3.2.1. Incorporation of Silver Nanoparticles

The in situ synthesis of AgNPs favors the interaction between the NPs and the hydrogel obtained on PET fabrics surface. As described above, immobilization of Ag+ was carried out within the hydrogel and the PET fibers because silver ions from AgNO3 solution have affinity toward R-COOH and R-OH groups [45]. The silver ions reduction reaction was carried out using NaBH4, this reduction was optically evident since this was accompanied by a color change in the modified fabrics. In Figure 8a,b, the PET fabric with coatings obtained by the photochemical and the gamma irradiation methods, respectively, are observed; white transparent coatings were observed for both samples, however the sample obtained by gamma irradiation presented a thicker coating than the one obtained by the photochemical method. On the other hand, the fabrics modified with AgNPs changed their color. Figure 8c,d shows the back and front of the fabric without hydrogel and with hydrogel obtained by the photochemical method. A yellow color on the front of the fabric is clearly observed, indicating the presence of dispersed AgNPs. Figure 8e,f shows the back and front of the fabric without hydrogel and with hydrogel obtained by gamma radiation. The front cover is brown due to the fact that this side of the fabric has a thick layer of hydrogel, which provides the ability to trap more AgNPs allowing the agglomeration of these within the hydrogel cover. The back of the fabric shows also brownish translucent color from the AgNPs accumulated on the front side.

Figure 9 shows the images obtained by SEM along with mapping of silver and elemental analysis (spectrum) from EDS of PET fabrics loaded with AgNPs. From the SEM images, it is not clear where the AgNPs are located; some clustering that can be observed do not correspond with the mapping of silver, which is distributed along the whole sample, both in the surface and also in the cross-section. In Figure 9a,b, some examples of hydrogel-coated PET samples by UV-method (surface and cross-section) are shown. The apparent size of the silver mapping spots do not represent a true size. The same can be concluded from Figure 9c,d, which shows some examples of hydrogel-coated PET samples by the γ60–method. The distribution of AgNPs on the surface of coatings obtained by both the photochemical and the gamma radiation methods were similar; meanwhile, it was evident that the cross-sections demonstrate a high concentration of AgNPs in the PET fabrics prepared using both grafting methods, independently of the thickness of the grafted hydrogel on the surface. The size of the obtained AgNPs

was not directly measured on the fabrics, however as an approximation, the same synthetic protocol was repeated but without the presence of the PET fabrics. The obtained AgNPs showed a surface plasmon resonance at a wavelength of 400 nm, which, according to the literature, corresponds to sizes below 20 nm [46].

**Figure 8.** Images of PET fabrics grafted with hydrogels without silver nanoparticles (AgNPs) by (**a**) the photochemical method, (**b**) the gamma irradiation method; and photos of both sides of PET fabrics grafted with hydrogel and AgNPs by method: (**<sup>c</sup>**,**d**) Photochemical, back and front view, respectively, and (**<sup>e</sup>**,**f**) gamma irradiation, back and front view, respectively.

**Figure 9.** SEM images, EDS mapping of silver, and EDS spectrum from PET fabric modified with hydrogel and AgNPs: (**a**) surface of UV PET95:5:0.5, (**b**) cross-section of UV PET100:0:0.5, (**c**) surface of γ60 PET90:10:30, and (**d**) cross-section of γ60 PET100:0:50.
