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標題: | 結合自製樹莓派光譜儀之高光譜影像於可攜式微電漿重金屬檢測裝置之應用 Application of a Portable Microplasma Generation Device for Heavy Metal Detection Integrating Hyperspectral Images of a Homemade Raspberry Pi Spectrometer |
作者: | Ting-Ting Pan 潘婷婷 |
指導教授: | 徐振哲(Cheng-Che Hsu) |
關鍵字: | 微電漿,重金屬檢測,光譜儀,高光譜影像, Microplasma,Heavy metal detection,Spectroscopy,Hyperspectral image, |
出版年 : | 2020 |
學位: | 碩士 |
摘要: | 微電漿為三維尺度中有一維小於1 mm之系統,其體積小、能耗小、具有高能量密度,且在大氣中可以穩定生成,因此非常適合作為可攜式檢測裝置的能量來源。本研究利用特製形狀之濾紙使樣品濃縮並產生微電漿,利用微電漿的激發與去激發反應使樣品水溶液中之重金屬放光,藉由不同原子具有不同特徵波長之特性,利用電漿光譜資訊來判斷樣品中的組成成分並進行定量分析。 本研究之濾紙微電漿系統使用9V行動電源結合一個高壓電路模組輸出約3kV之電壓,並將拱橋形狀之濾紙作為待測水溶液之載體,因為待測水溶液具有導電性,故將浸濕導電水溶液之濾紙作為電極來產生微電漿。其主要是利用幾何形狀之不同造成系統之電流密度分布不均,使濾紙寬度最窄處有最大的電流密度,因此產生最多的熱能將水蒸發,而水溶液亦會從濾紙兩側同時補充,使樣品濃縮於此。當水溶液加熱速度大於補充之擴散速度時,濾紙最窄處將會蒸乾,並在兩端形成足夠的電壓差而產生微電漿。微電漿產生所伴隨的熱讓濾紙蒸乾的範圍擴大,使得兩電極間距越來越大,直到施加的電壓無法維持電漿,即結束實驗。 本研究發現微電漿不一定會如上方所述產生於濾紙最窄處(正中央),若使用低濃度的樣品,電漿會產生於偏負極的位置,其原因為本系統在負極的濾紙與鋁箔交界處會因電解反應而產生氫氣,此氣泡會使電阻上升而讓熱能分散。此外,亦發現微電漿會隨著時間空間不斷地變化,且每次產生的位置不盡相同,因此使用市售光譜儀將無法擷取完整的電漿光譜資訊,促使本系統使用自製的樹莓派光譜儀,以擷取電漿一維空間隨時間變化之高光譜影像。 樹莓派光譜儀主要由狹縫、光柵、樹莓派相機與資料擷取系統等四個要件所組成,本研究藉由連拍的方式獲得時間上的資訊。透過樹莓派高光譜影像可取得四維之光譜資訊:波長、一維空間、時間與光譜強度。分析後發現本系統微電漿產生的光源會隨著時間一分為二,靠近負極端之光源為不連續之金屬放光,而靠近正極端則為連續之火焰放光。然而,火焰放光產生之連續寬帶在不同的波長會有不同的強度貢獻,且火焰為不受控制之變因,故其會增加分析之困難度與系統之不穩定性。故本研究藉由高光譜影像的優勢,僅分析金屬的放光,以減少火焰所造成的影響。 本研究比較三種不同的濃縮流程,其中發現先以9 V直流電加熱的預熱濃縮系統於光譜強度上沒有增強,以示波器量測後得知,使用9 V預熱時因電流太小,加熱氣化的水溶液量近乎零,因此沒有達到濃縮的效果。然而,若使用脈衝式濃縮系統,鉛的淨強度可增強約2倍,並且於光譜上出現原本看不見之鈣、鋅之金屬峰,因此可確認將電源以脈衝的方式供給,可使水溶液有更多時間補充,以達濃縮之效果。 濾紙系統結合樹莓派光譜儀系統,其成本便宜、體積小,且可使用行動電源驅動,使得裝置具有普及化、可攜式的潛能。若結合遠端控制、存取資料並同時運算的特性,進行重金屬檢測之定性與定量分析,以達即時限地檢測之目標。然而,如何降低偵測極限、降低系統變異量以及定量分析皆為本系統日後可以努力的目標。 Microplasma is defined as a system with one dimensional scale less than 1 mm in three dimensions, which is suitable as an energy source for portable detection devices thanks to its small size, high energy density, low consumption, and stability in the atmosphere. In this work, we use specially-cut filter paper to concentrate sample and generate the microplasma. Metallic ions in the sample solution would be excited and de-excited, and then emit the light. Through spectral analysis, we can determine the composition of the plasma and perform quantitative analysis. In this work, the high voltage module is powered by a 9 V power supply and delivers 3 kV DC to drive the plasma. The plasma generation device consists of a specially-cut filter paper absorbed with the test sample solution. The test solution is conductive and contains metallic elements to be tested. It serves as the electrode for plasma generation. With the specially designed geometry of the filter paper, the largest current density appears at the thinnest part, so the solution will evaporate fastest. Meanwhile, the replenish from both sides makes the sample solution concentrate. When the evaporate rate of the aqueous solution is faster than the diffusion rate of the replenish, the filter paper will dry out and the plasma will be ignited at the designated location with self-determined gap. We modulate the high voltage application scheme such that the test solution is concentrated before the plasma is ignited. Such a concentrating step is the key advantage used in the plasma generation device shown in this work. It plays an important role for quantitative analysis and reducing limit of detection (LOD). When using low concentrated sample solution, we find the plasma is generated near the cathode side instead of the thinnest part of filter paper. Due to the electrolysis reaction, there is hydrogen generated between aluminum and filter paper on the cathode side. The bubble may increase the resistance, making the heat dispersed in the position near the cathode. The homemade spectrometer integrates a slit, a diffraction grating, and a camera module controlled by a Raspberry Pi (RPi), which is a low-cost single board computer. This homemade spectrometer allows for acquisition of spatially and temporally-resolved optical emission of the plasma. There are four dimensional information in the RPi hyperspectral image: wavelength, one-dimensional space; time, and spectral intensity. With these information, we can find the light-spot of plasma splits from one to two as time goes on. The one near cathode is metal spectrum, and the other one is broad band of flame. The flame is an uncontrollable parameter and therefore makes the spectral analysis more difficult. By the advantage of hyperspectral image, we can improve signal-to-noise ratio of spectra, which is benefit to lower the LOD. In addition, we can also reduce the effect of flame. Furthermore, we compare the concentrated effect of three different processes in this system. We find the evaporation barely occurs in preheating process, which leads to no concentrated effect. However, in the pulsed power process, the Pb net intensity increases about 2-folds, and we can also find the peaks of Ca and Zn which cannot be observed in other process. Thus, the pulsed power allows the solution to have more time to replenish, so this process shows the good concentrated effect. Such an integrated system is portable and allows for in-situ, real time, and simultaneously analysis of multiple metallic elements in solution. However, the decrease of LOD, and the method of quantitative analysis are the prospective study in this work in the days to come. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/51376 |
DOI: | 10.6342/NTU202002764 |
全文授權: | 有償授權 |
顯示於系所單位: | 化學工程學系 |
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