Manganese oxide nanoflakes/multi-walled carbon nanotubes/chitosan nanocomposite modified glassy carbon electrode as a novel electrochemical sensor for chromium (III) detection

• CNTs/chitosan/GC electrode used as platform for electrodeposition of MnOx-nanoflakes.
• Modified electrode has excellent catalytic activity for oxidation of Cr3+ at pH 3–7.
• Detection limit and sensitivity of sensor for Cr3+ detection were 0.3 μM and 18.7 nA/μM.
• Sensor has good stability and high selectivity in the presence of common interferences.
• Sensor applied for the detection of Cr3+in real samples with satisfactory results.

In this research a nanocomposite containing chitosan (Chit) and maltiwalled carbon nanotubes (MWCNTs) was applied as platform for immobilization of electrodeposited manganese oxide (MnOx) nanostructures. First, glassy carbon (GC) electrode modified with thin film of Chitosan/MWCNTs nanocomposite. Then MnOx nanostructures was electrodeposited onto Chitosan/MWCNTs modified GC electrode using combination of constant potential step (0.6 V) and cyclic voltammetry(0.3–0.6 V) techniques. The XRD patterns and scanning electron microscope images indicated immobilization of uniformly MnOx nanoflakes with high crystallite onto MWCNTs/Chit film. The modified electrode shows a well-defined redox couple for Mn2+/MnO2 system. Charge transfer coefficient (α), electron transfer rate constant (ks) and surface concentration (Γ) were 0.394, 3.44 s−1 and 3.3 × 10−11 mol cm−2, respectively. The modified electrode showed excellent electrocatalytic activity toward oxidation of chromium (III) at natural pH solutions. Cyclic voltammetry and hydrodynamic amperometery were applied as measuring techniques for chromium detection. Detection limit, sensitivity and linear concentration range of the sensor were, 0.3 (μM), 18.7 nAμ M−1 and 3 μM to 200 μM, respectively. Moreover, the sensor retained about 90% of its original response toward Cr(III) after storage three months in ambient condition. Furthermore, the sensor response toward different common interferences was negligible. Finally, the developed sensor was applied for the detection of Cr(III) in real samples with satisfactory results.

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