Probe molecules of XTT and terephthalic acid were used as electron scavenger and hydroxyl radical scavenger, respectively, in the presence of excess oxygen and without the interference methanol. Hydroxyl radicals react with terephthalic acid to produce 2-hydroxyterphthalic acid quantifying the hole-mediated reaction pathway as demonstrated in reference . On the other hand, XTT is reduced by superoxide radicals and an electron to form formazan, and is used to measure the electron-mediated reaction pathway as demonstrated in reference . As observed in Figure and Figure , the terephthalic acid probe experiments indicate that the photocatalytic activity of pristine TiO2 relies more strongly on hole-mediated pathways compared to all of the Au-TiO2 SP composites under both solar light and UV light. Under