以普魯士藍薄膜作為固態式離子選擇電極之離子電子傳導層

Abstract

在開發固態式離子選擇電極時會面臨到離子電子轉移障礙與水層效應(water layer effect) 等問題，而此些現象會使得電極在感測時電位訊號不穩定。因此在過往研究中，離子選擇電極會被引入一層離子電子傳導層以改善上述情況。本研究探討普魯士藍 (Prussian blue) 作為硝酸根離子選擇電極之傳導層，比較普魯士藍結構對於離子選擇電極表現的影響。經實驗後發現裂痕較少之傳導層結構能防止水層滲入，而團簇較多之表面能增加粗糙度使疏水性提高減少水層產生，此些情況能使離子選擇電極之電位訊號較為穩定。表現最佳之普魯士藍傳導層結構比起未經傳導層修飾之離子選擇電極減少89%的電位飄移。普魯士藍傳導層硝酸根離子選擇電極靈敏度為50 mV/decade，比起過去應用於鉀離子選擇電極研究中的44mV/decade還高。此外，本研究利用循環伏安法針對普魯士藍薄膜之硝酸根離子選擇電極進行分析，以探討其在感測時之作用機制。然而，我們發現循環伏安圖形在除了0.1 M硝酸鉀外，其他濃度未有明顯的氧化還原對，且氧化還原對之峰值並不會隨著硝酸鉀濃度提高而增加，因此可推測硝酸根離子無法氧化還原普魯士藍。而為了解釋其感測現象，本研究提出普魯士藍利用鉀離子作為離子選擇電極內導電媒介以場效應方式傳遞電荷之模型。而根據此模型，我們使普魯士藍薄膜還原以增加內部鉀離子數量，製成選擇電極後即能獲得更好的電化學表現。而經還原之普魯士藍製成之選擇電極比起未還原者感測時能再次降低73%的電位飄移量。最後，經過還原之普魯士藍傳導層與其他離子選擇電極常用材料進行比較後發現，普魯士藍為傳導層之離子選擇電極電位飄移量僅有2.5 μV/s，在所有材料中具有最好的電位穩定性。

The potential instability of an all-solid-state ion selective electrode (ISE) owing to ion-to-electron transduction and water layer effect can be overcomed by inducing an ion-to-electron transducer into the ion selective electrode structure. In this study, we investigated a Prussian blue (PB) thin film as the ion-to-electron transducer for a nitrate ISE. PB thin film with fewer cracks and more clusters on its surface can presented a stable potential signal better. Compared with an ISE without ion-to-electron transducer, the ISE with PB thin film can reduce 89% potential drift. The sensitivity of nitrate ISE with a PB thin film is 50.0 mV/decade, and it’s better than that of the potassium ISE with a PB thin film in previous work. We also investigate the mechanism of the PB thin film as an ion-to-electron transducer by cyclic voltammetry. However, the CV plot of the ISE with a PB thin film has no apparently redox peaks but scanning in 0.1 M KNO3 solution. Besides, the redox peak doesn’t increase with the concentration of KNO3. It implies that the PB thin film doesn’t have redox reaction in the ISE. In order to explain this phenomenon, we set up a model that describes how the charge transports in the ISE. We suppose that the potential signal results from the field effect which causes by potassium ions transporting in the PB thin film as charge carriers. According to the model, we can improving the performance of an ISE by filling more potassium ions in PB thin film by reduction reaction. The ISE fabricated with a reduced PB thin film can reduced 73% potential drift comparing to an ISE with non-reduced PB. At last, the PB thin film and some commonly used materials of ion-to-electron transducer are brought into comparison. The ISE with a PB thin film transducer has the smallest potential drift, 2.5 μV/s, which does means that it has the most stable potential signal.