*3.3. ATR FT-IR*

FT-IR spectra of untreated and treated cotton fabrics were analyzed after the normalization at 1362 cm −1, absorption band relative to the CH bending of cellulose. In Figure 2, FT-IR of COL untreated and treated samples with GPTES sol and G-PNPA sol (COL\_UT, COL\_GPTES and COL\_G-PNPA, respectively) are reported and compared with those relative to COH untreated and treated fabrics with the same solutions (COH\_UT, COH\_GPTES and COH\_G-PNPA, respectively). In particular, in all spectra, it is possible to distinguish clearly the characteristic absorption bands relative to cellulose moieties, such as: the broad bands around to 3331 cm<sup>−</sup><sup>1</sup> and 2894 cm<sup>−</sup><sup>1</sup> (stretching mode of OH and CH, respectively), and the absorption bands between 1097 cm<sup>−</sup><sup>1</sup> and 895 cm<sup>−</sup><sup>1</sup> relative to the asymmetric in-plane ring stretch and to C–O stretch and asymmetric out-of-phase ring stretch (C1–O–C4) [31]. In particular, in the inset in Figure 2A,B the presence of a silica coating is evident through the increase of the bands in the range 1145 cm<sup>−</sup>1–895 cm<sup>−</sup><sup>1</sup> for the COL, assigned to the asymmetric stretching of the -Si–O–Si, and in the range between 995 cm<sup>−</sup>1–760 cm<sup>−</sup><sup>1</sup> for the COH, due to the Si–O–Si absorption bending (852 cm<sup>−</sup>1) and stretching (790 cm<sup>−</sup>1).

**Figure 2.** FT-IR spectra of COL and COH untreated and treated with GPTES sol and G-PNPA sol (**A** and **B**, respectively). (**A**) FT-IR spectra of COL untreated and treated with GPTES sol and G-PNPA sol; (**B**) FT-IR spectra of COH untreated and treated with GPTES sol and G-PNPA sol.

With the aim of investigating the chemical structure and interactions between silica precursor and antioxidant molecule without the interference of the intense absorption bands of cotton fabrics, the FT-IR spectra of each sol was carried out on the pure xerogel. The latter was obtained by depositing a few drops of each solution onto optical glass slides further subjected to a thermal treatment (100 ◦C) to remove the solvent [26]. Indeed, by analyzing the FT-IR spectra of PNPA, it was possible to identify the characteristic peaks in order to establish its interaction with the GPTES sol. Spectra of the GPTES sol (Figure 3, green line) clearly shows the formation of the inorganic network due to the absorption bands relative to: asymmetric (1093–1010 cm<sup>−</sup>1) and symmetric stretching of Si–O–Si (756 cm<sup>−</sup>1) and its bending mode (850 cm<sup>−</sup>1) [17,18,20]. Furthermore, the absorption bands at 3072–3000 cm<sup>−</sup>1, 1255 cm<sup>−</sup><sup>1</sup> and 906–850 cm<sup>−</sup><sup>1</sup> were assigned to asymmetric and symmetric C–H stretch, ring breathing, as well as the asymmetric and symmetric ring deformation, respectively [17,18], indicating that some unopened epoxy ring remain in GPTES sol.

**Figure 3.** FT-IR spectra of PNPA, GPTES sol and G-PNPA sol.

These peaks relative to the GPTES sol are also evidenced in the sol containing PNPA (Figure 3, black line), in which the main characteristic absorption bands of the antioxidant molecules are present. As shown in Figure 2 (red line), PNPA is featured by the asymmetric and symmetric CH2 stretching mode of alkyl chain (2916 and 2849 cm<sup>−</sup>1, respectively) with relative bending (1470–1458 cm<sup>−</sup>1), the C=O and C–N stretching of the secondary amide (1737 and 3075 cm<sup>−</sup>1, respectively) and the C–N stretching mode (1596 cm<sup>−</sup>1) [32].
