Improving CH4/N2 selectivity within isomeric Al‐based MOFs for the highly selective capture of coal‐mine methane

Selectively separating CH4 from N2 in coal‐mine methane is significantly important in the chemical industry, but challenging and energy‐intensive. Using porous materials as adsorbents can separate CH4/N2 mixtures with low energy consumption, but most adsorbents encounter the problem of poor separation selectivity. Here, we propose a strategy for improving CH4/N2 selectivity by controlling pore wall environment in two isomeric Al‐based metal–organic frameworks (MOFs) with four highly symmetric polar sites for strengthened adsorption affinity toward CH4 over N2. At 298 K and 100 kPa, CAU‐21‐BPDC with four highly symmetric polar sites in the pore walls exhibits 2.4 times higher CH4/N2 selectivity than CAU‐8‐BPDC without four highly symmetric polar sites. Gas adsorption isotherms, CH4/N2 selectivity calculations, Qst of CH4, interaction energy calculations, adsorption density distributions of CH4 and N2, and breakthrough curves reveal that CAU‐21‐BPDC is a potential candidate for selective capture coal‐mine methane.