Structure–Activity Relationship of Critical Pore Size for Radon Adsorption in Porous Materials

In addition, oxygen-containing functional groups (hydroxyl groups) enhanced radon adsorption via the polar induction effect, yet the material performance was deteriorated by the competitive adsorption of water molecules in actual humid environments. The experimental results confirmed that 3A and 4A molecular sieves, with pore sizes smaller than the kinetic diameter of radon (4.17 Å), only presented surface adsorption with extremely low adsorption coefficients (0.1-0.12 L/g).

By contrast, the pore size-matched 5A and ZSM-5 molecular sieves achieved a significant increase in adsorption coefficients, up to 0.37-0.48 L/g. Pearson correlation analysis revealed that the radon adsorption coefficient had a significantly positive correlation with the volume of 5-6 Å effective micropores, but only a weak correlation with the specific surface area. The above experimental and simulation results collectively demonstrate that 5-6 Å is the critical pore size for radon adsorption in porous materials, and increasing the effective micropore volume can improve radon adsorption capacity.

This work provides a theoretical basis for the optimal pore structure design of high-efficiency radon removal materials.