High Selectivity and Sensitivity in Chemiresistive Sensing of Co(II) Ions with Liquid-Phase Exfoliated Functionalized MoS2: A Supramolecular Approach

Chemical sensing of water contamination by heavy metal ions is key as it represents a most severe environmental problem. Liquid-phase exfoliated two-dimensional (2D) transition metal dichalcogenides (TMDs) are suitable candidates for chemical sensing thanks to their high surface-to-volume ratio, sensitivity, unique electrical characteristics, and scalability. However, TMDs lack selectivity due to nonspecific analyte-nanosheet interactions. To overcome this drawback, defect engineering enables controlled functionalization of 2D TMDs. Here, ultrasensitive and selective sensors of cobalt(II) ions via the covalent functionalization of defect-rich MoS2 flakes with a specific receptor, 2,2 ':6 ',2 ''-terpyridine-4 '-thiol is developed. A continuous network is assembled by healing of MoS2 sulfur vacancies in a tailored microfluidic approach, enabling high control over the assembly of thin and large hybrid films. The Co2+ cations complexation represents a powerful gauge for low concentrations of cationic species which can be best monitored in a chemiresisitive ion sensor, featuring a 1 pm limit of detection, sensing in a broad concentration range (1 pm - 1 mu m) and sensitivity as high as 0.308 +/- 0.010 lg([Co2+])(-1) combined with a high selectivity towards Co2+ over K+, Ca2+, Mn2+, Cu2+, Cr3+, and Fe3+ cations. This supramolecular approach based on highly specific recognition can be adapted for sensing other analytes through specific ad-hoc receptors.

Automated summary

Chemical sensing of water contamination by heavy metal ions is a severe environmental problem. Two-dimensional transition metal dichalcogenides (TMDs) show potential as chemical sensors due to their high surface-to-volume ratio and unique electrical characteristics, but lack selectivity. In this study, defect-rich MoS2 flakes were functionalized to develop ultrasensitive and selective sensors for cobalt(II) ions. Through a tailored microfluidic approach, a continuous network was formed by healing the sulfur vacancies in MoS2, enabling high control over the assembly of thin and large hybrid films. The developed sensor exhibited a low limit of detection, broad concentration range, and high selectivity towards Co2+ ions.