本研究主要探討不同的氧化石墨烯製程做為光觸媒的差異性，分別比較修改式Hummer’s氧化石墨烯(Hummer’s GO, H GO)以及改良式氧化石墨烯(Improved GO, I GO)，根據在氧化過程中不同的操作參數對於二氧化碳光催化還原的影響。
在光催化之實驗中，主要利用批次光催化還原系統，以二氧化碳及水氣連續通入不鏽鋼之反應器中，利用300瓦之鹵素燈照射在氧化石墨烯光觸媒上，再經由自動注射系統注入氣相層析儀-火焰離子偵測器(Gas Chromatography/Flame Ionization Detector, GC/FID)測得產物，本實驗中測得之主要產物為甲醇。在實驗上的參數包括在H GO製程中加入的過錳酸鉀含量，以及在I GO製程中加入的磷酸含量。不同操作參數之結果顯示，在H GO製程中當過錳酸鉀量增加，能隙及氧化程度將增加，但光催化還原產率下降，而在I GO製程中隨著磷酸量增加，能隙及氧化程度也將增加，光催化還原產率也隨之增加，當氧化過程中加入過多磷酸反而降低能隙及氧化程度，產率也將下降。
根據XPS實驗結果與文獻比較，磷酸的添加可以避免氧化石墨烯基面形成C=O之缺陷，所以I GO製程相對於H GO製程可能有較少的缺陷形成在氧化石墨烯基面上，並在三倍磷酸的條件下(I-3P GO)將有最較少的缺陷及較大之氧化程度，對於光催化還原時親水性將有提升，進而幫助還原反應，其中甲醇產率最高將可達到0.124 μmol g-cat-1 hr-1，產率相對於商用二氧化鈦 (Degussa P25)有三倍以上的提升。

In this study, we investigate different oxidation processes of graphene oxide. The original process follows the modified Hummer’s method for the synthesis of graphene oxide (H GO). We also used another process that replaces NaNO3 during oxidation reaction with H3PO4 and called it improved graphene oxide (I GO). We studied the relation between the operating parameters in the oxidation process and methanol yield from the photocatalytic reduction of CO2.
In our experiment, CO2 and water vapor continuously flow into the stainless steel reactor. Then, a 300 W ELH lamp was used to irradiate the photocatalyst. The product was then analyzed using GC-FID. The main product of the experiment was found to be methanol.
In the synthesis of the photocatalyst, we tried to tune the parameters of H GO by changing the amount of KMnO4 during oxidation process. While the amount of KMnO4 increases, the band gap and oxidation level of the GO increases. However, the methanol yield decreases during the photocatalytic reduction reaction. We also tried to tune the parameters of I GO by changing the amount of H3PO4 during oxidation process. Similarly, the amount of H3PO4 increases, the band gap and oxidation level also increases. Importantly, the methanol yield would increase during the photocatalytic reduction reaction. However, excessive H3PO4 passivates the oxidation reaction thus decreasing methanol yield during photocatalytic reduction reaction.
We believe that in the I GO oxidation process, adding H3PO4 could avoid the formation of C=O defects on graphene oxide basal plane. Therefore, I GO process contains less defect formation on graphene oxide basal plane than H GO process. For the optimized conditions, triple H3PO4 treatment (I-3P GO) achieved larger oxidation level and less defect formation. It did not only enhance hydrophilic properties of the catalyst but also promote photocatalytic reduction reaction. In the photocatalytic reduction reaction, we determined that the methanol yield can achieve up to 0.124 μmol g-1 hr-1 using triple H3PO4 treatment (I-3P GO) catalyst. The methanol yield is three times that of TiO2, which is the conventional catalyst in CO2 photoreduction.

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