莊博超
新穎奈米碳管/二氧化鈦複合光觸媒之研製與降解雙酚 A 效能之研究
Preparation of innovative CNTs/TiO2 hybrid photocatalyst for BPA degradation 摘要 本研究探討Sol-gel 法和 Hydrothermal 法以不同改質後的奈米碳管來改良傳統 CNTs/TiO2 複合光觸媒之結合特性，其分別是藉由添加界面活性劑(SDS)提昇與 TiO2 溶膠的均勻性和分散性，以及利用亞硫醯氯(SOCl2)使奈米碳管表面帶有醯 氯基之官能基，以提昇與TiO2 結合力，成功的複合於自製二氧化鈦光觸媒中。 本實驗藉由表面特徵分析、比表面積分析、塗佈量分析、官能基分析、特徵波 長分析以及界達電位分析，檢測自製TiO2 光觸媒與 CNTs/TiO2 複合光觸媒，以 建立最佳製備技術以及觸媒分析鑑定，並進行光催化降解BPA 試驗，其實驗參數 包含觸媒種類、酸鹼值、增益劑、觸媒劑量以及不同光源各參數間之影響，以探 討光觸媒在紫外光和可見光降解BPA 之效能。 由 XRD 分析結果得知，TiO2 光觸媒於 sol-gel 法製備技術中鍛燒溫度在 400℃ ~500℃之間，其晶相皆為 100% Anatase；當溫度提高至 800℃時為 13.6% anatase 和86.4% rutile，於 900℃時可形成 100% rutile 之光觸媒，發現鍛燒溫度對晶相變 化具有相關性，而鍛燒時間(＜120 分鐘)對晶相改變較不顯著； Hydrothermal 法 製備技術無須高溫鍛燒(＜200℃)，便可形成 100% Anatase 晶相。 由 FEG-SEM-EDS 及N2-吸脫附曲線量測分析結果得知，sol-gel 法製備之光觸媒，其粒徑較大，有 燒結現象產生；反之Hydrothermal 法製備之光觸媒於表面形成 TiO2 粒子層層堆 疊，可造成較高之比表面積及孔洞特性(SBET 大約介於 124～148 m2/g 以及 Vp 大 約介於0.45～0.65 cm3/g)。 在紫外光降解雙酚A 研究中，發現混晶相複合光觸媒對液相 BPA 光催化降解效 能，依序分別為HGCT1-82 (84%)＞SSCT1-82 (81%)＞SSGCT1-82 (76%)＞HCT1 (72%) ＞SCT1-82 (70.4%)＞HSCT1-82 (64%)，從結果發現複合觸媒比單一 TiO2 有較佳的 降解效能，約提升1.4 倍的降解效率，證實 CNTs 具增進降解反應之效果，而當 複合觸媒(100% Anatase)觸媒轉變為混晶相複合觸媒(82% Anatase)，反應速率大 約提升1.25 倍，同時降解效能提升 1.2 倍，所以混合晶相複合觸媒具有比單一晶 相複合觸媒更佳的光催化效能。最後於紫外光光源的系統下，BPA 初始濃度 10 mg/L、pH=9、劑量為 100 mg/L 及添加 PO43-=10-4 mg/L 於有最佳光降解效率， 分別為85.4%及 92.6%。
實驗結發現混晶相 TiO2 光觸媒於可見光下降解 BPA，其 sol-gel 法與水熱法皆 在Anatase 含量為 50%時，有最佳光催化降解效率，分別為 32 及 36%；而 SSCT1-50 和HGCT-50 混合晶相複合光觸媒於可見光下降解 BPA 的效果，分別為 47 %和 54 %，其降解效果較混晶相 TiO2 光觸媒佳，主要是因為 CNTs 獨特的導電特性，使
得TiO2 於光催化所釋放之電子可以暫時儲存於 CNTs，降低電子電洞對再結合
降解效能。 在可見光發現 SSCT1-50 混晶相複合光觸媒於中性環境下有較佳降解 BPA 的降解 效率(47%)；但是 HGCT1-50 複合光觸媒於 pH=9 的環境下有較佳 BPA 降解效率 (54%)，主要是由於光觸媒的表面界達電位所導致。另外在太陽光模擬器下加入 PO43-可有效增進光催化反應，與可見光比較的降解效率果顯示，可分別提昇到 61.4%及 64.2%，表示縱使只有少量紫外光光源，仍然可提升光催化降解效能， 證明CNTs 確實可以延長電子-電洞對再結合速率，提升光降解效果。 整體實驗結果顯示，以改質後的奈米碳管製備 CNTs/TiO2 複合光觸媒降解液相 BPA，可藉由探討混晶相之比例及表面物化特性並藉由改變 pH 值及添加增益劑 PO43-的劑量，提昇 BPA 於紫外光及可見光下的降解效率。由於製備方式的不同 可能影響光觸媒的型態，影響光催化活性；此系統之光降解反應符合 Langmuir-Hinshelwood 動力學方程式。
This study was aimed to improve the binding and absorption characteristics of CNTs/TiO2 hybrid photocatalyst for BPA degradation via Sol-gel and Hydrothermal methods. An anionic surfactant, sodium dodesulfate (SDS), was added to improve the uniformity and dispersibility of TiO2 and SOCl2 was used to form acyl chloride
function group on carbon nanotube surface, which results in stronger binding with TiO2. The surface characteristics, specific surface area, ratio of CNTs/TiO2, functional group, characteristic wavelength and Zeta-potential of hybrid photocatalysts were analyzed in this study in order to establish the optimal preparation parameters. Photocatalytic experiments of BPA were also conducted, which experimental
parameters included catalyst type/quantity, pH, enhancing agent, and light sources of 365 and 400 nm.
The XRD analysis results showed that the crystalline phase of TiO2 prepared by sol-gel method was 100% anatase at calcining temperature of 400℃~500℃. It converted to 13.6% anatase and 86.4% rutile when the temperature increased to 800 ℃ and the photocatalyst of 100% rutile can be formed at 900℃. It is found that the calcining temperature is an important factor affected the crystalline phase of TiO2, whereas the effect of calcining time (<120 minutes) on the crystalline phase is not obvious. The crystalline phase of 100% anatase for TiO2 can be prepared by
hydrothermal methods at calcination temperature less than 200℃. According to the FEG-SEM-EDS and N2-adsorption/desorption curve, the photocatalysts prepared by sol-gel method have large particle size and sintering phenomenon; on the contrary, the photocatalysts prepared by hydrothermal method were found layers of
TiO2 stacked on its surface, which resulted in larger specific surface area (124~148 m2/g) and pore volume (0.45~0.65 cm3/g).
The photocatalytic degradation efficiency of BPA by mixed crystal phase hybrid photocatalysts was in decreasing order as HGCT1-82 (84%)>SSCT1-82
(81%)>SSGCT1-82 (76%)>HCT1 (72%)>SCT1-82 (70.4%)>HSCT1-82 (64%). Results showed that the degradation efficiency of BPA by hybrid catalysts is 1.4 times greater than that by pure TiO2, which confirmed that CNTs can enhance photodegradation. The reaction rate and degradation efficiency of BPA by mixed crystal phase hybrid catalyst of 82% anatase was 1.25 times and 1.2 times greater than that by mixed crystal phase hybrid catalyst of 100% anatase, respectively. It was confirmed that better photocatalysis performance was found for mixed crystal phase hybrid catalysts. Finally, in the UV illuminant system, the best photodegradation efficiency occurs, 85.4% and 92.6% respectively, when the initial concentration of BPA is 10 mg/L, pH = 9, dosage is 100 mg/L and PO43-=10-4 mg/L is added.
Under visible light, the best photocatalytic degradation efficiency of BPA was found 32% (sol-gel method) and 36% (hydrothermal method) by mixed crystal phase TiO2 photocatalysts contained 50% antase. The effect of SSCT1-50 and HGCT-50 mixed crystal phase hybrid photocatalysts on degrading BPA in visible light is 47 % and 54%, respectively. The degradation effect is better than that of mixed crystal phase TiO2 photocatalyst; this is because of the unique conduction characteristic of CNTs, so that the electrons released from TiO2 in photocatalysis can be stored in CNTs temporarily, and the rebinding rate of electron-hole pairs is reduced. Therefore, it is confirmed that the SSCT1-50 and HGCT-50 mixed crystal phase hybrid photocatalysts can really increase the degradation efficiency effectively.
In visible light, the SSCT1-50 photocatalyst of exhibited a better BPA degradation efficiency (47%) in neutral environment; however, the HGCT1-50 photocatalyst exhibited better BPA degradation efficiency (54%) when pH=9. This might largely because of the surface Zeta-potential difference between photocatalysts. In addition, the photocatalytic reaction can be enhanced effectively by adding PO43- in the sunlight simulator. The degradation efficiency is increased to 61.4% and 64.2%, respectively, as compared with that in visible light, indicating that slight UV illuminant can still increase the photocatalytic degradation efficiency. This finding proved that CNTs can prolong the electron-hole pair rebinding and improve the photodegradation performance.
To sum up, the modified carbon nanotube is used for preparing CNTs/TiO2 hybrid photocatalyst degraded liquid phase BPA, the degradation efficiency of BPA in UV-light and visible light was related to the ratio of mixed crystal phase, surface physical and chemical characteristics, pH, and the addition of PO43-. The difference in the preparation methods may influence the form of photocatalyst and the
photocatalytic activity. The photodegradation reaction of this system agreed to Langmuir-Hinshelwood dynamical equation.
