# Metachrylate-Based Polymeric Sorbents for Recovery of Metals from Aqueous Solutions
## 9 Overview of Characterization Methods
### X-ray Photoelectron Spectroscopy (XPS)  
X-ray photoelectron spectroscopy (XPS) is a quantitative technique for measuring the elemental composition of the surface of a material, and it also determines the binding states of the elements [148]. XPS normally probes to a depth of 10 nm. The energy and intensity of these peaks enable the identification and quantification of all surface elements present (except hydrogen). This technique was used to elucidate the adsorption mechanism of metal binding to a new Cd(II) imprinted sorbent with interpenetrating polymer [149]. It was observed that after the Cd(II) adsorption, the N 1s bands shifted from 400.0 to 405.0 eV, indicating the formation of complexes, in which a pair of lone electrons from the N atoms was shared with the Cd(II), reducing the electron cloud density of the nitrogen atom, resulting in a higher BE peak observed. The mechanism of Cu(II), Cd(II), and Pb(II) ions sorption from aqueous solutions by PGME-data was studied by XPS and FTIR analysis [117]. Both techniques suggested complexation through the formation of Me-O and Me-N bonds with the OH, NH, and NH\({}_{2}\) groups as the possible mechanism of Cu(II), Cd(II), and Pb(II) sorption on PGME-data. The main Cu 2p peak (Figure 3a) for PGME-10/12-data/Cu was positioned at 934.4 eV, which corresponds to Cu\({}^{2+}\). The presence of the well-known shake-up satellite found in Cu 2p spectra indicates the presence of Cu(II) species. The peak Cd3d\({}_{5/2}\) (Figure 3b) (which appears quite close to nitrogen N1 s peak) for sample PGME-10/12-data/Cd was positioned at 404.8 eV, corresponding to Cd\({}^{2+}\). The Pb 4f doublet peak for sample PGME-10/12-data/Pb (Figure 3c) was composed of two peaks with different oxidation state. The main peak Pb4f\({}_{7/2}\) can be thus fitted with two peaks positioned at 137.2 eV and 138.7 eV, corresponding to Pb\({}^{4+}\) and Pb\({}^{2+}\), respectively. According to the authors, this indicates probable interaction between amino groups and Pb(II) ions due to chelation, electrostatic interaction with protonated amino groups, or formation of ternary complexes. In addition, FTIR and XPS analyses suggest complexation via Me-O and Me-N bonds with the -OH, -NH, and -NH\({}_{2}\) groups as the possible mechanism of Cu(II), Cd(II), and Pb(II) sorption. XPS analysis was used for the investigation of the changes in the chemical composition and functional groups of the surface of magnetic macroporous crosslinked 10 MAG-SGE60-data prior and after sorption of Mo(VI) and Re(VII) ions [130]. The Mo 3d core-level spectrum (Figure 4a) of the sample was fitted into two components for Mo 3d\({}_{5/2}\) at 231.8 eV and 229.4 eV, which indicates molybdenum binding with reactive sites onto the 10 MAG-SGE60-data surface. The first peak was ascribed to Mo\({}^{5+}\), and the second one to the MoO\({}_{2}\) phase. The Re 4f narrow scan XPS spectra (Figure 4b) of 10 MAG-SGE60-data after adsorption show Re 4f\({}_{5/2}\) and Re 4f\({}_{7/2}\) doublet positioned at 45.7 eV and 39.2 eV indicating perhenate binding with reactive sites onto the polymer surface. The more intense Re 4f\({}_{7/2}\) peak was deconvoluted into three components at 44.8, 46.6, and 48.1 eV, which signified the complexation and the existence different Re oxidation states in the sample. XPS spectroscopy was used to understand the chemical interactions between polyaminophophonic acid-functionalized polyglycidyl methacrylate (PGMA) and lanthanum (La(III)) and yttrium (Y(III)) ions [64]. After the sorption from a binary La(III)/Y(III)solution, characteristic bands for La and Y appeared in the XPS spectra, i.e., La 3d\({}_{5/2}\) peaks with two couples of multiplet-splits at 836.2/839.9 eV, and 837.9/841.7 eV, as well as six Y 3d peaks (3 pairs for Y 3d\({}_{3/2}\) and Y 3d  
Figure 4: HRES spectra of (**a**) Mo 3d and (**b**) Re 4f for 10 MAG-SGE60-data after adsorption [130]. bands) ascribed to chloride and phosphonate species.