Innovative fabrication of diamond film electrode for environmental applications

Diamond film on titanium substrate has become extremely attractive because of the combined properties of these two unique materials. Diamond film can effectively improve the properties of Ti for applications as aerospace and biomedical materials, as well as electrodes. Effects of process parameters, including gas composition, substrate temperature, gas flow rate and reactor pressure on diamond growth on Ti substrates has been studied using the hot filament chemical vapor deposition (HFCVD) method. The nucleation density, nuclei size, the diamond purity and growth tendency indices were used to quantify these effects. The crystal morphology of the material was examined with scanning electron microscopy (SEM). Micro-Raman spectroscopy provided information on the quality of the diamond films. The growth tendency of TiC and diamond film was determined by X-ray diffraction analysis. The optimal HFCVD conditions were found to be: CH4:H2 =1%, gas flow rate=300sccm, substrate temperature Tsub=750oC, reaction pressure=40mbar. Under these conditions, high-quality diamond film was deposited on Ti with a growth rate of 0.4μm/hr and sp2 carbon impurity content of 1.6%. The challenge for Ti/BDD is the stability especially when it is used as an electrode. In order to meet this challenge, two staged substrate temperature (2-T) HFCVD method was newly developed. The accelerated working life time was significantly increased to 804 hours for the 2-T electrode, compared with 244 hours for the electrode obtained under one substrate temperature (1-T). With the characterization of micro-Raman, XRD, and cross-sectional SEM, a multilayer of Ti/TiC/(Diamond+Amorphous Carbon)/Diamond can be found in the 2-T sample and the structure of Ti/TiC/Diamond in the 1-T sample. There was less void space observed in the interlayer of the 2-T sample. The multi-layered compact structure plays an important role in improving the adhesion of diamond film to the titanium substrate which in turn increases the electrode working life time by over 2 times. Needle shape diamond film electrode was fabricated with tantalum wire as substrate. Electrochemical quantitative analysis of nonylphenol (nine) ethoxylates (NP9EO) in water was realized using this electrode with linear sweep voltammetry method. High linear relationship (R2 ≥ 0.99) between the peak current with NP9EO concentration in the range from 162 nM to 40.6 μM (or 100 μg/L to 25 mg/L) was obtained. Electrochemcial pretreatment influences the redox Fe(CN)63-/4- behavior. After cathodic amperimetric polarization, the redox shows quasireversible behavior, instead of irreversible behavior on the electrode without polarization treatment. Electrochemical incineration of NP9EO and PEG-400 in water was conducted with the planar shape Ti/BDD electrode. By monitoring COD and TOC, it has been shown the degradation process followed pseudo first order kinetics. Moreover, effect of parameters, including initial concentration and electrolyte temperature, was studied