以氧化鋅覆鍍奈米碳管添加CeO2進行光纖光催化技術降解水中氯黴素之研究

Photocatalyzation of Chloramphenicol in Water by Optical Fibers coated with ZnO-CNTs and CeO2

鄭媚方(Zheng Mei-Fang)

指導教授 ： 陳冠中 ； 謝連德

國立屏東科技大學/工學院/環境工程與科學系所/碩士(2021年)

https://doi.org/10.6346/NPUST202100466

摘要

本研究以光纖光催化技術處理水中氯黴素(Chloramphenicol, CAP)，並探討不同操作參數對於處理水中CAP之影響。研究使用365 nm LED-UVA作為光催化之光源，並將光觸媒覆鍍於高導光性之石英光纖表面，用於水中進行光催化去除CAP，探討其光催化效果。研究三種光觸媒基本特性以SEM/EDS、XRD及DRS進行分析，由SEM/EDS得知氧化鋅/奈米碳管(ZnO/CNT)及二氧化鈰-氧化鋅/奈米碳管(CeO2-ZnO/CNT)皆有參雜CNT，且由mapping分析可發現Ce元素均勻分佈於光觸媒表面；從XRD結果發現CNT的結晶訊號低於ZnO，而與ZnO繞射峰重疊，因此未出現在光觸媒中，少量CeO2的添加，因濃度過低，導致XRD中僅在2θ=28.8∘出現的訊號；接著再以DRS分析觸媒能隙與光觸媒吸收波長，實驗用之光觸媒能隙範圍為2.95~3.1 eV，而在光觸媒吸收波長可發現ZnO/CNT和CeO2-ZnO/CNT在400-800 nm的吸收率有增加，可證明添加CNT可較容易被可見光波長之光源所激發。
本實驗之連續攪拌槽反應系統(Continuous Stirred-Tank Reactor, CSTR)探討操作參數包括不同CAP初始濃度(3、5 mg/L)、光觸媒種類(ZnO、ZnO/CNT和CeO2-ZnO/CNT)以及不同光源光強度(20 W、50 W)等。首先，以光催化批次試驗進行光觸媒之比較並評估處理效率，而後再以光纖光催化試驗進行操作參數比較。實驗結果發現，光觸媒種類方面，其CAP之去除率為CeO2-ZnO/CNT＞ZnO/CNT＞ZnO。研究發現，隨著CAP初始濃度提升，光催化去除率會相對下降。在不同光照強度下，20 W去除效果優於50 W，此一現象藉由氫氧自由基轉換效率試驗(ROH·UV)證明，20 W光催化之ROH·UV高於50 W。另外，在試驗對於溶解性有機碳(Dissolved Organic Carbon, DOC)之影響中，發現光纖光催化試驗後，DOC濃度均有降低，顯示部分CAP被礦化。在光觸媒耐久性部分，實驗以最佳條件參數進行，在重複3次試驗，其去除率並沒有隨著時間而下降，因此得知，光觸媒在此光催化系統中可維持一定的光催化效果。

關鍵字

光催化 ； 光纖 ； 氯黴素 ； 奈米碳管 ； 氧化鋅 ； 二氧化鈰

並列摘要

This study used photocatalytic technology to treat Chloramphenicol (CAP) in water by a photocatalyst coated optical fiber. The effects of different operating conditions on the treatment of CAP were investigated. A LED-UVA with a wavelength of 365 nm was used as the light source of the photocatalytic system. Laboratory synthesized photocatalysts were coated on the surface of high light-conducting silica fiber and used for photocatalytic removal of CAP in water. The characteristics of synthesized photocatalysts were analyzed by SEM, XRD, and DRS. According to SEM/EDS, zinc oxide (ZnO) and ceria-zinc oxide (CeO2-ZnO) were both doped on carbon nanotubes (CNT) and formed (ZnO/CNT) and ceria-zinc oxide/carbon nanotubes (CeO2-ZnO/CNT), respectively. Ce was evenly distributed on the surface of photocatalysts by mapping analysis. From the XRD results, it was found that the crystallization signal of CNT was lower than that of ZnO but overlapped with the diffraction peak of ZnO. Therefore, its peak was not shown on the XRD spectrum of the photocatalyst. The XRD signal of CeO2 was only shown at 2θ= 28.8∘due to its low additive percentage. The photocatalysts’ energy gap and absorption wavelength were analyzed by DRS. The energy gaps of synthesized photocatalysts were between 2.95 ~ 3.1 eV. The absorption wavelength ZnO/CNT and CeO2-ZnO/CNT increased between 400-800 nm, which proved that the addition of CNT could be easily excited by the light source at the visible wavelength.
The investigated operating parameters of the Continuous Stirred-Tank Reactor (CSTR) in this study include initial concentration(3 and 5 mg/L), type of photocatalyst (ZnO, ZnO/CNT and CeO2-ZnO/CNT), light intensity of light source (20 and 50 W). Firstly, the photocatalytic batch test was used to evaluate and compare the treatment efficiency of CAP by different photocatalysts. Then the operating parameters were applied in the following optical fiber photocatalytic tests. The experimental results show that the removal efficiency of CAP follows CeO2-ZnO/CNT＞ZnO/CNT＞ZnO. The photocatalytic removal rate decreased with the increase of the initial concentration of CAP. Regarding light intensity on CAP removal, the 20 W LED was better than the 50 W LED. This is verified by conducting the test of hydroxyl radical conversion efficiency (ROH·UV) and found that the ROH·UV of 20 W is higher than that of 50 W. In addition, the photocatalytic system mineralized some CAP and decreased the concentration of dissolved organic carbon (DOC). The photocatalyst CeO2-ZnO/CNT was used to test its durability of photocatalysis under the optimal operating condition. It was found that the removal efficiency of CAP did not decrease with time after repeating the test for 3 times. It implies that the photocatalysts could maintain a stable photocatalytic effect in this photocatalytic system.

並列關鍵字

photocatalysis ； optical fiber ； chloramphenicol ； carbon nanotube ； zinc oxide ； cerium dioxide

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