# Metachrylate-Based Polymeric Sorbents for Recovery of Metals from Aqueous Solutions
## 9 Overview of Characterization Methods  
### Fourier Transform Infrared Spectroscopy (FTIR)  
The metal ions adsorption mechanism may include physical and chemical adsorption. Chemical adsorption mainly involves mechanisms such as ion exchange, electrostatic attraction, surface complexation, and inner-sphere complexation, redox, and precipitation [35]. Therefore, different techniques could be used in order to understand the adsorption mechanism, such as Fourier Transform Infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), 1H, and 13C solid-state nuclear magnetic resonance (NMR), etc. The disappearance of bands characteristic for functional groups/ligands and the appearance of the bands that can be ascribed to the metal ions bonding in the FTIR spectra could be used as evidence of successful metal ions bonding. For example, [PERSON] et al. used FTIR spectra of a copolymer of glycidyl methacrylate and ethylene glycol dimethacrylate, (PGME) modified with triethylene tetramine (PGME-teta) to prove the presence of -NH and -NH\({}_{2}\) groups as a result of successful functionalization [133]. Namely, a strong band occurs at 3500 cm\({}^{-1}\), where the valence vibrations for -NH, -NH\({}_{2}\), and -OH groups overlap. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used for the analysis of the mechanism of Cu(II), Cd(II), and Pb(II) ions sorption from aqueous solutions by macroporous PGME with attached diethylene triamine, PGME-data (sample PGME-10/12-data) (Figures 2a and 3) [118]. Figure 3: HRES (**a**) Cu 2p for PGME-10/12-data/Cu, (**b**) Cd 3d for PGME-10/12-data/Cd, and (**c**) Pb 4f for PGME-10/12-data/Pb [118]. Figure 2: (**a**) FTIR-ATR spectra of PGME-data before adsorption (black) and after adsorption: PGME-10/12-data/Cu (red), PGME-10/12-data/Pb (blue), and PGME-10/12-data/Cd (green) [118], (**b**) FTIR-ATR spectra of mPGME-data before adsorption (black) and after adsorption of Re(VII)/Mo(VI) (red) [130]. The disappearance of the peak for -NH at 1565 cm\({}^{-1}\), as well as the shift of the -NH\({}_{2}\) peak to \(\sim\)1645 cm\({}^{-1}\) in PGME-10/12-data/Cu, PGME-10/12-data/Cd, and PGME-10/12-data/Pb spectra, clearly indicate the metal ions binding with amino-groups of PGME-10/12-data. According to the literature data, the binding with the metal alters the hybridization type around nitrogen and causes the weakening of -NH bond [145]. However, from the standpoint of the metal ions sorption, the most significant part of the FTIR spectra was located in the 1000-700 cm\({}^{-1}\) region The clear evidence of the Me(II) binding to PGME-10/12-data was the appearance of new peaks at \(\sim\)770, \(\sim\)830 and \(\sim\)970 cm\({}^{-1}\) for PGME-10/12-data/Cd and PGME-10/12-data/Pb as well as the peaks at \(\sim\)750 and \(\sim\)970 cm\({}^{-1}\) for PGME-10/12-data/Cu, which can be ascribed to the formation of Me-O bond. Similarly, [PERSON] et al. observed the appearance of new bands in the region 700-1000 cm\({}^{-1}\) (Me--O absorption bands) and a strong \(\
u\)Cr--O band detected at 944 cm\({}^{-1}\), medium \(\
u\)Cr--O band at 890 cm\({-1}\) and the band at ca 774 cm\({}^{-1}\) in the FTIR spectra of PGME functionalized with hexamethylene diamine, PGME-HD, as the evidence of chromium binding [129]. [PERSON] et al. considered the appearance of the wide band at 3060-3700 cm\({}^{-1}\) (\(\
u\)(NH) + \(\
u\)(OH)), the bands at 1260 cm\({}^{-1}\)\(\
u\)(C-N), at 1560 cm\({}^{-1}\) and 1650 cm\({}^{-1}\) (\(\delta\) (NH), \(\delta\) (NH\({}_{2}\))), as well as the band at 1390 cm\({}^{-1}\) (\(\
u\)(NH)) in the FTIR spectra of PGME-data with sorbed Re(VII)/Mo(VI) (Figure 2b) as confirmation of functionalization with diethylenetriamine [111]. In addition, the absence of characteristic bands for -NH and -NH\({}_{2}\) groups and the presence of the bands in the region of Mo-O absorption (1000-700 cm\({}^{-1}\)) in the PGME-data/Re(VII)/Mo(VI) spectra indicate that adsorption proceeds partially via coordination and electrostatic interactions.