## 3 Results and Discussion  
### Characterization of Reactive Dyes  
The XPS spectra collected from Novacron Ruby S-3B reactive dye in the spectral range of C1s, Cl2p, N1s, Na1s, and S2p orbitals are shown in Figure 1. The C1s spectral region may be fitted using three major peaks: (i) one attributed to C atoms participating in the benzene/naphthalene rings (284.5 eV), (ii) a second peak attributed to the C-S bond (285.2 eV), and (iii) a third one associated with C atoms attached to the quaternary nitrogen atom, the O atom or/and the Cl\({}^{0}\) atom (286.2 eV) [32; 33; 34]. The N1s spectral region can be fitted with two peaks of non-quaternized nitrogen atoms. The main peak is attributed to either C-N-C or/and C=N-C and is found at 400 eV, while the weaker one attributed to either NH2 or N=N is observed at \(\sim\)398.9 eV [35; 36].  
The sodium counterions are observed in the Na1s spectral region (1071.9 eV), while in both Cl2p and S2p regions, doublets are recorded. The first doublet at \(\sim\)199.0 eV is assigned to Cl\({}^{0}\) attached to the triazine ring, while in the sulfur 2p spectral region, a twin doublet is assigned to -SO2-/SO3\({}^{-}\) contribution at 168 eV and to SO4\({}^{-}\) at 169.2 eV [14; 15]; the intensity ratio of the two peaks is \(\sim\)4/1, in close agreement with the chemical structure of the dye, Figure 1f.  
XPS spectra of Remazol Brilliant Blue R reactive dye of C1s, S2p, N1s, Na1s, and O1s orbitals' characteristic spectral regions are shown in Figure 2. For this dye, as for the previous one, the stoichiometry derived from peak intensity ratios is close to the corresponding structure at the molecular level. Notice that there is no signal in the Cl2p spectral region and for the S2p doublets the intensity ratio of the -SO2-/SO3\({}^{-}\) to -SO4- species is \(\sim\)2/1, in agreement with the structure given in Figure 2f.  
Figure 1: XPS spectra of Novacron Ruby S-3B in the spectral region of: (**a**) C\({}_{1\varphi}\), (**b**) Cl\({}_{2\varphi}\), (**c**) N\({}_{1\varphi}\), (**d**) Na\({}_{1\varphi}\), and (**e**) S\({}_{2\varphi}\). The molecular structure of the reactive dye is given in (**f**). The doublet of weak Cl peaks in (**b**) denoted by * had to be included in the fitting and may be explained as in reference [37].  
Figure 2: XPS spectra of Remazol Brilliant Blue R in the spectral region of (**a**) C\({}_{1\varphi}\), (**b**) S\({}_{2\varphi}\), (**c**) N\({}_{1\varphi}\), (**d**) Na\({}_{1\varphi}\) and (**e**) O\({}_{1\varphi}\). The molecular structure of the reactive dye is given in (**f**).  
The characteristic ATR-FTIR vibrational bands of both reactive dyes in the solid phase can be identified in Figure 3. The spectral contribution of major structural groups, such as benzene/naphthalene/anthraquinone rings, chloro-triazine, and sulfone/sulfonate/sulfate is found in the 950-1650 cm\({}^{-1}\) region; the most characteristic of them are listed in Table 2.  
The bands at 1040 cm\({}^{-1}\) and 1183 cm\({}^{-1}\) (1038 cm\({}^{-1}\) and 1194 cm\({}^{-1}\) for Remazol Brilliant Blue R) can be assigned as symmetric and antisymmetric stretching vibration of the sulfonate (SO\({}_{3}\)\({}^{-}\)) group, respectively. In the same manner, the symmetric stretching vibration of the O=S=O group, which can be found separated or/and in the sulfate SO\({}_{4}\)\({}^{-}\) group, is found at 1110 cm\({}^{-1}\), while the antisymmetric one at 1210 cm\({}^{-1}\) (1118 cm\({}^{-1}\) and 1215 cm\({}^{-1}\) for Remazol Brilliant Blue R).