## 4 Results
### Characterization Techniques
In addition, all biomasses showed pore sizes between 2-50 nm, indicating that these materials are mesoporous and can be appropriate for use as adsorbents in the aqueous phase, because they facilitate the diffusion of adsorbates into adsorbent structures [36; 37]. The adsorption-desorption isotherms of N\({}_{2}\) are shown in Figure 2 for YP, OPB, BP, and CP biomasses. For the YP and OPB biomasses (see Figure 2a,b), the isotherms were classified as type II, i.e., associated with a mesoporous structure, confirming the results obtained by a surface area analysis. A mesoporous structure is extremely beneficial for metal ion transportation from aqueous solution onto the adsorbent surface, which increases the adsorption capacity. Therefore, many functional groups in this type of material can provide efficient active sites at the interface of the solid-liquid surface for higher adsorption capacities for Pb(II) uptake [38]. For BP and CP biomasses (see Figure 2c,d), isotherms feature an open curve that is common in microporous materials with a slightly mesoporous tendency. The isotherms for both biomasses showed types I and II, and a hysteresis type H3. A large increase in the adsorption of N\({}_{2}\) to P/P\({}_{0}\) > 0.9 was found, suggesting that the measured surface area coincides with the external surface area of banana and cassava peels, which demonstrates the existence of micropores and mesopores [39]. \begin{table}
\begin{tabular}{c c c c} \hline
**Biomass** & **Surface Area (m\({}^{2}\)/g)** & **Pore Volume (cm\({}^{3}\)/g)** & **Pore Size (nm)** \\ \hline Yam peel & 0.9463 & 0.005452 & 23.04419 \\ Banana peel & 3.0889 & 0.004977 & 6.44567 \\ Oil palm bagasse & 2.7317 & 0.011207 & 16.410 \\ Cassava peel & 2.0509 & 0.002233 & 4.35428 \\ \hline \end{tabular}
\end{table} 
Table 4: Surface area and porosity analysis of biomasses. Figure 1: Spectrum from Fourier Transform Infrared Spectroscopy of biomasses before and after the Pb(II) adsorption process. Figure 3a,b show the SEM micrographs of yam and cassava peels, that present irregular and porous surfaces, allowing better heterogeneous biosorption to occur due to the large interface. For banana peels (see Figure 3c), a defined appearance was observed in the form of cylinders that were agglomerated with each other. For oil palm bagasse (see Figure 3d), the morphology was fibrous with a porosity that is typical of lignocellulosic materials [40; 41]. Figure 4 shows the SEM micrographs for biomasses after batch adsorption experiments. It was found that Pb(II) ions were adsorbed onto the surface of banana peel biomasses according to an electrostatic attraction mechanism. However, on the surface of the YC, CP, and OPB biomasses, agglomerations of Pb(II) ions were observed, which may be attributed to the formation of microprecipitated complexes or chelates on the samples [42]. Figure 2: Adsorption-desorption isotherm for: (**a**) yam peels, (**b**) oil palm bagasse, (**c**) banana peels, and (**d**) cassava peels. Figure 4: Micrographs from Scanning Electron Microscope after adsorption process: (**a**) YP, (**b**) CP, (**c**) BP, and (**d**) OPB biomasses. Figure 3: Micrographs from Scanning Electron Microscope before the adsorption process: (**a**) YP, (**b**) CP, (**c**) BP, and (**d**) OPB biomasses. Figure 5 shows the spectrogram and elemental composition of the selected biomasses obtained by EDS analysis. The results revealed that carbon and oxygen contribute most to the elemental composition of all biomasses, which is attributed to the organic nature of lignocellulosic residues. For the YP biomass (see Figure 5a), the elemental composition by atomic weight is as follows: 57.07% C, 39.05% O, and 1.65% of K and other elements in small proportions, i.e., Si, P, S, Ca, Fe, and Cu. For the BP biomass (see Figure 5b), the composition was: 75.18% C, 23.34% O, and 1.11% of K, Al, and Cl. For the CP biomass (see Figure 5c), 73.56% C, and 24.97% of O, Al, Si, S, K, Ca, and Fe. For the OPB biomass (see Figure 5d), 59.07% C, 38.85% O, and 1.92% of Si, Ca, and Cu.