Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)


Electrical Engineering and Computer Science

First Advisor

Qiquan Qiao


Electrochemical, Graphene oxide, Mercury, microflowers, silver nanowires, WS2


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.

Library of Congress Subject Headings

Mercury -- Toxicology.
Nanostructured materials.
Metal ions.
Electrochemical sensors.
Electrochemical analysis.
Drinking water -- Contamination.
Nanocomposites (Materials)



Number of Pages



South Dakota State University


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