Abstract
A low cost alternative to the electrochemical detection of methylene blue (MB) is demonstrated using a novel Ni–Fe/glassy carbon (GC) composite electrode. Ni-Fe microstructures were electrodeposited from a sulfate-boric acid electrolyte at a pH of 3 by a pulse galvanostatic method, and the morphology and composition was identified by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Deposition with the electrode rotation rate and duty cycle as variables were examined and both influenced the composition as well as morphology. For example, a 2 s deposition time and a 63 s relaxation time was Ni-rich, 84 wt% Ni, 16 wt% Fe, and the morphology of the microstructures had a circular shape with a central hole, attributed to gas evolution from the side reaction. The composition distribution had more iron at the edge and more nickel close to the center which may reflect a local pH change occurring during deposition. A longer duty cycle resulted in micro-sized deposits that included nano-cracks. A low duty cycle accompanied with rotation of the electrode resulted in no deposit, due to corrosion during of the off-time. Detection of MB was greatly enhanced with the Ni-Fe/GC composite electrode compared to GC alone. The MB concentration varied from 0.5 to 10 µM in a phosphate buffer solution (PBS). Voltammetry and chronoamperometry were used under conditions where a Ni-Fe surface oxide may be initially present. The limits of detection were investigated. When adsorption of MB is too high, then the current density is not sensitive to its concentration. Also, the reduction of the surface oxide on Ni-Fe can limit detection of MB. Therefore, voltammetry with high sweep rate and the chronoamperometry at short times is most sensitive to low concentrations of MB on the microstructured Ni-Fe nano-cluster/GC electrode.
Published Version
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