like morphology and the pores of DE were almost wrapped with LDH. The composition of DE-LDH showed additional elements such as magnesium (Mg) and aluminum (Al) and it was confirmed that Mg-Al LDH was formed on the DE surface. Furthermore, the morphology of prepared adsorbents was analyzed after dye adsorption to confirm any morphological changes and it was observed that there were not many morphological changes even after dye adsorption. Figure 3a shows the XRD pattern of DE and DE-LDH before and after dye adsorption. The broad spectrum of DE shows the amorphous structure of SiO\({}_{2}\) diffraction peaks which matches Joint Committee on Powder Diffraction Standards (JCPDS) file no. 89-3435. After modification with LDH, the XRD pattern was obtained for the both DE and LDH diffraction peaks (JCPD file no. 89-0460). The presence of LDH diffraction peaks shows a hydrotalcite structure and these peaks evidenced that LDH was modified on DE. Additionally, there is a slight impurity observed at around 18-20\({}^{\circ}\) (JCPDS file no. 77-0114) in the XRD pattern of DE-LDH due to the presence of Al(OH)\({}_{3}\) which has low solubility compared with Mg(OH)\({}_{2}\) in water and, hence, there could be undissolved Al(OH)\({}_{3}\) present during the synthesis [20]. Similarly, the same adsorbents were recorded after dye adsorption using XRD (Figure 3a). The peaks of DE-CR and DE-LDH-CR did not change, which shows the stability of the adsorbents [25] during the whole adsorption process. This study revealed that the adsorbent can be further regenerated and reused in the dye adsorption process. Figure 2: Field emission scanning electron microscopy-energy-dispersive X-ray spectroscopy (FESEM-EDX) images of before adsorption (**a**) DE, (**b**) DE-LDH and after dye adsorption (**c**) DE-Congo Red (CR) and (**d**) DE-LDH-CR. Furthermore, DE and DE-LDH before and after dye adsorption were analyzed by FTIR, the results of which are shown in Figure 3b. DE showed a broad peak at 3435 cm\({}^{-1}\) because of the presence of -OH on its surface. The characteristic peak at 1641 cm\({}^{-1}\) was found to be bending vibration of the water molecules on DE. The characteristic peaks at 1103, 798 and 473 cm\({}^{-1}\) are found to be asymmetric and symmetric stretching vibrations of the Si-O-Si bond and Si-O bending vibration of siloxane, respectively [26]. For DE-LDH, the broad peak at 3471 cm\({}^{-1}\) is due to the -OH stretching vibration. The peaks at 3027 and 2786 cm\({}^{-1}\) are because of the C-H stretching of LDH [27]. The sharp peak at 1384 cm\({}^{-1}\) was attributed to the stretching vibration of the NO\({}_{3}\)- ions of LDH [18]. Furthermore, the peaks from 500 to 800 cm\({}^{-1}\) denoted the M-O lattice vibration of LDH (M=Mg and Al) [19]. After the dye adsorption, additional peaks were not observed for DE-CR, which is due to the reduced adsorption of CR. On the other hand, DE-LDH-CR showed major changes by showing the shift of hydroxyl peaks from 3471 to 3448 and 3027 to 3122 cm\({}^{-1}\) due to the hydrogen bond between DE-LDH and CR. Furthermore, an additional peak was found at 1020 cm\({}^{-1}\), attributed to the symmetric stretching of the sulfonate group (-SO\({}_{3}\)-) present in CR dye (Figure S2, Supplementary Materials) [28]. Figure 3c,d shows the N\({}_{2}\) adsorption-desorption isotherm and BJH pore size distribution for DE and DE-LDH before and after dye adsorption.