Structural diversity of three new Co(ii)-based MOFs as a UV light-driven photocatalyst: photocatalytic performance

Abstract

The incremental use of herbicides is now posing a pollution problem in aquatic systems. Therefore, it is necessary to decompose this class of harmful components existing in wastewater. Metal–organic frameworks (MOFs) are a peculiar class of multidimensional materials that can be employed as a photocatalyst to decompose pesticides present in the wastewater discharged. For this we have synthesized three high-stability Co(II)-based metal organic frameworks (MOFs) [Co(H₂L)(bb)·DMF]_n (1), [Co(L)_0.5(bb)]_n (2), and [NH₂(CH₃)₂][Co₂(μ₃-OH)(L)(bb)] (3), where H₄L = 5,5′-(1,2-phenylenebis(methyleneoxy)diisophthalic acid and bb = 4,4′-bis(imidazolyl)biphenyl. These MOFs are characterized by thermal analyses and single-crystal X-ray diffraction. 1 features a new 3D, 2-nodal 4,4-connected network with a Schläfli symbol of (4⁴·6²). 2 displays a 3D, 4,4-c network, with a Schläfli symbol (6⁴·8²). 3 shows a 3D two nodal (3,8) connected net with a Schläfli symbol (4³)₂(4⁶·6¹⁸·8⁴). 1–3 are semiconducting in nature with E_g of 3.31 eV, 2.95 eV, and 3.25 eV, respectively. These three MOFs show high catalytic activities for the degradation of different pesticides, including four common pesticides thiabendazole (TBZ), dinotefuran (DTF), metamitron (MMT), and ciprofloxacin (CIP) in an aqueous solution. TBZ shows photocatalytic degradation by the synthesized MOF, which demonstrated 89% degradation. Moreover, the possible photodegradation mechanism was proposed and explored by a radical tapping experiment. The Hirshfeld surfaces study demonstrated that these synthesized coordination polymers contain various forms of intermolecular contacts (C⋯C, H⋯C, H⋯H, and O⋯H).