Synthesis of layered double hydroxide/different carbon material _{and 90Sr2+} composites for simultaneous adsorption of ⁷⁹ SeO ₄ ^2-

After the Fukushima Daiichi Nuclear Power Plant accident, a variety of radionuclides has been treated by Advanced Liquid Processing System including different adsorbents. This work aims to synthesize layered double hydroxide (LDH)/different carbon materials composites for simultaneous adsorption of radioactive anion and cation, where ⁷⁹ SeO ₄ ^2- and ⁹⁰ Sr ²⁺ have been selected as targets for removal. As carbon materials, carbon-dot and graphene oxide (GO) were synthesized to modify LDH, in which the presence of carboxylic groups was confirmed by FTIR. TEM observation revealed the sizes of C-dot and LDH particles are 3-5 nm and around 100 nm, respectively, while the size of GO has been reported 1-2 mm. Simultaneous adsorption of SeO ₄ ^2- and Sr ²⁺ was achieved in both composites using surrogates, though ion-exchange of SeO ₄ ^2- with NO ₃ ^- in LDH and complexation of Sr ²⁺ with carboxyl group in carbon materials. Comparable adsorption capacities of SeO ₄ ^2- was observed on both composites. However, Sr ²⁺ adsorption capacities were much larger in LDH/GO than LDH/C-dot in any cases of different carbon contents. In addition, Sr ²⁺ adsorption capacities in mmol/g-GO were much larger in LDH/GO composites than pure GO. Zeta potential of LDH/GO was +31.0 mV closer to LDH, while that of LDH-C-dot was -16.4 mV closer to C-dot. These observation suggests there is a clear contrast between two composites. That is, the composite of LDH/GO consists of coverage of larger sheets of GO with smaller sheets of LDH, while the composite of LDH/C-dot consists of coverage of larger sheets of LDH with nano-sized C-dot. Accordingly it is promising to customize the ratio of LDH/GO in the composite considering the different radioactive waste water compositions to treat in various stages.