奈米磁性二氧化鈦可見光光觸媒之合成與鑑定

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Title:	奈米磁性二氧化鈦可見光光觸媒之合成與鑑定
Other Titles:	Synthesis and Characterization of Visible-Light-Active Titania Photocatalysts of Magnetic Core-shell Type
Authors:	莊富鈞 Chuang, Fu-Chun
Contributors:	張瓊芬 Chang, Chiung-Fen 東海大學環境科學與工程學系
Keywords:	磁性、光降解、可見光、二氧化硫、Langmuir-Hinshelwood動力式模擬、鄰苯二甲酸二甲酯(DMP)、二氧化鈦 magnetic, photodegradation, visible-light-active, sulfide, Langmuir-Hishelwood model, Dimethy
Date:	2010
Issue Date:	2011-01-24T07:27:37Z (UTC)
Abstract:	由於光催化反應直接在接收光照之觸媒表面上進行，因此具大外表面積之材料在選擇上佔較高的優勢。因奈米材料具新穎之物化特性及高反應面積，近年來學者致力於奈米材料之開發，尤其是光觸媒材料二氧化鈦。在光觸媒材料方面，較常使用在固液反應的方法不外乎是將光觸媒批覆於穩定之基材上的固定床式及泥漿式兩種系統，固定床式簡單易操作但是受限於受光面積而侷限其處理效率；而利用泥漿式系統雖可完全的在液相中均勻分散並有較大的受光面積及降解效果，但奈米尺寸顆粒之固液分離卻是個必須考量的任務，若對於奈米光觸媒賦於磁性，簡單的磁性分離技術對於所使用之奈米光觸媒進行固液分離乃是一可行之方法。另，未經改質之奈米材料，於可見光下並無良好的活性，因此利用改質技術使其增加在可見光下之活性，將可使奈米光觸媒之應用更加具實用性。因此，本研究之標的為合成與鑑定奈米磁性二氧化鈦可見光光觸媒，並將其應用於環境荷爾蒙鄰苯二甲酸二甲酯（DMP）之光催化降解。本實驗室先前利用溶膠凝膠法成功的合成其磁性載體(SiO2/Fe3O4,M)，接著利用改質技術將硫摻雜至二氧化鈦中並批覆於磁性載體上，合成硫改質之可見光光觸媒(S-TiO2/SiO2/Fe3O4, SM-TiO2)。此外亦利用穿透式電子顯微鏡(TEM)、超導量子干涉儀(SQUID)、化學分析電子能譜儀(ESCA)、傅氏轉換紅外線光譜儀 (FTIR)、X-ray繞射(XRD)、螢光光譜(PL) 、紫外光可見光吸收光譜儀(UV-VIS-NIR spectrometer) 及電泳(Electrophoresis)等，以得知合成之觸媒物化特性。研究結果顯示，SM-TiO2之摻雜量及鍛燒溫度之最佳條件範圍區域分別在1.3-1.88 at.%及514-550oC之間;改質過後之材料粒徑皆小於20 nm且分散性較較良好，晶相主要為銳鈦礦相，而鍛燒溫度提升至750oC時，才會產生金紅石相;隨著硫摻雜量的增加，其pHpzc值也隨之下降;摻雜量在1.6at.%時，其電子電洞對結合速率較慢，其SQUID測量之飽和磁化度為6.88emu g-1;由FTIR圖譜可發現在波長1050及1131 cm-1有SO42-的產生，而由XPS可得之SM-TiO2只發現硫替換鈦的情形，且在529.6、530.4及531.6的地方有明顯之波鋒，分別為Ti-O-Ti、Ti-O-S及S-O-S之鍵結。SM-TiO2在催化系統當中，最佳投入劑量為1.2 g L-1，其等溫吸附及光催化動力皆可成功的使用Langmuir與Freundlich等溫吸附方程式及Langmuir-Hinshelwood動力模式進行良好之模擬。SM-TiO2之回收再利用之探討，經過六次重複實驗後，其反應速率皆保持在0.0185至0.0147 mg L-1 min-1 g-1之間，其物化特性相當穩定。故本研究成功的合成奈米磁性二氧化鈦可見光光觸媒並有效的降解水中汙染物DMP。 Photocatalysts of high surface area (SA) possess superiority for photocatalytic reaction. Therefore, nano-size materials of high SA have been attracting extensive attention for decades due to the novel characteristics and high activity. Nano-sized photocatalysts are mostly used in slurry or immobilized systems, in which the latter does need the further separation equipments. Although the slurry system demands special separation process, the high photocatalytic ability makes it popularly adapted. However, the simple separation of nano-particles from liquid phases is still a difficult task up to now. Another task for traditional photocatalysts is to broaden the application of photocatalysts and make them effective under the visible-light irradiation. In order to overcome these two tasks, this study, therefore, investigated the synthesis of magnetically visible-light-active photocatalysts and their applications on the degradation of the endocrine disrupting chemical of dimethy phthalate (DMP). <br>A series of magnetic S-doped (sulfide doped) TiO2 photocatalysts were synthesized by means of TTIP and thiourea with sol-gel routes. The synthetic parameters (e.g., water concentration of admixture and calcination temperature) were designed with response surface methodology (RSM). Prior to synthesis of S-TiO2, the magnetic carrier (SiO2/Fe3O4, M) was firstly prepared by precipitation (Fe3O4) and sol-gel (SiO2) routes. Sequentially, S-doped TiO2 was coated on magnetic carrier to obtain magnetic visible-light-active photocatalysts (SM-TiO2). The obtained photocatalysts have been characterized by TEM, SQUID, ESCA, FTIR, XRD, PL, UV-VIS-NIR spectrometer and Electrophoresis.<br>The results showed that the optimal condition for SM-TiO2 synthesis is at sulfide loading ratio of 1.3-1.88 at.% and calcination temperature of 514-550oC, judged by the photocatalytic degradation of DMP. The obtained SM-TiO2 was at an average diameter smaller than 20 nm. The UV-VIS-NIR spectrometry showed that the red shift existed in the samples of SM-TiO2. The PL indicated that recombination rates of electron–hole pairs were the slowest for the SM-TiO2 synthesized at the optimal condition. The peaks at around 529.6, 530.4 and 531.6 eV of XPS spectra can be attributed to the oxygen in Ti–O–Ti, Ti–O–S and S–O–S linkages, respectively. The peaks corresponding to 1050 and 1131 cm-1 of FITR spectra confirmed the existence of SO42-. XRD spectra showed that the main crystal of SM-TiO2 was anatase phase. However, as the calcination temperature was as high as 750oC, the rutile phase occurred and was inhibited by the existence of sulfide. With respect to the adsorption and photodegradation of DMP with SM-TiO2, Langmuir and Freundlich isotherms and Langmuir-Hinshelwood model can well describe adsorption and photocatalytic behavior, respectively. In addition, the SM-TiO2 of 6.88 emu g-1 can be easily recovered from the heterogeneous system. After 6 run experiments (e.g., photo-degradation and then recovery for one run), the reaction rate of k was between 0.0185 to 0.0147 mg L-1 min-1 g-1, indicating that the stable physicochemical property. This study demonstrated that novel visible-light-active titania photocatalysts of magnetic core-shell type were successfully synthesized and applied on the degradation of DMP.
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