“…Previous studies have shown that doping with metals improved the photocatalytic efficiency of TiO 2 and could be considered as a promising strategy 29 . The verified metal dopants, including Mn 30,31 , Cu, Co 32 , Ag 33 , La 34 , Sn 35 , and so on, not only reduced the rate of recombination of electron/hole, but also increased the adsorption in the visible light region 27 . Extensive studies have been carried out in terms of mono doping TiO 2 with transition metals, such as La, Ag, Mn, Co, Cu, Mo, Au, Pt, etc 34 .…”