All SAC-modified photocatalysts were prepared by impregnation of anatase TiO2 powders with very small amounts of copper(II) or iron(III) nitrate or ammonium vanadate, whereby the metal amount was optimized by screening for the highest photocatalytic activity (for details see the Supporting Information, Figures and). The best performing anatase TiO2 photocatalysts comprising Cu(II), Fe(III) or vanadate single atom (SA) catalytic sites are designated as a-TiO2-Cu SA , a-TiO2-Fe SA , and a-TiO2(400)-V SA with the actual metal content of 0.08 wt% Cu, 0.11 wt% Fe, and 0.03 wt% V, respectively, as determined by inductively coupled plasma optical emission spectrometry (ICP-OES).