Efficient Thorium/Barium Separation by Quaternary Ammonium Functionalized Silica Composite toward Sustainable Production of ²¹² Pb for Targeted Alpha Therapy

²¹²Pb has become a critical parent isotope for ²¹²Bi, which is an alpha-emitting radionuclide utilized in targeted alpha therapy (TAT) for oncology; however, its limited availability impedes broader clinical use. To tackle this significant challenge, this study focuses on a strategic approach to separate ²²⁸Th (a precursor to ²¹²Pb) from its parent isotope ²²⁸Ra within the decay chain of naturally occurring ²³²Th. A novel porous silica composite, functionalized with quaternary ammonium groups through in situ polymerization (referred to as SiPVP-N4), was developed to efficiently achieve Th/Ba separation under highly acidic conditions. This material displays a unique spherical morphology with high porosity (25.4 nm pore size), rapid kinetics (achieving equilibrium within 30 min, which is six times faster than commercial resins), and exceptional selectivity for Th over Ba (with a separation factor SFTh/Ba of 1.6 × 10³). The adsorption behavior aligns well with that of the Langmuir model, indicating a maximum adsorption capacity of 89.77 mg/g. Column experiments demonstrated 100% thorium recovery with high radiochemical purity under 9 M HNO₃ adsorption conditions. Notably, SiPVP-N4 sustains over 95% capacity retention through five regeneration cycles, underscoring its potential for industrial application. This study establishes a robust platform for the production of medical isotopes, presenting a cost-effective alternative to traditional high-acid separation systems and contributing to the advancement of radiopharmaceutical development.