在核燃料循环中，不可避免产生含铀废水，含铀废水的处理对于保护环境和人体健康都具有重要意义。通过光催化还原的方法，将在水溶液中有良好溶解性和流动性的U(VI)转化为具有低溶解度的U(IV)，是一种新的除铀策略。其关键在于合成具有优异性能的光催化剂。石墨相氮化碳（g-C3N4）是一种具有可见光响应的非金属半导体光催化材料，有良好的应用前景，但需要对其进行改性以提升其光催化除铀性能。目前已经报道的石墨相氮化碳改性方法还存在着一些问题，例如会引入强酸、强腐蚀性和强氧化性等有毒有害的试剂，带来操作危险，造成环境污染等。针对上述问题，本论文发展了三种对于g-C3N4的改性方法。论文的主要研究结果如下：（1）基于微等离子体电化学发展了一种简便的，在常温和常压下对石墨相氮化碳进行表面改性的方法。改性后的石墨相氮化碳，在氮气气氛下，光催化去除铀酰离子的反应速率有所下降；而在空气气氛下，反应速率有所提升，其中阴极处理90 min的样品CN-C-90具有最好的去除性能，去除容量即可达500 mg(U)/g 以上。在空气气氛下，光催化反应得到的产物是水丝铀矿（UO2(O2)·4H2O），以此推测可能的机理是：在光催化反应过程中生成了H2O2，H2O2进一步与铀酰离子反应生成水丝铀矿，并沉积在催化剂表面，从而达到了去除铀的效果。（2）以具有网状结构的三聚氰胺海绵为模板，合成了三聚氰胺海绵氮化碳（MSCN），其比表面积比尿素氮化碳（UCN）增大约24.7倍；MSCN的吸附容量较UCN显著增大，在选定实验条件下，MSCN对铀酰离子的吸附容量可达到252 mg/g，约为UCN的吸附容量（60 mg/g）的4倍。提高水相铀浓度，MSCN在暗反应和光反应阶段对铀的总去除容量可以达到842.2 mg/g。（3）通过水热法成功制备了7种碳点，并将其与石墨相氮化碳复合得到了复合材料。复合材料保留了石墨相氮化碳的基本结构组成特征，但其能带结构和光电性能发生明显变化。与碳点复合之后，光催化去除铀酰离子的反应速率都有提高，其中，样品SerCDs/CN的反应速率最快，约为以双氰胺为前驱体制备的氮化碳的两倍，去除容量可以达到1690 mg/g以上。综上所述，本文发展了三种改性方法，都实现了对光催化去除铀酰离子性能的提升，为开发含铀废水的处理新方法提供了科学依据。
In nuclear fuel cycle, it is unavoidable to produce uranium-containing wastewater, and the treatment of uranium-containing wastewater is of important significance for protecting the environment and human health. The transformation of U (VI) with good solubility and mobility in the aqueous solution into U (IV) with low solubility by photocatalytic reduction is a new strategy for uranium removal. The key lies in the synthesis of photocatalysts with excellent performance. The graphite phase carbon nitride (g-C3N4) is a nonmetallic semiconductor photocatalytic material with visible light response, has good application prospects, but needs to be modified to enhance its photocatalytic deuranium performance. There are also some shortcomings in the reported method of carbon nitride modification, such as introducing strong acids, strong corrosive reagents or strong oxidants, which will probably bring operation and environmental pollution risks. In order to avoid the above problems, three kinds of modification methods for g-C3N4 were developed in this work. The main research achievements are as follows: (1) A simple surface modification method for g-C3N4 was developed based on the microplasma electrochemistry. Using modified g-C3N4, the reaction rate of photocatalytic removal of uranyl ions decreased in the nitrogenn atmosphere, but increased in the air atmosphere. In the air atmosphere, the sample CN-C-90 of the cathode processing 90 min achieved the best removal performance with a capacity of more than 500 mg (U) / g. The product of the photocatalytic reaction was found to be Water Uranium Mine (UO2 (O2) · 4H2O), The possible mechanism is that H2O2 was generated during the photocatalytic reaction and further reacted with a uranium-acyl ion to produce a water-wire uranium mine, and the product deposited on the catalyst surface. This resulted in the removal of uranium. (2) Using melamine sponge with mesh structure as the template, melamine sponge carbon nitride (MSCN) was synthesized. Its specific surface area is about 24.7 times larger than that of urea carbon nitride (UCN). Under the selected experimental condition, the adsorption capacity of uranium by MSCN significantly increased to 252 mg/g, which is 4 times as high as the value by UCN (60 mg/g adsorption capacity). Increasing the concentration of uranium, the removal capacity of uranium in dark reaction and photoreaction stage reached 842.2 mg/g. (3) Seven kinds of carbon dots were prepared by hydrothermal method and in-suit combined with g-C3N4. The composites kept the the basic structure of g-C3N4. However, the band structure and photoelectric properties changed obvisously after combined with carbon dots. The reaction rate of uranium removal by sample SerCDs/CN is the fastest, about twice as fast as the rate by DCN. The removal capacity of uranium reached 1690 mg/g. In general, three kinds of modification methods were developed and improved the photocatalytic performance of uranyl ion removal. The present work provides scientific support for the development of new method to treat uranium-containing wastewater.
