## 2 Materials and Methods
### Photolytic/Photocatalytic Experiments  
A simulated solar radiation lamp (model SOL 500 by Dr. Honle AG, Gilching, Germany) was used as the source of radiation for both photolytic and photocatalytic experiments. The irradiation spectrum of the lamp is given in Figure S1 in the Supplementary Materials.  
During the photolytic experiments, a reactor filled with 100 mL of the model TMP solution (10 mg/L, 25 \(\pm\) 0.2 \({}^{\circ}\)C) was solely exposed to the lamp radiation.  
In contrast, during the photocatalytic experiments, a glass ring with a deposited photocatalyst was placed at the bottom of the same reactor (Figure 1). The dimensions of the glass ring were \(D_{\text{external}}\) = 90 mm, \(D_{\text{internal}}\) = 30 mm, and height = 5 mm. The UV-A irradiation intensity in the reactor was adjusted to 33 \(\pm\) 2 W/m\({}^{2}\), with global irradiation set to 975 \(\pm\) 6 W/m\({}^{2}\), and was regularly monitored to simulate the near maximum natural noon solar irradiation for the region of Zagreb, Croatia. Adjustment of the irradiation intensity was achieved by positioning the lamp 15 cm above the reactor. Global irradiation from the solar simulator lamp was measured using a pyranometer model CMP11 (Kipp & Zonen Co., Delft, The Netherlands), while UV-A irradiation was measured using a radiometer equipped with a UV-A sensor in the 315-400 nm range, model RM 21 (Opsytec Dr. Grobel Co., Ettlingen, Germany).  
The photocatalytic mechanism was investigated through scavenger studies utilizing isopropanol, ammonium oxalate, and triethanolamine as scavengers for hydroxyl radicals, superoxide radicals, and positive holes, respectively [41; 42]. The experimental study consisted of the following:  
* evaluation of adsorption processes (stirring \"in the dark\");
* photolytic degradation experiments (irradiation without TiO\({}_{2}\) ring);
* photocatalytic degradation experiments (irradiation with the TiO\({}_{2}\) film at the bottom of the reactor);
* photocatalytic degradation experiments carried out using different scavengers.  
Figure 1: Schematic representation of the experimental set-up.  
Typically, in photocatalytic degradation processes, a continuous stream of oxygen or air is supplied to the solution through bubbling. However, in this experiment, such a supply was not required because the stirring created a whirlpool in the solution, which allowed for sufficient oxygen uptake to approach the maximum saturation level in the solution.  
Finally, the total energy consumption for the photodegradation process of TMP was followed by a power meter, the model Voltcraft Energy Check 3000 (Conrad Co., Wernberg-Koblitz, Germany). The projection of energy savings is based on the assumption of the same irradiation intensity in the experimental region of Zagreb, Croatia, during the period from 10.30 a.m. to 1.30 p.m., when the solar radiation intensity is at its highest.  
Samples were periodically withdrawn from the reaction mixture and analyzed for the residual amount of TMP using HPLC-PDA and HPLC-MS/MS.  
All experiments were made in triplicates and the values shown in diagrams are the average arithmetic values of the three experiments, with all experimental results obtained within \(\pm\)5% from the average value that is shown in diagrams.