Preparation of chitosan-based asymmetric electrodes by co-imprinting technology for simultaneous electro-adsorption of multi-radionuclides

Abstract

The operation of the nuclear industry generates a great deal of radionuclides-containing low-level radioactive wastewater (LLRW). The development of new adsorbents and techniques for radionuclides separation from LLRW will be of great significance for environmental safety and sustainable development of nuclear energy. Electro-adsorption is a potential technique for the separation of radionuclides, but the simultaneous recovery of multiple radionuclides by electro-adsorption have not been reported before. Here, a novel approach was reported for the simultaneous electro-adsorption of strontium (Sr2+), cesium (Cs+), uranium (UO2(CO3)22–) and rhenium (ReO4−) (the non-radioactive surrogate of technetium) from LLRW by chitosan-based asymmetric electrodes. The UO2(CO3)22–/ReO4− co-imprinted chitosan hydrochloride (URIC) and Sr2+/Cs+ co-imprinted chitosan (SCIC) prepared by co-imprinting technique were loaded on the surface of carbon clothes and used as asymmetric electrodes. The maximum electro-adsorption capacities of URIC for U(VI) and Re(VII) were 427.4 mg and 531.9 mg/g and the maximum adsorption capacities of SCIC for Sr(II) and Cs(I) were 254.5 mg and 231.5 mg/g at the potential of 1.2 V, which were at least 3.7 times higher than the values obtained without potential. The electro-adsorption for all these ions conformed to pseudo-second-order kinetics and the adsorption equilibrium can be reached within 30 min at pH 8.0 and 298.15 K, which were more than twice faster than physicochemical adsorption. The electrodes revealed better selectivity for these four target ions against other competing ions in comparison with non-imprinted chitosan functionalized electrodes. Furthermore, the electrodes showed conspicuous salt resistance in simulative LLRW with high ionic strength (1 mol/L NaCl) and high removal efficiencies can be retained after five adsorption and desorption cycles. XPS studies revealed that UO2(CO3)22– and ReO4− anions were bound to URIC mainly through electrostatic interaction, while Sr2+/Cs+ were bound to SCIC by complexation interaction between Sr2+/Cs+ and –NH2/–OH on the backbone of chitosan. This work reports an innovative approach for the simultaneously selective electro-adsorption of multiple radionuclides from LLRW assisted by co-imprinting technology, which can be popularized to the simultaneous separation of other charged contaminants efficiently, thus achieving deep purification of wastewater.