可見光雙功觸媒氫化二氧化碳與產氫反應

Duel function visible light photocatalyst in hydrogenation of carbon dioxide via hydrogen production.

游勝閎(Sheng-Hung Yu)

指導教授 ： 吳紀聖

國立臺灣大學/工學院/化學工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.00761

摘要

由於人類經濟活動不斷的發展並且無節制地排放二氧化碳，導致大氣中的二氧化碳濃度持續增加、溫室效應增強造成全球暖化。二氧化碳回收再利用不僅可以解決全球暖化的危機，還可以帶來可觀的經濟價值。
本研究主要分為兩部分: (1) 合成可見光光觸媒 GaN:ZnO與觸媒分析 (2) 測試GaN:ZnO 光催化能力。以固態熔融法在氨氣的環境下鍛燒氧化鎵與氧化鋅至1123K能夠合成出可見光光觸媒GaN:ZnO，由UV-Vis圖得知該觸媒可以吸收的波段達到可見光的範圍，能隙為2.6eV，由EDS與XRD圖的結果可以判斷是否成功合成出GaN:ZnO，最後再由TEM與XPS來確認附載共觸媒與其價態。
經過光觸媒反應發現共觸媒附載GaN:ZnO具有兩種能力: (1) 還原二氧化碳 (2)產氫。具有雙種功能的觸媒可大幅度提升光觸媒反應的光亮子效率。本實驗除了製備雙功觸媒之外，額外的還發現了一個有趣的現象，還原二氧化碳與產氫具有相輔相成的功能。
當以GaN:ZnO產氫時，可以利用所產生的氫氣進行二氧化碳氫化反應來製造碳氫化合物，而氫化反應的吉布士自由能為負值，其所代表的意義是該反應為自發性反應，能使反應較容易進行。此外反應中被氫化的二氧化碳所產生的甲醇，其扮演的腳色為犧牲試劑並捕捉電子以進行光催化反應。因此，由氫化二氧化碳與甲醇當犧牲試劑所產生的循環可以提升光催化反應的效率，而其效率值超越現有可見光光觸媒所能達到的效率，在可見光的照射下，氫氣、甲烷、甲醇、甲醛的產率分別為 3.16, 1.12, 2.24, 0.312, μmol/h/g，此外一氧化碳也是其中的產物，而光電子效率為 0.0245%。

關鍵字

可見光光觸媒 ； 氫化二氧化碳 ； 產氫 ； GaN:ZnO ； 單反應器

並列摘要

Global warming has become a major environmental issue to be considered in the 21th century. One possible solution of global warming is the reduction of carbon dioxide. The reduction of carbon dioxide could not only solve the crisis of global warming, but provide a high economic value. Carbon dioxide could be reduced to useful chemicals such as methane, methanol, and other hydrocarbons.
In this research, co-catalyst loaded GaN:ZnO is found to have the ability to perform both photocatalytic reduction of carbon dioxide and produce hydrogen (water splitting) simultaneously. Having the duel functions ability gives the advantages of increasing the conversion of solar energy. An interesting phenomena found while performing photocatalytic reaction of duel function catalyst is that providing the ability of water splitting, carbon dioxide reduction ability is enhanced through the hydrogenation of CO2 [1] through the produced hydrogen. For the reaction in the hydrogenation of carbon dioxide to produce hydrocarbons, the change of Gibbs energy becomes a negative value meaning that the reaction is favorable and is spontaneous. Furthermore, the as produced methanol acted as an electron trap for the enhancement of hydrogen production [2]. Therefore the efficiency of the photocatalyst introduced in this research is higher than recent developed visible light catalyst. The result of Ni/NiO-GaN:ZnO showed a yield of 3.16, 1.12, 2.24, 0.312 μmol/h/g of hydrogen, methane, methanol, formaldehyde respectively.

並列關鍵字

Visible light ； GaN:ZnO ； Photocatalyst ； Water splitting ； CO2 reduction

參考文獻

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3. T. Sakata, T.K., Photosynthesis and Photocatalysis with semiconductor powders. Energy Resources through Photochemistry and Catalysis, 1983: p. 331.

5. Izumi, Y., Recent advances in the photocatalytic conversion of carbon dioxide to fuels with water and/or hydrogen using solar energy and beyond. Coordination Chemistry Reviews, 2013. 257(1): p. 171-186.

6. Abe, R., Recent progress on photocatalytic and photoelectrochemical water splitting under visible light irradiation. Journal of Photochemistry and Photobiology C-Photochemistry Reviews, 2010. 11(4): p. 179-209.