界面活性劑對電化學/機械複合剝離製程之石墨烯產率與品質影響

Abstract

本研究結合液相剝離法中的電化學剝離法與剪切剝離法(Shear exfoliation)，另外輔以界面活性劑的添加，企圖以此製程技術提升產率，期望解決電化學剝離法無法連續性生產的缺點。傳統電化學剝離法多是以塊狀、棒狀、箔片狀石墨作為研究材料，一旦電解剝離完後，其剩下非石墨烯之產物(細小石墨微粒)無法再反覆剝離成為石墨烯，只能丟棄造成浪費或另尋其他用途。然而，本研究所提出的實驗方法可以連續性生產，而且以較低成本之天然石墨顆粒為剝離原料，非石墨烯之產物也能夠重複剝離。本研究整合兩種技術，在剪切高速剝離處理前，以施加電壓進行電化學離子插層處理，增加石墨層與層間距離而使剪切剝離較為容易，以獲得較大尺寸的石墨烯薄片，藉由上述的複合方式來達到提升產率與品質之目標。本研究透過X光粉末繞射儀(XRD)分析樣品結晶，判斷是否為石墨烯，再輔以拉曼光譜分析儀(Raman spectroscope)確認樣品有無缺陷，另以化學分析影像能譜儀(ESCA)判別氧碳值，另藉由掃描式電子顯微鏡(SEM)、穿透式電子顯微鏡(TEM)及原子力顯微鏡(AFM)等儀器設備，評估石墨烯片的大小、表面形貌及厚度均勻性。本研究成功藉由此製程製備石墨烯片，具有低成本與高產量的優勢，期許未來可應用於導電漿料、透明導電層、超級電容或鋰電池等開發。本研究藉由整合電化學插層法、剪切剝離法與複合式界面活性劑的使用，成功將石墨粉剝離為石墨烯，剝離後石墨烯的氧碳比值(O/C)提升至2.39，經過後處理之氧碳比值降為1.37，接近初始石墨粉氧碳比1.02，剝離後經酒精清洗的石墨烯缺陷程度ID/IG為0.899，再經過高溫處理的缺陷程度為0.630，亦較近於初始材料石墨粉之缺陷程度0.604，剝離後石墨烯層數多為2奈米，經兩次反覆實驗後，寡層石墨烯的整體產率為72.48 %，意為投入10克石墨粉，可獲得7.248克之寡層石墨烯。In this study, using the liquid phase electrochemical and shear exfoliation process with surfactant for increasing yield, and overcome shortcomings that unable to continuous process. General electrochemical exfoliation using the massive, clavate and schistose graphite for research material. After exfoliation process, non-graphene of product has become refuse, thus process of this study has continuous and low cost. Before shear exfoliation process, applied voltage for use of electrochemical process that intercalation ions and gas to form an expanded graphite, then homogenized using high speed to exfoliating graphite powders. This study through X-ray powder diffraction (XRD), raman spectroscope, electron spectroscopy for chemical analysis (ESCA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and other equipment, to evaluated the crystallinity, defect degree, O/C ratio, surface morphology, size and thickness of the graphene sheet. This study has confirmed that electrochemical/mechanical hybrid method, prepared graphene sheets for low cost and high yield of advantages for development into conductive paste, transparent conductivity layer super capacitor, lithium battery and other element. The experimental results showed that SEM images clearly show effective exfoliation. The produced graphene are ∼2 nm thick in average. The conductivity (7.743 S/cm), defects degree (ID/IG = 0.63) and element ratio (O/C ratio = 1.37) in close proximity to starting materials. Using the hybrid surfactant in this research may be useful in increasing the yield of graphene for 47.43 %. With secondary experiment, we have successfully again prepared graphene, nearly 72.48 % of sheets possess thickness ranging from 1 to 5 nm.