Preparation of PAO/TiO2 Electrode and Efficient Extraction of Uranium from Seawater

In order to investigate the reduction performance of U(Ⅵ) in seawater by electrochemical technology, TiO2 nanotube array electrode was firstly prepared by anodizing method, and then the amidoxime-modified TiO2 electrode (PAO/TiO2 electrode) was prepared by using the drip coating method to make the amidoxime functional groups loaded on the surface of TiO2 electrode. The electrode was characterized by scanning electron microscopy, infrared spectroscopy and X-ray Auger electron spectroscopy. The uranium extraction performance of PAO/TiO2 electrode in spiked seawater and real seawater was investigated respectively. The reaction mechanism was also proposed. The results of scanning electron microscopy and infrared spectroscopy show that the surface of the prepared TiO2 nanoarray is smooth and the tube diameter is uniform. PAO containing amidoxime functional groups is successfully introduced on the surface of TiO2 electrode. The results of performance test in spiked seawater show that PAO/TiO2 electrode has a good ability to extract uranium. The extraction rate of uranium is 89.01% when the reaction time is 600 min. The pseudo-second-order kinetic model (R2=0.99583) can better describe the adsorption kinetic process of U(Ⅵ) on PAO/TiO2 electrode than the first-order kinetic model (R2=0.98208), indicating that the adsorption process of the electrode material is dominated by chemical adsorption. The selective adsorption performance of U(Ⅵ) on PAO/TiO2 electrode is better than that of other competitive metal ions (such as , Fe3+, Co2+, Ni2+, Cu2+, Na+, Mg2+, Ca2+). The desorption test was carried out on the electrode material after uranium adsorption, and the results show that the desorption rate of the electrode is 92.12% when 0.4 mol/L Na2CO3 used as the desorption agent. The test results in real seawater show that the extraction rate of uranium is 59.4% and the adsorption capacity of uranium is 4.07 mg/g when the reaction time is 28 h. X-ray Auger electron spectroscopy was used to characterize PAO/TiO2 electrode before and after uranium adsorption. The results show that the electrode can reduce part of U(Ⅵ) to U(Ⅳ), and U(Ⅵ) is deposited in the form of UO2 on the surface of PAO/TiO2 electrode. PAO/TiO2 electrode can extract uranyl ions from seawater by electroadsorption and electrodeposition, which is a potential electrode material. These results are expected to lay the foundation for the development of large scale sustainable uranium extraction systems from seawater.