A metal-organic capsule self-assembled by hydrogen bonds for adsorption of methylene blue

Dyes are a class of hazardous chemicals that can cause harm to the environment and life on earth. However, it remains a huge challenge for the effective removal of the dyes. Herein, a new metal-organic capsule {[Cu(L)(bpy)(H₂O)]·H₂O}_n (<b>1</b>) was synthesised by (4,4’-(((1,3,4-thiadiazole-2,5-diyl)bis(sulfanediyl))bis (methylene)) dibenzoic acid, 2,2’-bipyridine and CuCl₂∙2 H₂O under solvothermal condition. Interestingly, two inversion asymmetric units are connected by O-H···O and O-H···N to form a centrosymmetric capsule with cavity. The intermolecular interactions were further quantitatively analysed and visualised by the CrystalExplorer 17.5. Notably, complex <b>1</b> can effectively adsorb methylene blue (MB), and the adsorption performance is linearly correlated with MB concentration. When the concentration of MB was increased from 10 to 50 mg∙L⁻¹, the adsorption performance of <b>1</b> was increased from 17.68 to 66.79 mg∙g⁻¹, while reduced the MB removal efficiency from 88.4% to 66.4%. The adsorption process is suitable for the pseudo-second-order and the Langmuir model. Furthermore, complex <b>1</b> showed the good recyclability and stability for at least five runs.