Catalyst-free synthesis of phenolic-resin-based carbon nanospheres for simultaneous electrochemical detection of Cu (II) and Hg (II)

In this study, monodisperse and uniform carbon nanospheres (CSs) were applied for the electrochemical detection of heavy metal ions. As-obtained CSs prepared without any template and catalyst mainly exhibited a diameter of similar to 485 nm. Colloidal spherical carbon precursors were spontaneously formed via effects of hydrogen bonding and electrostatic interactions at low concentrations. By the introduction of surfactant Octaphenyl polyoxyethyiene-30 (OP30), the particle size of CSs further decreased to 259 nm due to the formation of OP30 micelles, which prevent the aggregation of spherical colloidal clusters during polymerization. As-prepared CSs were characterized by scanning electron microscopy. Next, the obtained carbon samples were fabricated on a glassy carbon electrode (GCE), which exhibited excellent properties for the simultaneous electrochemical sensing of Cu2+ and Hg2+. The limits of detection for Cu2+ and Hg2+ were 4.5 nM and 12.5 nM (S/N = 3), respectively; these values are less than that of the given value by the World Health Organization. Notably, by the introduction of other metal ions, drastic changes in the limit detection of metal ions were observed. The individual detection performance (limit of detection of 9.8 nM and 30.3 nM for Cu2+ and Hg2+, respectively) was nearly twice as much as that observed by simultaneous detection. Clearly, the interference experiment results demonstrated that rather a slight change in the concentration of the additional ions leads to a drastic decrease in the limit of detection. This study may provide a new idea in terms of highly selective and sensitive electrochemical detection of heavy metal ions by the addition of a minor concentration of additional ions.