*2.2. Preparation and Evaluation of the Samples*

Samples were prepared into disc-shaped specimens of white cement paste with a 1.62 cm diameter and a 0.3 cm thickness. Deionized water was used for a water/cement ratio of 0.5. Previously, the nanoparticles were added in the mixed water and dispersed using a superplasticizer (Plastol HR-DF), provided by the company Toxement in Colombia. The dispersant agent was used with 19% by weight relative to the nanoparticles. Afterwards, this suspension was sonicated with 90 W and 35 kHz frequency (VWR® Symphony™ 97043-992) for 15 min [18]. Samples were prepared with three different percentages of cement content, for TiO2í*x*N*y* 0.5%, 1%, 3%. Other samples were prepared with two levels of TiO2, 1% and 3%. After, the samples were cured in a wet room for 65 h. Additionally, samples were prepared with 0.5%, 1%, 3% of TiO2í*x*N*y*, and another set with 1% and 3% of TiO2, in order to evaluate the Rhodamine B abatement in visible light. Following the provisions of the standard [19], the pastes were immersed in water with Rhodamine B for one hour, at a concentration of 0.5 g/L in order to ensure a uniform color for each sample. The samples were irradiated with UV light using lamps emitting a wavelength spectrum between 350 and 400 nm (Phillips, Amsterdam, The Netherlands, Actinic BL TL-D(K), 30 W). In order to evaluate the behavior of the samples in visible light, a fluorescent lamp was used with a wavelength spectrum between 410 and 560 nm (Lite-Way, C13101, 24 W). The samples were irradiated to 20 W/m2 ± 0.3 for the UV experimental setup, as set out in the standard [19]. For the setup with visible light, the samples were irradiated to 10 W/m2 ± 0.5. For this setup, the height between the lamp and the samples was determined using a radiometer (PMA 2210, Solar Light Co., Philadelphia, PA, USA) coupled to a probe to detect wavelengths between 400 and 700 nm (LDC 21300, Solar Light Co., Philadelphia, PA, USA). To determine the color coordinates CIE (Commission Internationale de l'Eclairage) *L*\**a*\**b*\* [20], a UV/Vis Spectrometer was used (BWTEK Inc., Newark, NJ, USA, GlacierTM X, BTC112E), coupled with a probe for measuring reflection and backscatter (Ocean Optics, QR200-7-UV-VIS) and a support to hold it at 45° angle to the samples (Ocean Optics, Dunedin, FL, USA, RPH-1).
