# Adsorption of Emerging Pollutant by Pecan Shell-Based Biosorbent
## 3 Results and Discussion  
### Characterization of the Biosorbent  
The yield (\(Y_{PS}\)) of the biosorbent after the physical and chemical processes for pecan shell activation was 33.6\(\%\). The FT-IR analysis was conducted for pecan shell samples _in__natura_ (PS), biosorbent (PSB), microcrystalline cellulose, and the two samples of commercial activated charcoal, one of which is powdered coal (CAP) and the other is granular charcoal (CAG), for comparison purposes. Figure 1 shows the spectra.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Model** & **Equation** & **Variables** & **References** \\ \hline \multirow{4}{*}{Kinetic models} & Pseudo-first order & \(\frac{\partial q}{\partial t}=k_{1}(q_{e}-q)\) & \(q_{e};k_{1}\) & [15] \\ \cline{2-5}  & Pseudo-second order & \(\frac{\partial q}{\partial t}=k_{2}(q_{e}-q)^{2}\) & \(q_{e};k_{2}\) & [15] \\ \cline{2-5}  & [PERSON] & \(\frac{\partial q}{\partial t}=k_{2}(q_{e}-q)^{2}\) & \(\alpha;\beta\) & [16] \\ \hline \multirow{2}{*}{Equilibrium models} & [PERSON] & \(q_{e}=\frac{4\alpha_{max}K_{L}C_{e}}{1+K_{L}C_{e}}\) & \(q_{max};K_{L}\) & [17] \\ \cline{2-5}  & [PERSON] & \(q_{e}=K_{f}(C_{e})^{\frac{1}{2}}\) & \(K_{f}\,n\) & [17] \\ \hline \hline \end{tabular}
\end{table}
Table 1: List of the equilibrium and kinetic models.  
The PS sample is characteristic of lignocellulosic materials. It presents typical bands of materials with high cellulose (it can be compared to that obtained for microcrystalline cellulose) and hemicellulose contents. The manifestation of a broadband at 3342 cm\({}^{-1}\) suggests the presence of alcoholic and phenolic hydroxyl \(\
u\)O-H involving hydrogen bonds; at 2929 cm\({}^{-1}\), it suggests the presence of alkyl \(\
u\)C-H. The 1027 cm\({}^{-1}\) band can be attributed to the elongation of \(\
u\)C-O bonds, which is characteristic of monosaccharide units. The bands at lengths of 1727 and 1623 cm\({}^{-1}\) are characteristic of the carbonyls (\(\
u\)C=O) of ketone (1727 cm\({}^{-1}\)) and aldehyde (1623 cm\({}^{-1}\)), which make up lignocellulosic material structures. In addition, there are movements of aromatic rings (1421 and 1318 cm\({}^{-1}\)), COC asymmetric vibration bands of lignin phenols (1232 cm\({}^{-1}\)), and distension vibration in aromatic C=C bonds (1504 cm\({}^{-1}\)) ([PERSON], 2008). When observing the spectrum obtained in the analysis of the carbonized pecan shell (PSB), the bands present in the raw material disappear completely, indicating that the pyrolysis resulted in the oxidation of these compounds, this made the spectrum very similar to that of the patterns of CAP and CAG commercial charcoal.  
In addition, the surface morphology of the material in nature and of the biosorbent was also monitored through micrographs using SEM (Figure 2a,b). It is possible to observe that the structure of the PS has a heterogeneous morphology without porosity. As for the PSB sample, the physical and chemical activations (with ZnCl\({}_{2}\)) led to the development of micropores on the material surface. The activating agent, once incorporated in the precursor material, promotes dehydration or oxidation of some compounds present in the material; this results in the unblocking of pores and consequently in an adsorbent with a high porosity and a more carbonaceous and aromatic structure [18].  
Figure 1: Characterization of the biochar via FT-IR for the PS, PSB, CAP, CAG and cellulose.  
Figure 2: SEM micrographs (\(\times\)800 and \(\times\)1000) of (**A**) an in natura pecan shell (PS); and (**B**) the biosorbent (PSB).