Pore Chemical Modification of Bimetallic Coordination Networks for Coal-Bed Methane Purification under Humid Conditions

The recycling of low-concentration coal-bed methane (CBM) is environmentally beneficial and plays a crucial role in optimizing the energy mix. In this work, we present a strategy involving pore chemical modification to synthesize a series of bimetallic diamond coordination networks, namely CuIn(ina)₄, CuIn(3-ain)₄, and CuIn(3-Fina)₄ (where ina = isonicotinic acid, 3-ain = 3-amino-isonicotinic acid, and 3-Fina = 3-fluoroisonicotinic acid). Among these, the amino-functionalized CuIn(3-ain)₄ exhibits excellent CH₄ adsorption capacity (1.71 mmol g^–1) and CH₄/N₂ selectivity (7.5) due to its optimal pore size and chemical environment, establishing it as a new benchmark material for CBM separation. Dynamic breakthrough experiments confirm the exceptional CH₄/N₂ separation performance of CuIn(3-ain)₄. Notably, CuIn(3-ain)₄ demonstrates excellent stability under wet conditions and maintains outstanding separation performance even in high-humidity environments. Additionally, theoretical simulations provide valuable insights into how selective adsorption performance can be fine-tuned by manipulating the pore size and geometry. Regeneration tests and cycling evaluations further underscore the remarkable potential of CuIn(3-ain)₄ as a highly efficient adsorbent for the separation of CBM.