K⁺-Doped Cu-BTC Achieves Doubled CO₂ Adsorption Capacity and Unprecedented Cycle Stability via Atomic-Scale "Rivet" Architecture

Metal-organic frameworks (MOFs) show promise as high-efficiency CO₂ adsorbents due to their large surface areas, tunable pore structures, and chemical adaptability. However, practical applications face challenges including insufficient adsorption capacities and poor cyclic stability in certain MOF variants. This study investigates a potassium ion (K⁺) doping strategy to enhance the performance of copper-based MOF (Cu-BTC). The proposed approach leverages a "pinning effect" to modify material properties. Experimental results demonstrate that K-doped Cu-BTC with a K⁺ : Cu²⁺ molar ratio of 1:10 achieves a CO₂ adsorption capacity of 7.99 mmol g⁻¹ at 0 °C and 1 bar — a 111% improvement over undoped samples (3.78 mmol/g). The modified material maintains over 98% capacity retention after 10 adsorption-desorption cycles, indicating exceptional stability. Mechanistic analysis reveals that K⁺ ions (ionic radius: 1.38 Å) act as structural rivets at copper sites through strong ionic bonding. This configuration effectively prevents framework collapse caused by Cu-O bond rupture or interlayer slippage during cyclic operation. The substitution of high-valence Cu²⁺ with low-valence K⁺ creates localized charge imbalance, inducing an electron-pinning effect. This modification optimizes electron cloud density around adjacent copper nodes, enhancing electrostatic interactions with CO₂ quadrupole moments and improving adsorption affinity. This work provides both theoretical insights and practical methodologies for developing cost-effective, stable MOF-based adsorbents for carbon capture applications.