在旋轉盤反應器中利用金屬摻雜的二氧化鈦光催臭氧化降解亞甲基藍

Photocatalytic Ozonation for Degradation of Methylene Blue in Spinning Disk Reactor by Metal Doped TiO2

宋俊辰(Chun-Chen Song)

指導教授 ： 陳昱劭

中原大學/工學院/化學工程研究所/碩士(2021年)

https://doi.org/10.6840/cycu202100628

摘要

過去文獻已證實旋轉盤反應器具有高質傳效率，由於光催臭氧化程序屬於氣-液-固三相的複雜反應，因此使用旋轉盤反應器不只增加臭氧的質傳效果，還能以極薄液膜的形式減少光穿透的阻力。本研究於旋轉盤反應器中以金屬摻雜之二氧化鈦薄膜為觸媒，利用光催臭氧化程序對亞甲基藍進行連續式降解，探討二氧化鈦塗佈層數、觸媒摻雜金屬種類、亞甲基藍初始濃度、臭氧濃度、紫外燈差異、進料流率和轉速對光催臭氧化降解和礦化的影響。
實驗結果顯示，在UV-LED（波長370 nm）照射下，二氧化鈦薄膜在大於三層時對於降解效率不會有明顯的提升，甚至會造成觸媒的剝落。UV-LED面光源相較於UVC燈管可以均勻的照射整個圓盤且能量轉換效率較高，使更多觸媒的電子被激發，導致光催化和臭氧化的結合效果更好，進而促進強氧化性氫氧自由基的生成來提高降解能力。降解/礦化效率會隨亞甲基藍濃度和液體流率的增加而下降，並且會隨轉速的增加而上升，並且在500-1000 rpm之間降解效率明顯上升較為明顯。添加臭氧的情況下發現降解/礦化效率隨臭氧濃度的增加而明顯提升，但是在濃度1 g/m3之後提升的效率迅速減緩。
觸媒的摻雜雖然可以降低電子-電洞的複合提高氫氧自由基的生成，但也會影響觸媒表面電荷和臭氧的反應途徑。本研究在摻雜金和銀於觸媒之後，發現在光催化和低臭氧濃度的光催臭氧化會有明顯的提升效果，但是在高臭氧濃度的光催臭氧化提升效果會不明顯，摻雜金的觸媒甚至會導致降解/礦化降低，而摻雜銀的觸媒則會先降低之後再提升需要進一步的調整操作的參數，最後摻雜鈷的觸媒在光催化和光催臭氧化降解/礦化效最差，卻在觸媒臭氧化有最佳的礦化效率。此外，確認了本研究之光催臭氧化程序存在協同效果（synergistic effect），其增幅與過去文獻中的光催臭氧化系統相比無太大的差距，可能是因為超重力系統著重於質傳的改善，而協同效果主要受反應速率的影響，證實了在不同的汙染物中光催化臭氧化系統都存在著協同效果。
在最佳條件UV-LED功率18.7 W、轉速1000 rpm、液體流率50 mL/min、臭氧流率5 L/min下和臭氧濃度1 g/m3時，摻雜銀的二氧化鈦降解效率達98.5 %與過去文獻中的幾種光催化反應器相比，旋轉盤反應器在光催臭氧化系統中能使用較低的臭氧劑量和光強度達到高的降解效率。總和結果得知，旋轉盤反應器應用於連續式光催臭氧化反應中具有極高的潛力。

關鍵字

超重力 ； 旋轉盤反應器 ； 高級氧化法 ； 光催臭氧化 ； 光觸媒 ； 臭氧 ； 亞甲基藍

並列摘要

The high mass transfer efficiency of the spinning disk reactor has been confirmed in the past literature. Since the photocatalytic ozonation process is a complex gas-liquid-solid three-phase reaction, the spinning disk reactor increases the mass transfer effect of ozone, reduces the resistance of light penetration because of the extremely thin liquid film in the reactor. This study used a photocatalytic ozonation process to continuously degrade methylene blue in a spinning disk reactor with metal-doped TiO2 as catalysts. The effects of the number of coating layers of TiO2, the initial concentration of methylene blue, the metal types, the ozone concentration, the types of UV lamps, the feed flow rate, and the rotation speed on the efficiency of degradation and mineralization were investigated.
The experimental results show that under UV-LED (wavelength 370 nm) irradiation, the degradation efficiency will not be significantly improved when the layer of the titanium dioxide film is larger than three, which may probably be due to the peeling of the catalyst. Compared with the UVC lamp tube, the UV-LED flat light source can more uniformly illuminate the entire disk and has a higher energy conversion efficiency, so that more electrons of the catalyst are excited, resulting in a better combination of photocatalysis and ozonation, thereby promoting the strong generation of oxidizing hydroxyl radicals improves the degradation ability. The degradation/mineralization efficiency will decrease with the increase of methylene blue concentration and liquid flow rate and will increase with the increase of rotating speed. The degradation efficiency will increase obviously between 500-1000 rpm. The degradation/mineralization efficiency increases significantly with the increase of ozone concentration, but the effect of increasing after the ozone concentration of 1 g/m3 slows down rapidly.
Although catalyst doping can reduce the electron-hole recombination and increase the generation of hydroxyl radicals, it also affects the reaction pathways of the surface charge of the catalyst and ozone. In this study, after doping gold and silver in the catalyst, it was found that the photocatalytic and low ozone concentration photocatalyzed ozonation will have a significant improvement effect, but the photocatalyzed ozonization effect at high ozone concentration will not be obvious. The gold-doped catalyst can even cause degradation/mineralization reduction, while the silver-doped catalyst will first reduce and then increase the parameters that require further adjustments. Finally, the cobalt-doped catalyst is used for photocatalysis and photocatalytic ozonation. The degradation/mineralization effect is the worst, but the catalyst ozonation has the best mineralization effect. In addition, it is confirmed that the photocatalyzed ozonation process in this study has a synergistic effect, and its increase is not much different from that of the photocatalyzed ozonation system in the past literature. It may be because the supergravity system focuses on mass transfer. The synergistic effect is mainly affected by the reaction rate, which proves that the photocatalytic ozonation system has a synergistic effect on different pollutants.
Under the optimal condition of UV-LED power of 18.7 W, rotating speed of 1000 rpm, the liquid flow rate of 50 mL/min, the ozone flow rate of 5 L/min, and ozone concentration of 1 g/m3, the degradation efficiency of silver-doped titanium dioxide reached 98.5 %. Compared with several photocatalytic reactors in the past literature, the spinning disk reactor uses lower ozone dosage and light intensity in the photocatalytic ozonation system to achieve high degradation efficiency. The results show that the rotating disk reactor has extremely high potential in the continuous photocatalytic ozonation reaction.

並列關鍵字

Higee ； Spinning disk reactor ； AOPs ； Photocatalytic ozonation ； Photocatalyst ； ozone ； Methylene blue

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