CO2是造成溫室效應的主因之ㄧ，近年大氣層中的二氧化碳濃度劇烈增加，使得全球暖化日益嚴重。因此探討及應用二氧化碳固定（carbon dioxide fixation）技術減少其在大氣的含量是目前減緩全球暖化的重要課題。使用半導體光觸媒將CO2光還原成甲醇或其他碳氫化合物，不僅可應用於減低CO2排放，更進一歨轉換成具經濟效益的有機化合物。
本研究透過含氟離子的有機電解液可以在金屬鈦片基材上，在固定電壓下生長直立且分佈密集的二氧化鈦奈米管陣列，並且透過與尿素的共同鍛燒下，進行氮的摻雜。二氧化鈦奈米管相對與奈米粒子，長管狀奈米材料以及垂直站立的陣列式分佈，提高了電子電洞的分離效率，而且固定在基材上的二氧化鈦奈米管可避免分散在液中而難以收集；另外氮的摻雜可以提昇可見光區吸收的能力，藉此提升光觸媒在太陽下使用的效率，使用熱分解尿素產生氨氣來進行氮摻雜，相對使用氨氣通入管型爐的方法來的便宜且效果不錯。因此本實驗藉由此新穎的材料來進行二氧化碳催化還原的試驗。
在光催化還原二氧化碳方面，在同條件下與二氧化鈦奈米粒子所組成的薄膜比較下，二氧化鈦奈米管陣列薄膜展現出優異的催化效率，比起P25所構成的薄膜好上5倍 。而在氮摻雜提昇可見光吸收的實驗中，發現以500℃中進行氮摻雜的光觸媒展現出來的效率最佳，和未經氮摻雜的光觸媒比較，在模擬太陽燈下，提昇了約2.5倍的催化效率。

Carbon dioxide is the major contributor to greenhouse effect. Recent year, the concentration of carbon dioxide increased dramatically, and made global warming become more serious. Discussion and application of carbon dioxide fixation technology to reduce its content in the atmosphere is an important topic of global warming mitigation. The use of semiconductor photocatalyst to photoreduce CO2 into methanol or other hydrocarbons. This way can be applied not only to reduce the CO2 emissions, but also convert CO2 into economic organic compounds .
In this study, we can fabrication vertical distribution and density of titanium dioxide nanotubes arrays on titanium foil, through the organic electrolyte containing fluoride ions and fixed-voltage DC power. And we doped nitrogen into catalyst by annealed it with urea. Compare to nanoparticles, titanium dioxide nanotubes arrays can promote the separation of electron-hole pair. The immobilized catalyst film is much easy to recycle and be used again. Doping nitrogen can enhance the capacity of absorption of visible light, by this way, we can enhance the efficiency of the use of photocatalysis under solar light.
In the study of CO2 reduction, the yield of titanium dioxide nanotubes arrays thin film is much better than nanoparticles thin film. Under simulator solar light, the yield of catalyst which doped nitrogen is better than undoped one, and the one annealed under 500 ℃ show the highest yield.

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