以生質炭製備石墨烯之研究

Preparation of Graphene Sheet Contented Carbon Materials from Biochars

劉晏嘉(Yan-Jia Liou)

指導教授 ： 黃武章

國立屏東科技大學/工學院/環境工程與科學系所/博士(2014年)

https://doi.org/10.6346/NPUST.2014.00230

摘要

石墨烯為單層或少層石墨，其具有比矽高的電子遷移率與特殊的光學特性。因此可用於透明導電薄膜、染料敏化太陽能電池、超級電容器與其他複合材料的製備上。目前石墨烯的製備方法有化學氣相層積法、石墨氧化還原法與物理剝離法等。然而這些方法均無法量產石墨烯且其製程產生的副產物難以去除，因此目前石墨烯的市場機制尚未明確。本研究提出以生質碳進行酸浸漬裂解與催化裂解法製備高石墨烯含量的碳材料(GSCCMs)。
從研究結果發現所有炭材中均含有石墨烯片層，且可藉由XRD分析結果推導出石墨烯含量的定量方式並計算碳材中石墨烯含量。根據分析結果預估以生質碳製備所製備之理想石墨烯粉體的電阻值為0.01 Ω‧cm，此結果與市售以石墨氧化物進行還原所得之石墨烯粉體一致。以油棕果生質炭經CH3COOH浸漬後或以Na2O作為催化劑於於1500 oC進行熱裂解所製備的石墨烯純度分別可達83.86與82.88 %；平均導電度分別為84.690與78.985 S/cm。
從SEM分析中發現，石墨烯含量與生質物所含的α-纖維素含量有關，且添加Na2O在1500 oC進行熱裂解，其碳材表面會留下與石墨球型微晶大小相符的孔洞(約0.5 ~ 1 μm)。推測是由於α-纖維素因鈉離子的浸漬後在高溫形成的石墨微晶產生膨脹與分離的現象，因此在碳材料的製備中添加金屬氧化物作為催化劑將可製備出可調控尺寸的碳材料。而以純α-纖微素進行高溫裂解製備石墨烯碳材料，其石墨烯片層含量為93.01 %。且以自製的石墨烯碳材料製備之石墨烯氧化物薄膜具高溫相轉變的特性，且從結果顯示其平均相轉變的焓為9.41 J/g，較市售石墨所製備的石墨烯氧化物薄膜高出2.87倍。根據產業報導指出，目前人造石墨的價格為1,450 美元/噸，而石墨稀價格為28.57 美元/克。在本研究中生質炭與石墨稀炭材料之收率分別為31.46與23.44 %，其生產成本約為400元。因此利用生質碳製備之石墨烯碳材料與其氧化物薄膜可大幅降低開發成本。

關鍵字

生質物 ； 碳材料 ； 生質碳 ； 石墨 ； 石墨烯

並列摘要

Graphene is a monolayer graphite and has higher electron mobility than silicon, high heat conduction and special optical properties. It can be a potentially new semiconductor material and could be applied in transparent conductive thin film, dye-sensitized solar cells, super capacitors and composites. Many graphene manufacturing methods have been proposed, such as chemical vapor deposition, chemical reduction of graphene oxide and the exfoliation method. However, these processes are complicated by a high cost and the difficulty of removing byproducts. Therefore, the market mechanisms of graphene have not yet been established. In this study, we would like to propose a feasible method to characterize graphene sheet content quantitatively in carbon materials and processes for preparing high graphene sheet content carbon material (GSCCM) from biochar.
From our results, an empirical equation was found to calculate the graphene sheet content quantitatively in carbon-containing materials using an XRD spectrometer. Graphene sheet content, in a series of pyrolized biochar material powders, was calculated at a peak 2θ = 41° (d100) using XRD and resistivity measurement. The resistivity of ideal graphene powder was predicted to be 0.01 Ω‧cm, which was consistent with commercial reduced graphene oxide, and the highest graphene sheet content of GSCCMs from Elaeis biochar materials after CH3COOH impregnated through pyrolysis processes and catalytic pyrolized (added Na2O) is 83.86 and 82.88 %, respectively; its average conductivity is 84.690 and 78.895 S/cm, respectively.
From SEM analysis, the formation of graphene sheet related with α-cellulose content of woody biomass materials, and that with the processes of GSCCMs added to some metal oxides as catalysts, the graphite spherical grains and cytoskeleton surface of wood cells were separated leaving some holes by Na2O catalyst at 1500 oC, and the size (~ 0.5 to 1 μm) of the holes was similar to the graphite spherical grains. We conjecture that the Na2O catalyst can cause the swelling of graphite spherical grains at high temperatures (above 1500 oC), and the phenomenon might have resulted from the sodium impregnation of α-cellulose. Therefore, we can produce carbon materials with adjustable hole sizes through the addition of metal oxides as catalysts. With the production of GSCCMs from pyrolized α-cellulose powder, the graphene sheet content is 93.01 %.
The prepared GOPs from homemade graphene sheets contained carbon materials (GSCCMs) and evaluated the thermal properties of GSCCM derived GOPs. Results show that the GSCCM derived GOPs have high temperature phase transitions, and the average phase change enthalpy is 9.41 J/g, which is 2.87 times higher than graphite derived GOP. According to the industry reports, the cost of artificial graphite and graphene for the CVD process is 1,450 USD/ton and 28.57 USD/g, respectively. In this study, the yield of biochar and GSCCMs was 31.46 and 23.44 %, respectively. The production cost of GSCCMs was about 400 TND/ batch. Therefore, preparing GOP from GSCCMs could highly reduce the cost.

並列關鍵字

Biomass ； Carbon materials ； Biochar ； Graphite ； Graphene

參考文獻

117. 蔡伯達，2014，以濕式化學法自炭材中分離出石墨烯氧化物之研究，碩士論文，國立屏東科技大學，環境工程與科學系研究所，屏東縣。

69. 張齡尹，2008，應用奈米二氧化鈦及奈米碳管於開發新穎處理含苯乙烯廢水及廢氣之聚合去除系統，碩士論文，國立屏東科技大學，環境工程與科學系研究所，屏東縣。

51. 暉盛科技股份有限公司，http://www.nemstek.com.tw/ch/film_2.htm。

46. Milla, O. M. V., 2013, Preparation and Plant-growth Efficiency Assessment of Biochars, Ph.D. Dissertation, National Pingtung University of Science and Technology, Department of Tropical Agriculture and International Cooperation, Pingtung.

29. 林文清，2007，微晶纖維素廢料之活性碳熱裂解資源化研究，碩士論文，國立中央大學，環境工程研究所，桃園縣。