利用臨場紅外光譜研究二氧化鈦材料與硫化銦材料在光催化二氧化碳還原中所扮演之角色

Abstract

光催化還原是現今熱門研究的主題。為了解決光觸媒材料現今困於低效率以及低選擇性。因此需要對光觸媒材料以及二氧化碳還原有更進一步的認識。本論文利用臨場紅外光技術研究二氧化碳還原反應在光觸媒材料表面的行為。在光觸媒材料裡面，二氧化鈦材料已經被廣泛研究，本論文針對Pure-TiO2、H-Ni-TiO2以及SCN-H-Ni-TiO2 三種二氧化鈦基材料進行探討尤其是表面處理。除了二氧化鈦材料本論文選用ZnS、In2S3以及ZnS/In2S3 混和物進行探討尤其是異質介面。 此研究發現在二氧化鈦基材料裡面SCN-H-Ni-TiO2表現出了與兩個二氧化鈦材料對於二氧化碳及水有更多的吸附量。而在ZnS/In2S3 (2:1)材料可以觀察到In2S3是主導二氧化碳吸附的分子，同時在ZnS/In2S3 (2:1)有比另外兩者有更多的吸附。在光催化二氧化碳還原過程中，二氧化鈦材料以及硫化銦材料裡面都可以觀察到COOH*的生成，這表示兩者有同樣的中間產物。 二氧化碳以及水是光催化二氧化碳還原過程中必備的兩個反應分子。為了更進一步探討二氧化碳以及水在光觸媒材料表面的作用，本論文設計了順序實驗去進行探討。二氧化鈦材料以及硫化銦基材料依先二氧化碳再水的順序以及先水再二氧化碳的順序利用臨場紅外光譜以及氣相層析光譜分析。在氣相層析光譜結果是先二氧化碳再水的效率會比先水再二氧化碳的效率還要好。結合紅外光譜的數據，本論文針對順序實驗提出了兩種不同的表面機制行為。第一個是先通二氧化碳再通水，此實驗會讓二氧化碳直接先吸附在活性位形成CO2-，這是有利於二氧化碳還原反應的發生；第二個是先通水再通二氧化碳，此實驗會讓水先吸附在活性位，造成大量水分解的發生，不利於二氧化碳還原的進行。總結，水及CO2- 在二氧化鈦材料以及硫化銦材料上的二氧化碳還原反應是重要的反應物。未來可以在二氧化碳還原中去探討是否可以利用二氧化碳及水的比例去抑制水分解的行為進行更進一步的研究。

Photocatalytic CO2 reduction is one of the most popular subjects of recent research. However, the photocatalyst is still showing low efficiency and low selectivity. In order to solve this problem, further understanding of photocatalyst materials and carbon dioxide reduction is important. In this thesis, the in-situ FTIR studies the behavior of carbon dioxide reduction reaction on the surface of photocatalyst materials. In the photocatalyst material, titanium dioxide has been widely studied because of their unique physicochemical properties. The adsorption behavior of CO2 and H2O of three kinds of TiO2-based materials including Pure-TiO2, H-Ni-TiO2 and SCN-H-Ni-TiO2 were studied. In addition to TiO2-based materials, the role of sulfide-based materials such as ZnS and In2S3 and their hybrid in photocatalytic CO2 reduction was examined. The adsorption behavior of CO2 and water H2O vapor before photocatalytic CO2 reaction was investigated by in-situ FTIR. In the TiO2-based materials, SCN-H-Ni-TiO2 shows more adsorption of carbon dioxide and water than the other TiO2-based materials. In sulfide-based materials, In2S3 dominates the adsorption behavior of carbon dioxide species. The hybrid materials such as ZnS/In2S3 show when used alone more adsorption of carbon dioxide and water than the ZnS and In2S3 samples. In this thesis, CO2 reduction on the samples were investigated by GC and FTIR. In FTIR, the formation of COOH* can be observed in both TiO2-based materials and the In2S3-based materials. Carbon dioxide and water are two essential molecules in photocatalytic CO2 reduction. In order to study the role of CO2 and H2O on the photocatalyst surface including TiO2-based materials and In2S3-based materials, in-situ FTIR and GC measurement were performed under CO2 and H2O in sequence and H2O and CO2 in sequence. In GC results, introducing CO2 and H2O in sequence showed better performance than H2O and CO2 in sequence. Combined FTIR results, this thesis proposes two different surface mechanism behaviors for sequence experiment. In CO2 and H2O in sequence experiment, the CO2 will directly adsorb to the active site to form CO2-, which is beneficial to the CO2 reduction. In H2O and CO2 in sequence experiment, water will occupy active site, causing the water splitting, which adversely affects CO2 reduction. In summary, H2O and CO2- are important reactants for CO2 reduction on TiO2-based materials and In2S3-based materials. This work provides the insights of controlling the amount of CO2/H2O to control water splitting process on the surface during photocatalysts CO2 reduction, which can be further studied in the future.