Mechanochemical Synthesis and Ethylenediamine Functionalization of High-Entropy ZIFs for CO₂ Adsorption and Selectivity at Elevated Temperatures

Abstract

The development of efficient adsorbent materials for carbon dioxide (CO2) capture is essential for reducing greenhouse gas emissions. In this study, high-entropy zeolitic imidazolate frameworks (HE-ZIFs) were synthesized via a mechanochemical ball-milling approach, providing a solvent-free and scalable route. ZIF-8 (Z8) and bimetallic ZIF (BZ) were also prepared for comparison. The materials were functionalized with ethylenediamine (EDA) at different loadings (15, 30, and 45 wt%) to enhance CO2 adsorption and selectivity. Structural and textural analyses confirmed that moderate amine loading improves performance, while excessive loading leads to pore blockage. CO2 adsorption results showed enhanced uptake due to combined physisorption and chemisorption effects, with HZ-15EDA exhibiting the highest capacity (~0.81 mmol g-1). Selectivity analysis using mass spectrometry at 20 °C demonstrated superior CO2 removal (~69%) for HZ-15EDA, while elevated temperature (100 °C) resulted in reduced performance due to the exothermic nature of adsorption, though amine-functionalized samples maintained relatively high selectivity. Cyclic stability tests indicated good regenerability with minimal performance loss. Overall, mechanochemically synthesized HE-ZIFs with optimized amine functionalization show strong potential for efficient CO2 capture, particularly under elevated temperature conditions.