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.

染料是一类可对地球环境与生命造成危害的危险化学品，然而实现染料的高效去除仍是一项极具挑战性的研究课题。在此，我们以(4,4'-((((1,3,4-噻二唑-2,5-二基)二硫代亚甲基))二苯甲酸)、2,2'-联吡啶（2,2'-bipyridine，缩写bpy）与二水合氯化铜为原料，通过溶剂热法合成了一种新型金属有机胶囊（metal-organic capsule）{[Cu(L)(bpy)(H₂O)]·H₂O}_n（化合物1）。有趣的是，两个反演不对称单元通过O-H···O与O-H···N氢键相互作用连接，形成具有空腔的中心对称型胶囊结构。借助CrystalExplorer 17.5软件，我们对分子间相互作用进行了定量分析与可视化展示。值得注意的是，化合物1可高效吸附亚甲基蓝（methylene blue，MB），且其吸附性能与MB浓度呈线性相关关系。当MB浓度从10 mg·L⁻¹提升至50 mg·L⁻¹时，化合物1的吸附量从17.68 mg·g⁻¹增至66.79 mg·g⁻¹，而MB去除率则从88.4%降至66.4%。该吸附过程符合准二级动力学模型与朗缪尔吸附等温模型。此外，化合物1至少可循环使用5次，展现出优异的循环稳定性与结构稳定性。