## 3 Results and Discussion
### Characterization of the Adsorbents
#### 3.1.2 Morphology Determination of MOP and AC-MOP  
Figure 3 shows MOP (Figure 3a,b) and AC-MOP (Figure 3c,d) surface morphologies. The surface characterization of MOP in Figure 3a,b shows morphological variations before converting the adsorbent to activated carbon. The MOP indicates a filamentous morphology with longitudinal strips or fibres with grooves between irregular fibres. The SEM images shown in Figure 3c,d for the AC-MOP revealed a smoother and rough surface in certain areas after activation. Pores were also observed. A similar observation was recorded during the activation of coconut for the adsorption of Congo red, methylene blue and neutral red dyes [32]. The activation process resulted in numerous pores and cavities formed under high temperatures [32]. To determine the changes in the elemental components before and after the activation of carbon, the EDS spectra of the MOP and AC-MOP were analyzed and are shown in Figure 4a,b, respectively. The results indicated that both adsorbents contained different percentage weights of carbon, oxygen and potassium (Table 1) before and after activation. Oxygen (O) and carbon (C) are the main components of the MOP and AC-MOP, which are characteristic of plant-based materials [33]. The AC-MOP contained high levels of carbon and potassium because these elements form part of the MOP. Other elements with trace amounts in the AC-MOP included magnesium (Mg) and calcium (Ca) as well as potassium (K). The observed chloride (Cl) traces were from the activation agent (HCl). Figure 2: FTIR spectra of MOP and AC-MOP. 3.1.3. Physicochemical Characterization of MOP and AC-MOP  
The BET analysis of the MOP and AC-MOP are shown in Table 2. The results showed that the surface area of the MOP was 1.43 m\({}^{2}\)/g with a pore width of 2.57 nm and pore size of 0.0034 cm\({}^{2}\)/g. On the other hand, the surface area, pore width and pore size of AC-MOP were 5.48 m\({}^{2}\)/g, 3.41 nm and 0.0089 cm\({}^{2}\)/g, respectively. Thus, the AC-MOP adsorbent experienced an increase of 383% in surface area, 133% in pores and 261% in pore size compared to the MOP adsorbent. Table 2 shows that the BET surface area of AC-MOP was greater than that of the MOP. This was ascribed to the formation of cavities on the surface of the AC-MOP [34]. The results also indicated that the values for pore sizes and width were higher for AC-MOP than for MOP. It was, therefore, expected that AC-MOP would adsorb more than MOP. The point zero charge of MOP and AC-MOP is indicated in Table 2. The results show that the pH(pzc) is 3.31 for MOP and 5.29 for AC-MOP. The \(\Delta\)pH values were negative before the pH values of 3.31 and 5.29 for MOP and AC-MOP, respectively. This showed that MOP and AC-MOP surfaces had a negative charge, and at pH values above pH(pzc), the adsorbent surfaces developed positive \(\Delta\)pH values. [PERSON] et al. (2022) [21] incorporated triethylenetetramine (TETA) in mandarin orange peels for the adsorption of acid brown 14 dye. Their study showed a BET-specific surface area of 5.88 m\({}^{2}\)/g and a monolayer volume of 1.3519 cm\({}^{3}\)/g. The total pore volume of 0.017 cm\({}^{3}\)/g, a mean pore diameter of 11.715 nm (mesoopres), a mesosurface area of 6.1776 m\({}^{2}\)/g and a mesopore volume of 0.01835 cm\({}^{3}\)/g were attained. The adsorption capacity was found to be 416.67 mg/g. The adsorption capacity of mandarin orange peels was investigated for methylene blue by Lima 2023 [23]. They obtained a BET-specific surface area of 0.9632 m\({}^{2}\)/g and an average pore diameter of 1.603 nm. [PERSON] et al. (2018) [19] used mandarin orange peels to prepare nanoporous carbon via chemical activation with  
Figure 3: SEM images of (**a**,**b**) MOP and (**c**,**d**) AC-MOP. H\({}_{3}\)PO\({}_{4}\) using microwave radiation. They reported a specific surface area of 1021 m\({}^{2}\)/g for removing methylene blue. Mandarin orange peel biochar was used for the adsorption of methyl orange (Park) [20].