A Sulfur-Containing Capsule-Based Metal-Organic electrochemical sensor for Super-Sensitive capture and detection of multiple Heavy-Metal ions

Development of an effective way for super-sensitive capture and sensing of heavy metal ions (HMIs) is a great challenge because they are extremely toxic to public health and environment. Herein, a new sulfur-containing nano-capsule-based electrochemical metal–organic framework (MOF) sensor [Co2(TMC4R)(1,4-BDC)2(μ2-H2O)]·3DMF·CH3OH·5CH3CN·H2O (Co-TMC4R-BDC) was designed for capture and detection of HMIs in aqueous solutions (TMC4R = tetra(4-mercaptopyridine)calix[4]resorcinarene, 1,4-BDC = 1,4-benzenedicarboxylic acid and DMF = N,N’-dimethylformamide). Remarkably, the designed MOF sensors exhibited excellent capture and detection performances for HMIs under the optimal experimental condition. The wide linear ranges of 0.05–12.0, 0.05–13.0, 0.1–17.0 and 0.75–18.0 μM are obtained for Cu2+, Pb2+, Cd2+ and Hg2+, respectively. The corresponding limit of detection (LOD) values are 13, 11, 26, and 18 nM, respectively. Particularly, the LOD values for Cu2+, Pb2+ and Cd2+ are lower than the standard drinking water ones from the World Health Organization. X-ray photoelectron spectroscopy (XPS) confirmed that the exposed S atoms of the nano-capsule units effectively captured HMIs through the complexation between S atoms and HMIs. Further, density functional theory (DFT) calculations indicated the presence of cation···π interactions between phenyl rings and HMIs. Thereby, the synergistic effects accomplished the effective capture and sensitive detection of HMIs. This work provides a feasible strategy for the capture and electrochemical detection of HMIs in an aqueous solution with the sulfur-containing MOF sensors.