# Yeast-Based Magnetic Biocomposite for Efficient Sorption of Organic Pollutants
## 3 Result and Discussion
### Characterizations of Materials
EDX analysis of the YL-M-L-AC biocomposite shows the presence of oxygen (O), carbon (C), calcium (Ca), chlorine (Cl), and iron (Fe), which indicates the presence of organic components (biochar, yeast), alginate, and magnetic particles in the obtained biocomposite. Additionally, the presence of sulfur (S) is detected on the surface of the biocomposite after the sorption process, which is evidence of the presence of the MB dye. FTIR analysis shows the presence of various characteristic functional groups in both materials (YL-M-L-AC before and after MB sorption) (Figure 4). The range of wave numbers and functional groups obtained from the absorption spectra are presented in Table 1. The tests confirm that after the MB sorption process, there are differences in the intensity of the bands, their frequencies, the nature of the bonds, and the chemical structure. Figure 2: Thermal analysis of dried lotus pods (argon). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Wavenumber (cm\({}^{-1}\))** & **Functional Group** & **Reference** \\ \hline
3000–3675 & Stretching vibrations of –OH groups & [41] \\ \hline
2916 & \(\
u_{\text{asym}}\) CH\({}_{2}\) & [42] \\ \hline
2850–2851 & \(\
u_{\text{sym}}\) CH\({}_{2}\) & [43] \\ \hline
1723–1725 & Stretching C=O & [44] \\ \hline
1648 & C–N axial deformation and C–O bonding & [44] \\ \hline
1605–1608 & C=O vibrations & [45] \\ \hline
1514–1516 & C=C & [46] \\ \hline
1375–1378 & C-N stretching vibration/N-H bending vibration & [47] \\ \hline
1277 & Aromatic ring vibration and aromatic C-O stretching & [48] \\ \hline
1175–1177 & Alcohol C–O stretches, ethers, and carboxylic acids & [48] \\ \hline
1100 & The stretching of the C–O–C bond & [49] \\ \hline
1053 & The stretching vibrations of C–O & [49] \\ \hline
1053–1025 &
\begin{tabular}{c} OH groups in sugars or C–O-C stretching vibrations \\ in lignin or hemicellulose, \(\delta\) C–H bonding of aromatic \\ ring, S=O stretching \\ \end{tabular} & [50; 51; 52] \\ \hline
828–825 &
\begin{tabular}{c} Represent the presence of sugars, mainly \\ monosaccharides and deformation band \(\delta\)(C–H) \\ \end{tabular} & [53] \\ \hline
600–400 & Deforming vibrations from C-N-C & [54] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: FTIR spectra of YL-M-L-AC before and after MB sorption. Figure 3: SEM–EDX analysis of YL-M-L-AC: (**A,B**) before sorption, (**C,D**) after MB sorption. The magnetic properties of the YL-M-L-AC biocomposite were tested using VSM analysis, and the results are shown in Figure 5. It was found that the magnetization value of YL-M-L-AC in a 1.5 T field is 10.56 A m\({}^{2}\)/kg and the loop is within the measurement accuracy limits and is closed. The slow saturation process resulting from the high number of fine particles may be caused by intense relaxations of these particles, which makes them less susceptible to the influence of an external field. The magnetization value is lower than Fe\({}_{3}\)O\({}_{4}\) itself, which is obvious because the biocomposite includes alginate, biochar, and yeast. Similar observations related to the decrease in magnetization values were observed by other researchers [55; 56]. The results show that the obtained biocomposite has magnetic properties and can be separated from the aqueous solutions with the use of a magnet. The surface properties of a solid are often influenced by the surface potential. Taking this fact into account, for many processes in industry it is necessary to know under what conditions the charge and surface potential is zero. Such knowledge, under appropriate conditions, allows the surface potential to be changed (within specific limits) and, consequently, the surface properties of a solid body can be changed (sorbent). For many solids (especially oxides), the potential-forming ions are H\({}^{+}\) and OH\({}^{-}\). The point of zero charge PZC (according to the IUPAC definition) is defined as the concentration of potential-forming ions (PDI) at which the surface charge is zero [57]. Figure 6 shows the determined pH\({}_{\text{ZPC}}\).