- 學位論文
亞鐵氰化銅修飾電極於伏安式愈創木酚感測之研究
Study of Copper Hexacyanoferrate Modified Electrodes for Voltammetric Guaiacol Determination
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摘要
本研究旨在開發一基於亞鐵氰化銅之伏安式咖啡風味分子感測器。亞鐵氰化銅為一普魯士藍類似物，能以電化學氧化還原躍遷的方式催化許多分子進行氧化反應，因此被用於本研究所開發之感測器。然而，此材料由於水相溶液中之Ksp較低以及較差的黏著性而不利於電鍍修飾。因此，本研究針對鍍液進行KCl, HCl含量進行調控，並比較各電位下電鍍之電極穩定度。於製程優化後，於掃描式電子顯微影像將呈現一均勻薄膜之表面微結構。並且可以電化學循環伏安法中檢驗達0.93 mC/cm2之電量與70 %之電鍍庫倫效率，以及於電化學阻抗頻譜中呈現4.89 Ω之電荷轉移阻抗 (Rct)。以此電極用於伏安式分子感測器可對不同分子具有不同峰值電位響應，分別為0.52 V之咖啡酸、0.53 V之綠原酸、0.71 V之愈創木酚以及0.82 V之香草醛。各風味分子中，愈創木酚具有燃木焦香味，對於咖啡為之風味影響甚大，因此本研究便以此分子為例，進行感測應用與反應機制探討。本研究首先以電化學循環伏安法探討其反應機制。以亞鐵氰化銅催化愈創木酚之氧化反應為牽涉兩電子轉移之ErCi反應，其速率決定步驟為愈創木酚分子於水溶液中之質量傳遞並符合Randles–Ševčík 公式。於感測應用中，此感測器於低濃度下具有對愈創木酚109.5 µA/cm2 mM之靈敏度，並可達7.09 µM之理論偵測下限。此感測器於長時間、多圈數使用或於較高濃度環境下則容易被毒化。此毒化現象經循環伏安法與電化學阻抗頻譜分析推論係由愈創木分之氧化物所造成。然而由於此感測器足夠低之偵測下限，依舊可於稀釋之咖啡樣品中完成感測。
並列摘要
This study aims to develop a voltammetric sensor for coffee flavor molecules based on copper hexacyanoferrate. Copper hexacyanoferrate, a Prussian blue analogue, catalyzes the oxidation of various molecules through electrochemical redox hopping, making it suitable for the development of sensors. However, its application is hindered by its low solubility in aqueous solutions and poor adhesion for electrodeposition. Therefore, this research focused on adjusting the KCl and HCl contents in the plating solution and compared the electrode stability at different applied potentials. After process optimization, the scanning electron micrograph showed a uniform thin film surface microstructure. The thin film was characterized with a charge capacity of 0.93 mC/cm2, a plating efficiency of 70%, and a charge transfer resistance (Rct) of 4.89 Ω. This electrode was applied for a voltammetric sensor, which exhibits distinct peak potentials for various flavor molecules, including 0.52 V for caffeic acid, 0.53 V for chlorogenic acid, 0.71 V for guaiacol, and 0.82 V for vanillin. Among these molecules, guaiacol imparts a smoky aroma to coffee and is significant in flavor discrimination. Therefore, this study focuses on guaiacol to investigate its sensing application and reaction mechanism. Using cyclic voltammetry, the oxidation of guaiacol catalyzed by copper hexacyanoferrate was found to be an ErCi reaction involving two-electron transfer. The rate-determining step corresponds to the mass transfer of guaiacol molecules in the aqueous solution and fits with the Randles–Ševčík equation. In the sensing application, this guaiacol sensor exhibits a sensitivity of 109.5 µA/cm2 mM at low concentrations and a theoretical LOD of 7.09 µM. However, prolonged use or exposure to higher concentrations could lead to poisoning of electrodes. This is attributed to the oxidation products of guaiacol, as observed with cyclic voltammetry and electrochemical impedance spectroscopy. Nevertheless, due to its low enough LOD, the sensor remains capable of detecting guaiacol in diluted coffee samples effectively.
參考文獻
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