Unusual metallic microporous boron nitride networks

Two metallic zeolite-like microporous BN crystals with all-sp² bonding networks are predicted from an unbiased structure search based on the particle-swarm optimization (PSO) algorithm in combination with first-principles density functional theory (DFT) calculations. The stabilities of both microporous structures are confirmed via the phonon spectrum analysis and Born-Oppenheimer molecular dynamics simulations with temperature control at 1000 K. The unusual metallicity for the microporous BN allotropes stems from the delocalized p electrons along the axial direction of the micropores. Both microporous BN structures entail large surface areas, ranging from 3200 to 3400 m²/g. Moreover, the microporous BN structures show a preference toward organic molecule adsorption (e.g., the computed adsorption energy for CH₃CH₂OH is much more negative than that of H ₂O). This preferential adsorption can be exploited for water cleaning, as demonstrated recently using porous boron BN nanosheets (Nat. Commun. 2013, 4, 1777).