本研究將商業化的二氧化鈦置於氫氧化鈉溶液中，經水熱法處理後再以鹽酸清洗後可合成具有不同性質的奈米管凝團體。孔洞結構分析顯示較小的孔是屬於奈米管的貢獻，較大的孔徑則為奈米管凝團體的間隙所造成。當水熱溫度介於110-150°C時，發現合成條件不只會影響粒狀物形成板狀物的轉換程度，也會導致酸洗過程奈米管的形成，另外在煅燒熱處理時，其合成溫度也會使奈米管從anatase相轉成rutile相的轉換溫度隨之增加。奈米管凝團體的表面積隨水熱溫度的增加到130°C時可達到最大值400 m2/g，而當水熱溫度高於130°C則隨溫度的增加而下降。在鹽酸清洗過程中，板狀結構的表面電荷移除速率和最後的靜電荷狀態都會對板狀結構捲成奈米管產生影響。這說明了奈米管結構是可由酸洗的條件所控制。
　　本研究說明二氧化鈦經水熱處理後由酸洗所合成的奈米管，可藉由簡單的酸洗和鹼洗步驟的順序不同，而使其結晶結構重覆出現。二氧化鈦經鹼液水熱處理後，其板狀結構的晶相為一種二價鹽的鈦酸結構Na2Ti2O5·H2O。在酸洗的過程中，隨著酸性的增加，板狀結構中的鈉離子被氫離子所取代，而使板狀結構捲成奈米管，最後再轉成anatase相的二氧化鈦粒狀物。藉由晶相結構分析也証明了titanate/titania可透過一種簡單結構重組而轉換。最後本研究用完整的流程圖說明了二氧化鈦經水熱處理再酸洗而形成奈米管，以及奈米管經由酸鹼清洗而產生結構轉換的過程。
　　在應用方面，NO氣體於選擇性觸媒還原反應(SCR)中被氨氣還原的實驗，証明了奈米管的高表面積較容易使反應氣體進入觸媒表面而使還原轉換效率提高。

　Titania nanotube aggregates with different porosities were prepared from hydrothermal treatment on commercial TiO2 particles in NaOH followed by HCl washing. Pore structure analysis reflects that pores of smaller sizes are mainly contributed by the nanotubes while those of larger sizes by the interspace region of the aggregates. The hydrothermal treatment temperature, ranging within 110-150°C, was shown to affect not only the extent of particle-to-sheet conversion, and thus the resulting structures of the nanotubes, but also the anatase-to-rutile transformation at high temperatures. The surface area of the nanotube aggregates increases with the treatment temperature to reach a maximum of ca. 400 m2/g at 130°C, and then decreases with further increase of the temperature. In HCl washing, both the charge-removal rate and final state of the electrostatic charges on TiO2 affects the rolling of TiO2 sheets into nanotubes. This demonstrates that the nanotube structure can be regulated by adjusting the washing condition. Selective catalytic reduction of NO with NH3 has been conducted to prove that the vast surface of the nanotube aggregates is accessible to the interacting molecules.
　We demonstrated that nanotubes synthesized from NaOH treatment on TiO2 with subsequent acid washing could proceed with repeatable crystalline-structure transformation through a simple acid/base washing step. By providing the unit cell parameters, a divalent-salt titanate (Na2Ti2O5·H2O) with layered structure was identified to be the structure formed after the NaOH treatment. With the increase of the acidity in the post-treatment acid washing, the layered titaniate transformed into nanotube through Na+/H+ substitution and eventually transformed into anatase TiO2. Crystalline-structure analysis has shown the feasibitity of this titanate/titania transformation through a simple structure rearrangement. A complete scheme for the formation and transformation of nanotubes caused by the NaOH treatment and the post-treatment washing was proposed.

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