The need for efficient remediation of the radioactive waste caused by undesirable nuclear accidents and overspending of radionuclides has gained worldwide attention, with extensive recent efforts made to protect the environment from radioactive contamination. Although various treatment processes for the removal of radionuclides and the purification of liquid waste have been reported, the development of a better decontamination method is still necessary for obtaining enhanced desalination performances. Herein, we report a dual-functional composite adsorbent composed of a cellulose acetate membrane as a solid support, gold nanoparticles (AuNPs), and a metal chelating agent which can potentially be used to efficiently remove radioactive iodine and cobalt. In the desalination experiments, the sorption membrane was able to remove cobalt ions rapidly in water. Isotherm data shows that approximately 180 Co2+ atoms were captured per AuNP. Next, the same material was used for the adsorption of iodide anions. Within a few minutes, more than 99% of radioactive iodine was removed even in the presence of other ion species. These findings clearly demonstrate that the desalination method presented in here provides a useful approach for the sequential removal of toxic metal and halogen species in aqueous media.