Nitrogen-Containing Heterocyclic Aluminum-Based Metal-Organic Frameworks for Methane Adsorption and Separation

The adsorption and separation of CH₄ from coal-bed methane are both attractive and challenging. Here, we synthesize two nitrogen-containing heterocyclic aluminum-based metal-organic frameworks using a simple aqueous solvent reflux method for the selective separation of CH₄ and N₂. Adsorption experiments show that Al-PzDC exhibits a higher adsorption capacity and selectivity for CH₄ compared to Al-PyDC, achieving an adsorption capacity of 43.99 cm³/g at 273 K and 1 bar. Dynamic breakthrough experiments further confirm the excellent CH₄ and N₂ separation performance of Al-PzDC under practical conditions. More importantly, Al-PzDC shows good reusability, with no significant change in adsorption capacity after 10 consecutive adsorption-desorption cycles. Grand Canonical Monte Carlo simulations indicate that the nitrogen-rich Al-PzDC has a higher adsorption density and a wider adsorption range for CH₄. Density functional theory calculations show that Al-PzDC has a lower adsorption energy for CH₄, thus significantly improving its adsorption selectivity.