This paper introduces the first attempt of using well organized Co@CoO core-shell nanocrystals as an alternative toward noble metal catalysts for photocatalytic water splitting reactions. In this work, four kinds of stable magnetic Co@CoO core-shell nanocrystals were fabricated through a one-pot toluene water two-phase interfacial reaction with oleic acid as a surfactant. The size and shape of the as-prepared crystals can be carefully adjusted through dynamically coating the closely packed monolayer of coordinating ligand onto the growing crystals. It is notable that spherical pine-nut-like hierarchical assemblies of Co@CoO core-shell nanoplates exhibit excellent photocatalytic activity (the maximum value of O-2 yield is over 96%). Even after the sixth run, the high catalytic activity of the recovered Co@CoO core-shell nanoplates remained. (C) 2017 Elsevier B.V. All rights reserved.