Simulated Removal of Radioactive Co2+ and 14C-Containing Organic Pollutants by in Situ-Synthesized ZIF-67

Abstract The coexistence of radioactive Co2+ and 14C-containing organic pollutants in nuclear wastewater causes mutual interference that hinders conventional treatment. In this study, ZIF-67-R18 was synthesized in a pure water system without surfactants or organic solvents under self-homogenization conditions. During the synthesis-coupled adsorption process, residual Co2+ was simultaneously adsorbed onto the growing framework. The synthesis-coupled adsorption process achieved adsorption equilibrium within 24 h, and the adsorption capacity was 237.4 mg·g–1 at an initial Co2+ concentration of 800 mg·L–1. The adsorption kinetics followed the pseudo-second-order model. The removal efficiency of the synthesis-coupled adsorption process reached 80.1%, which was significantly higher than that of individual adsorption (35.7%). Furthermore, in a mixed solution containing competing metal ions such as K+, Mg2+, and Na+, selective adsorption of Co2+ was observed. Using methyl orange (MO) and phenol as model organic contaminants, ZIF-67-R18 achieved removal efficiencies of 92.0% and 89.2%, respectively. These results indicate great adsorption potential of ZIF-67-R18 toward organic pollutants. In combination with DFT, XPS, and zeta potential analysis, the adsorption energy of MO on ZIF-67-R18 was calculated to be −0.11 eV, and the MO structure remained intact during the adsorption process. This confirms that the removal of anionic organic pollutants by ZIF-67-R18 is dominated by physical adsorption, including electrostatic attraction and aromatic π–π stacking. The synthesis-coupled adsorption strategy not only realizes the combined removal of cobalt and carbon pollutants but also minimizes the introduction of cobalt precursor. This strategy reduces the generation of cobalt-bearing hazardous waste.