# Effective Uptake of Cadmium and Chromium from Wastewater Using Carbon-Based _Capsicum annuum_
## 4 Results
### Adsorption Data
#### 4.3.4 Proposed Sorption Mechanism  
FTIR Results After Adsorption of Cd(II) and Cr(VI)  
The FTIR spectrum (Figure 9) was used to predict the possible uptake of Cd(II) and Cr(VI) ions. Based on the FTIR results, -OH, -CH from -CH\({}_{3}\), -CH from -CH\({}_{2}\), -COOH, -C=O, -CO, and -COC were present on the adsorbent surface. However, these functional groups shifted to higher wavenumbers, while others shifted to lower numbers. This shift in wavenumbers indicates the involvement of functional groups as binding sites for Cd(II) and Cr(VI) ions during the sorption process [68]. The peak intensity of the -C=O, -OH, and -COOH on the activated carbon differed after the uptake of the pollutants, suggesting that a complexation reaction between Cd(II) ions and functional groups had occurred [69]. Previous research suggests that the adsorption of pollutants by the adsorbent _C. annuum_ occurs through various mechanisms controlled by processes such as electrostatic attraction, ion exchange, \(\pi\)-interactions, complexation, and hydrogen bonding between the pollutants and the oxygen-containing groups on the surface, namely carboxyl, hydroxyl, and carboxylate [70; 71]. \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{2}{c}{**Pollutants**} \\ \cline{2-3}
**Parameters** & **Cd(II)** & **Cr(VI)** \\ \hline \(\Delta\)H\({}^{\circ}\) (K) mol\({}^{-1}\)) & \(-2.15\) & \(-3.23\) \\ \(\Delta\)S\({}^{\circ}\) (K) mol\({}^{-1}\)K\({}^{-1}\)) & \(0.0567\) & \(0.0245\) \\ \(\Delta\)G\({}^{\circ}\) (K) mol\({}^{-1}\)) 298 K & \(-5.91\) & \(-7.93\) \\ \(308\) K & \(-4.24\) & \(-4.31\) \\ \(318\) K & \(-3.74\) & \(-4.21\) \\ \(328\) K & \(-2.53\) & \(-1.56\) \\ \(338\) K & \(-1.90\) & \(-1.13\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Thermodynamic parameters for the adsorption of Cd(II) and Cr(VI). Figure 9: FTIR spectrum of activated carbon after the sorption of Cd(II) and Cr(VI). XRD Results After Adsorption of Cd(II) and Cr(VI)  
The XRD pattern in Figure 10 shows the activated carbon before adsorption and after the adsorption of Cd(II) and Cr(VI). The broad peak corresponding to the (002) plan is observed between 8.09 and 26.80\({}^{\circ}\), which is due to cellulosic material [67]. After adsorption of Cd(II), the peak is observed between 10.53 and 26.57\({}^{\circ}\) and shifted to 17.42 and 29.22\({}^{\circ}\) after the adsorption of Cr(VI). The activated carbon before adsorption also exhibits sharp peaks due to crystallinity at 27.05, 29.61, 32.19, and 38.96. However, after the adsorption of Cd(II) and Cr(VI), the sharp peaks disappeared. The disappearance of crystalline peaks after adsorption confirms that the adsorbent contains mainly amorphous compounds as a result of the decomposition of cellulose, indicating an amorphous carbon structure [72]. This may be due to the adsorption of Cd(II) and Cr(VI) on the carbonized \(C\). _annuum_[73]. SEM Images After Adsorption of Cd(II) and Cr(VI)  
Figure 11A,B shows the surface morphologies determined by SEM of the activated carbon after the adsorption of Cd(II) and Cr(VI). The SEM images of the prepared carbon show a different morphology after the adsorption of Cd(II) and Cr(VI). Both images display pore structures that could not be seen clearly. The images show that the surface of the adsorbent no longer displays wrinkles but rather that the surface is rough. The total change in the surface morphology after the adsorption process may have contributed to the sorption capacity of the adsorbent. Proposed Adsorption Mechanism of Cd(II) and Cr(VI)  
Figure 12 shows the proposed uptake mechanism of both metal ions. Functional groups, electrical charge, and the structure of the adsorbate and the adsorbent determine the uptake mechanism [74]. The structure of the adsorbate and the functional groups on the adsorbent are the two main factors that determine the adsorption mechanism [74]. [PERSON] et al.