## 3 Results and Discussion  
### Characterization of Na-Mt, Ti-Mt, and Ti-Mt-APTES  
Figure 2 shows the XRD patterns of the Na-Mt and Ti-Mt-APTES. The characteristic peaks for montmorillonite can be clearly seen in all samples, while peaks of quartz and cristobalite were present owing to the introduction of impurities. It can be found that the (001) plane assigned to the parent  
Figure 1: Preparation of Ti-Mt-APTES. Mt. Mt, montmorillonite; APTES, (3-aminopropyl)triethoxysilane.  
Na-Mt (20 = 6.91\({}^{\circ}\)) is shifted toward lower values of 20 (20 = 5.92\({}^{\circ}\)), due to the intercalation of titanium hydrate and APTES, which lead to the increase of the basal spacing. The crystal surface spacing \(d_{(001)}\) of montmorillonite is estimated according to Bragg's law:  
\[n\lambda=2d\sin\theta \tag{2}\]  
where [26] the basal spacing (\(d_{(001)}\)) of Na-Mt is 1.28 nm, and the spacing (\(d_{(001)}\)) for Ti-Mt-APTES is 1.49 nm. The similarities in the spectra of the two samples indicate no structural changes have occurred in the clay matrix.  
The FTIR spectra of Na-Mt and Ti-Mt-APTES are illustrated in Figure 3. For Na-Mt, it is possible to assign the peaks located at 3618 and 1036 cm\({}^{-1}\) to the Al-O-H and Si-O-Si stretching vibrations [27]. Extra peaks relevant to H-O-H stretching and bending vibrations can be found at 3448 and 1640 cm\({}^{-1}\), respectively. In the case of Ti-Mt-APTES, additional peaks at 2925 and 2852 cm\({}^{-1}\) are attributed to antisymmetric [28] and symmetric stretching vibrations of -CH\({}_{2}\)[29], signifying that APTES successfully loaded onto montmorillonite.  
Figure 2: XRD patterns of Na-Mt and Ti-Mt-APTES.  
The nitrogen adsorption/desorption isotherms of Na-Mt and Ti-Mt-APTES are displayed in Figure 4. As can be seen from curves, Na-Mt demonstrates type III isotherms on the base of the BDDT classification, showing macroporous adsorbents [30], while the Ti-Mt-APTES curve is characteristic for type IV solids, indicating mesoporous structures [31]. The specific surface areas of Na-Mt and Ti-Mt-APTES are calculated to be 45.14 and 190.20 m\({}^{2}\)/g, respectively. The Ti-Mt-APTES specific surface areas increased, indicating the materials have strong adsorption capacity, which might be ascribed to intercalation of titanium hydrate and grafted APTES.  
Figure 4: N\({}_{2}\) adsorption/desorption isotherms of Na-Mt and Ti-Mt-APTES.  
Figure 3: FTIR spectra of Na-Mt and Ti-Mt-APTES.  
The typical SEM images of Na-Mt and Ti-Mt-APTES are observed in Figure 5a-c. The Na-Mt micrograph exhibits larger particle aggregates with smooth surfaces. Layer structure of Na-Mt can be clearly observed, and the structure is more compact. However, Ti-Mt-APTES shows relatively disordered and loose layer structures, attributed to titanium hydrate entering the interlayer of montmorillonite and acting as a spacer for the clay layer, and does not destroy the layer structure of montmorillonite. Furthermore, a mass of small aggregates, which are presumably broken platelets and agglomerates of titanium hydrate, result from hydrolysis of surface Ti(OC\({}_{3}\)H\({}_{7}\))\({}_{4}\)[32]. The EDS mapping of Ti-Mt-APTES is given in Figure 5c. This clearly indicates that C, N, and Ti elements in the Ti-Mt-APTES are evenly distributed, suggesting the successful intercalation of titanium hydrate and grafted APTES. The above results verify Figure 1.