Introduction
Adsorption and gas separations are two important topics in the chemical, environmental, medical and electronic gas industries applications.1-6 Many studies have been performed to improve the chemical activity of different materials for adsorber and separate gases. The technologies of gas separation include cryogenic separation, absorption/adsorption separation, supersonic separation, and membrane separation. 7-9 Researchers have developed strategies to design materials to separate gas mixtures. Most of the materials used are membranes,10polymers,11 zeolites,12carbons,13 and metal-organic frameworks (MOFs).14
The biogas is an effective, clean and renewable energy resource. It is obtained by process of organic matter.15-21 The biogas is composed mostly of CH4 and CO2, with traces of N2, H2, H2S, and other gases.22 The separation of CO2 and CH4 from biogas would enable using it for various chemicals processes. Several authors investigated materials as Co-MOF,23 Cu-BTC,24MIL-53,25 UTSA-16,26MOFs,27 Cu-MOF,28Cu-TDPAT,29 and others30 for CO2/CH4 separations. Most of the studies investigate the biogas purification (CO2/CH4) as mentioned above. Interesting to highlight that reports of CO2/H2 separation are scarce. Soonchul Kwon, et al. investigated competitive CO2 and H2 adsorption on carbon allotropes such as graphene, which has only hexagonal rings, and graphyne. They found, graphyne provides high CO2 selectivity for gas mixtures.31 In 2017 Zhou et al . investigated the theoretical simulation of CH4 separation from H2 in metal−organic frameworks CAU-17.32 Another research group reported that metal-organic frameworks containing strongly adsorbing sites are excellent candidates for CO2/H2separations.33 Previous reports showed that porous graphene membrane showed high selectivity of H2 by DFT calculation, over several other gas molecules that often accompany H2 in industrial steam methane reforming or dehydrogenation of alkanes (such as N2, CO, and CH4).34 Studies in this direction, Arjmandi et al . have investigated the adsorption properties of H2 and CO2 on the organic MOF-5ligand. Their results revealed that ZnO-doped system has higher adsorption energy values than those for the pristine MOF.35Recently, the graphydine like membrane was studied for separate a mixture of hydrogen (H2) and carbon dioxide (CO2) gases by density functional theory. The results showed that the selectivity of H2/CO2 is increased from 70 to 100% in the presence of 1,3,5 three amine benzene.36
Synthesis and characterization of ortho-phenylene-bridged cyclic trimeric oligopyrrole has recently been reported. These molecules have cavities with electron donating atoms.37-38 Motivated by the promising properties of these materials, “MPBCP” (meta-phenylene-bridged cyclic pyrrole) was designed, to study the ability to adsorb molecules from biogas. We investigate the effect of coordinating the “MPBCP” with a lanthanum atom with neutral and +3 charge. The lanthanum systems were studied for adsorption of biogas molecules. Theoretical computations have been conducted to open up opportunities for design of materials for capture and sensing biogas.