Introducing dense sulfonic acid in metal-organic framework for effective adsorption of radioactive barium ion

The irreversible adsorption of radioactive barium (Ba2+) ion is highly necessary while still faces large challenge especially in adsorption capacity. In this work, we report two novel adsorbents, Zr-MSA-SO3H (MSA, 2-mercaptomalic acid) and Zr-DMSA-SO3H (DMSA, meso-dimercaptosuccinic acid). Due to the nanoscale particle and higher content of active sulfonic acid group, Zr-DMSA-SO3H exhibits rapid adsorption equilibrium (30 min) and higher adsorption capacity for Ba2+ (224.0 mg g-1), superior to other reported MOFs. Optimal adsorption happens at neutral pH and higher temperature can promote the adsorption. Besides, co-existing metal ions exhibit negligible effects on the adsorption. The combination of FTIR and XPS analysis confirms the dominant contribution of sulfonic acid group on Ba2+ adsorption. Our work proves Zr-DMSA-SO3H can serve as a potential adsorbent for Ba2+, and proposes a design strategy for MOFs with dense sulfonic acid groups.