Structural modified metal-organic frameworks by hierarchical layer-by-layer method for efficient CO2 capture enhancement

The emission of CO2 has attracted a plenty of concerns owing to its hazardous influence on the climate. In this study, the strategy for structural modification of metal-organic frameworks (MOF) by hierarchical layer-by-layer method is proposed to improve the CO2 capture performance using polyethylenimine-grafted SBA-15 (PEI/SBA) as a substrate. The growth procedure of hierarchical layer-by-layer framework based on HKUST-1 (HLF) was investigated based on the substrate role of PEI/SBA, serving as epitaxial growth sites of the original MOF (HKUST-1) due to the strong coordination interactions between PEI groups and Cu2+ ions. As varying the PEI loading (20, 40, and 60 wt% corresponding to HLF-1, 2, and 3, respectively), the HLFs present superior CO2 adsorption capacity at 25 ℃ and 1 bar, showing the maximum enhancement of 29.2% (4.20 mmol/g at the HLF-2) compared with HKUST-1. The result of CO2 adsorption experiment under post-combustion conditions for the optimal adsorbent (HLF-2) suggests its sufficient feasibility for industrial applications. The structural analysis of HLFs suggests an amelioration in the mass diffusion of CO2 molecules toward the active sites. The isosteric heats of CO2 adsorption for HLFs exhibit an increase compared with that of HKUST-1, indicating the strong interactive affinity toward CO2. The optimal adsorbent confirms stable reusability for 10 cycles under relatively low temperature in the CO2 desorption, suggesting the feasibility of exploiting renewable energy for desorption thermal energy. Abovementioned results can carve out a way to efficiently achieve the carbon neutrality by improving the performance of CO2 adsorbents.