Fluorine-Functionalized Zr-Based Metal-Organic Framework for One-Step Methane Purification from Natural Gas

Natural gas, as a clean energy source, requires the elimination of co-occurring impurities such as C2H6 and C3H8 to enhance its energy utilization efficiency. Herein, by using a Zr-based MOF as a platform, we fabricated an isostructural pair, NU-1400(-H) and fluorine-functionalized NU-1400(-F), through rational ligand fluorination, and systematically investigated their adsorption and separation performances toward CH4, C2H6 and C3H8. This isostructural pair allows the effect of fluorine functionalization on the pore microenvironment and adsorption affinity to be directly evaluated. Single-component adsorption isotherms reveal that fluorine functionalization significantly improves the uptake capacities of C2H6 and C3H8 (from 25.4/28.8 to 34.1/38.9 cm3 g-1), while causing only marginal changes in CH4 adsorption. Isosteric heat of adsorption (Qst) analysis confirms that NU-1400(-F) exhibits weakened affinity for CH4 (19.2 kJ mol-1) and remarkably enhanced interaction with C3H8 (47.3 kJ mol-1). Benefiting from such optimized differences in adsorption affinity, NU-1400(-F) achieves excellent IAST selectivity of 516 for C3H8/CH4 and 21 for C2H6/CH4, which are far higher than those of pristine NU-1400(-H) (145 and 18). Dynamic breakthrough experiments and cyclic regeneration tests further validate its reliable separation capability and outstanding recyclability. The rational fluorine functionalization effectively tailors the pore microenvironment for selective heavy-hydrocarbon adsorption, making NU-1400(-F) a promising adsorbent for one-step methane purification from natural gas. This work thus highlights a practical pore-microenvironment engineering strategy via ligand fluorination for efficient light hydrocarbon/CH4 separation.