Tuning the Pore Architecture of HKUST-1 via PVP for Superior CH4 Capture

Efficient CH4 capture from low-concentration coal mine gas is of great significance. Metal–organic frameworks (MOFs) are promising adsorbents owing to their high porosity and structural tunability. Nevertheless, regulating the relationship between the MOFs structure and CH4 capture performance, as well as developing rational strategies to overcome the adsorption bottleneck of MOFs, remain critical challenges. Herein, we present the first systematic study on the effect of pore environment and adsorption sites on CH4 capture, employing archetypical MOFs incorporating diverse metal centers (Zr, Zn, Fe, Co, and Cu). Interestingly, HKUST-1(Cu), with a matched pore size and open-metal sites, exhibited the highest adsorption capacity. Furthermore, by leveraging polyvinylpyrrolidone(PVP)-assisted pore modulation, HKUST-1-Px exhibited concentration-dependent growth. At low PVP concentrations, it selectively modulates the growth kinetics of crystallographic facets through coordination and steric effects, whereas at high concentrations, excessive PVP preferentially forms a dense layer that stabilizes the crystal dimensions and promotes isotropic growth. Moreover, the CH4 adsorption capacity of HKUST-1-Pₓ follows an intriguing volcano-type trend with varying PVP content. Notably, HKUST-1-P0.4 affords the best adsorption performance—30% higher than that of HKUST-1. Grand Canonical Monte Carlo simulations reveal that the coordination between PVP and Cu nodes tactfully reconstructs the pore distribution of HKUST-1-Px and strengthens CH4 binding, as evidenced by the decrease in the adsorption energy of the CH4 molecule from -18.05 kJ/mol (HKUST-1) to -27.15 kJ/mol (HKUST-1-P0.4). This study provides experimental and theoretical insights to clarify the MOF structure–property relationships involved in CH4 capture, as well as innovative polymer-induced strategies for designing high-performance CH4-capture adsorbents for low-concentration coal mine gas.