Dication-accelerated anion transport inside micropores for the rapid decontamination of pertechnetate

Over 70% of the treated contaminated water at the Fukushima Daiichi Nuclear Power Station contains radionuclides beyond the regulatory standard for discharge that need to be re-purified. Technetium-99 (99Tc), mainly in the form of pertechnetate Tc(VII)O4−, is one of the main sources of long-term radiotoxicity that jeopardizes the environment and human health. Herein, we used a series of dicationic pyridinium (DCP) derivative groups (–Py+CnH2nN+Me3, n = 2, 3, and 5) to modify commercial Reillex 425 resins containing tertiary pyridyl groups to improve the adsorption performance of rhenium (Re, an analog of radioactive Tc) and Tc. As the quaternary pyridinium and ammonium sites in one DCP group can adsorb ReO4− simultaneously, DCP-modified Reillex 425 (Reillex-Cn) exhibited high maximum adsorption capacities for Re under neutral conditions. Adsorption capacities reached 344.8, 416.7, and 588.2 mg g−1 for Reillex 425-C2, Reillex 425-C3, and Reillex 425-C5, respectively. Intraparticle diffusion of ReO4−/TcO4− in Reillex 425-Cn was verified to be the rate-limiting step of adsorption. However, adsorption can be adjusted by the length of the alkyl spacers between the two positively charged N sites in DCP. –Py+C2H4N+Me3 significantly enhanced intraparticle diffusion compared to –Py+C5H10N+Me3. The two positive sites in –Py+C2H4N+Me3 would be laterally distributed, leading to a smaller steric hindrance for ReO4–/TcO4− transport inside the microporous channels. Meanwhile, the longer alkyl spacers in –Py+C5H10N+Me3 formed hydrophobic microphases, repulsing the hydrated ReO4–/TcO4− anions. Thus, the adsorptions of both ReO4− and TcO4− on Reillex 425-C2 were faster than those on Reillex 425-C5. Moreover, Reillex 425-Cn exhibited an exothermic nature, good selectivity, excellent reusability, and strong salinity tolerance. This study provides a simple strategy to enhance the Tc removal performance of adsorbents containing abundant micropores, which implies enormous environmental and economic benefits.