*2.1. Characterization Data*

The TEM (Transmission Electron Microscopy) analysis of noble metals dispersed on TiO2 prepared by laser pyrolysis shows well dispersed Pt on TiO2 support (Figure 1A). The Ag and Au particles are significantly larger than of Pt (see TEM images in Figure 1B,C). Individual spherical Au nanoparticle of around 5 nm can be observed in Figure 1C.

**Figure 1.** Suggestive TEM images of metal-loaded TiO2 samples: Pt/TiO2 (**A**), Ag/TiO2 (**B**) and Au/TiO2 (**C**).

The most relevant characterization data obtained by various experimental methods are presented comparatively in Table 1. More details are given in Supplementary Information.



a—TiO2 crystallite size determined by Scherrer method from XRD diffractograms; b—metal loading evaluated by EDAX; c—metal content estimated from XPS data; d—metal particle size determined from TEM micrographs; e—metal particle size determined by CO chemisorption measurements; <sup>f</sup> —atom percentage of Ti3+ in TiO2 matrix derived from XPS measurements; g—metal oxidation state analysis performed XPS measurements.

> The XPS analysis revealed that the supported noble metals on TiO2 were in metallic state (see the XPS data presented in Supplementary Information). Titanium in TiO2 was in the form of Ti4+ whereas the metal-loaded TiO2 contained variable amounts of Ti3+ (see Table 1 and Supplementary Information).

> The average size of Pt particles supported on TiO2 estimated from CO chemisorption measurements is ≈1 nm, corresponding to metal dispersion of around 40%. This result is in fair agreement with TEM result evidencing supported Pt nanoparticles of 1–2 nm (see Figure 1A).

> The light absorption features of all investigated materials exhibit the characteristic band edge energies of TiO2 at ≈ 400 nm (see Figure 2). The plots of Kubeka–Munk function

(F(R)) in Figure 2 describe light absorbance of solid samples. The SPR maxima of Ag and Au nanoparticles are clearly visible at 460 and 544 nm, respectively. Assuming the indirect allowed transitions, the optical band gaps of all investigated materials, obtained by extrapolation of linear part of ([F(R)] hν) 1/2 versus hν plots, are around 3.1 eV (see the inset of Figure 2). The close values of optical band gaps, makes difficult to predict the order of photocatalytic activity, based only on light absorption data.

**Figure 2.** Comparative F(R) spectra and indirect optical band gap derived from Tauc representation (inset) for investigated photocatalysts.
