Applied Catalysis B: Environmental 200 (2017) 378–385 Contents lists available at ScienceDirect Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb Photocatalytic reduction elimination of UO 2 2+ pollutant under visible light with metal-free sulfur doped g-C 3 N 4 photocatalyst Changhai Lu a , Peng Zhang c , Shujuan Jiang a,∗ , Xi Wu a , Shaoqing Song a,∗ , Mingshan Zhu c , Zaizhu Lou c , Zhe Li b,∗ , Fen Liu a , Yunhai Liu a,∗ , Yun Wang a , Zhanggao Le a,∗ a Key Laboratory for Radioactive Geology and Exploration Technology, Fundamental Science for National Defense, East China University of Technology, Nanchang 330013, PR China b Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission & Ministry of Education, South-Central University for Nationalities, Wuhan, Hubei Province 430074, PR China c The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan a r t i c l e i n f o Article history: Received 27 May 2016 Received in revised form 13 July 2016 Accepted 19 July 2016 Available online 20 July 2016 Keywords: Photocatalysis g-C3N4 Sulfur doping Uranium reduction Visible light a b s t r a c t 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 UO 2 2+ pollutant by constructing the highly efficient metal-free photocatalysts. Doping sulfur for substituting the lattice nitrogen of g-C 3 N 4 (S-g-C 3 N 4 ) modifies the electronic structure of g-C 3 N 4 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 UO 2 2+ reduction for S-g-C 3 N 4 is 1.86 and 32 times of that for pristine g-C 3 N 4 and N-TiO 2 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-C 3 N 4 in the reduction of UO 2 2+ . The results may shed light on improving the reduction technology to eliminate U(VI) pollutant by doping strategies to design potentially efficient photocatalysts. © 2016 Published by Elsevier B.V. 1. Introduction With the rapid development of nuclear industry, much atten- tion has been given to the harm of nuclear waste released from uranium mining, milling, and processing [1,2]. Study has confirmed that a long-term exposure to uranium would cause serious health problems (e.g., severe liver damage, kidney damage and eventu- ally death) [3]. Therefore, how to eliminate uranium pollution is an important issue in the protection of environment and alleviation of the nuclear material resource [4,5]. It is seen that uranium species exist in several chemical states (e.g., U(0), U(III), U(IV), and U(VI)), in which the predominant chemical states in the ambient environ- ment are soluble U(VI) and slightly soluble U(IV) [6–9]. Therefore, reduction of soluble U(VI) to insoluble U(IV) oxide has been pro- posed as an important approach to eliminate radioactive pollution and reuse uranium resource [8,10–13]. However, most of reported ∗ Corresponding authors. E-mail address: sqsong@ecit.edu.cn (S. Song). reduction strategies are expensive and involve a high consumption of chemicals, generating parallel toxic wastes [14]. Semiconduc- tor photocatalysis, a green strategy that can reductively remove harmful heavy metals using semiconductor photocatalysts under sun light irradiation, provides a new option to address the above challenges [15–20]. For example, TiO 2 particles were employed as photocatalysts for photo-induced reduction of U(VI) under UV with the aid of humic acid, formic acid, and 2-propanol [14,17–19]. TiO 2 is undoubtedly the most studied semiconductor photocata- lyst with its low cost, high activity and stability. However, due to its wide band gap (3.2 eV), TiO 2 cannot be activated by the visible light. In order to make full use of solar energy for photocatalytically reducing U(VI) to U(IV), it is desirable to develop efficient visible light-responsive metal/metal oxides semiconductor photocatalysts or even metal-free photocatalysts. Recently, graphitic carbon nitride (g-C 3 N 4 ) has attracted inten- sive interest for its promising applications in photo-splitting water, photo-decomposition of organic pollutants, and photosynthesis under visible light, because this material shows good visible light response (up to 455 nm), high thermal, and chemical stability http://dx.doi.org/10.1016/j.apcatb.2016.07.036 0926-3373/© 2016 Published by Elsevier B.V.