Morphology of ZnO nanoparticles bound to carbon nanotubes affects electrocatalytic oxidation of phenolic compounds

The electrocatalytic activity of ZnO nanoparticles attached to carboxylic acid functionalized multi-walled carbon nanotubes (MWCNTs) was investigated controlling the morphology and size of ZnO nanoparticles hydrothermally synthesized. A strong dependence of electrocatalytic activity on nanosized ZnO shape toward electrochemical oxidation of dopamine, hydroquinone, and tert-butylhydroquinone is demonstrated. High activity was verified for the oxidation of all phenolic molecules when ZnO nanoparticles were hydrothermally produced at 120 °C for 120 min, which resulted in nanosized flower-shape nanoparticles. Two other procedures for production of ZnO were evaluated using the microwave hydrothermal method and resulted in spherical and non-uniform ZnO nanoparticles. The cyclic voltammetry experiments in Britton-Robinson buffer revealed that the composite ZnO/MWCNT using the nanosized flower-shape ZnO nanoparticles provided intense (around 4-fold) increase in current and decrease in peak-to-peak separation for the electrochemical oxidation of the three phenolic molecules in comparison with the other ZnO/MWCNT composites and with MWCNT-modified electrodes. Improved performance of this sensor was in agreement with electrochemical impedance spectroscopy measurements. Amperometric measurements also revealed the improved performance of the composite ZnO/MWCNT using the nanosized flower-shape ZnO (superior sensitivity).