Two-Dimensional Nanomaterials and Their Composites for Electrochemical Detection of Toxic Mercury Ions in Water

The presence of trace amounts of mercury ion (Hg2+) in drinking water has a detrimental effect on human health. The development of an electrochemical sensor for Hg2+ detection is still challenging to obtain ultra-trace sensitivity, excellent selectivity, wide Linear Detection Ranges (LDRs), and ultra-low detection limit. This work presents an electrochemical sensor based on two-dimensional nanomaterials and their composites for the enhanced sensing of Hg2+ in water. Graphene oxide (GO)-silver nanowires (AgNWs) composite and metallic 1T phase tungsten disulfide (WS2) microflowers were utilized for the fabrication of electrochemical sensors using drop-casting. Under the optimized experimental conditions, the GO-AgNWs composite modified sensor showed a high sensitivity of ~ 0.29 μA/nM and linear response in the range of 1-70 nM toward Hg2+, whereas 1T-WS2 microflowers modified sensor showed excellent sensitivities of ~ 15.9 μA/μM, 2.54 μA/μM, 13.84 μA/μM, and 0.04646 μA/μM toward Hg2+ with LDRs of 1- 90 nM, 0.1-0.4 μM, 0.5-1.0 μM, and 0.1-1.0 mM, respectively. An ultra-low detection limit of 0.1 nM and 0.0798 nM or 79.8 pM toward Hg2+ was obtained by GO-AgNWs composite and 1T-WS2 modified sensors, which are well below the guideline value recommended by the World Health Organization and the United States Environmental Protection Agency. The sensors exhibited excellent selectivity for Hg2+ against other heavy metal ions including Cu2+, Fe3+, Ni2+, Pb2+, Cr3+, K+, Na+, Ag+, Sn2+, and Cd2+. The thus obtained excellent sensitivity and selectivity with wide LDRs and ultra-low detection limits can be attributed to the synergistic effect of GO and conductive AgNWs, high conductivity, large surface area microflower structured 1T-WS2, and the complexation of Hg2+ ions with sulfur (S2-) and GO. In addition to good repeatability, reproducibility, and stability, these sensors showed practical feasibility of Hg2+ detection in tap water suggesting a promising device for real applications