二氧化鈦奈米管應用於處理染料廢水之研究

Application of Titanium Dioxide Nanotubes on Dye Wastewater Treatment

羅兆鈞(Chao-Chun Lo)

指導教授 ： 林錕松

元智大學/工程學院/化學工程與材料科學學系/碩士(2006年)

https://doi.org/10.6838/YZU.2006.00144

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表面積，本研究乃使用水熱法來製備二氧化鈦奈米管，具有不需繁複的設備及步驟即可得到大量的產物之優點，並且摻雜金屬以增加其光催化能力，因此，本實驗之主要目的在於對二氧化鈦奈米管之合成條件及特性分析進行討論，並探討二氧化鈦奈米管對7種不同特性染料廢水測試光催化之效能及求得反應動力參數。
實驗主要部份包括：使用前驅物二氧化鈦銳鈦礦，以不同反應時間12 ~ 60 h、反應溫度110 ~ 270 ℃及反應濃度5 ~ 10 M，製備二氧化鈦奈米管/棒，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，二氧化鈦奈米管管長約400 ~ 500 nm，管徑約10 ~ 20 nm，奈米棒長度至10 ~ 20微米，管徑在100 ~ 200 nm左右，經X光粉末繞射儀(XRPD)可得知其組成具有二氧化鈦銳鈦礦的晶相，化學分析電子光譜儀(ESCA)、化學成分分析(EDX)發現二氧化鈦奈米棒表面成分包含鈦、氧及鈉，表示二氧化鈦奈米管產物可能生成NaCl。BET分析結果顯示奈米管比表面積達277 m2/g及總孔體積為1.145 cm3/g，高於奈米棒之比表面積18 m2/g及總孔體積為0.101 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)來觀察二氧化鈦奈米管/棒結構，由XANES實驗數據分析結果可知二氧化鈦奈米管/棒兩者氧化價數為Ti4+，並有銳鈦礦與微弱的金紅石的混合晶型存在。另由EXAFS光譜分析之結構參數，可說明二氧化鈦奈米管第一層結構Ti-O之鍵長約為1.94 Å、配位數為2，二氧化鈦奈米棒第一層結構Ti-O之鍵長約為1.96 Å、配位數為3，表示二氧化鈦奈米管/棒之結構不同。此外，也探討二氧化鈦奈米管之生成機制，結果顯示二氧化鈦銳鈦礦粉末在強鹼中溶解成層狀，並以捲曲的生成方式，降低其結晶能量，提升二氧化鈦奈米管之生成可能。
為了探討摻雜金屬對二氧化鈦奈米管之催化提昇效果，使用化學還原法及含浸法製備Tube/Ag、Tube/Pd、Tube/Cu及Tube/Fe，以傅立葉轉換光譜(FTIR)分析發現，奈米管有H-O-H鍵及Ti-O-Ti鍵的存在，表示奈米管有水分存在。由UV之實驗結果得知，奈米管臨界波長為420 nm、奈米棒為400 nm，均較銳鈦礦的380 nm為長，表示比前驅物更容易激發，但是摻雜金屬後的奈米管除了Fe之外，反而臨界波長降低。照射紫外光催化染料廢水實驗中，奈米管的光催化對pH為7的不同染料的去除率依序為Methylene Blue>Basic Violet 3>Basic Green 5>Basic Violet 10>Acid Blue 9>Acid Orange 7>Acid Red 1，其原因經界面電位測定得知，二氧化鈦奈米管在pH 7的溶液下呈負電性，會與陽離子性染料因靜電力而吸引。而由摻雜金屬的奈米管光催化分解染料實驗中，發現Ag、Pd和Cu能夠提昇光催化的速率，但Fe則會明顯降低，表示摻雜金屬確實影響二氧化鈦奈米管的催化能力。不同濃度染料實驗下，發現濃度愈高分解速率愈慢，度愈低速率愈快。光催化動力模式使用簡化的Langmuir-Hinshelwood動力學模式ln(C0/Ca)=kt，並將反應速率分為兩段處理描述染料的分解反應，其中Methylene Blue分解速率最佳，k1為0.02718 min-1，k2為0.01077 min-1。

關鍵字

二氧化鈦奈米管 ； 水熱法 ； 光觸媒 ； 染料廢水 ； 摻雜金屬 ； 同步輻射光譜

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) with high specific surface area have been also studied due to its excellent catalytic activities, long - term stability, nontoxicity, and low cost. Therefore, the main objectives of the present study were to prepare titanium dioxide nanotubes in large quantities by hydrothermal routes and to characterize the photocatalytic properties, fine structures, formation mechanisms of TDNs or removal efficiency of dye pollutants in wastewaters by TDNs.
Experimentally, anatase TiO2 nanoparticle was used as a precursor for TDNs synthesis. The TDNs characterized by FE-SEM and TEM techniques were fabricated in different reaction times of 12 ~ 60 h, reaction temperatures of 110 ~ 270 ℃, and NaOH concentrations of 5 ~ 10 M. The results showed that the length and diameter of TDNs ranged of 400 ~ 500 nm and 10 ~ 20 nm, respectively. In addition, the length and diameter of titanium dioxide nanorods (TDRs) are 10 ~ 20 μm and 100 ~ 200 μm, respectively. The XRPD patterns showed TDNs and TDRS are both anatase-typed structures. The ESCA and EDX data indicated TDNs consist of Ti, O, and Na atoms and therefore it may produce NaCl in the synthetic processes. The BET surface area/pore volume of TDNs and TDRs are 277 m2/g /1.145 cm3/g and 18 m2/g /0.101 cm3/g, respectively. X-ray absorption near edge structure (XANES) or extended X-ray absorption fine structure (EXAFS) spectroscopy was performed to identify the fine structures of TDNs and TDRs. By using XANES spectra, the valency and framework of TDNs are Ti(VI) with anatase-typed structure. The EXAFS data revealed that TDNs (TDRs) have a first shell of Ti-O bonding with bond distances of 1.94 Å (1.96 Å) and coordination numbers were 2 (3). Furthermore, investigation of the formation mechanism of these TDNs 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.
In order to improve the photocatalytic efficiency of TDNs, the Ag and Pd with chemical reduction method, or Cu and Fe with impregnation method were doped in TDNs. FTIR spectra showed the existence of moisture with H-O-H and Ti-O-Ti bondings on the surface of TDNs. The UV/Vis spectra revealed that the critical wavelength of TDNs and TDRs are 420 nm and 400 nm, respectively. But after doping the metals besides Fe atoms in TDNs, the reduced critical wavelength of UV-Vis foe TDNs was observed. From the experimental data of the dye wastewaters removal under ultraviolet light irradiation, the photodegradative efficiencies of seven kind of dyes solutions on TDNs were Methylene Blue>Basic Violet 3>Basic Green 5>Basic Violet 10>Acid Blue 9>Acid Orange 7>Acid Red 1 in series at pH 7. By using zeta potential meter, the static electricity surface of TDNs attracted with the dye cations presented negative electricity under the dye solution of pH 7 is also determined. Moreover, the photocatalytic efficiencies for kinds of metal-doped TDNs were Ag > Pd > Cu > metal-undoped > Fe in series. It indicated that metal-doped TDNs indeed influenced the photocatalytic efficiencies significantly. In the photocatalytic experiments of differ concentrations of dye solutions, the higher dye concentrations with lower photodegradative efficiencies were found. Finally, a simple Langmuir-Hinshelwood was used and calculated by the relationship of ln(C0/Ca) versus time to describe the two-stage reactions of the dye wastewaters. Methylene blue photodecomposion rate was the highest photocatalytic efficiency one with k1 of 0.02718/min and k2 of 0.01077/min.

並列關鍵字

Titanium dioxide nanotube ； Hydrothermal ； Photocatalyst ； Dye wastewater ； Doped metal ； XANES/EXAFS

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