Development of adsorbent materials that can efficiently remove radioactive species, in particular, iodine from aqueous waste streams is of great importance to prevent the discharge of these highly toxic chemicals into waterways, while providing a means for a safe disposal of nuclear wastes. In this study, we present a detailed investigation of the performance of a series of bismuth-loaded alumina adsorbents (Bi/Al) grafted with three different aminosilanes including 3-Aminopropyl-triethoxysilane (APS), N-methylaminopropyl-trimethoxysilane (MAPS), and 3-N,N-dimethylaminopropyl-trimeth-oxysilane (DMAPS), in the removal of iodine from aqueous solutions. Specifically, we studied the effects of bismuth loading, amine type and content, as well as iodine concentration and capture temperature to determine the best performing material and removal conditions for iodine immobilization from caustic scrubber solutions. Our results indicated that amine grafting can enhance the iodine removal performance of Bi-Al, with DMAPS giving rise to highest capacity. It was also found that iodine capture over amine-grafted Bi/Al changes dramatically with amine content. Among the materials investigated, Bi5/Al-DMAPS with an amine content of 60 wt% exhibited the highest iodine capture capacity of 215.7 mg/g at 50 °C. Moreover, amine grafting improved the retention of adsorbed iodine species within the adsorbent over time with no degree of leaching after 24 h, unlike Bi/Al2O3 analogue.