Typical metals for TiO₂ photocatalyst doping.

Metals	Properties	References
(1) Transition metal ions such as V, Cr, Mn, Fe, Co, Ni, or Cu	(1) Extend light absorption into the visible region	27 and 41
	(2) There is a considerable reduction in the photocatalytic activity in the UV region
(2) Presence of metals, such as Li+, Zn2+, Cd2+, Ce3+, Co3+, Cr3+, Fe3+, Al3+, Mn2+ and Pt	(1) Considerably change the photocatalytic activity of TiO2	39 and 41
	(2) Sol–gel systems can be used to prepare the Mn+/TiO2 layers for phenol degradation
(3) The presence of Co3+, Cr3+, Ce3+, Mn2+, Al3+ and Fe3+ ion (5 mol% Mn+: Ti4+)	(1) Has an opposing influence on the photocatalytic activity of the TiO2 photocatalyst	41
	(2) There is a decline in the photocatalytic activity of TiO2 under UV irradiation
	(3) These metal ions act as recombination sites for the photogenerated charge carriers