利用石墨烯/矽異質結構應用在光合生物混合系統之研究

Abstract

自工業革命以來，隨著人類的活動大量使用化石燃料，使大氣中二氧化碳濃度逐漸升高，造成全球暖化與氣候變遷等問題，因此開發出除了大自然以外的人工固碳途徑相當重要。其中光電化學系統結合光電轉換與觸媒催化，概念與綠色植物的光合作用相仿，是個建構人工固碳途徑的良好模板。 光電轉換部分以地球含量豐富且能隙較小的矽半導體捕捉太陽能，並利用內部掩埋的方式對傳統的矽基板改植形成矽異質結構，可增加內建電壓並分離照光面與催化面，表面微米級的金字塔抗反射結構也能幫助更多入射光吸收。經由EVA轉印法將單原子層的二維材料石墨烯轉印於矽異質結構基板，以石墨烯的化學惰性作為矽的保護層防止氧化；再搭配其高導電度作為電化學沉積金屬介面的平台，相較物理氣相沉積法更省時、耗費能量更少，所成長的金屬介面也更加牢固。 觸媒催化部分選用細菌生物觸媒，由於電子是經由酵素系統構成的代謝傳導途徑推動反應，因此相較無機觸媒對產物有更高的選擇性。同時細菌生物觸媒具有自我複製的特性，在觸媒老化時能夠自我更新，因此能夠有更持久穩定的催化。將細菌生物觸媒結合矽異質結構基板，能夠分離照光面與催化面，巧妙避開細菌不適合直射太陽光的問題。且以石墨烯作為電化學沉積的平台，可以利用參數略微控制金屬介面之表面形貌供細菌成長，形成一個良好的生物-無機介面，更利於建構生物混合系統。 實驗中Si-HJ/Gr/InSn/Moorella thermoacetica為結構，並利用各式儀器分析，包含以拉曼光譜鑑定轉印在Si-HJ的石墨烯性質、X光繞射儀鑑定InSn合金介面晶體結構與掃描式電子顯微鏡鑑定表面形貌、厭氧醋酸菌M. thermoacetica成長的分布狀況。接著更進一步以電化學實驗與光電化學實驗量測，搭配氣相層析質譜儀定量分析醋酸產物計算法拉第效率。透過建構出一個光合生物混合系統，達到加強細菌生物觸媒代謝途徑轉換二氧化碳成醋酸的目標。

Since the Industrial Evolution, the concentration of carbon dioxide in the atmosphere has gradually increased due to the extensive use of fossil fuels in human activities, causing problems such as global warming and climate change. Therefore, developing artificial carbon fixation methods other than nature is quite critical. Among multiple methods, a photoelectrochemical system combining solar to electricity conversion and catalytic catalysis, which is similar to photosynthesis in plants, can serve as a good template for constructing an artificial carbon fixation. For the solar to electricity conversion, we captured the solar energy with an earth-abundant, small band gap silicon-based semiconductor. The traditional silicon substrate was processed with internal buried junction methods to form a silicon heterostructure, which can increase the built-in voltage and decouple the light-harvesting side and catalytic reaction side of the photoelectrode. Besides, the micro-scale pyramid-like anti-reflection structure on the surface can also increase the absorption of incident light. The two-dimensional graphene of a single atomic layer was transferred to the silicon heterostructure by ethylene-vinyl acetate (EVA), and the chemical inertness of graphene acted as a protection layer of silicon from oxidation. Furthermore, compared to physical vapor deposition methods, graphene can serve as a platform for electrochemical deposition of metals due to its high conductivity, which can save time and consume less energy, forming stronger metal interfaces. Bacterial biocatalysts were selected for the catalytic part of the catalyst. Since the metabolic pathway is constructed by the electron-driven enzyme system to complete the conversion, the selectivity of bacterial biocatalysts to the products is higher than that of inorganic catalysts. Meanwhile, bacterial biocatalysts exhibit a more durable and stable catalytic effect due to their ability to self-replicate and self-renewal while aging. Therefore, the combination of bacterial biocatalysts with silicon heterostructure substrate can prevent direct exposure of bacteria to sunlight by decoupling the light-harvesting side and catalytic reaction side of the photoelectrode. In addition, with the use of graphene as a platform for electrochemical deposition, the surface morphology can be slightly controlled by the experimental parameters for bacteria growth, forming a favorable bio-inorganic interface, which was conducive to the construction of a biohybrid system. In this experiment, the Si-HJ/Gr/InSn/Moorella thermoacetica structure was constructed for the biohybrid system for artificial carbon fixation, and various instruments were used for analysis, including Raman spectrum for the property of graphene transferred on Si-HJ, X-ray diffraction (XRD) analysis for the crystal structure and scanning electron microscope (SEM) for the surface morphology of InSn alloy interface, and the grown distribution of strictly anaerobic acetic acid bacteria M. thermoacetica. Furthermore, we can calculate the Faradaic efficiency through the results obtained from electrochemical and photoelectrochemical chronoamperometry measurements and the quantitative analysis of acetic acid production by gas chromatography-mass (GC-MS). In conclusion, a photosynthetic biohybrid system was successfully constructed with the Si-HJ/Gr/InSn/M. thermoacetica structure to enhance the bacteria biocatalyst metabolic pathway for converting carbon dioxide into acetic acid.