Lanthanide (III) Metal-Organic Frameworks: Syntheses, Structures and Supercapacitor Application

Three new lanthanide-MOFs, [(TATMB)₂Ce₂⋅3DMSO-H₂O]⋅7H₂O (MOF−Ce), [(TATMB)₂Pr₂⋅4DMSO]⋅7H₂O⋅DMF (MOF−Pr) and [(TATMB)₂Nd₂⋅3DMSO⋅H₂O]⋅6H₂O (MOF−Nd) were synthesized by the reaction of hydrated lanthanide salts and 3,3′,3′′-((1,3,5-triazine-2,4,6-triyl)tris(azanediyl))tribenzoic acid (H₃TATMB) under solvothermal reaction condition. All MOFs were characterized by standard instrumentation techniques, for example, FT-IR spectroscopy, elemental analysis, etc. The solid-state structures were determined by single-crystal X-ray diffraction analyses. It revealed that all MOFs formed two-dimensional frameworks by the coordination assisted pathway of ligand molecules and lanthanide(III) ions. All MOFs were investigated as supercapacitor electrode material by using the conventional three-electrode method by using TEABF₄ in acetonitrile as electrolyte. It was observed that MOF−Ce exhibited a maximum specific capacitance of 572 Fg⁻¹ at a current density of 1 A g⁻¹ among all three MOFs. The specific capacitance retention of the material was found to be 81% after successful completion of 5000 charging-discharging cycles. To the best of our knowledge, the specific capacitance of MOF−Ce is highest reported for lanthanide MOFs without any redox-active additive until now. Moreover, for the first time, MOF−Ce has been used to fabricate a device, which exhibited significant responses for various LED lights and showed a maximum specific capacitance of 88 Fg⁻¹ at a current density of 2 A g⁻¹.