Interwoven Architectural Complexity in Ni(II) Ion-Based 3D MOF Using Bipyridine and Tetrabenzenecarboxylic Acid: Adsorption Insights in Highly Efficient Iodine and Cationic Dye Capture

Abstract

In this study, the 1,2,4,5-benzene tetracarboxylic acid (H₄btc) linker, 4,4′-bipyridine (4,4′-bipy) auxiliary ligand, and nickel nitrate salt were used to synthesize a Ni-loaded metal–organic framework (AR-1) hydrothermally. Various techniques were employed to characterize AR-1, including elemental analysis, single crystal X-ray diffraction (SCXRD), Fourier transform infrared (FTIR) spectroscopy, and powder X-ray diffraction (PXRD) investigations. According to single-crystal X-ray data, the AR-1 exhibits a three-dimensional framework constructed from propagating secondary building units (SBUs) containing [Ni(btc)_0.5(4,4′-bipy)H₂O]·H₂O. Furthermore, water molecules in the lattice provide extra stability to the present MOF via hydrogen bonding interactions. Interestingly, the AR-1 displays efficient, reversible iodine adsorption in the vapor (maximum adsorption capacity 580 mg g^–1) and solution phase. The high absorption of ¹²⁷I is caused by the physisorption and chemisorption attraction, creating a strong interaction with the conjugated π-electron-rich aromatic system from both ligands. Along with these interactions, free carbonyl oxygen also exhibits chemical interaction. Specifically, Ni-MOF has excellent water resistance and pH stability. Furthermore, dye adsorption studies showed that AR-1 can adsorb cationic dyes (Methylene blue) in an aqueous solution with a higher rate and selectivity than the neutral dye (Martius yellow) but not anionic dyes (Cango red). And, even after multiple cycles, the MOF retains its adsorption ability. The outcome is that the AR-1 has improved ¹²⁷I absorption and efficient cationic dye adsorption. This work sheds light on the potential of three-dimensional (3D) Ni-MOF as dual-functional adsorbents capable of addressing complex contamination scenarios involving radioactive and organic pollutants. The insights gained from this study provide a foundation for further optimization of MOF-based materials to tackle the challenges associated with water pollution and hazardous substance removal.