2.4. Cyclic voltammetry
An Autolab potentiostat PGSTAT 12 (Eco-chemie, Netherlands), equipped with the GPES 4.9 software, was used for all the cyclic voltammetric studies. The active surface area of the GC electrode was approximately 0.07 cm2. A three-electrode system, consisting of the working electrode (GC or CNT/GC electrode), a reference electrode (Ag/AgCl/KCl (sat.)) and a counter electrode (platinum wire) was employed. Measurements were carried out in the phosphate-ethanol buffer solution as supporting-electrolyte.