以微電漿光譜法檢測空氣中揮發性有機物之研究

Abstract

微電漿具有激發反應物並產生放光的能力，透過分析不同波長強度的變化，作為辨識反應物質的特徵峰，因此這種特性也被應用在分析化學中。微電漿低成本、可在常壓下操作等特性使其具有很大的潛力應用在可攜式的氣體檢測裝置上。近幾年發展的微電漿光譜系統需要使用氦氣或氬氣作為載流氣體，因此無法達到真正意義上即時即地的檢測系統。本研究使用兩套系統，分別是以交流電驅動的DBD系統，以及由直流電驅動的針尖對平面微電漿系統，直接在空氣氣氛下進行揮發性有機氣體的檢測，透過調控不同的電漿行為，找出在空氣氣氛下最適合的檢測方法。 第一套系統是採用交流電驅動的DBD系統，透過改變MGD在高壓電極的形狀，如圓形、正方形、正三角形、長方形、箭頭形和等腰三角形等探討對有機氣體檢測的表現，以及探討浮動電極的面積大小，最終找出最適合的MGD設計。分析電源的輸出電壓(3.2至5.2 kVpp)和輸出頻率(1至30 kHz)，以及電源的輸出波形找出提升CN特徵峰響應的參數，再透過電性分析了解造成檢測能力差異的原因。 第二套系統是利用直流電驅動的針尖對平面微電漿系統，直流電源使用自製的高壓模組，透過改變電極材料(鐵線、鋁線和鎢線)得到電漿放光表現的差異，同時透過改變系統的電極間距(100至500 μm)、整體流量(1.28到4.55 SLM)等參數條件對於電漿放光的影響，以及在檢測有機氣體能力上的差異。探討直流微電漿系統在不同有機氣體的檢測能力，以及該系統對於區分不同氣有機體的表現，由於在很多檢測系統中是不能有水氣的存在，因此在本研究中也探討水氣對該系統的影響。最後透過改變鎮流電阻的電阻值探討電漿放電的電性變化，以及對於有機氣體檢測表現的影響。 最後會比較DBD系統和直流微電漿系統的放電電性對於檢測能力的差異原因，並且比較兩者的定量分析能力，找出最適合在空氣中檢測揮發性有機氣體的方法，以及該系統的參數控制。

Microplasma possesses the ability to excite reactants and emit light. By analyzing the variations in intensity at different wavelengths, it serves as characteristic peaks for identifying reactant substances. Therefore, this characteristic is also applied in analytical chemistry. The low-cost and operability at atmospheric pressure of microplasma make it highly promising for applications in portable gas detection devices. However, the microplasma spectroscopy systems developed in recent years require helium or argon as carrier gases, preventing the realization of real-time, on-site detection systems. In this study, two systems were used: an alternating current (AC) driven dielectric barrier discharge (DBD) system and a direct current (DC) driven needle-to-plane microplasma system. The volatile organic gas detection was performed directly in ambient air. By manipulating different plasma behaviors, the most suitable detection method in ambient air was determined. The first system employed an AC-driven DBD system. The performance of organic gas detection was investigated by altering the shapes of the micro-gap discharge (MGD) in the high-voltage electrode, such as circular, square, equilateral triangle, rectangular, arrow, and isosceles triangle shapes. The influence of the floating electrode area was also explored to find the optimal MGD design. The output voltage (3.2 to 5.2 kVpp) and frequency (1 to 30 kHz) of the power supply, as well as the output waveform, were analyzed to identify the parameters that enhance the response of the characteristic peaks. Electrical analysis was further conducted to understand the causes of differences in detection capability. The second system utilized a DC-driven needle-to-plane microplasma system with a home-made high voltage module. By changing the electrode materials (iron wire, aluminum wire, and tungsten wire), the differences in plasma luminescence performance were obtained. The influence of parameters such as electrode gap (100 to 500 μm) and overall flow rate (1.28 to 4.55 SLM) on plasma luminescence and its impact on the detection capability of organic gases were investigated. The detection capabilities of different organic gases by the DC microplasma system and its performance in distinguishing different organic gases were explored. As moisture should not exist in many detection systems, the effect of moisture on this system was also examined in this study. Finally, by varying the resistance value of the ballast resistor, the electrical characteristics of plasma discharge and its impact on the performance of organic gas detection were investigated. Ultimately, a comparison will be made between the discharge characteristics of the DBD system and the DC microplasma system to identify the reasons for differences in detection capability. The quantitative analysis abilities of both systems will be compared to determine the most suitable method for detecting volatile organic gases in ambient air, along with the parameter control of the system.