Hydrogen isotope adsorption and separation in ion-exchanged ZSM-25 zeolites

• Ion concentration in ZSM-25 zeolites is controlled by ion exchange processes. • Na + and K + cations show opposite effect on D 2 and H 2 adsorption. • D 2 and H 2 adsorption uptake is regulated by Na + and K + concentrations. • ZSM-25-K shows a high D 2 uptake and a high D 2 /H 2 kinetic selectivity at 77 K. Given the only difference between hydrogen isotopes is the number of neutrons, their separation is doubtlessly challenging. Among various separation methods, adsorption-based separation technology is considered energy-efficient and effective. Zeolites, as eco-friendly porous materials, hold great promise for hydrogen isotopes separation, making their adsorption behaviours worth investigating. Here, we regulate the accessibility of hydrogen gas (H 2 ) and deuterium gas (D 2 ) in ZSM-25 zeolites by changing the cation type of K + and Na + . The K + cations allow hydrogen isotopes to pass through, while the Na + cations block the pathway. Notably, ZSM-25-K exhibits a high D 2 adsorption capacity of 3.3 mmol/g at 100 kPa and 77 K, together with the highest D 2 /H 2 kinetic selectivity of 4.6 in a 50/50 D 2 /H 2 mixture at 7 kPa and 77 K. This adsorption behaviour results from a combination of kinetic quantum sieving and chemical affinity quantum sieving mechanisms, as revealed by equilibrium isotherms and kinetic analysis.