A robust two–dimensional layered metal–organic framework for efficient separation of methane from nitrogen

Abstract

Selective capture and separation of methane (CH4) from nitrogen (N2) is a feasible approach to mitigate the effects of global warming and to improve the heating value of low-quality natural gas. However, the efficient separation of CH4/N2 is a challenge issue since their very close kinetic diameters and thermodynamic properties. In this work, a new type of two-dimensional (2D) layered metal–organic framework (MOF) with permanent rhomboid pore channels, denoted as Ni(4-DPDS)2CrO4, (4-DPDS = 4,4′-dipyridyldisulfide) was synthesized for the first time and used for CH4/N2 separation. This novel 2D MOF not only performs high stability as outstanding as or even better than previously reported 3D MOFs but also exhibits a relatively high CH4 adsorption capacity of 0.95 mmol/g. Ni(4-DPDS)2CrO4 has a high affinity towards CH4 with the highest reported Qst value of 28.4 kJ/mol as well as a high CH4/N2 selectivity of 7.3, which is comparable to the state-of-the-art MOF materials reported so far. DFT calculations revealed the energy favorable binding sites for methane molecules are located in the middle of the cavity decorated with CrO42- anion. Such an angular inorganic anion provides polar sites and makes guest–host interactions in close proximity, affording tight binding affinity. Breakthrough experiments and regenerability tests suggest it is a promising material in natural gas purification.