# Removal of Chromium(VI) by Chitosan Beads Modified with Sodium Dodecyl Sulfate (SDS)
## 3 Results and Discussion
### Characterization of SDS Modified Chitosan  
The SEM-EDS images of chitosan beads and SDS-chitosan beads (40 mg/L SDS loading) are shown in Figure 8. From SEM images, it could be determined that the diameter of these beads was roughly 800 \(\upmu\)m. These figures show that the surface of the membrane appears concave and convex. This may be attributable to the loss of water (about 98%) contained in the sorbent upon the drying of chitosan. It is considered that adsorption proceeded with physical and chemical adsorption. From the mapping images, it is shown that Cr ions were sufficiently adsorbed on the adsorbent. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Target Ions** & **Adsorbent** & **Effect Factor** & \begin{tabular}{c} **Final Concentration** \\ **(ug-L-1)** \\ \end{tabular} & \begin{tabular}{c} **Adsorption** \\ **Capacity** \\ **(ug-S-1)** \\ \end{tabular} & \begin{tabular}{c} **Acdsorption** \\ **Capacity** \\ **(ug-S-1)** \\ \end{tabular} \\ \hline \multirow{7}{*}{Cr(VI)} & \multirow{7}{*}{pH} & 4 & 966.69 & 1665.39 & 0.034 \\  & & 5 & 966.37 & 1681.62 & 0.035 \\  & & 6 & 970.3 & 1484.99 & 0.031 \\  & & 7 & 970.24 & 1488.23 & 0.031 \\  & & 8 & 977.8 & 1114.81 & 0.022 \\  & & 9 & 993.55 & 322.60 & 0.0065 \\  & & 10 & 999.29 & 35.87 & 0.00071 \\ \cline{2-6}  & \multirow{7}{*}{\begin{tabular}{c} Cr(VI) \\ (h) \\ \end{tabular} } & 3 & 982.28 & 354.31 & 0.018 \\  & & 9 & 974.53 & 509.35 & 0.026 \\  & & 12 & 969.69 & 606.23 & 0.031 \\  & & 24 & 957.04 & 859.12 & 0.045 \\  & & 48 & 948 & 1039.91 & 0.055 \\  & & 72 & 945.51 & 1089.86 & 0.058 \\  & & 96 & 945.50 & 1009.21 & 0.058 \\ \cline{2-6}  & \multirow{7}{*}{\
\begin{tabular}{c} SDS \\ \end{tabular} } & 0 & 985 & 300 & 0.015 \\  & & 10 & 955.93 & 881.49 & 0.046 \\  & & 20 & 954.67 & 906.69 & 0.047 \\  & & 40 & 952.63 & 947.37 & 0.050 \\  & & 80 & 954.25 & 915.02 & 0.048 \\  & of SDS & 100 & 955.20 & 896.11 & 0.047 \\  & (mg-L-1) & 200 & 957.41 & 851.81 & 0.044 \\  & & 600 & 962.73 & 745.33 & 0.039 \\  & & 1000 & 963.44 & 731.16 & 0.038 \\ \hline \multirow{7}{*}{
\begin{tabular}{c} Dose \\ (mg-L-1) \\ \end{tabular} } & 0.4 & 800 & 500 & 0.4 \\  & 0.6 & 646.6 & 589 & 0.86 \\ \cline{1-1}  & 0.8 & 434.4 & 707 & 1.93 \\ \cline{1-1}  & & 1.0 & 292 & 708 & 2.42 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Detailed experimental data of the adsorption process under different effect factors. Figure 7: Effect of competitive anions on the adsorption of Cr(VI) on the SDS-modified chitosan beads. The FT-IR spectra of the chitosan and SDS-chitosan beads are exhibited in Figure 9. The broad and intense peak at 3400 to 3500 cm\({}^{-1}\) corresponds to O-H and -NH\({}_{2}\) stretching vibrations of hydroxyl groups of chitosan and SDS-chitosan [55; 56; 57]. The peak at 2871 cm\({}^{-1}\) is related to the aliphatic methylene group [58; 59]. The wide peaks at 1560 to 1640 cm\({}^{-1}\) and 1110 cm\({}^{-1}\) show the imine group and ether group [57]. The SDS-modified chitosan bands at around 1248 cm\({}^{-1}\) are characteristic of the asymmetrical vibrations of the C-O-S group [59; 60]. The adsorbent could be identified as a composite of SDS and chitosan. XPS analysis was employed to survey the chemical compositions and binding condition of the surface on the samples. Chitosan beads with different amounts of SDS loading were analyzed (Figure 10a--Chitosan; Figure 10b--SDS100-chitosan; Figure 10c--SDS600-chitosan; Figure 10d--SDS600-chitosan). As can be seen in Figure 10, the C1s spectra of these samples displayed peaks at 284.5 eV and 286.5 and 288.5 eV, corresponding to C-C bonds C-O and C=O, respectively. It also shows that the S 2p spectra of SDS600-chitosan and SDS6000-chitosan displayed peaks at 169 eV. From Table 3, it could be found that the predominant elements were carbon and oxygen, and that the SDS100-chitosan and SDS600-chitosan atomic values of the N element are 1.75% and 1.69%, respectively.