*3.1. Preparation of Catalytic Materials*

The photocatalysts employed in this study are TiO2, Pt/TiO2, Ag/TiO2, and Au/TiO2. High surface area TiO2, formed of nanometric sized particles, were prepared by laser pyrolysis using TiCl4 as precursor material. The detailed experiental setup and procedures are described elswhere [41]. Metal deposition was perfomed by impregnating TiO2 with H2PtCl6, AgNO3, and HAuCl4 precursors followed by reduction with NaBH4 [42]. For additional information on preparation of photocatalytic materials, see the Supplementary Information. Finally, the catalysts were dried and calcined 100 and 300 ◦C, respectively. The elemental composition, identification of crystalline phases and measurements of average crystallite size of photocatalytic materials was made by Energy Dispersive X-ray analysis (EDAX) and XRD, respectively. In the case of Pt/TiO2, the dispersion and average Pt particle size was estimated by CO chemisorption measurements, carried out with a ChemBet−3000 Quantachrome Instrument (Odelzhausen, Germany) equipped with a thermal conductivity detector (TCD) apparatus [43].

The values of optical band gap are estimated from the Tauc plots of diffuse reflectance UV-VIS data converted into absorbance by Kubelka–Munk function [44].

The X-ray Photoelectron Spectroscopy (XPS) measurements were performed in an ES-CALAB Xi+ (Thermo SCIENTIFIC Surface Analysis, Baltimore, MD, USA) setup equipped with a multichannel hemispherical electron Analyzer (dual X-ray source) working with Al Kα radiation (hν = 1486.2 eV), using C 1s (284.8 eV) as the energy reference. The chemical compositions of surface and oxidation states were estimated from the XPS spectra by calculating the integral of each peak after subtraction of the "S-shaped" Shirley-type background using the appropriate experimental sensitivity factors.

The Photoluminescence (PL) emission spectra were recorded with Cary Eclipse Fluorescence Spectrophotometer (Agilent Technologies, Santa Clara, CA, USA) apparatus [45].

Experimental setup for photocatalytic tests. Photocatalytic experiments were conducted in a batch-type photo reactor depicted in Figure 14. The AM 1.5 (1000 W m<sup>−</sup>2) light beam of 4.5 × 4.5 cm<sup>2</sup> was provided by a solar light simulator (Peccell-L01, Yokohama, Japan) equipped with a 150 W xenon short-arc lamp. The double-walled photoreactor was provided with optical degree quartz window. For each test, 110 mL of 50 mg·L−<sup>1</sup> phenol aqueous solution containing the suspended catalyst powder (0.05 g) were placed into the photoreactor, thermostated at 18 ◦C with a chiller. Prior tests, the suspension was kept in dark for 30 min, under stirring, to attain equilibration of experimental system. Typically, one experiment consisted of light irradiation of liquid-suspended photocatalysts for 360 min.

**Figure 14.** Experimental setup used for photocatalytic tests composed of quartz reactor provided with quartz window, AM 1.5 light source, liquid and gas sampling systems, gas and liquid chromatographs, and chillers to control the temperatures of glass condenser (−5 ◦C) and of reactor (18 ◦C).

During tests, the Ar carrier gas was purged continuously into the phenol aqueous solution at a flow rate of 10 mL·min−1, passed through a refrigerant cooled to −<sup>5</sup> ◦<sup>C</sup> with a chiller to remove liquid vapors, and then sent to GC for on-line composition analysis at 30 min time interval with a gas chromatograph (Buck Scientific, Norwalk, CT, USA) equipped with TCD detectors. The H2 and O2 were separated and quantified on Molecular Sieve 5Å, whereas CO2 and the eventually formed C2H6 and C2H4 on the Hayesep column. Meanwhile, aliquots of 2 mL were extracted every 30 min from the liquid phase, filtered through 0.22 μm Q-Max membrane filter, and then injected for analysis into a liquid chromatograph (Alliance e2659, Waters, Milford, MA, USA). The organic components of liquid phase (phenol (Ph), hydroquinone (HQ), benzoquinone (BQ), and 1,2 dihydroxibenzene (1,2 DHBz)) were separated on HPLC column (C18–3.5 μm Symmetry, Waters), identified, and then quantified using the UV-VIS detector set at 273 nm. The mobile phase of HPLC (isocratic elution program) was a mixture of Milli-Q ultrapure water (18 MΩ) and methanol (80/20 *<sup>v</sup>*/*v*). The flow rate of the mobile phase was 1 mL·min−<sup>1</sup> and the sample injection volume was 2 μL.
