Experimental Study On The Photocatalytic Reduction Of U(Ⅵ) By Z-type Photocatalytic System

Uranium is considered to be a major highly chemically toxic and highly radioactive nuclear component with dire health effects on the entire human population.The aim of the researchers is to effectively and reasonably remove the contaminants containing uranium.Graphite phase carbon nitride（g-C₃N₄）,as a nonmatellic materials,has attracted wide attention in photocatalytic degradation due to its advantages such as low cost,easy preparation and visible light response.However,the simple g-C₃N₄ quantum efficiency is low,and the photocatalytic activity is not ideal.In this paper,g-C₃N₄ material was prepared by calcination method,and then TiO₂ was synthesized with it by solvothermal method to form a binary Z-scheme photocatalytic system-g-C₃N₄-TiO₂,which effectively improved the activity of g-C₃N₄ photocatalytic reduction of U（Ⅵ）.Then graphene（GO）was introduced to form a ternary Z-scheme photocatalytic system-g-C₃N₄-RGO-TiO₂ by solvothermal method.By creating a new electron transfer bridge,GO greatly increased the contact the contact area and tightness between g-C₃N₄ and TiO₂,which improved the response to visible light.The experimental results of photocatalytic reduction of U（Ⅵ）by g-C₃N₄-TiO₂ under UV irradiation show that the efficiency of photocatalytic reduction of U（Ⅵ）by g-C₃N₄-TiO₂ was 31 times and 1.48times higher than that by g-C₃N₄ and TiO₂,respectively.The experimental results of the influencing factors show that when p H=6.0,catalyst concentration is 0.25 g/L,light intensity is 600 W,the efficiency of g-C₃N₄-TiO₂ photocatalytic reduction of U（Ⅵ）is the best and can reach99.8%.The results of quenching experiment show that photogenerated electron（e^-）and superoxide radical（˙O₂^-）are involved in the reduction of U（Ⅵ）.Moreover,after four cycle tests,the photocatalytic reduction efficiency of U（Ⅵ）by g-C₃N₄-TiO₂ is still greater than 90%.The experimental results of photocatalytic reduction of U（Ⅵ）by g-C₃N₄-RGO-TiO₂ under visible light irradiation show that when the mass percentage of RGO is 5%,the photocatalytic reduction efficiency of U（Ⅵ）by g-C₃N₄-5RGO-TiO₂ was 4.01 times and 2.98 times than that by g-C₃N₄ and g-C₃N₄-TiO₂,respectively.The experimental results of influencing factors show that the efficiency of photocatalytic reduction of U（Ⅵ）by g-C₃N₄-5RGO-TiO₂ can reach 99%when the p H is 6.0.the concentration of catalyst is 0.2 g/L and the light intensity is 600 W.At the same time,the coexistence ion test results showed that Cl^-promoted the photocatalytic reaction,while Fe³⁺and Cu²⁺competed e^-with U（Ⅵ）inhibited the photocatalytic activity.Finally,methanol,ethanol and propanol were used as hole capture agents respectively.The test results showed that the reaction effect of the propanol group was greater than the methanol and ethanol group.It was confirmed by electron spin resonance（ESR）that the propanol group produced a kind of carbon dioxide reduction group(CO₂^-.)which further promoted the photocatalytic reduction of U（Ⅵ）by g-C₃N₄-5RGO-TiO₂.The reproducibility test results of g-C₃N₄-5RGO-TiO₂ could still maintain more than 90%after four cycles.g-C₃N₄-5RGO-TiO₂ is expected to be a potential functional material for the treatment of low concentration uranium-containing wastewater.