Photocatalytic water oxidation is one of the critical reactions for solar fuel production from abundant sources. Among all the metal oxides, Co3O4 spinel exhibits a high activity as an oxygen evolution catalyst. In this paper, we demonstrate that the photocatalytic oxygen evolution activity of Co3O4 spinel can be further enhanced by substituting cobalt with manganese in the spinel structure. Using a facile hydrothermal approach, we have successfully synthesized pure, Mn-substituted, and Ni-substituted Co3O4 nanopartides with a typical particle size of 5-7 nm. The morphologies and crystal structures of the as-synthesized nanoparticle catalysts have been carefully examined using various structural characterization techniques, including PXRD, TEM, gas adsorption, and XAS. The photocatalytic activities of as-made nanoparticles have been investigated using a well-studied visible light driven [Ru(bpy)(3)](2+)-persulfate system. In both Clark electrode and reactor/GC systems, Mn-substituted Co3O4 nanoparticles exhibited the highest TOF among all the three catalysts. The data presented in this paper suggest that the photocatalytic water oxidation activity of Co3O4 spinel catalyst could be further enhanced by Mn3.1+ substitution at the octahedral sites. (C) 2013 Elsevier B.V. All rights reserved.