**3. Materials and Methods**

## **3. Materials and Methods**  *3.1. Synthesis and Characterization*

*3.1. Synthesis and Characterization*  The ZnO synthesis was carried out according to a previous report [69]: Twenty five mL of ammonium hydroxide (NH4OH) (25%**–**35% *w/w*) reactive grade (Merck) was placed in a 250 mL glass beaker, then 0.500 M (Zn(CH3COO)2.2H2O) (Merck) was added dropwise at a rate of 1.7 mL.min−1 for 1 hour, at a temperature of 85 °C under constant agitation at 300 rpm. After that, the The ZnO synthesis was carried out according to a previous report [69]: Twenty five mL of ammonium hydroxide (NH4OH) (25–35% *w*/*w*) reactive grade (Merck) was placed in a 250 mL glass beaker, then 0.500 M (Zn(CH3COO)2·2H2O) (Merck) was added dropwise at a rate of 1.7 mL.min−<sup>1</sup> for 1 h, at a temperature of 85 ◦C under constant agitation at 300 rpm. After that, the suspension stood for three days at room temperature then the solid was filtered and dried for 5 h at 100 ◦C [72,73].

suspension stood for three days at room temperature then the solid was filtered and dried for 5 h at 100 °C [72,73]. For the ZnO doping process, we used a similar procedure as previously described. While adding Zn2+ ions, we also added salts of the doping metals (CuSO4.5H2O) (Merck) for copper doping and (Co(CH3COO)2.4H2O) (JT Baker) for the cobalt doping processes. The synthesis of doped ZnO powder was performed at 1.0%, 3.0%, and 5.0%. The thin films were deposited using the doctor blade method, and the suspension was placed in a glass measuring 2 cm high and 2 cm wide. The thin films were heated for 30 min at 90 °C to evaporate the solvent, and finally, the sintering process was performed at 500 °C for 2 h [73,74]. Using this procedure, we obtained thin films (6 μm thickness). The film thickness was measured through a Veeco Dektak 150 profilometer. The physical chemistry properties of the films were studied by X-ray diffraction, diffuse reflectance spectrophotometry, and Raman spectroscopy assay. X-ray diffraction patterns were obtained using a Shimadzu 6000 diffractometer using Cu Kα radiation (λ = 0.15406 nm) as an X-ray source with a diffraction angle in the 2θ range (20**–**80°). Diffuse reflectance spectra were obtained with a Lambda 4 Perkin**–**Elmer spectrophotometer equipped with an integration sphere. The compositional properties of the materials were studied by Raman spectroscopy in a DXR device equipped with a 780 nm laser. The morphological properties were studied by scanning electron microscopy, under an excitation energy For the ZnO doping process, we used a similar procedure as previously described. While adding Zn2<sup>+</sup> ions, we also added salts of the doping metals (CuSO4·5H2O) (Merck) for copper doping and (Co(CH3COO)2·4H2O) (JT Baker) for the cobalt doping processes. The synthesis of doped ZnO powder was performed at 1.0%, 3.0%, and 5.0%. The thin films were deposited using the doctor blade method, and the suspension was placed in a glass measuring 2 cm high and 2 cm wide. The thin films were heated for 30 min at 90 ◦C to evaporate the solvent, and finally, the sintering process was performed at 500 ◦C for 2 h [73,74]. Using this procedure, we obtained thin films (6 µm thickness). The film thickness was measured through a Veeco Dektak 150 profilometer. The physical chemistry properties of the films were studied by X-ray diffraction, diffuse reflectance spectrophotometry, and Raman spectroscopy assay. X-ray diffraction patterns were obtained using a Shimadzu 6000 diffractometer using Cu Kα radiation (λ = 0.15406 nm) as an X-ray source with a diffraction angle in the 2θ range (20–80◦ ). Diffuse reflectance spectra were obtained with a Lambda 4 Perkin–Elmer spectrophotometer equipped with an integration sphere. The compositional properties of the materials were studied by Raman spectroscopy in a DXR device equipped with a 780 nm laser. The morphological properties were studied by scanning electron microscopy, under an excitation energy of 5 and 1 kV. The metallic content of the films was determined by plasma emission spectroscopy using the SM 3120 B technique, EPA 3015A modified for solids (see Supporting Information).

### of 5 and 1 kV. The metallic content of the films was determined by plasma emission spectroscopy using the SM 3120 B technique, EPA 3015A modified for solids (see Supporting Information). *3.2. Photocatalytic Test*

*3.2. Photocatalytic Test*  Methylene blue (MB) was chosen as the pollutant model in this study. The experiments were Methylene blue (MB) was chosen as the pollutant model in this study. The experiments were carried out in a batch reactor using an LED tape as a source of visible radiation (cold white light 17 watts), and the incident photon flow per unit volume I<sup>o</sup> was 5.8 <sup>×</sup> 10−<sup>7</sup> Einstein\*L−<sup>1</sup> s −1 . Before irradiation,

carried out in a batch reactor using an LED tape as a source of visible radiation (cold white light 17 watts), and the incident photon flow per unit volume Io was 5.8 × 10−7 Einstein\*L−1s−1. Before the MB solution was kept in the dark for 90 min at 250 rpm to reach adsorption–desorption equilibrium on the catalysts' surface. Photodegradation was carried out using 50 ± 0.025 mL of an MB solution (10 mg·L −1 ) saturated with oxygen at pH 7.0. The concentration of dye was determined through the spectrophotometric method (Thermo Scientific–Genesys 10S) using 665 nm as a fixed wavelength, with a calibration curve (correlation coefficient R = 0.997) for the use of the Lambert–Beer equation.
