人類對於石化能源過度使用的結果，已導致大氣中二氧化碳(CO2)的濃度劇烈增加，造成全球暖化現象愈來愈嚴重，嚴重地影響氣候變遷，導致海平面上升，危害到整個生態環境。因此，對於減少大氣二氧化碳含量已是刻不容緩的事。此外，將二氧化碳捕捉下來，利用光觸媒將其還原成碳氫化合物再利用，不僅能減少大氣中的二氧化碳含量，也能開發出新能源的來源。
本研究透過陽極氧化法，並藉有改變電壓方式，來製備出獨立雙開口式二氧化鈦奈米管陣列(open-ended TiNT)，相對於一端封閉的奈米管陣列結構(close-ended TiNT)而言，此流通式奈米管結構，使反應物能更容易進到管柱內部，增加反應物接觸面積。此外，藉有尿素於高溫下會熱裂解產生氨氣，來將氮摻雜到二氧化鈦晶格中(ON-TiNT)，進而修飾觸媒能隙以增加對可見光能量的吸收。
本研究以亞甲基藍光降解實驗，測試在紫外光燈照射下的觸媒降解效率，發現OA-TiNT約四小時即可將亞甲基藍完全分解，其光降解效率約為CA-TiNT的1.45倍。光還原二氧化碳效率，在模擬太陽燈照射下，OA-TiNT的甲醇產率約為CA-TiNT的1.7倍，ON-TiNT的產率約為CN-TiNT的1.6倍。顯示出將薄膜底部阻礙層移除後，能增加反應物與觸媒接觸的機會，推論為雙開口奈米管結構具有較好的光還原甲醇產率的原因。

The excessive use of fossil fuels has dramatically increased the concentration of CO2 in the atmosphere. Global warming has become more serious and made a significant impact on the climate change and ecological environment. Therefore, the reduction of atmospheric CO2 is an urgent issue. The use of photocatalyst to convert CO2 into hydrocarbons can not only reduce atmospheric CO2 but also develop new energy sources.
In this study, free-standing open-ended TiO2 nanotube array has been successfully fabricated by raising the voltage at the end of anodization process. Compared with the close-ended structure, the flow-through nanotube structure facilitate the reactants to flow into the inside of the tube. Moreover, in order to absorb more visible light, we doped nitrogen into TiO2 to modify the band gap by annealing under urea ambient (ON-TiNT).
The degradation of TiNT catalyst was tested by the photodegradation of methylene blue solution under UV irradiation. The complete decoloration of methylene blue solution by the OA-TiNT was observed in 4 hours with a degradation efficiency about 1.45 times of the CA-TiNT. For CO2 photoreduction experiment, the methanol yield by OA-TiNT was 1.7 times of the CA-TiNT, whereas ON-TiNT was 1.6 times of the CN-TiNT under Xe lamp irradiation. Our results show that open-ednded TiNT provides the increase of the methanol yield which might be attributed to the increased reaction surface area after removing the bottom cap of close-ended TiNT.

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