Synergistic Enhancement of Pb ²⁺ Adsorption by Hierarchical Pore Structure and Ultralow Si/Al Ratio in Bentonite-Derived Sodalite

To address the critical limitations of natural bentonite, including restricted specific surface area and low cation exchange capacity (CEC) caused by interlayer impurities, this study proposes an in situ structural reconstruction strategy via simultaneous alkaline activation and aluminum doping. This approach directly transforms bentonite frameworks into a hierarchically porous SOD-type sodalite with an ultralow Si/Al ratio. The engineered material integrates three synergistic advantages: abundant surface hydroxyl groups, maximized CEC (saturation capacity, 242.56 mg/g), and a dual-scale pore architecture (micropores/mesopores). Combined experimental and computational analyses reveal the underlying mechanisms: The ultralow Si/Al ratio generates Al-O-Si bridging sites, strengthening electrostatic interactions with Pb²⁺ (adsorption energy: -1.356 eV) and reducing the migration energy barrier. Local charge redistribution at Al-rich domains optimizes Pb²⁺ occupation, achieving a stable Pb-O bond length of 2.35 Å. Hierarchical porosity facilitates rapid mass transfer, enabling 93% adsorption capacity retention after eight regeneration cycles. This work establishes a quantitative structure-performance relationship among Si/Al ratio, charge distribution, and adsorption efficiency through bentonite interlayer reconstruction. It provides fundamental insights for designing high-performance, low-cost heavy metal adsorbents, demonstrating a 2.7-fold increase in Pb²⁺ uptake compared to conventional bentonite, developing high-performance, low-cost heavy metal adsorbents.