Mixed-ligand Cd(II) coordination polymers for efficient photocatalytic degradation of metronidazole

The overuse and improper disposal of important chemicals such as biomolecules, antibiotics, and pesticides have become serious global problems, creating an urgent need for simple and effective methods to remove them quickly from the environment. To address this issue, two mixed-ligand Cd(II) coordination polymers (CPs), {[Cd(H₃L)(bb)₂]_n} (1) and {[Cd₅(L)₂(Bid)₃(H₂O)₄]·4H₂O}_n (2), incorporating the multicarboxylate ligand H₅L (H₅L = 3,5-di(2',4'-dicarboxylphenyl)benzoic acid) and the N-donor linkers bb (bb = 4-(1H-imidazol-1-yl)-4'-bromo-biphenyl) and Bid (Bid = 1,4-bis(1-imidazolyl)-2,5-dimethylbenzene), were constructed under solvothermal conditions. Detailed structural and physicochemical characterization was carried out using FT-IR, PXRD, TGA, UV-vis spectroscopy, and single-crystal X-ray diffraction. CP 1 demonstrates excellent photocatalytic activity toward the UV-induced degradation of the antibiotic metronidazole (MDZ), achieving 95.32% degradation within 60 min. Radical-trapping experiments confirm that superoxide radicals (˙O₂^-) are the predominant reactive species involved in the degradation mechanism. Overall, these results suggest that structurally adaptable Cd(II) coordination polymers are promising photocatalysts for the removal of emerging pharmaceutical pollutants from aqueous environments.