## 3 Results and Discussion
### Characterization of the Adsorbent
These corresponded to the planes of (100), (011,101), (012,102), (200), and (021,201), respectively. The peaks at 22.65\({}^{\circ}\), 24.39\({}^{\circ}\), 27.90\({}^{\circ}\), 29.12\({}^{\circ}\), 29.82\({}^{\circ}\), 30.28\({}^{\circ}\), 34.89\({}^{\circ}\), and 35.45\({}^{\circ}\) represent the (\(-\)120,020), (210), (200,111), (00-21,\(-\)211), (1-21,021), (\(-\)220,120), (012), and (030) plane of a triclinic structural Ky (JCPDS card no. 11-46). The calculated basal \(d\)-spacing at the (001) plane in clay was 14.149 A. From the XRD pattern of the MCC (Figure 2b), the three distinguishable reflection groups with a lower intensity and a broad peak of chitosan were observed. It was noticed that the peak of Mt at the (001) plane was shifted to a lower degree of 20 from 6.62\({}^{\circ}\) to 6.19\({}^{\circ}\), elucidating the insertion of the biocompatible polymer into the Mt interlayers and filling the pores of clay. This resulted in the expansion of the \(d\)-spacing at the (001) plane in the MCC to 14.376 A. Moreover, it was noticeable that a lower intensity of peak reflected a lower degree of crystallization. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Adsorbents**} & \multicolumn{4}{c}{**Textural Properties**} & \multirow{2}{*}{**Contact**} & \multirow{2}{*}{**\(d\)-Spacing 1**} \\ \cline{2-2} \cline{4-6}  & **BET Surface** & & & & **Angle (\({}^{\circ}\))** & **(Å)** \\ \cline{2-2} \cline{4-6}  & **Area (m\({}^{2}\) g\({}^{-1}\))** & & & & \\ \hline Mt-rich clay & 98.84 & 0.1363 & 47.98 & 15.3 & 14.15 \\ Chitosan & 1.22 & 0.0002 & 19.43 & 76.7 & – \\ MCC & 4.61 & 0.0075 & 60.14 & 85.0 & 14.38 \\ \hline \hline \end{tabular} \({}^{1}\) Calculated from (001) crystalline plane of montmorillonite.  
\end{table} 
Table 1: Characterization of the adsorbents. Figure 2: Representative XRD pattern of the **(a)** Mt-rich clay and **(b)** MCC. To analyze the hydrophobic property of the adsorbents, the water contact angle was measured, and the results are summarized in Table 1. The magnitude of contact angle was ordered as the MCC > chitosan >> Mt-rich clay. The possible reason to explain was that the negative charges in the hydrophilic head regions of the SDS molecules interacted with the positive charges of chitosan and Mt-rich clay, while the hydrophobic tail regions of SDS headed out. Then, MCC was expressed as more hydrophobic. A higher magnitude of water contact angle represents a greater hydrophobicity. Thus, the adsorption performance of the hydrophobic part in the dye structure on the MCC is likely to be enhanced compared to the chitosan or especially the clay. Then, to characterize the surface charges of the adsorbents and adsorbate, the zeta potential was measured by DLS. The magnitude of the zeta potential corresponds to the degree of electrostatic repulsion/attraction, and the sign of zeta potential represents the sign of the net surface charge. From the DLS results (Figure 3), the magnitude of the zeta potential decreased with increasing pH. The zeta potentials of the dye and Mt-rich clay were negative over the complete pH range of 3-10, which was due to the negative charge of the SO3- group on the structure of the RR120 dye molecule and the hydroxylated silicate sites in the clay, respectively. The MCC was positively charged over the whole pH range, but it decreased in magnitude with increasing pH to an almost zero net charge at pH 10. This decreased positive charge likely reflected the deprotonation of the protonated amino group (-NH3+) with increasing pH to form the uncharged amino group (-NH2) in chitosan and then, with further increasing the pH, the hydroxide ions (OH-) were bound to the cations contained in the clay together with deprotonation of the amino group in chitosan to form -NH-[24; 25]. The zero point charge of the dye, clay, and MCC were not observed, whilst it was pH 6.5 for chitosan. The positive surface charges of the chitosan were present when the pH was lower than 6.5, but the negative charges were expressed when the pH was higher than 6.5.