## 2 Materials and Methods  
Ti target (99.99%) and Ag target (99.99%) were used as sputtering targets. Ag/TiO\({}_{2}\) films were prepared on glass slides, monocrystalline silicon, and quartz glass substrates via the DC magnetron sputtering method [12; 17]. Firstly, the substrate was placed in anhydrous ethanol and washed twice with an ultrasonic cleaner for 15 min each; then, the washed substrate was placed in ultrapure water and washed twice with an ultrasonic cleaner for 15 min each. Secondly, the targets were mounted on the corresponding bases, respectively, and the substrate was fixed on the sample fixing table. The targets were located below the sample and sputtered upwards at an angle of 60\({}^{\circ}\), and the distance between the targets and the substrate was about 100 mm. The sputtering process for preparing TiO\({}_{2}\) films is as follows: Before sputtering, the deposition chamber was evacuated to 1 \(\times\) 10\({}^{-3}\) Pa, and then Ar (99.999%) and O\({}_{2}\) (99.999%) were introduced into the vacuum chamber. The gas flow rates of Ar and O\({}_{2}\) were 12 sccm and 4 sccm, respectively. During the deposition process, the total sputtering pressure of the Ti target and the substrate temperature were maintainedat 0.7 Pa and 300 \({}^{\circ}\)C, respectively. The total deposition time and the sputtering power of the Ti target were 7200 s and 120 W, respectively. The preparation process of the Ag-modified TiO\({}_{2}\) (Ag/TiO\({}_{2}\)) films is as follows: First, the TiO\({}_{2}\) films were deposited using the Ti target at a total pressure of 0.7 Pa. Next, the Ti target was turned off, the O\({}_{2}\) was stopped, and the Ar flow rate remained unchanged. Then, the Ag target was turned on. The modification of TiO\({}_{2}\) film surfaces with different amounts of Ag was performed by controlling the sputtering power and time of Ag. In maintaining a constant sputtering power of 5 W for Ag targets, the corresponding sputtering time was 50 s (Ag/TiO\({}_{2}\)-5 W-50 s), 100 s (Ag/TiO\({}_{2}\)-5 W-100 s), and 150 s (Ag/TiO\({}_{2}\)-5 W-150 s), respectively. When the sputtering power of the Ag target was 10 W and 15 W, the corresponding sputtering time was 100 s, respectively (Ag-TiO\({}_{2}\)-10 W-100 s and Ag/TiO\({}_{2}\)-15 W-100 s). Then, the sputtered samples were annealed, and a tubular atmosphere furnace was used. The heating and cooling rate was 4 \({}^{\circ}\)C/min; the temperature increased from the initial temperature to 450 \({}^{\circ}\)C, was kept for 90 min, and the temperature then dropped from 450 \({}^{\circ}\)C to room temperature after 90 min. Using a field emission scanning electron microscope (FESEM: JSM-7800, Tokyo, Japan) with an accelerating voltage of 15.0 kV, energy-dispersive spectroscopy (EDS) in field emission scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS, Thermo SCIENTIFIC (Waltham, MA, USA) K-Alpha, JEOL with Mg K\(\alpha\) X-ray light source (photon radiation energy of 1486.68 eV)), the morphologies and structural and compositional properties of the TiO\({}_{2}\) and Ag/TiO\({}_{2}\) films were examined. X-ray diffraction (XRD, Empyrean Panaco Netherlands, Cu-K\(\alpha\) radiation) was used to describe the film's crystalline structure. The scan speed was 2.33 \({}^{\circ}\)/min, the step length was 0.06, and the 20 scan range was 10\({}^{\circ}\) to 80\({}^{\circ}\). The spectral range of the UV-VIS diffuse reflectance spectra (UV-VIS DRS) of all samples was 200-800 nm. It was measured with a UV-VIS-NIR spectrophotometer (UV-VIS-NIR: Shimadzu Solid Spece-3700 (Shimadzu, Beijing, China)). The Kubelka-Munk function was used to convert the UV-VIS DRS to the absorption coefficient F(R). Using the Tauc method, the energy band gap (\(E_{g}\)) of the samples was calculated from the plot of (F(R)h\(\
u\))\({}^{1/2}\) against h\(\
u\)[19]. The surface topography of the films was analyzed using an atomic force microscope (AFM, Shimadzu SPM-9700) operated in the tapping mode with a measured area of 5 \(\times\) 5 \(\upmu\)m\({}^{2}\).