Conclusions
Using DFT, we explored geometries, predicted adsorption energies,
donor-acceptor natural orbitals were analyzed, and the nature of the
coordination of CO2, H2,
N2 and CH4 gas molecules on La-MPBCP and
[La-MPBCP]+3 complexes was studied with the help
of a NBO analysis. It is clear to note that by introducing the lanthanum
atom into the MPBCP structure, causes better contact area, so that the
gas molecules can be adsorbed. The La-MPBCP]+3complex is more reactive with Eg = 1.39 eV. The results reveal
that all gases are physically adsorbed with considerable adsorption
energy values. Based on their adsorption energies, it can be understood
that CO2 are strongly physisorbed on La-MPBCP or
[La-MPBCP]+3 systems. In contrast, the
H2 molecule is weakly physisorbed on both structures.
The NBO analysis shows the gas molecule acts as donor through the σ and
n interaction (O, N atoms and H-H, C-H) towards the lanthanum atom. Our
calculations have predicted that the La-MPBCP or
[La-MPBCP]+3 systems are a good candidates as a
biogas absorbing material and as a separator for
CO2/H2 mixtures.