Two Novel Nitrogen-rich Metal-organic Nanotubes: Syntheses, Structures and Selective Adsorption toward Rare Earth
The construction and potential application development of metal-organic nanotubes (MONTs) with the nanoscale interior channel diameters is of great interest. An angular nitrogen-rich ligand, 3,6-bis(2-ethylimidazole)-2-methylpyrimidine (beim-CH3), was designed to construct MONTs by coupling with the V-shaped carboxylate ligands of benzophenone 4,4'-dicarboxylic acid (H2bpndc) and 4,4'-oxybisbenzoic acid (H2obba). Two new MONTs are named as NCD-166 ([Zn(bpndc)(beim-CH3)]·H2O) and NCD-167 ([Zn(obba)(beim-CH3)]·H2O), and they are isostructural and have almost identical tube inner diameters of about 1.76 nm. Benefiting from abundant exposed nitrogen and oxygen atoms in their tube walls and open nanoporous channels, they display superior adsorption capacities for Eu3+ (150.90 mg g-1) and high adsorption selectivity (> 96%) in the low-concentration solutions. Additionally, it was revealed that the adsorption effect of ether oxygen on rare earth was significantly better than that of carbonyl oxygen. The adsorption isotherm conforms Langmuir model and the adsorption kinetic obeys pseudo-second-order model. These results clearly indicate that such novel MONTs are favorable sorbents for REEs.
