## 3 Results
### Surface Treatments of Montmorillonite
#### 3.1.3 TGA and DTG Analysis  
Figure 4 shows the thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) curves of MMT, PMMT, P-SLS-MMT, and P-KH570-MMT samples. In Table 1, the mass loss associated with the different temperature ranges is listed. Two distinct thermal degradation events were obtained in the DTG curves of the MMT. The first mass loss, occurring at a temperature of 75 \({}^{\circ}\)C, was assigned to the elimination of physically adsorbed water, and the second at 660 \({}^{\circ}\)C corresponded to the dihydroxylation of clay layers [32]. The mass loss of OMMT was higher than that of MMT at 200-600 \({}^{\circ}\)C, which was evidence of intercalated surfactants and/or grafted silane coupling agents. For the P-MMT, the mass loss below 200 \({}^{\circ}\)C was lower when compared with the MMT, implying less adsorbed water in the P-MMT. Furthermore, the mass loss of the P-MMT between 200 \({}^{\circ}\)C and 600 \({}^{\circ}\)C was obviously higher than that of the MMT, which was attributed to the degradation of adsorbed surfactant molecules on the external surface and of intercalated surfactant molecules in the interlayer space of the MMT. The overall mass loss of P-MMT (20.7 wt %) was higher than that of MMT (5.6 wt %). Compared with P-MMT, a greater mass loss in the range of 200 \({}^{\circ}\)C to 600 \({}^{\circ}\)C was found in P-SLS-MMT, which could be attributed to the intercalation of SLS molecules into the interlayer space of P-MMT. In addition, the maximum mass loss rate temperature of P-SLS-MMT occurred at 499 \({}^{\circ}\)C, higher than 15 \({}^{\circ}\)C in P-MMT, indicating the thermal properties of P-MMT were enhanced owing to the introduction of the SLS molecules. These results suggested that the SLS molecules were successfully intercalated into the interlayer space of the P-MMT. This result was consistent with the results of XRD analysis. In the case of P-KH570-MMT, the first mass loss occurred at a temperature below 200 \({}^{\circ}\)C which was attributed to the evaporation of adsorbed water and/or of free molecules of solvent in the pores of MMT. The mass loss observed over the range of 200-600 \({}^{\circ}\)C was assigned to the loss of surfactant molecules combined with the decomposition of adsorbed and/or grafted KH570 molecules introduced during the silylation reaction. Compared with the P-MMT, the observed increase in mass loss for the P-KH570-MMT between 200 \({}^{\circ}\)C and 600 \({}^{\circ}\)C was attributed to the intercalated and/or grafted silane molecules. Combining this with the result of XRD, the interlayer space of P-KH570-MMT was smaller than that of P-MMT, the increasing amount of KH570 molecule was mainly grafted on the broken edges and the external surface of MMT, not intercalating in the interlayer space of MMT [33].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**Temperature Range**} \\ \cline{2-3}  & **\textless{}200 \(\pm\) 1.5 \({}^{\circ}\)C** & **200–600 \(\pm\) 1.9 \({}^{\circ}\)C** & **30–800 \(\pm\) 2.2 \({}^{\circ}\)C** \\ \hline MMT & 1.9 & 1.5 & 5.6 \\ P-MMT & 0.6 & 19.0 & 20.7 \\ P-SLS-MMT & 0.2 & 23.9 & 24.9 \\ P-KH570-MMT & 2.3 & 19.9 & 23.3 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Relative mass loss during decomposition of investigated samples (wt %).  
Figure 4: **(A)** Thermogravimetric analysis (TGA) and **(B)** Derivative thermogravimetry (DTG) curves of MMT, P-MMT, P-SLS-MMT, and P-KH570-MMT.