以原位聚合方式合成之聚(3,4-乙烯二氧噻吩)/3-噻吩甲酸複合膜電阻式一氧化氮感測器

Abstract

於本研究中，利用氧化聚合及原位聚合方法， 將3,4-乙烯二氧噻吩，混摻3-噻吩甲酸，使之聚合於黃金製之指插式電極上，製成電阻式氣體感測器。 我們將探討[3-噻吩甲酸]/[ 3,4-乙烯二氧噻吩]之組成比例對於氣體感測所產生之效應，以及經過酸鹼處理後之感測訊號。結果顯示隨著[3-噻吩甲酸]/[ 3,4-乙烯二氧噻吩]之組成比例增大，本感測器對於50 ppm之一氧化氮感測結果，從原來幾乎沒有訊號，增加到2.2%。然而，我們還可以利用氨水以及鹽酸處理，藉以還原高分子膜，以及增加表面粗糙度，進而使反應面積增加，使訊號又從2.2%上升至5.1%。 溫度效應實驗顯示本系統最適合操作於室溫。本感測器於1 ppm到10 ppm的一氧化氮濃度範圍間，訊號與相對應之濃度具線性關係；靈敏度約為0.93%/ppm；偵測下限經計算約為25 ppb (在訊號/雜訊 = 3 之標準下) ；反應時間(t95)，以及恢復時間分別為756秒及超過一小時。從感測器為期一個月的穩定性測試並無發現明顯的靈敏度衰退趨勢。在最後我們藉由系統改進，使原本較長的恢復時間(超過一小時)，大幅降至約十分鐘即可使訊號恢復至基線。 關鍵字：氧化聚合、原位聚合、3,4-乙烯二氧噻吩、3-噻吩甲酸、指插式電極、電阻式氣體感測器、一氧化氮。

In this study, 3,4-ethylenedioxythiophene (EDOT) was in situ oxidatively polymerized and doped with 3-thiophenecarboxylic acid (TCA) on a gold interdigitated electrode, and the resulted films were used as a resistive type gas sensor. The effects of the composition, ie. the ratio of [TCA]/[EDOT], and the acid/base treatment on the sensor response were investigated. The results showed that as the ratio of [TCA]/[EDOT] was increased, the sensor response to the exposure of 50 ppm NO gas was increased from nearly none to a slightly higher value of 2.2%. However, the sensor response can be further increased from 2.2 to 5.1% if the in situ synthesized film is to be treated with ammonia and hydrochloric acid sequentially during which the composite film is reduced, and the surface roughness increase. The temperature effect shows the optimum operation temperature is at room temperature. The sensor showed linear response in the concentration between 1 and 10 ppm. The sensitivity for the PEDOT/TCA composite sensor is ~0.93%/ppm. The limit of detection is 25 ppb (S/N = 3). The response time (t95) and recovery time (t95) were recorded to be 756 s and over 1 hr. respectively. The long-term stability was also tested for a month, which shows no obvious decay in sensitivity. The long recovery time (> 1 hr) appeared in the PEDOT/TCA composite film was also overcome (~10 min) by heating the sensor during recovery. Keywords: resistive type gas sensor, oxidatively polymerization, in situ polymerization, EDOT, 3-thiophenecarboxylic acid (TCA), interdigitated electrode, nitric oxide.