*2.4. Treatment of Fabric with SiO2 NPs*

The pad-dry-cure procedure was used to incorporate SiO2 NPs into the cotton/lycra composites. EDTA (1 g, as a crosslinking agent) was added to 19 mL distilled water to prepare a nano silica solution. Afterwards, the mixture was agitated with a magnetic stirrer. Drops of silica amounting to 0.2 g were added to the liquid and stirred constantly until complete dissolution. The solution was sonicated for 30 min at room temperature. The fabric was soaked in the solution for 60 min followed by drying in an oven at 100 ◦C until completely dried, then cured at 120 ◦C for 60 min.

#### *2.5. Characterization and Functional Properties of Fabrics Treated with Metal NPs*

#### 2.5.1. Scanning Electron Microscopy (SEM) Analysis

The surface morphologies of blank cotton/lycra composites and SiO2 NP/cotton/lycra composite fabrics were characterized via scanning electron microscope (JEOL JSM-6510LB with field emission gun, Tokyo, Japan).

The deposition of SiO2 NPs into cotton/lycra composites was confirmed using a surface energy dispersive X-ray (EDX) analysis unit (EDAX AMETEK analyzer, Mahwah, NJ, USA) attached to an SEM device. On the other hand, the elemental mapping analysis also reflects the presence of SiO2 NPs on the surface of the treated cotton/lycra composites.

#### 2.5.2. Antibacterial Activity

The antibacterial activity of the blank and SiO2NP/cotton/lycra composite fabrics against Gram-positive bacteria *Staphylococcus aureus* and *Bacillus cereus* and Gram-negative bacteria *Escherichia coli* and *Pseudomonas aeruginosa* was assessed qualitatively using the AATCC Test Method (147-1988) expressed as the zone of growth (mm) [18,35].

#### 2.5.3. UV Protection Properties

The blank and SiO2NP/cotton/lycra composites were examined for UV protection functionality, expressed as UV protection factor (UPF), according to the Australian/New Zealand standard (AS/NZS 4399: 1996), and rated as follows: excellent protection (UPF > 40), very good protection (UPF: 25–39), and good protection (UPF: 15–24) [18,19].

#### 2.5.4. Self-Cleaning

The blank and SiO2NP/cotton/lycra composites were tested for self-cleaning by dyeing in a methylene blue dye solution (0.2 g/L) for 5 min and then drying it off. A one-half portion of each stain on the fabric was exposed to sunlight for 24 h to determine their color strength (K/S), whereas the other half portion was covered with black paper to prevent irradiation with sunlight [17]. The K/S value was evaluated using a Spectrophotometer CM-3600A. According to the following equation, decreasing K/S values refer to the level of dye degradation, which is stated as the self-cleaning capacity (SCC):

$$\text{SCC} = \left[ \left( \text{K/S} \right) \mathbf{b} - \left( \text{K/S} \right) \mathbf{a} \right] / \left( \text{K/S} \right) \mathbf{b} \times 100 \tag{1}$$

where (K/S) a: color strength after exposing to daylight, and (K/S) b: color strength before.
