*3.3. Self-Cleaning Properties*

The reduction potential of MTC is about 0.011 V, whereas the energy level of the conduction band for TiO2 is about −0.5 V. Thus, MTC is a suitable model to investigate the photo-induced catalysis process. The self-cleaning performance of TiO2 or Ag0/TiO2 deposited onto viscose fibers could be studied by testing the decomposition of MTC underneath UV and visible lights, as shown in Figure 6. Ultraviolet/visible absorption spectral curves of MTC were collected for the treated viscose under irradiation with UV and visible light over 24 h. The absorbance peak at 665 nm decreased as a result of the degradation of MTC. The self-cleaning activity was tested by exploring the total content (C/C0) of MTC as a function of time. The degradation of MTC on the uncoated fibers showed almost no variations under irradiation with either UV or visible daylight to prove that the uncoated fibers do not exhibit any light-induced decay ability. The deposition of TiO2 NPs onto plasma-activated fibers proved an improvement in photoinduced degradation of MTC under UV light. However, this photo-induced degradation of MTC was incomplete. The deposition of TiO2 onto plasma-pretreated fibers displayed a negligible photo-induced degradation under visible light owing to the adsorption and diffusion of MTC within the coated viscose. The integration of the nanocomposite into the plasma-pretreated fibers induced a total photoinduced degradation of MTC under ultraviolet and visible light, as the blue shade was monitored neither on the coated fibers nor in solution to prove a complete photo-induced degradation of MTC. The photo-induced degradation of MTC for fibers coated with Ag0/TiO2 demonstrated improved activity in comparison with TiO2 NPs, proposing that the inclusion of AgNPs onto the surface of TiO2 is an efficient approach. The photo-induced degradation rate for TiO2 and Ag0/TiO2 coated onto viscose fibers decreased with washing. Nonetheless, they persisted higher than the plasma-inactivated viscose fibers. This proposed higher adhesion of particles onto plasma-activated viscose. After washing, the light-induced decay of methylthioninium chloride (MTC) for Ag0/TiO2 deposited onto viscose fibers was lower than the case of the viscose fibers coated with TiO2 under visible/UV light. Thus, the nanocomposite enhanced the self-cleaning activity of viscose as a beneficial effect of silver on the light-induced catalysis of TiO2.

**Figure 5.** FT-IR spectra of coated viscose fibers.

**Figure 6.** Degradation of MTC on fibers under UV (**a**) and visible (**b**) lights for pristine fibers (Vis0), TiO2/fibers after wash (Vis1), TiO2/fibers before wash (Vis2), Ag0/TiO2/fibers after wash (Vis3), and Ag0/TiO2/fibers before wash (Vis4).

#### *3.4. Antibacterial Activity*

The antibacterial properties of plasma-cured and coated viscose were examined against *E. coli* by measuring optical density (OD) at 620 nm versus time, as shown in Figure 7. OD was found to improve, reflecting the decrease in the quantity of growing bacteria in the tested sample. Both blank and TiO2 coated viscose fibers displayed no inhibition. The viscose fibers coated with Ag0/TiO2 showed antibacterial properties at all contents, yet followed by washing to confirm the positive effect of loading Ag<sup>0</sup> onto TiO2. AgNPs have been described to exhibit a broad of activity against a variety of pathogens. It has been recognized that the increase in surface area results in improved antibacterial properties [32].

**Figure 7.** Activity of coated viscose fibers against *E. coli*; Vis0 is pristine viscose, Vis1 is 103 (**a**) or 106 (**b**) bacterial density, Vis2 is NPs/fibers, Vis3 is nanocomposite/fibers following washing, and Vis4 is nanocomposite/fibers prior to washing.

#### **4. Conclusions**

Multifunctional viscose fibers coated with Ag/TiO2 nanocomposite were developed by the simple pad–dry–cure technology. The synthesis, characterization, and use of nanocomposite as an antibacterial and light-induced self-cleaning agent were explored. Ag/TiO2 was prepared using a double-stage procedure of sol–gel TiO2 synthesis, followed by depositing of Ag0 onto the surface of TiO2 by ultraviolet irradiation. The deposition of Ag0/TiO2 onto plasma-pretreated viscose fibers was accomplished using the facile pad–dry–cure technology. Ag0/TiO2 displayed better absorption in the visible spectrum and higher antibacterial activity and light-induced catalysis in comparison with plasma-activated viscose coated with TiO2. This considerable improvement in antibacterial and self-clean properties could be attributed to AgNPs deposited onto the surface of TiO2. The current study presented a good strategy to produce Ag/TiO2 composite with the ability to impart antibacterial, self-cleaning photo-induced catalytic properties to plasma-cured fibers, under irradiation with UV/visible lights to make this Ag0/TiO2 nanocomposite potentially practical as a multifunctional agent for a variety of applications, such as medical clothing. **Author Contributions:** Conceptualization H.E.-H. and M.E.E.-N.; methodology, M.E.E.-N., T.A.K. and A.E.-F.; formal analysis and discussion, M.E.E.-N., A.E.-F. and T.A.K.; writing—original draft preparation, H.E.-H. and M.E.E.-N.; writing—review and editing, H.E.-H., M.E.E.-N., T.A.K. and A.E.-F.; supervision, H.E.-H. and M.E.E.-N. All authors have read and agreed to the published version of the manuscript.

**Funding:** Deanship of Scientific Research at King Saud University, Research Group Program (no. RGP-201), King Saud University, Riyadh, Saudi Arabia.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Acknowledgments:** The authors would like to extend their appreciation to the Deanship of Scientific Research at King Saud University for funding this work through research group (no. RGP-201).

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

