## 3 Results and Discussion  
### Characteristics of MPHAC  
The synthesized MPHAC was characterized by means of different techniques and the obtained results are shown in Figures 1 and 2. The obtained SEM images of MPHAC microstructure are displayed in Figure 1a,b. As can be seen, the synthesized MPHAC exhibits a rough surface with cracks and pores, together with aggregation having a mean size of 57.61 \(\pm\) 8.65 nm. In order to determine the chemical composition of MPHAC, EDS analysis was carried out and the results are presented in Figure 1c. The MPHAC powder contains not only carbon (C) with the highest fraction (52.3 wt%), oxygen (O) with 35 wt%, and a very low fraction of sulfur (S, 0.1 wt%), but also a high proportion of the metal iron (Fe, 12 wt%) and a lower proportion of zinc (Zn, 0.7 wt%). Moreover, the MPHAC was characterized by FTIR to analyze its chemical structure and functional groups. The obtained FTIR spectrum is plotted in Figure 1d. The vibrations at 3423.8 cm\({}^{-1}\) are assigned to the bands O-H stretch, while the band located at 2922.6 cm\({}^{-1}\) corresponds to the C-H vibrations in methyl and methylene groups [2]. The peak band at 1623.3 cm\({}^{-1}\) is related to the aromatic ring mode [27]. The C-H band is associated to the peak at 1388 cm\({}^{-1}\), while the C-O stretching of phenolic or carboxylate groups corresponds to the peak at 1086.9 cm\({}^{-1}\)[27]. The band at 564.7 cm\({}^{-1}\) is assigned to Fe-O vibration [28]. The C-H out-of-plane bending causes the band at 477.8 cm\({}^{-1}\)[27]. [PERSON] [29] reported that the functional groups of PH include hydroxylic groups, the aliphatic C-H group, C=O stretching of the carbonyl group, and C-O groups of carboxylic acid, alcoholic, phenolic, ether, and ester groups. Figure 1: Characteristics of the synthesized MPHAC: Scanning electron microscopy (SEM) images (**a**) 500 nm magnitude (**b**), 200 nm magnitude, (**c**) Energy dispersive spectroscopy (EDS), (**d**) Fourier-transform infrared spectroscopy (FTIR), (**e**) X-ray diffraction (XRD), and (**f**) Vibrating sample magnetometry (VSM) patterns. Figure 2: (**a**) Isotherms of N\({}_{2}\) adsorption and desorption, (**b**) distribution curve of pore size, and (**c**) effect of background electrolytes on pH\({}_{\text{PZC}}\) of the synthesized MPHAC. The diffractogram of the MPHAC shown in Figure 1e presents a broad peak at approximately 2\(\theta\) = 23.5\({}^{\circ}\), corresponding to the plane, which is a feature of amorphous carbon. In addition, the peak of Fe\({}_{3}\)O\({}_{4}\) particles was detected at 2\(\theta\) = 35.2\({}^{\circ}\), confirming their presence in MPHAC. The magnetic property of MPHAC was also evaluated and displayed in Figure 1f. The saturation magnetization value, related to Fe\({}_{3}\)O\({}_{4}\) formation in the matrix of MPHAC, was 1.75 emu/g. This is higher than the reported value for the magnetic separation by [PERSON] et al. [30], who synthesized magnetic activated carbon (AC/Fe\({}_{3}\)O\({}_{4}\)) with iron contents of 5%, and reported that the saturation magnetization was 0.3 emu/g. In contrast, [PERSON] et al. [31] reported that the saturation magnetization of magnetic activated carbon is around 13 emu/g at room temperature. All the above results confirmed the successful synthesis of MPHAC. Figure 2a,b shows the BET isotherms of N\({}_{2}\) adsorption and desorption cycles, together with the porosity distribution of MPHAC. Based on the classification of IUPAC [32], the Type I adsorption isotherm was observed for MPHAC and the curve raised rapidly when the relative pressure _P/P\({}_{0}\)_ was low, and then seemed to stabilize for higher _P/P\({}_{0}\)_ values. When the relative pressure _P/P\({}_{0}\)_ was lower than 0.1, the isothermal adsorption curve was related to the number of microspores [2; 33]. The estimated specific total pore volume (\(V_{total}\)), specific surface area (\(S_{BET}\)), and mean pore diameter of the synthesized MPHAC were 0.75 cm\({}^{3}\)/g, 1363.4 m\({}^{2}\)/g and 2.19 nm, respectively.