| 摘要: | 本研究製備具高表面積之中孔洞分子篩SBA-15 再嫁接二氧化鈦 薄膜， 製得具有高表面積之光觸媒材料。藉由摻入光敏劑 (2,9-dichloroquinacridone, DCQ)作為可見光的光觸媒，或負載貴重金 屬提升觸媒之活性。本研究製得之觸媒可運用於能源及環保技術上， 其中，光催化還原二氧化碳生成甲醇之反應可運用在溫室效應氣體減 量及新能源開發，水楊酸光降解反應以及一氧化碳氧化反應，可作為 環境之污染物之控制技術。 我們以不同種類模板劑製得兩種不同孔道型態的分子篩─以 P123 製備SBA-15 及以P123、SDS、C16TMAB 製備具垂直孔道之 vc-SBA-15。再以四丁基鈦為鈦源利用迴流嫁接法製得TiO2/SBA-15 及TiO2/vc-SBA-15。由HRTEM 照片顯示SBA-15、vc-SBA-15 皆具 有整齊的孔洞結構，但相較於SBA-15，vc-SBA-15 的孔道垂直且較 短。XRD 結果顯示SBA-15 及vc-SBA-15 均具有(100)之特徵繞射峰， 為典型二維六角結構；嫁接二氧化鈦後，分子篩TiO2/SBA-15 及TiO2/ vc-SBA-15 在形貌以及結構並無明顯改變。由氮氣等溫吸附測得 SBA-15、vc-SBA-15 之表面積分別為725 及797 m2/g，嫁接二氧化鈦 後，TiO2/SBA-15 及TiO2/vc-SBA-15 之表面積下降為573 及584 m2/g。 由UV-Vis 圖譜顯示波長在低於380 nm 有明顯吸收，表示二氧化鈦 成功嫁接於SBA-15 及vc-SBA-15 擔體表面。紫外光 (400 W Halide lamp) 光催化還原水中二氧化碳之結果顯示，具有垂直孔道的 TiO2/vc-SBA-15 具有較佳的光催化活性，在NaHCO3 (pH = 3) 的溶液 中照光48 hr 的甲醇產率可達到11.5μmole/g-cat.•hr。 摻入DCQ 的觸媒在波長500-600 nm 有明顯可見光吸收。經TGA 求得DCQ/TiO2/SBA-15 及DCQ/TiO2/vc-SBA-15 的DCQ含量約為2.0wt%及4.6 wt%。以可見光 (100 W Halogen lamp) 光催化還原水中二 氧化碳之結果顯示，具有垂直孔道的DCQ/TiO2/vc-SBA-15 具有較佳 的光催化活性，在NaHCO3(pH = 3)的溶液中照光48 hr 的甲醇產率可 達到0.44μmole/g-cat.•hr。 以光化學沉積法製備以含二氧化鈦中孔分子篩為擔體之鉑、銠及 鉑-銠觸媒。HRTEM 照片顯示各觸媒之顆粒大小約2-5 nm 且均勻分 布在各分子篩擔體上。XRD 結果顯示負載鉑、銠後，並未影響分子 篩之結構。紫外光光催化水中二氧化碳還原反應的結果顯示，擔體 鉑、銠及鉑-銠觸媒對光催化還原水中的二氧化碳均有相當好的反應 活性，其中以Pt/TiO2/SBA-15 的光催化活性最佳，在NaHCO3 (pH = 3) 的溶液中照光48 hr 的甲醇產率可達到40 μmole/g-cat.•hr，相較於未 負載鉑之觸媒其活性提升了三倍。在水楊酸光催化降解反應中，觸媒 的光降解活性為：鉑觸媒 > 鉑-銠觸媒 > 銠觸媒。在一氧化碳氧化 反應結果顯示，相較於TiO2/SBA-15，具有垂直孔道之TiO2/vc-SBA-15 有較佳轉換效率；且鉑-銠觸媒 > 銠觸媒 > 鉑觸媒。 In this study, TiO2 photocatalyst materials with high surface area were prepared by grafting a TiO2 thin layer onto SBA-15. Photosentisizer (2,9-dichloro quinacridone, DCQ) is impregnated to extend their use of visible light. And metal nanoparticles are immobilized to promote their photocatalytic activities. These prepared catalysts were employed in photocatalytic reduction of CO2 for mitigating the greenhouse gas effect and serving as a new energy source. We used P123 surfactant as a template to prepare conventional SBA-15, and used ternary surfactants (C16TMAB/SDS/P123) to prepare vc-SBA-15 with vertical nanochannels. TiO2/SBA-15 and TiO2/vc- SBA-15 were prepared by grafting a thin layer of TiO2 onto SBA-15 and vc-SBA-15 with TBOT as Ti source. HRTEM images showed that vc-SBA-15 had short and face-up nanochannels, which was extremely different from SBA-15 of longer parallel channels. The XRD patterns of SBA-15 and vc-SBA-15 exhibited a characteristic (100) peak, indicating that they were of highly ordered hexagonal structures. After grafting with TiO2, there were no significant changes in the morphology and structure. Meanwhile, the surface area of SBA-15 was decreased from 725 m2/g to 573 m2/g, and that of vc-SBA-15 was also decreased from 797 m2/g to 584 m2/g as determined by N2 sorption isotherms. UV-Visible spectrum showed that a strong absorption band occurred at the wavelength less than 380 nm, indicating that TiO2 was successfully grafted onto the mesoporous silica. Photosensitizer DCQ was then introduced in order to facilitate the TiO2-containing catalysts to extend the use of visible light. As shown by UV-Visible spectrum, the obtained catalysts had obvious absorption ranged from 500 to 600 nm. The DCQ uptake of DCQ/TiO2/SBA-15 and DCQ/TiO2/vc-SBA-15 were 2.0 wt% and 4.6 wt%, respectively, as estimated by TGA. The photoreduction of CO2 was conducted in NaHCO3(aq) under visible and UV light illumination. As a result of the short and face-up nanochannels that permits the higher accessibility for the reactants, the methanol yield of vc-SBA-15 supported photocatalysts were much higher than those of SBA-15 supported ones. The methanol yield of DCQ/TiO2/vc-SBA-15 was 0.44 μmole/g-cat./hr under visible light irradiation, whereas that of TiO2/vc-SBA was 11.5 μmole/g-cat./hr under UV irradiation. Platinum and/or rhodium nanoparticles were immobilized on the TiO2/SBA-15 and TiO2/vc-SBA-15 by photochemical deposition method. The metal particle size of the prepared catalysts were about 2 - 5 nm as observed by HRTEM. The catalytic activities of were evaluated by photoreduction of CO2, photodegradation of salicylic acid and CO oxidation. For photocatalytic reduction of CO2, it was found that the methanol of TiO2-containing catalysts can be substantially enhanced by metal modification. For photodegradation of salicylic acid, the activities were in the order: Pt > Pt-Rh > Rh. For CO oxidation, it was found that the activity of TiO2/vc-SBA-15 was higher than TiO2/SBA-15. The catalytic activities of catalysts supported the metal for CO oxidation were in the order: Pt-Rh > Rh > Pt. |
