Hybrid diamond/graphite nanostructures were synthesized in CH4/H2 mixture gas using microwave
plasma enhanced chemical vapor deposition (MPCVD) at a power of 10 kW. The microstructure and
the composition of the films were characterized by scanning electron microscope (SEM), transmission
electron microscope (TEM), Raman spectroscopy and X-ray diffraction (XRD). The as-deposited diamond
films at high methane level in hydrogen plasma show good conductivity and excellent electrochemical
activity, owing to the co-existence of diamond and graphite phases in the films. The largest electrochemical
potential window of the hybrid diamond/graphite films is 3.1 V, which is comparable with the
B-doped diamond. The films exhibit quasi-reversible, mass controlled electrode reactions in both aqueous
and organic solutions. In the application of trace heavy metal ion detection, the hybrid diamond/graphite
electrodes present low background currents and detection limits (S/N
≥
3):
∼1.5 A/cm2 and 5.8 ppb for
Ag+,
∼4.7 A/cm2 and 5.6 ppb for Cu2+. The diamond/graphite electrodes also possess good linearity over
a wide concentration range from 10 ppb to 1 ppm. In addition, the simultaneous determination of silver
and copper ions was also successful. The good recovery values for the analysis of the tap water samples
with standard addition method demonstrate the accuracy of the hybrid diamond/graphite electrodes.
Hence, the hybrid diamond/graphite films are promising for electrochemical applications such as trace
heavy metal ions detection because of its wide potential window, lower background current and high
sensitivity.