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| 題名: | 以紫外光/二氧化鈦光催化降解程序去除水溶液相內分泌干擾物質壬基苯酚之研究;Removal of an Endocrine Disrupting Chemical , Nonylphenol, from Aqueous Solutions Using UV/TiO2 Photocatalytic Decomposition Processes. |
| 作者: | 曾郁婷;Tseng,Yu-ting |
| 貢獻者: | 環境工程研究所 |
| 關鍵詞: | 紫外光/二氧化鈦光催化降解;內分泌干擾物質;壬基苯酚;包埋 |
| 日期: | 2013-12-30 |
| 上傳時間: | 2014-02-13 17:57:15 (UTC+8) |
| 出版者: | 國立中央大學 |
| 摘要: | 傳統淨水與廢水處理程序對於內分泌干擾物質的去除效果有限，故常需倚賴高級氧化處理等技術以達到理想的去除率，而紫外光/二氧化鈦(UV/TiO2)光催化程序即為當中一項吸引人的處理技術，因此法可有效去除頑抗、難分解的有機物，且最終可將污染物礦化成CO2和H2O等無二次污染的產物。本研究嘗試應用UV/TiO2光催化程序處理含壬基苯酚(nonylphenol, NP)之水溶液，實驗採批次式，選用波長352 nm的紫外光燈管為光源，從中探討TiO2 劑量、pH值、離子效應及TiO2包埋與否對其光催化降解的影響。實驗結果顯示隨著TiO2劑量的增加，NP受光催化降解之效率也隨著提升，其中TiO2的最佳添加劑量為100 mg/L，在反應2小時內即可達到100%之NP去除效率，且光催化降解反應符合擬一階反應速率方程式。利用總有機碳分析儀量測最佳處裡效率下之溶液內有機碳含量時，顯示在UV/TiO2系統中照射紫外光兩小時後，即使NP已達100%去除，仍有23%之溶解性有機碳殘餘在溶液中，推測NP在反應過程中可能產生其他中間產物而尚未完全礦化。調整反應系統之酸鹼度後，觀察到相較於酸性(pH=3)及鹼性(pH=11)條件，系統於中性狀態下有較佳之光催化降解效率，此乃因在異相光催化機制中，污染物必須先與TiO2表面接觸，再藉由系統中具強氧化力之OH?的幫助，啟動後續氧化還原反應而達到催化降解之目的。由於TiO2之pHpzc約為6.5，而NP之pKa為10.28，故當反應溶液落在鹼性範圍時，TiO2及NP皆因帶負電型式，兩者相斥導致彼此接觸機會降低，因而催化效果不佳；在酸性及中性狀態下，TiO2及NP因靜電力/凡德瓦力的關係而互相吸引，雖然兩者接觸機會相似，但因在中性條件下，OH-之濃度相對較高，所能形成之OH?的濃度也相對提高，故其光催化降解的效率較佳。此外，在反應系統中添加NaCl及Na2SO4等離子化合物，卻未觀察到因離子化合物的加入而使TiO2顆粒產生不同程度的團聚，或者離子與污染物競爭TiO2表面活性位置之現象，簡言之， NP之光催化降解效率並未因離子化合物的加入而有顯著降低之趨勢。在TiO2包埋方面，發現不論利用海藻酸鈉或幾丁質，所形成之包埋顆粒其光催化降解效率皆劣於懸浮態且未包埋之顆粒，當中尤以幾丁質包埋之顆粒因網絡結構較為鬆散，易於反應攪拌過程中受到破壞。兩者經由掃描式電子顯微鏡(SEM)的觀察發現，大部分之TiO2皆被包覆於顆粒內部，減緩TiO2和污染物接觸機會，因此無法有效發揮TiO2光催化作用。
Due to the efficiency of conventional drinking and wastewater treatment processes to remove endocrine disruptors is frequently unsatisfactory, other technology units such as advanced oxidation processes oftentimes are needed in order to achieve ideal discharge quality. One of the appealing technologies is the UV/TiO2 photocatalytic decomposition process, as it has the capacity to nonspecifically oxidize organic compounds ultimately to CO2 and H2O, hence being able to successfully eliminate recalcitrant organic pollutants from the solution.
In this study, photo-degradation experiments of nonylphenol (NP) were conducted in batch reactors using P-25 Degussa particles and UV-A lamps with an emitting wavelength of 352 nm as the TiO2 and UV sources, respectively. In addition to investigating the effects of TiO2 dosage, solution pH and the ionic strength on NP removal during the photocatalytic decomposition process, the potential of applying immobilization techniques in this process was also assessed.
Experimental data showed that photo-degradation efficiency of NP increased with increasing amounts of TiO2, resulting in 100 mg/L as the optimal TiO2 dosage that caused 100% of NP removal in 2 hr. Further, the pseudo first order model was successfully used to explain the kinetic behavior of NP destruction in the solution as the model fitted the data well. However, results of TOC analysis on samples taken after 2-hr reactions showed that 23% of organic carbons remained in the solution, suggesting that some intermediates were produced and retained over the course of the experiment. When the pH of the system varied, higher NP removal was observed at pH 6-7 than at pH 3 and pH 11. This can be explained by the nature of the heterogeneous photocatalytic degradation process, which involves an initial contact between pollutants and the surface of TiO2 before the degradation kicks in. Given that the point of zero charge (pHpzc) of TiO2 is approximately 6.5 and the pKa of NP is 10.28 or so, under alkaline conditions both TiO2 and NP would have negatively-charged surfaces and may experience electrostatic repulsion when they proceed to each other
therefore, ineffective NP photo-degradation resulted from a decrease in the sorption of NP to TiO2 is anticipated. On the other hand, under acidic and neutral conditions, TiO2 particles and NP may have a better contact chance through the electrostatic pairing force and the van der Waals attractive force, therefore resulting in higher photo-decomposition rates
nonetheless, compared to acidic conditions, neutral conditions still have relatively high reduction rates because of more hydroxyl free radicals generated under such circumstances. Addition of ionic compounds such as NaCl and Na2SO4 did not lead to significant aggregation of of TiO2, nor was the competition between the ions and the pollutant (i.e., NP) for the active sites of TiO2 surface observed. In other words, the degradation efficiency was not affected to a great deal after the ionic compounds were supplemented into the system. Lastly, NP removal through immobilization of TiO2 particles using alginate or chitosan was worse than the use of the powder-formed TiO2 in the photo-degradation system. Scanning electron microscopic analysis of these immobilized particles indicated that the majority of TiO2 powders were entrapped inside the structure of the immobilized particles, thus preventing TiO2 from the contact of pollutants and further resulting in decreases in the degradation efficiency. |
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