## 3 Results and Discussion
### FT-IR Characterization  
Figure 2 depicts the FT-IR spectra of the adsorbents. SW shows bands at 3400 cm\({}^{-1}\) and 3255 cm\({}^{-1}\) attributed to OH and NH\({}_{2}\) stretching, respectively. Further, the bands at 2900 cm\({}^{-1}\), 2918 cm\({}^{-1}\), and 2850 cm\({}^{-1}\) are ascribed to CH symmetric stretching. On the other hand, the signal at 1652 cm\({}^{-1}\) is attributed to C = O stretching from the N-acetyl glucosamine subunits of chitin. Further, the signal at 1560 cm\({}^{-1}\) is attributed to the in-plane deformation of the secondary amide of the acetylamine group. Other bands at 1423 cm\({}^{-1}\) and 1311 cm\({}^{-1}\) are due to the CH deformation and flexion of CH\({}_{2}\). Bands at 1064 cm\({}^{-1}\), 870 cm\({}^{-1}\), and 713 cm\({}^{-1}\) corresponds to C-O-C ring stretching (chitin ring), glycosidic bond stretching, and out-of-plane -OH stretching, respectively. The bands between 400 and 700 cm\({}^{-1}\) are due to C-C stretching. The elimination of proteins by pyrolysis was confirmed by the absence of a signal at 1560 cm\({}^{-1}\). Further, bands at 1419 cm\({}^{-1}\) and 1056 cm\({}^{-1}\) were amplified due to the CH deformation and C-O-C ring stretching vibrations, respectively [44]. In general, acidic activation produced changes in the adsorption bands between 900 and 1400 cm\({}^{-1}\) due to C-H vibrations and loss of oxygen on the surface of the adsorbents. Further, the emerging band at 1100 cm\({}^{-1}\) is ascribed to the incorporation of the new phosphate moiety. Interestingly, bands around the region of 1050-1070 cm\({}^{-1}\) decreased upon activation of SW. In fact, these bands completely disappeared when the pyrolyzed sample (CM) was activated with phosphoric acid and a new band at 1100 cm\({}^{-1}\) appeared. Further, a small signal at 1625-1641 cm\({}^{-1}\) emerged due to the C = O stretching possibly attributed to ketones, aldehydes, lactones, or carboxylic acids formed during combustion [45].  
Figure 1: Surface characteristics of the adsorbents.  
Likewise, activated charcoals (AC1 and AC2) showed a wide band around 3300 cm\({}^{-1}\) corresponding to the -OH stretching vibration attributed to the presence of carboxylic, phenolic, and alcohol groups. This signal is very small in magnitude in the activated charcoals due to the action of phosphoric acid. This finding agrees with the decrease of O in the activated materials as described in the elemental analysis (Table 1). Furthermore, the acidic activation caused the absence of the band at 2920 cm\({}^{-1}\) attributed to C-H stretching of aliphatic carbon, but created a strong band at -900 cm\({}^{-1}\) ascribed to the glycosic bond stretching. Further, the peak at 1630 cm\({}^{-1}\) corresponds to aromatic C = C and suggests the existence of aromatic rings in the activated charcoals.  
On the other hand, CAC shows bands at 3420 cm\({}^{-1}\) due to OH stretching, adsorbed water, or hydrogen bonds interaction of OH groups derived from alcohols and phenols. The signals at 2918 cm\({}^{-1}\) and 2848 cm\({}^{-1}\) are attributed to symmetric stretching of CH. The signal at 1620 cm\({}^{-1}\) can be assigned to C=O and C-O stretching of phenolic esters, carboxylic acids or conjugated ketone structures.