As illustrated in Figure , UV irradiation on TiO2 and Au@CloseSmall presents a 6-line EPR spectrum of a C centered radical, whereas for Au@CloseLarge no signal is observed. The C centered radicals are formed when ·OH radicals or ·OCH3 radicals are generated in the presence of methanol, that are readily trapped by DMPO. The assignment is confirmed by simulations (Figure ). With green light alone, no signal was observed for any of the catalysts, indicating negligible radical generation, which is also in line with the catalytic test results. However, when both UV and visible light were used simultaneously, the EPR spectra for Au@CloseSmall SPs showed an additional signal due to the DMPO-adduct of the ·OH radical (signal 2, Figure ), whereas an additional triplet signal (signal 3, Figure ) was observed for Au@CloseLarge SPs representing oxidation of the spin adduct, often indicated as the DMPO-X adduct. The difference in the spectra under simultaneous illumination can be attributed to several effects.