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.