From layered structure to 8-fold interpenetrated MOF with enhanced selective adsorption of C2H2/CH4 and CO2/CH4

Abstract

Nature gas plays an important part in daily life and petrochemical industry, but it always coexists with impurities of considerable amount, which hinders full utilization of methane and thus makes its purification an urgent issue to be addressed. Herein, via solvothermal reaction of N,N′-bis(3-methylbenzoic acid-4-yl)-1,4,5,8-naphthalenetetracarboxydiimide (H2L) and cadmium cation, we obtained a layer structure of [Cd2(L)2(H2O)2]·4H2O (UPC-71) with sql/Shubnikov tetragonal plane net topology, where tiny pores are formed due to direct dense packing of layer by layer. After adding 1, 2-bis(4-pyridyl) ethane (BPEA) as ancillary ligand, a rare 8-fold interpenetrated framework, [Cd(L)(BPEA)]·4H2O (UPC-72), was obtained. Limited by their tiny pore volume, UPC-71 and UPC-72 both display somewhat small gas sorption capacities, but an obvious increase in the adsorption/separation performance can be observed in UPC-72 due to the effect of pore confinement strategy. In particular, the quantities of C2H2 and CO2 adsorbed are 1.54 and 0.83 ​mmol/g at ambient condition, and the IAST selectivities of C2H2/CH4 and CO2/CH4 are up to 20.1 and 4.7 for UPC-72. With the aid of GCMC simulation, we prove that there exist stronger binding interactions between C2H2 and CO2 with the active sites in UPC-72, and thus enhances the separation selectivity.