Unusual Reactivity of Graphene Quantum Dot-Wrapped Silver Nanoparticles with Hg(II): Spontaneous Growth of Hg Flowers and Their Electrocatalytic Activity

Abstract

The galvanic reaction (GR) between a graphene quantum dot (GQD)-stabilized AgNP (Ag-GQD)-modified glassy carbon (GC) surface and Hg­(II) leads to complete dissolution of AgNPs within 15 min and subsequent growth of Hg(0) as a “flower” on the GQD surface. This is unusual because generally the GR of bulk Ag/AgNPs with Hg­(II) leads to the formation of a Hg–Ag amalgam/core shell structure. The appearance of peaks at 99.9 and 103.9 eV in X-ray photoelectron spectroscopy confirms Hg(0) on GQDs, whereas the disappearance of a peak at 370 eV indicates complete dissolution of Ag(0). When 200 ppm Hg­(II) interacts with Ag-GQDs for 10 min, coalescence of AgNPs takes place along with the formation of Hg(0) petals separately. However, Hg(0) is grown as a flower with 2 μm size, and complete dissolution of AgNPs occurs subsequently after 15 min. The reason for anti-amalgamation is the direct deposition of Hg(0) by the available oxygen functional groups, followed by its strong adsorption on the graphene surface of GQDs. The subsequent growth of Hg(0) as a flower is due to the GR between AgNPs and Hg­(II). Interestingly, the Hg flower-GQD-modified GC electrode acts as a good electrocatalyst toward H2O2 reduction by decreasing its overpotential by 150 mV in contrast to GC/Ag-GQDs.

Probing the Interaction of Heavy and Transition Metal Ions with Silver Nanoparticles Decorated on Graphene Quantum Dots by Spectroscopic and Microscopic Methods

“…For example, apart from the formation of a Ag−Hg amalgam, a complete replacement of Hg 2+ with Ag 0 was noticed when a GQD-capped AgNP-coated glassy carbon surface interacted with Hg 2+ . 24 Taking this combined effect of oxygen functional groups and graphene surface into account, we focus on the interaction of transition and heavy metal ions with the colloidal solution of AgNPs stabilized by GQDs (AgGQDs) and how the morphology of AgNPs varies after the injection of each metal ion into the solution phase. One may expect that the interaction of Hg 2+ with AgGQDs may result in amalgamation, whereas the interaction of other metal ions leads to the aggregation of AgNPs.…”

“…In a similar way, certain anomalous interactions between GQD-stabilized AgNPs and metal ions are to be expected. For example, apart from the formation of a Ag–Hg amalgam, a complete replacement of Hg 2+ with Ag 0 was noticed when a GQD-capped AgNP-coated glassy carbon surface interacted with Hg 2+ . Taking this combined effect of oxygen functional groups and graphene surface into account, we focus on the interaction of transition and heavy metal ions with the colloidal solution of AgNPs stabilized by GQDs (AgGQDs) and how the morphology of AgNPs varies after the injection of each metal ion into the solution phase.…”