Synthesis of sulfur and bromine co-doped bentonite-chitosan composite hydrogels for selective adsorption of cobalt and strontium radionuclides

The present study focuses on the synthesis of sulfur (S) and bromine (Br) co-doped bentonite and its three-dimensional chitosan composite hydrogels (S/Br-B-CB-x) for the selective removal of hazardous radiotoxic pollutants, specifically the radionuclides ⁶⁰Co and ^85,90Sr. The physicochemical properties of the synthesized materials were analyzed using various characterization techniques. Batch adsorption studies for ⁶⁰Co and ^85,90Sr were conducted under batch mode to evaluate the adsorption performance of the prepared materials. The influence of key parameters such as contact time, solution pH, adsorbent mass, temperature, and coexisting anions was systematically examined to determine the maximum adsorption efficiency. The adsorption of ⁶⁰Co and ^85,90Sr onto S/Br-B-CB-50 followed pseudo-second-order kinetics and aligned with the Langmuir adsorption isotherm, indicating a chemisorption mechanism governed by monolayer formation. Regeneration experiments revealed that S/Br-B-CB-50 maintained excellent adsorption efficiency for ⁶⁰Co and ^85,90Sr over five consecutive cycles, demonstrating the high stability of the materials. The outstanding adsorption performance of the hydrogels can be attributed to several mechanisms, including electrostatic interactions, ion exchange, surface complexation, and the principles of the hard and soft acids and bases theory. These results confirm that S/Br-B-CB-50 is an effective adsorbent for removing ⁶⁰Co and ^85,90Sr, highlighting its potential for the remediation of liquid radioactive waste.