ZIF-8有机框架衍生的D-ZnO@Fe_(x)O_(y)S型异质结用于光辅助铀还原

S-Scheme Heterojunction D-ZnO@Fe_xO_(y)Derived From ZIF-8 Organic Framework for Photoassisted Reduction of U(Ⅵ)

光催化辅助铀提取作为一种新型的铀提取技术,有望克服传统工艺中多种金属离子与U(Ⅵ)的竞争配位以及富集容量有限的难题。在这项研究中,以ZIF-8为前驱体,通过浸渍和高温热解制备了S型ZIF-8衍生氧化锌@铁氧化物(D-ZnO@Fe_(x)O_(y))异质结,用于光辅助还原铀矿废水中的U(Ⅵ)。相比于铁氧化物(Fe_(x)O_(y))和ZIF-8衍生ZnO(D-ZnO),S型异质结D-ZnO@Fe_(x)O_(y)在竞争离子存在下,表现出优异的光辅助铀还原能力(>95%)。通过能带计算证实了在异质结界面形成内置电场,能够有效增强电子定向迁移,并为促进铀的光辅助还原提供了强大的驱动力。机理研究表明,羟基自由基和超氧自由基是参与光催化还原U(Ⅵ)的主要物质。本研究为探索具有高效光电子分离功能的光催化剂还原U(Ⅵ)提供了一条有价值的途径。

With the rapid development of nuclear energy,uranium as the main element of nuclear energy production,its source has been widely explored.At present,uranium resources mainly come from uranium mining,and a lot of radioactive uranium containing wastewater is produced in the process of uranium mining.Until now,the treatment technology of uranium mine wastewater is still in the research and development stage in China,which leads to the storage of a large amount of uranium mine wastewater and the discharge of nuclear waste liquid,which poses a threat to human health and the environment due to the comprehensive effect of chemical toxicity and radiation toxicity.On the other hand,other metal cations in uranium wastewater,such as Ca^(2+)and Mg^(2+),compete with U(Ⅵ)for active sites,making it difficult for most treatment methods to effectively recover uranium resources from uranium wastewater.Therefore,how to effectively treat radioactive uranium mine wastewater is full of challenges.Photocatalysis is a kind of green environmental protection technology with natural selectivity to non-variable valence ions,which can precipitate the soluble U(Ⅵ)in wastewater.The photocatalysis technology is expected to overcome the competition between metal cations and uranium for active sites,and realize the efficient extraction of U(Ⅵ)in uranium mine wastewater.In this study,ZIF-8-derived Zinc@iron oxide(D-ZnO@Fe_xO_y)heterostructures were prepared by impregnation of metal salt solution and high-temperature pyrolysis using ZIF-8 as a precursor for photoassisted reduction of U(Ⅵ)in uranium ore wastewater.The electron transport mode of D-ZnO@Fe_xO_(y)in S-scheme heterojunction is deduced by calculating the work function and band structure.Under photoexcitation,the direction of electron flow changes,the useless electrons and holes recombine at the interface,and the electrons and holes with strong redox ability are retained and participate in the photocatalytic reaction.Compared with D-ZnO and Fe_xO_y,this kind of spatially separated photogenerated electrons and holes have stronger redox ability and longer electron lifetime.Meanwhile,the internal electric field formed at the heterojunction interface can effectively enhance the directional electron migration,providing a strong power for promoting the photoassisted reduction of uranium.Therefore,compared with iron oxide(Fe_xO_y)and ZIF-8-derived ZnO(D-ZnO),the S-type heterostructure DZnO@Fe_xO_(y)exhibits stronger photoassisted uranium reduction ability(>95%)in the presence of multiple competing ions,and the material has good anti-interference and stability.High U(Ⅵ)removal performance(above 86%)is maintained after 5 cycles.The mechanism study shows that hydroxyl radical and superoxide radical are the main active species of photocatalytic reduction of U(Ⅵ).U(Ⅵ)is deposited on the surface of the material in the form of(UO_(2))O_(2)·2H_(2O)crystals.This study provides a valuable way to explore the photocatalyst with high efficiency photoelectron separation to reduce U(Ⅵ).