## Materials and Methods
### Experimental Conditions  
The AMX initial concentration of 50 mg/L [11] was prepared by diluting AMX in distilled water and stirring the solution for half an hour. Volume samples of 2 and 3 L were required for reactors 1 and 2, respectively. For photocatalysis experiments, 2 g/m\({}^{2}\) TiO\({}_{2}\) P25 was impregnated on the frosted glass plates by direct spraying [8; 23; 35].  
The influence of pH on contaminant degradation was tested by carrying out the experiments at different initial pH of 3.5, 4.15, 7, and 9; the AMX solution pH was modified by adding, drop by drop, HNO\({}_{3}\) or NaOH solutions. pH was measured with an Orion Star A211 potentiometer (Thermo Fisher Scientific Inc., Waltham, MA, USA).  
The influence of H\({}_{2}\)O\({}_{2}\) was studied as well. For this purpose, experiments were performed in the absence of H\({}_{2}\)O\({}_{2}\) and repeated by adding 4 mM H\({}_{2}\)O\({}_{2}\) to the solution just before starting the experiment [36]. Sample recirculation through the reactor lasted for 60 min, with sampling times of 0, 5, 10, 15, 20, 30, 45, and 60 min.  
UV-Vis spectrophotometry in a DR 5000 TM device (HACH Company, Loveland, CO, USA) served to measure AMX removal in samples, considering the maximum absorption range from 200 to 300 nm [37; 38]. As a response variable, Chemical Oxygen Demand (COD) change was measured, using the Hach 2000 method with a DR 2010 spectrophotometer (HACH Company, Loveland, CO, USA).  
Control experiments were performed in the absence of radiation at different pH magnitudes to ensure that H\({}_{2}\)O\({}_{2}\) presence was not the only factor contributing to AMX degradation.  
A meteorological station of the Secretaria de Recursos Naturales y Medio Ambiente provided the radiation, temperature, and humidity data; the station uses a WE300 Solar Radiation Sensor pyranometer (Global Water, Yellow Springs, OH, USA) for measurements. Experiments were conducted on sunny, windless days, from 12:00 to 14:00 h from April to July. The average solar radiation incidence reported was close to 1000 W/m\({}^{2}\), as shown in Figure 4.  
A 2 \(\times\) 2 \(\times\) 4 factorial design with covariates and repeated measures was used to analyze the degradation results for the different FPR areas as described by Equation (2) for a 0.1 m\({}^{2}\) surface FPR and Equation (3) for a 1 m\({}^{2}\) surface FPR:  
\[\mathrm{Y_{jklm}}=\mu+\mathrm{P_{j}}+\mathrm{pH_{k}}+\mathrm{H_{2}O_{2l}}+( \mathrm{pH^{*}}\mathrm{H_{2}O_{2}})_{kl}+\mathrm{t_{m}}+a\mathrm{RadS}+b \mathrm{COD_{0}}+\mathrm{\epsilon_{jklm}} \tag{2}\]  
Figure 4: Average solar radiation between the months of April and July (2022) in the city of Durango, Mexico.  
\[\mathrm{Y_{\bar{\eta}klm}}=\mu+\mathrm{A_{j}}+\mathrm{P_{k}}+\mathrm{H_{2}O_{2l}}+ \mathrm{t_{m}}+a\mathrm{RadS}+b\mathrm{COD_{0}}+\mathrm{\varepsilon_{jklm}} \tag{3}\]  
In Equation (2), the response variable (COD) corresponds to \(Y_{\mathrm{ijklm}}\), the general average of the model is \(\mu\), \(\mathrm{P_{j}}\) is the process (photolysis and photocatalysis), \(\mathrm{pH_{k}}\) is the pH (3.5, 4.15, 7, and 9), \(\mathrm{H_{2}O_{2}}\)\(l\) is the \(\mathrm{H_{2}O_{2}}\) dose (nil and 4 mM), \(\mathrm{t_{m}}\) is the sample time, \(a\mathrm{RadS}\) is the intensity of solar radiation, \(b\mathrm{COD_{0}}\) is the initial AMX concentration, and \(\mathrm{\varepsilon_{jklm}}\) represents the error. Due to the fact that it is an open system, the volume of the sample decreased during the reaction, which is why evaporation is considered as a correction factor applied to the dependent variable COD. As well as Equation (3), \(Y_{\mathrm{ijklm}}\) is the response variable, \(\mu\) represents the general means of the model, \(\mathrm{A_{j}}\) is the surface area of FPR (0.1 m\({}^{2}\) and 1 m\({}^{2}\)), \(\mathrm{P_{k}}\) is the process and \(\mathrm{H_{2}O_{2}}\)\(l\) is the \(\mathrm{H_{2}O_{2}}\) dose (0 and 4 mM), \(\mathrm{t_{m}}\) as the sample time, \(a\mathrm{RadS}\) the intensity of solar radiation and \(b\mathrm{COD_{0}}\) the initial AMX concentration.