三种小分子对光电子还原铀的影响及机理研究

Effects and Mechanism of Three Different Small Molecules on the Process of Uranyl Ion Reduction by Photoelectron

光电子具有较强的还原性,但在溶液中其还原性受到多种因素的影响。该研究通过在反应体系中添加不同的有机小分子并利用循环伏安(CV)、电化学交流阻抗(EIS)、恒电位I-t曲线和红外光谱(FTIR)等方法考察小分子对光电子还原铀的影响及其作用机理。结果表明:CV分析证实在半导体矿物-U(Ⅵ)体系中U(Ⅵ)经历两步单电子还原为U(Ⅳ),扩散系数D_(Ⅵ)=1.9×10^(-8)cm^2/s。加入Na_3C_6H_5O_7、CH_3COONa、C_2H_5OH 3种小分子后溶液体系具有更高的电活性;随着小分子浓度不断增加,电子转移的能力先升高后降低;体系存在最优条件,即U(Ⅵ)与小分子的摩尔浓度为1∶1时,电子转移能力最强。相较于半导体矿物-U(Ⅵ)体系,3种小分子加入后其还原率分别提高了27.4%、16.4%、14.6%。EIS表明加入小分子的溶液体系具有更低的传荷内阻,更有利于电子的快速传递;I-t曲线证实还原过程中添加小分子可以加快U(Ⅵ)还原反应动力学速度;FTIR表明作用后603.34 cm^(-1)处有一U(Ⅳ)的较强吸收峰,表明光电子可将U(Ⅵ)还原成低价铀。研究结果表明通过加入合适的小分子可提高光电子对铀的还原效率。

The photoelectron has strong reducibility,but it is affected by many factors in the solution system. In this research, the effects and mechanism of three different small molecules on the process of uranyl ions reduction by photoelectron were investigated through cyclic voltammetry（CV）,electrochemical impedance spectroscopy（EIS）,constant potential I- t curves and infrared spectra（FTIR）. The CV results showed that U（Ⅵ） was reduced to U（Ⅳ） in the semiconductor mineral-U（Ⅵ） system through two steps of single electron reduction process,and the diffusion coefficient D（Ⅵ）=1.9×10^-8cm^2/s. The solution system showed higher electrical activity after adding three kinds of small molecule such as Na3C6H5O7,CH3 COONa,C2H5OH. The ability of electron transfer first increased and then decreased with concentration increase of small molecule. There was an optimal condition for uranyl reduction that the ratio of U（Ⅵ）to small molecule was1 ：1. Compared to the semiconductor minerals- U（Ⅵ） system,the reduction rates increased by 27.4%,16.4%,14.6%,respectively,after adding small molecule. EIS showed that the solution system had a lower charge transfer resistance when adding small molecule and was more advantageous to the electronic transmission. The I-t curve confirmed that the reduction reaction kinetics can be accelerated by adding small molecule in the process of uranium reduction. There was strong absorption peak at 603.34 cm^-1 that has been identified as U（Ⅳ）by FTIR after reduction. It indicated that U（Ⅵ）could be reduced to low-valence uranium by photoelectron. The results showed that the suitable small molecule can enhance the reduction efficiency of uranyl by photoelectron.