Reduction of soluble U(VI) to insoluble U(IV) oxide has been considered as an important approach to eliminate radioactive pollution and recycle uranium resource. The technology is hindered by the high cost, consumption of chemicals, and parallel generation of toxic wastes which are severe challenges today. In this paper, the photocatalytic reduction technology was utilized to eliminate UO22+ pollutant by constructing the highly efficient metal-free photocatalysts. Doping sulfur for substituting the lattice nitrogen of g-C3N4 (S-g-C3N4) modifies the electronic structure of g-C3N4 that displays the narrowed band-gap with the tuned conduction band and valence band levels as well as a good ability of electron hole separation and carrier mobility. The photoreactivity of UO22+ reduction for S-g-C3N4 is 1.86 and 32 times of that for pristine g-C3N4 and N-TiO2 under visible light irradiation. The substitution of sulfur for lattice nitrogen was experimentally and theoretically identified as the cause of this unique electronic structure and, consequently, the excellent photoreactivity of S-g-C3N4 in the reduction of UO22+. The results may shed light on improving the reduction technology to eliminate U(VI) pollutant by doping strategies to design potentially efficient photocatalysts. (C) 2016 Elsevier B.V. All rights reserved.