Theoretical Study Of B₄₀ Fullerene As A Highly Sensitive Molecular Device For NH₃ Detection And For CO₂ Storage

After the discovery of C₆₀ fullerene, it took almost two decades for the possibility of boron-based fullerene structures to be considered. Before 2014, there has been no experimental evidence for these nanostructures, in spite of the progress made in theoretical investigations of their structure and bonding. In 2014, Zhai et al.[1] reported the first experimental observation of an all-boron fullerene-like cage cluster B₄₀-, whose neutral counterpart B₄₀ shows high symmetry（D2d symmetry） and is determined as the most stable structure among the B₄₀ allotropes. Small boron fullerene like B₄₀ has higher surface/volume ratio, and the adsorption sites are greatly reduced compared with B80 and B100, making it valuable and simple in adsorption, storage, separation and detection of gas molecules. The adsorption of small molecules（NH3, N2, H2 and CH4） on all-boron fullerene B₄₀ is investigated by density functional theory（DFT） and non-equilibrium green’s function（NEGF） for its potential application in the field of single molecular gas sensors. The high adsorption energies of NH3 on different adsorption sites of B₄₀ surface indicate that NH3 strongly chemisorbs to B₄₀. The charge transfer induced by the NH3 adsorption results in a modification of the density of states（DOS） of B₄₀ near the Fermi level, and therefore, changes its electronic transport properties. For all possible adsorption sites, the adsorption of NH3 exclusively leads to a decrease of the conductance of B₄₀. Taking into consideration that the non-polar gas molecules（e.g. N2, H2 and CH4） are only physisorbed and show negligible effect on the conductance properties of B₄₀, we would expect that B₄₀ can be used as a single molecular gas sensor to distinguish NH3 out of the non-polar gas molecules at low bias. Novel nanomaterials are promising for capture, storage and separation of CO2. By density functional calculations, we find that the newly discovered B₄₀ fullerene is a suitable candidate. CO2 forms stable chemisorptions with B₄₀ on specific sites of surface, which is validated by the high adsorption energy, large charge transfer, and kinetic feasibility for B₄₀（CO2） complexes. Due to the strong chemisorption and high surface/volume ratio, B₄₀ shows considerable adsorption capacity for CO2. In addition, B₄₀ fullerene shows good selectivity for CO2 and is efficient in separating it from gas mixtures like CO2/N2, CO2/H2, and CO2/CH4. In addition, with the aid of Monte Carlo simulations, we explored the guest-host interaction mechanism between CO2 and the MIL-68（In）.