The Study of Adenine and Guanine Electrochemical Oxidation Using Electrodes Modified with Graphene-platinum Nanoparticles Composites

Composite materials based on graphene and platinum nanoparticles (Gr-Pt-2 and Gr-Pt-3) were synthesized over two catalysts (Pt_x/MgO, where x = 2 or 3 wt.%) using radio-frequency catalytic chemical vapor deposition (RF-CCVD), with methane as carbon source. After morphological (TEM/HRTEM) and structural characterization (XRD, XPS, FTIR and UV-Vis) they were used to modify two gold electrodes and subsequently employed for the investigation of adenine and guanine electrochemical oxidation. For the Au/Gr-Pt-2 electrode, the oxidation peak potential of adenine was observed at +1.19 Vvs. Ag/AgCl, while, for Au/Gr-Pt-3 electrode, this was negatively shifted to +1.09 V vs.Ag/AgCl. In addition, the oxidation current densities were approximately 2.7 × 10⁻⁴ and 6.9 × 10⁻⁴ A·cm⁻² (for Au/Gr-Pt-2 and Au/Gr-Pt-3, respectively) demonstrating that the Gr-Pt-3 composite had a better electro-catalytic activity towards the oxidation of adenine. A similar behavior was observed for guanine oxidation. The excellent electro-catalytic properties of the Gr-Pt-3 sample were correlated with the fact that the composite material had a higher amount of platinum nanoparticles which were not fully covered by graphene layers (about 50%). In addition, it has a larger surface area (335 m²·g⁻¹) compared with that of the Gr-Pt-2 sample (271 m²·g⁻¹), which also greatly improved the electron kinetics.