## 3 Results and Discussion
### Characterization before and after Sorption  
FTIR spectra analysis on PPG-nZVI beads was conducted to identify the main functional groups involved in removal of the Pb\({}^{2+}\), Cu\({}^{2+}\) or Zn\({}^{2+}\) ions (Figure 5). The fresh PPG-nZVI beads were used as control samples to compare the shifts of FTIR peaks after reaction for identification of participated functional groups in metal uptake. The main PPG-nZVI beads bands observed in the FTIR spectra (a) were in accordance with previous report [7]. As shown in Figure 5, the band at 3436 cm\({}^{-1}\) is the characteristic peak of -OH stretching vibrations and functional group -OH usually forms a broad band region at the wavenumber of 3100-3700 cm\({}^{-1}\), which is attributed to the adsorption of water on nZVI and the exist of alcoholic and carboxyl groups [4; 7]. For PPG-nZVI beads after adsorption of the metal ions, the peak at 3436 cm\({}^{-1}\) was shifted to 3431 cm\({}^{-1}\), 3430 cm\({}^{-1}\), and 3427 cm\({}^{-1}\) for adsorption of Pb\({}^{2+}\), Cu\({}^{2+}\), and Zn\({}^{2+}\), respectively and the wave number decreased. This may be ascribed to the combination between the metal ions and the -OH group [19]. The vibrational band observed at 2919 cm\({}^{-1}\) referred to the stretching -CH from alkyl groups. The peak at wavelength of 1715 cm\({}^{-1}\) was due to the stretching vibration of carbonyl double bond. Two adsorption peaks at a wavenumber of 1713 cm\({}^{-1}\) observed in the PPG-nZVI beads after adsorption of Cu\({}^{2+}\) and Pb\({}^{2+}\) may be due to the stretching vibration of carbonyl double bond (-C=O) and carbon oxygen single bond (-C-O) in carboxyl groups, respectively. These results indicated that the alcoholic, carboxyl, alkyl groups in PVA and carboxylate ions in guar gum might be involved in the metal binding. While the band at 1635 cm\({}^{-1}\) was the asymmetrical and symmetrical stretching vibration of COO\(-\). These wave numbers were weakened suggesting the important role of COO\(-\) in the metal adsorption. Figure 6 shows the peaks of Fe 2p3/2 and Fe 2p1/2 located at 711 and 724 eV for Fe\({}_{2}\)O\({}_{3}\) and FeOOH [20]. In addition, the satellite peak at 719.81 eV is the characteristic of Fe\({}_{2}\)O\({}_{3}\). Furthermore, a feature peak of Fe\({}^{0}\) can be found at around 707.2 eV, suggesting that Fe\({}^{0}\) does exist on the PPG-nZVI beads [21]. FeOOH was a result of surface hydroxylation and exposed shell dehydration when iron nanoparticles contacted with aqueous solution. After the reaction, the peak of Fe\({}^{0}\) could not be found for Pb\({}^{2+}\), Zn\({}^{2+}\), Cu\({}^{2+}\), and the peak intensity for Fe\({}^{3+}\) and Fe\({}^{2+}\) increased, indicating that Fe\({}^{0}\) had been oxidized on the surface of PPG-nZVI beads. Figure 7 and Figure S1 show the XPS spectra of the PPG-nZVI beads before and after adsorption of Cu\({}^{2+}\), Zn\({}^{2+}\), and Pb\({}^{2+}\). From Figure 7, the photoelectron peak for the oxygen 1s region resolved into three curves with peaks of approximately 530, 531, and 532 eV, which represented for the binding energies of oxygen in O\({}_{2}\)-, OH\({}^{-}\) and chemically or physically adsorbed water. That is in accordance with literature. In Figure 7b-d, there was a shift of peak positions after the PPG-nZVI beads reacted with Cu\({}^{2+}\), Zn\({}^{2+}\) and Pb\({}^{2+}\) compared of PPG-nZVI beads before adsorption. The heavy metals sorption was accompanied by the change in oxygen binding, providing evidence that the oxygen-containing functional groups on the surface of the PPG-nZVI beads taking part in the sorption of heavy metals. Figure 5: FTIR of the PPG-nZVI beads. (**a**) is the result of the PPG-nZVI beads before adsorption. (**b**), (**c**), and (**d**) is the result of the PPG-nZVI beads after adsorption of Pb\({}^{2+}\), Cu\({}^{2+}\), and Zn\({}^{2+}\) respectively.