The control of actinide and transition metal ions valence states by heterogeneous photocatalysis is possible in aqueous solution environments. The change of metal ion oxidation state can proceed through four different mechanisms. While the photoreduction of Cr(VI), Pt(IV) and Au(III) is not hindered by molecular oxygen, O2 competes with Hg(II), Ni(II), Cu(II), Ag(I), Pt(II), Rh(II), and Pd(II) for photogenerated conduction band electrons. In the case of Tl(I), the reaction pathway switches from a photoreduction to a photooxidation in the absence and the presence of O2 respectively. Other factors influencing photocatalytic transformation of metal ions include the pH, the nature of the semiconductor and the presence and nature of the charge carrier scavenger. Applications of heterogeneous photocatalysis in actinide ion photoredox chemistry is of potential utility in the nuclear waste reprocessing industry but criteria for efficient photocatalytic transformation of actinide ions are complicated by factors additional to those already described such as the radiolysis of HNO3 and the disproportionation of transuranic elements.