新型摻硼鑽石-類鑽碳電極之開發、特性 及其於水中重金屬檢測與染料廢水處理之應用

Abstract

Electrochemical process is mainly relying on the nature of electrode material. An ideal electrode has to offer some features such as good physicochemical properties and wide potential range. Diamond is one of unique materials with outstanding properties including wide potential window approximately to 3-4 V, low adsorption ability and low background current that leads to its extensive utilization in electrochemical processes like electro-analysis of specific compound and electro-oxidation (EO) of organics. Diamond-like carbon (DLC) also have superior characteristic similar to diamond and composed of sp2 and sp3 carbon structure. However, there are few studies on the DLC-based electrochemical techniques. Therefore, the purpose of this thesis was to fabricate a high performance BDD-DLC electrode with wide potential, low background current which can be adapted for wastewater treatment and heavy metal detection. In this study, BDD-DLC thin film was coated on several Ti based substrate such as Ti, Ti-SiC and Ti-Pt by HFCVD. Surface analysis such as SEM, AFM, Raman, XRD and XPS were conducted to determine the morphology, chemical composition and crystal structure of the BDD-DLC film. CV and LSV was performed to determine the electrochemical properties of BDD-DLC film. The capability of as grown and polarized BDD-DLC in detecting heavy metal ion such as Pb, Cu and Hg in aqueous solution was studied using direct LSV method without stripping. Performance of BDD-DLC to anodically degrade organic was tested using an azo dye – metanil yellow (AY36) as target pollutant. The pH and electrolyte effects were studied. A hybrid module combining EO/MF process was develop to study the BDD-DLC EO capability when it is incorporated with MF system to simultaneously removed soluble organic (AY36) and particle pollutant (simulated by kaolin). A 2 µm thick BDD-DLC film with 3000 ppm B/C ratio was successfully deposited on the Ti based substrate. Background CV of as grown BDD-DLC on various Ti based substrates reveals that the film grown on Ti exhibited higher oxygen evolution overpotential (at 2.5 V), wider potential window (4 V, from －1500 to ＋2500 mV) and smaller background current (10 µA/cm2) compared to those grown on Ti-SiC and Ti-Pt. This result demonstrated that Ti is the most suitable substrate to coat BDD-DLC. Based on SEM and AFM image, it is clear that the BDD-DLC film contains dense nanocrystalline grains that aggregated into rough sphere forming cauliflower structure. Raman spectra of the BDD-DLC shows several peaks that associated with diamond Csp3 peak, graphitic G and D band as well as G’ and G’’ band. XRD spectra show diamond peak at 44.4° and graphite at 43°. Based on the XPS survey, carbon, boron, titanium and oxygen are evidently present. The existence of both sp2 and sp3 carbon was also confirmed. Surface analysis results confirm the existence of both diamond and graphitic carbon in the film with relative higher Csp2 than commercial diamond electrode. However, the results reveal polarization can improve the electrochemical properties of BDD-DLC film similar or even better than diamond electrode in other studies. In the feasibility test of heavy metal detection, detection limits for Hg, Cu and Pb in ppm were 1.34E-01, 6.49E-03 and 2.90E-01 with sensitivity of 0.057, 0.104 and 0.014 μA μM-1 cm-2, respectively. In anodic oxidation experiments, results show that acidic condition is slightly more favorable for decolorization compared to basic and neutral condition, with color removal reach > 99%. The EO/MF hybrid module in dye wastewater treatment practice can achieve satisfactory performance with respect to COD removal, decolorization and turbidity removal. In conclusion, the BDD-DLC/Ti electrode is applicable for both EO treatment practices and as the working electrode for electro-analysis of heavy metal ions due to its outstanding electrochemical properties.