Title
Study on the interactions between graphene quantum dots and Hg(II): Unraveling the origin of photoluminescence quenching of graphene quantum dots by Hg(II)
Year
2020
Journal
Colloids and Surfaces A: Physicochemical and Engineering Aspects
Abstract
The present investigation reveals that when Hg(II) interacts with the colloidal solution of graphene quantum dots (GQDs), initially it forms complex with GQDs and then reduces to Hg(0) and Hg(I) resulting the complete quenching of GQDs blue luminescence. This is in contradiction with the earlier reports in which the quenching of GQDs by Hg(II) is attributed to complexation alone. In order to understand the reasons for the quenching of GQDs by Hg(II), a detailed study was undertaken by varying the pH of GQDs solution, incubation time and concentration of Hg(II). The emission studies indicate that formation of Hg(0) is less favorable at pH 7 whereas its formation is more favorable at pH 13. It is assumed that the formation of Hg(OH)2 in alkaline pH facilitates Hg(II) reduction easier than at neutral pH. The SEM and TEM images confirm the presence of spherical Hg(0) particles with different sizes depending upon Hg(II) concentration, pH and incubation time. The results obtained from emission, XPS and differential pulse voltammetry (DPV) studies reveal that Hg(II) was reduced to Hg(0) via Hg(I) on GQDs surface. The differential pulse voltammogram of 40 min incubated Hg(II)-GQDs coated GC electrode shows three oxidation peaks at 0.34, 0.48 and 0.65 V, corresponding to Hg(I) to Hg(II) and Hg(0) to Hg (II), respectively
Instrument
V-750, FP-8500
Keywords
Absorption, Fluorescence, Quenching, Chemical stability, Coordination chemistry, Kinetics, Nanostructures, Materials