- 學位論文
二氧化鈦/鈦酸鹽奈米管之合成、特性鑑定其處理染料廢水之研究
Synthesis and Characterization of Titanium Dioxide/Titanate Nanotubes Applied to Dye Wastewater Treatment
摘要
近年來，半導體觸媒的異相光催化反應在環境污染防治的研究上相當廣泛，其中奈米二氧化鈦光觸媒材料因具有高活性、化學穩定性、無毒性及容易取得之優點，故應用性極具潛力，為了增加二氧化鈦的比表面積及催化效果，故進一步使用容易合成及可以量產之水熱法來製備二氧化鈦(TDNs)/鈦酸鹽奈米管(TNTs)，以提升目前光催化觸媒之分解能力。因此，本研究之主要目的在於開發TDNs/TNTs之合成條件及其特性分析，並深入探討TDNs/TNTs之結構差異，及對不同特性染料廢水測試光催化及吸附之效能。另外，亦以Langmuir-Hinshelwood動力模式及擬二階吸附動力模式，以求得光催化反應動力及吸附動力參數。 本研究中使用前驅物二氧化鈦銳鈦礦，以不同反應溫度110 ~ 270oC製備出鈦酸鹽奈米管/棒，並改變不同酸洗時間12 ~ 60 h製備TDNs(銳鈦鑛型)。經場發掃描式電子顯微鏡(FE-SEM)及穿透式電子顯微鏡(TEM)觀察發現，TNTs管長約50 ~ 100 nm，管徑約10 ~ 15 nm，經X光粉末繞射儀(XRPD)可得知其組成具有氫/鈉鈦酸鹽的晶相(例如(H,Na)2Ti3O7 •xH2O)，能量散射光譜儀(EDX)得知TNTs其成分包含鈦、氧及鈉。TDNs經場發掃描式電子顯微鏡(FE-SEM)及穿透式電子顯微鏡(TEM)觀察發現，TDNs管長約50 ~ 100 nm上下，管徑約10 ~ 15 nm，經X光粉末繞射儀(XRPD)可得知其組成具有二氧化鈦銳鈦礦及鈦酸鹽化合物的晶相，能量散射光譜儀(EDX)得知二氧化鈦奈米管其成分包含鈦及氧。 BET分析結果顯示，二氧化鈦奈米管比表面積高達292 m2/g及總孔體積為1.02 cm3/g，高於鈦酸鹽奈米管之比表面積277 m2/g及總孔體積為1.145 cm3/g。另外，以延伸細微結構X光吸收光譜(EXAFS)及X光吸收邊緣結構光譜(XANES)來觀察TDNs/TNTs結構，由XANES實驗數據分析結果可知，TDNs/TNTs兩者氧化價數為Ti4+，TNTs與銳鈦礦結構相似，而TDNs為octahedral配位結構。另外，由EXAFS光譜分析之結構參數，可說明TNTs第一層結構Ti-O之鍵長約為1.94 Å，配位數為2，而TDNs第一層結構Ti-O之鍵長約為1.95 Å，配位數為2，推估配位數的改變是因為結構上的變化，從原本的完整的晶體，先溶解後再捲曲形成管狀結構所造成的。故能證明本研究所製備的TDNs/TNTs已經改變了原本前驅物銳鈦礦之結構。以FTIR及ESCA分析得知，TDNs/TNTs有H-O-H、Ti-O及Ti-O-H鍵之存在，表示奈米管有水分存在。在紫外-可見光譜分析得知，TNTs及TDNs臨界波長分別為378及385 nm，表示TDNs比TNTs更容易受光激發，並且較前驅物銳鈦礦的382 nm更容易被激發。由RAMAN分析得知，TDNs(TNTs)的組成，包含部分鈦酸鹽結構以及部分二氧化鈦銳鈦礦結構(鈦酸鹽結構)。由TGA測試結果顯示，400 ~ 600oC之重量損失為管狀結構物轉換成顆粒狀物後，所產生的些微重量損失。 由Dubinin-Kaganer-Radushkevick (DKR) equation可以求出E吸附能對於Basic Green 5及Basic Violet 10可以符合離子交換機制之值皆位於8 ~ 16 kJ/mol。由凡德赫夫(van't Hoff equation)方程式可以求得其吸附熱，並且吸附過程為放熱反應。由Boyd kinetic model決定，表示外部質量傳送為速率決定步驟。照射UV催化染料廢水實驗中，TDNs/TNTs奈米管的光催化對的不同染料的去除率依序為Basic Violet 10>Basic Green 5>Methylene Blue>Acid Blue 9。光催化動力模式使用簡化之Langmuir-Hinshelwood動力學模式，來描述染料的分解反應，其中Basic Violet 10分解速率最佳，K值為0.00894 min-1。
並列摘要
Recently, titanium dioxide has been recognized as an excellent photocatalyst material applied on many field especially for environmental science or engineering. Titanium dioxide nanotubes (TDNs)/titanate nanotubes (TNTs) with high specific surface area have been also studied due to its excellent catalytic activities, long-term stability, non-toxicity, and low cost. Therefore, the main objectives of the present study were to prepare TDNs/TNTs in large quantities by hydrothermal routes and to characterize the photocatalytic properties, fine structures, formation mechanism, adsorption abilities of TDNs or removal efficiency of dye pollutants in wastewaters by TDNs/TNTs. In addition, via Langmuir-Hinshelwood model and pseudo-second-order equation determining the photocatalytic kinetic parameter and adsorption kinetic parameter was also investigated. Experimentally, anatase TiO2 nanoparticle was used as a precursor for TDNs/TNTs synthesis. The TNTs characterized by FE-SEM and TEM microphotos were fabricated in different reaction temperatures of 110 ~ 270 ℃. The results showed that the length and diameter of TNTs ranged of 50 ~ 100 nm and 10 ~ 15 nm, respectively. The XRPD patterns showed that TNTs are sodium/hydrogen titanate structures (e.g. (H,Na)2Ti3O7 xH2O). The EDX data indicated that TNTs consist of Ti, O, and Na atoms. In addition, the results showed that the length and diameter of TDNs ranged of 50 ~ 100 nm and 10 ~ 15 nm, respectively. The XRPD patterns showed TDNs are anatase-typed and titanate structures. The EDX data indicated that TDNs were composed of Ti and O atoms. The BET surface area (pore volume) of TDNs and TNTs are 292 m2/g (1.02 cm3/g) and 277 m2/g (1.145 cm3/g), respectively. X-ray absorption near edge structure (XANES) or extended X-ray absorption fine structure (EXAFS) spectroscopy was performed to identify the oxidative station and fine structures of TDNs and TNTs. By using XANES spectra, the valency and framework of TDNs (TNTs) are Ti(IV) with octahedral (similar anatase) structures. The EXAFS data revealed that TDNs (TNTs) have a first shell of Ti-O bonding with bond distances of 1.95 Å (1.94 Å) and coordination numbers were 2 (2). Furthermore, investigation of the formation mechanism of these TDNs/TNTs was also conducted. The results revealed that the TiO2 anatase nanoparticles can be solved into layer under strong alkaline. The layer may further curl itself to reduce the energetics and form these TDNs/TNTs. FTIR and ESCA spectra showed that the existence of moisture with H-O-H, Ti-O or Ti-O-H bonding on the surface of TDNs. The UV/Vis spectra revealed that the critical wavelength of TDNs and TNTs are 385 nm and 378 nm, respectively. RAMAN spectra showed that form of TNTs (TDNs) consist of titanate structure and anatase structure (titanate structure). The TGA curves of TDNs oxidation showed that the tubular structures transform to particle nanophases ranged of 400 ~ 600℃. The adsorption mechanisms of BG5 and BV10 onto TDNs/TNTs are examined with an aid of the DKR equation for ion-exchange mechanism, in which the sorption energy lies within 8-16 kJ/mol. The heats of adsorption, calculated from the van't Hoff equation and the adsorption is an exothermic process. Via Boyd kinetic model, implying external mass transport mainly governs the rate-limiting process. From the experimental data of the dye wastewaters removal under ultraviolet light irradiation, the photodegradative efficiencies of four kind of dyes solutions on TDNs/TNTs were Basic Violet 10>Basic Green 5>Methylene Blue>Acid Blue 9. Finally, a simple Langmuir-Hinshelwood was used and calculated by the relationship of ln(C0/Ca) versus time to describe the reactions of the dye wastewaters. Basic Violet 10 photodecomposion rate was the highest photocatalytic efficiency with K of 0.00894/min.