*2.3. Physical Characterization of SiO2@TiO2 Coating*

The microstructures of the materials were examined by transmission electron microscopy (TEM) using a JEOL JEM-1010 (Tokyo, Japan), operating at a voltage of 200 kV. The crystallinity of the SiO2@TiO2 coating was determined by X-ray diffraction (XRD) using Bruker D8 equipment (Billerica, MA, USA) with a sealed copper tube to generate Cu–Kα radiation (λ = 1.15406 Å) with angles of 10 < 2θ < 80◦ in a pitch of 0.01◦. To verify the crystallinity, the structures of the obtained samples were characterized using Raman spectroscopy with the LabRAM HR equipment (Horiba Scientific, Kyoto, Japan), which used an NdYGA laser (λ = 532 nm). The samples were analyzed using a microscope with an objective of 10× at a power of 6 mW over a circle 1.5 μm in diameter. The optical transmittance of the glass substrates coated with SiO2@TiO2 was measured with a Cary 5000 UltraViolet-Visibe-Near-Infra-Red spectrophotometer (Agilent, Santa Clara, CA, USA) at wavelengths ranging from 350 to 800 nm. Water contact angle was measured using an optical tensiometer (Analyzer-DSA100W Krüss, Hamburg, Germany), which produces water droplets with a volume adjusted to 10 μL using a needle (stainless steel, model NE60).

#### *2.4. Photocatalytic Evaluation*

#### 2.4.1. Evaluation of Photocatalytic Properties

The photocatalytic performance of the coating was evaluated using the method (UNI 11259-2016) based on Rhodamine B (RhB) degradation on the sample exposed to UV-A irradiation [19,20]. To monitor dye removal, the mortar samples were divided into three parts, in which TiO2, SiO2 and SiO2@TiO2 coatings were applied, as shown in Figure 1. Using a pipette, an RhB solution with a concentration of 50 ppm was evenly applied to 3 standardized positions on the samples, and they were left to dry overnight.

Then, the dye-contaminated samples were exposed to UV-A irradiation for 26 h using the UV reactor shown in Figure 2. In this reactor, UV-A irradiation was provided by an Electrolux T8 20 W/BLB. This lamp type emits light with a peak wavelength of 360 nm and an intensity of 10.3 W·m−<sup>2</sup> at a distance of 5 mm. Finally, changes in color at 0, 4, and 26 h were measured using a portable X-rite Ci60 spectrophotometer (Photometric Solutions International, Victoria, Australia). Measurements were reported in the *L*\*, *a*\*, *b*\* colorimetric coordinates of the CIE LAB system (32/64 bit software), which corresponds to the white and black color range, red and green color range and yellow and blue color range, respectively, where the *a*\* coordinate is the comparison parameter. Based on these

measurements, the following parameters were calculated, as shown in Equations (1) and (2). Where R stands for color removal at time 0, 4, and 26 h of UV light exposition.

$$R\_4 = \frac{\left(R\_4 - R\_0\right)}{R\_0} \times 100\tag{1}$$

$$R\_{26} = \frac{(R\_{26} - R\_0)}{R\_0} \times 100\tag{2}$$

**Figure 1.** Mortar surface coated with TiO2, SiO2 and SiO2@TiO2 coatings.

**Figure 2.** UV-A reactor using Electrolux T8 20W/BLB, <sup>λ</sup> = 360 nm, intensity = 10.3 W·m<sup>−</sup>2.
