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

電化學處理程序之效能主要取決於電極材料特性，導電鑽石中之摻硼鑽石(boron-doped diamond, BDD)因其具極寬的電位範圍(約3-4 V)、低吸附能力及低背景電流等特性而常被應用於電化學程序中；類鑽碳(diamond-like carbon, DLC)為特定sp2及sp3碳所組成之材料，相較於鑽石鍍膜易於製備，但其雖具有與鑽石相似之特性，目前應用於電化學程序之研究卻仍有限。因此，本研究將應用諸類材料開發一新型摻硼鑽石-類鑽碳(BDD-DLC)電極，使同時具有鑽石及類鑽碳之特性，並將其應用於水中重金屬檢測及有機物降解。

首先藉由熱絲化學氣相沉積法(Hot filament chemical vapor deposition, HFCVD)將摻硼鑽石-類鑽碳鍍膜披覆於不同鈦系基材之表面如純鈦、鈦-氧化銥及鈦-白金製成摻硼鑽石-類鑽碳電極，再以SEM、AFM、拉曼光譜儀、XRD及XPS進行表面型態、化學組成及晶相結構之分析；並藉由循環伏安法(Cyclic voltammetry, CV)及線性掃描伏安法(Linear sweep voltammetry, LSV)對於摻硼鑽石-類鑽碳電極之電化學特性進行分析。於可行性試驗中，重金屬監測為採用無傳統剝除(stripping)程序之LSV分析醋酸緩衝溶液及天然水體中銅、鉛及汞離子含量；而針對陽極氧化水中有機物之試驗則使用偶氮染料-酸性間胺黃(Metanil yellow, AY36)作為目標污染物，除評估其有機物降解效能並進一步探討水中酸鹼值與電解質對其影響，最後並將此陽極材料應用於電氧化/微過濾(EO/MF)複合膜組以進行水中有機物及無機顆粒之去除。

結果顯示2 µm厚度、3000 ppm硼碳比(B/C)之摻硼鑽石-類鑽碳鍍膜被成功披覆於鈦系基材表面，此鍍膜表面主要為奈米結晶所聚集而成之團粒，且可獲得較高之產氧電位(約2.5 V)、較寬電位範圍(4 V, －1500至＋2500 mV)及較低之背景電流值(10 µA/cm2)，此外，亦顯示此鍍膜同時具有鑽石Csp3、grahitic G、D及G’和G”峰，即同時具有鑽石及石墨之成分，但經極化處理後可獲得較鑽石電極寬之電位範圍；於應用重金屬量測分析，結果顯示Hg2+、Pb2+與Cu2+之偵測極限分別為1.34E-01、6.49E-03與2.90E-01，其相對之敏感度為0.057、0.104及0.014 μA μM-1 cm-2；此外，陽極氧化於酸性條件下之染料脫色效果(>99%)略高於鹼性及中性條件下，以電氧化/微過濾複合系統處理染料廢水，無論化學需氧量(COD)、脫色及濁度皆有良好去除效果。綜觀以上結果可知，本研究所開發之新型摻硼鑽石-類鑽碳電極具優異電化學特性，且具水中重金屬離子檢測及有機物分解之功能。

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.