Engineering Flexible Pristine and Core–Shell Triazolate Frameworks with Pressure-Induced Breathing for High-Pressure CO2 Capture

This study presents the synthesis of pristine zinc and cobalt triazolate frameworks (ZnTF and CoTF) and their bimetallic core–shell architectures (ZnTF@CoTF, CoTF@ZnTF) for high-pressure CO2 capture. Utilizing 1,2,4-triazole linkers integrates uncoordinated, nitrogen-rich Lewis basic sites into the pores, enhancing CO2 binding without surface modifications. Crystallographic and computational analyses reveal that these materials adopt flexible cubic lattices capable of pressure-induced "breathing". High-pressure evaluations up to 40 bar demonstrate a striking inverse correlation between the baseline surface area and gas uptake. The CoTF@ZnTF architecture exhibited the lowest intrinsic low-temperature porosity (BET maximum of 18 cm3/g) but achieved the highest high-pressure CO2 capacity of 2.4 mmol/g. This indicates that strongly interacting CO2 molecules provide the thermodynamic energy to physically pry open the constrained lattice, effectively excluding N2. Conversely, the ZnTF@CoTF composite maximized thermodynamic separation, reaching a peak CO2/N2 selectivity of 7.8 with a CO2 uptake of 2.15 mmol/g. Ambient-pressure cyclic testing via QCM-D highlighted the stability advantages of this interfacial locking mechanism. While the pristine CoTF lost 13.4% of its capacity over ten humidity cycles, encapsulating the system within a robust ZnTF shell (ZnTF@CoTF) effectively shielded the vulnerable cobalt phase, retaining 98.0% of its hydrolytic capacity. Ultimately, engineering interfacial lattice mismatch in core–shell triazolate heterostructures successfully balances dynamic structural flexibility, localized Lewis basicity, and hydrolytic shielding, yielding highly durable solid physisorbents for scalable carbon mitigation.