Heavy metal ions (HMIs) pose a detrimental risk to human health and environment due to their higher toxicity [1]. Among those ions, both mercury and lead are the well-known toxic and relatively widespread water pollutants that could damage to the brain, heart, kidneys, lungs, and the immune system [2]. The electrochemical method as a promising and elegant technique has been widely used for trace detecting of HMIs due to the excellent sensitivity, low cost, short analysis time, and easy portability [3-4].

We fabricated a nanostructured nitrogen-doped hollow carbon spheres (N-HCSs), which was a kind of modified carbon nanomaterials and used in HMIs detection with enhanced performance for the first time. As-prepared N-HCSs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption and desorption analysis, X-ray photoelectron spectroscopy (XPS). Electrochemical properties of modified electrodes were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The operational parameters which have influence on the deposition and stripping of metal ions, such as supporting electrolytes, pH value, and deposition time were carefully studied. Under optimized conditions, the anodic stripping voltammetric performance toward HMIs were evaluated using square wave anodic stripping voltammetry (SWASV) analysis. The detailed study of the enhancing electrochemical response in stripping voltammetry for the individual and simultaneous detection of ultratrace Pb²⁺ and Hg²⁺ in drinking water was described. The detection limits achieved (15 nM and 2.35 nM for Pb²⁺ and Hg²⁺) are much lower than the guideline values in drinking water given by the World Health Organization (WHO)[5]. In addition, an interesting phenomenon of mutual interference between Pb²⁺ and Hg²⁺was observed. When the concentration of Pb is fixed, the sensitivity to Hg lowers a little and the response current of Pd doesn't change with the increasing concentration of Hg. Meanwhile, when the concentration of Hg is fixed, the sensitivity to Pb lowers a little and the response current of Hg does increase with the increasing concentration of Pb. This study provides a novel nitrogen-decorated hollow spheres carbon-based material for the construction of sensitive electrochemical sensors that meet the needs of environmental control.

References

[1] L. Wang, W. H. Xu, R. Yang, T. Zhou, D. Hou, X. Zheng, J. H. Liu, X. J. Huang, Anal. Chem.2013, 85, 3984.

[2] L. Zhou, W. Xiong, S. T. Liu, J. Mater. Sci.2015, 50, 769.

[3] W. Xiong, L. Zhou, S. T. Liu, Chem. Eng. J.2016, 284, 650.

[4] Q. Guan, W. Xiong, L. Zhou, S. T. Liu, Electroanalysis. DOI: 10.1002/elan.201500481.

[5] R. X. Xu, X. Y. Yu, C. Gao, Y. J. Jiang, D. D. Han, J. H. Liu, X. J. Huang, Anal. Chim. Acta. 2013, 790, 31.