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Photocatalytic oxidation of emerging contaminants: Kinetics and pathways for photocatalytic oxidation of pharmaceutical compounds.

机译：新兴污染物的光催化氧化：药物化合物光催化氧化的动力学和途径。

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摘要

Pharmaceutical compounds are emerging contaminants in aquatic environments because they are bioactive, polar and persistent which may cause adverse effects in aquatic wildlife and humans. Degradation of these compounds by conventional activated sludge treatment ranged from complete to very poor, however, recent studies on new treatment technologies showed that photocatalytic oxidation is one of the most promising treatment technologies to remove these compounds from water. This study examined photocatalytic oxidation of four pharmaceuticals, using titanium dioxide (TiO2). Adsorption of naproxen, ibuprofen, clofibic acid and diclofenac on TiO2 under ambient conditions decreased for all compounds with increasing pH. Diclofenac, naproxen, ibuprofen and clofibric acid were 100%, 65%, 50% and 22% adsorbed at pH 3, respectively but adsorption decreased to 20%-5% at pH > 5. Adsorption of all compounds on TiO2 at pH 3 likely resulted from electrostatic attraction and hydrogen bonding. Diclofenac showed the highest adsorption probably because of the combined effects of carboxyl group and amine lone pair electrons to form bidentate complexes.; Photocatalytic oxidation of naproxen, ibuprofen, clofibric acid and diclofenac were studied in UV illuminated (lambda > 300nm) TiO2 suspensions at pH 3, 5 and 7 and 25°C with emphasis on kinetic rates, intermediate reaction products and oxidation pathways. The faster rates occurred at pH 3 except for diclofenac and coincided with the larger extent of adsorption on TiO2. Diclofenac showed the opposite behavior: oxidation rates increased as pH increased although adsorption decreased. The first order rate constants at pH 5 showed the order NP > IBN > CFA. > DC in the range from 0.098 to 0.026 min-1. The kinetics also followed Langmuir-Hinshelwood kinetics and showed a similar order. Two pH dependent oxidation pathways were identified. Electron transfer from a carboxyl group to a valence band hole dominated at pH 3 yielding a ketone and alcohol from ibuprofen and naproxen oxidation and chlorophenol from clofibric acid oxidation. The hydroxyl radical ring oxidation pathway was dominant at pH > 5 giving the Cl- ion from clofibric acid and diclofenac oxidation. Diclofenac oxidized only through hydroxyl radical substitution on aromatic rings with a carboxyl group to form phenolic intermediates and Cl- ions.
机译：药物化合物是水生环境中的新兴污染物，因为它们具有生物活性，极性和持久性，可能对水生野生生物和人类造成不利影响。通过常规活性污泥处理对这些化合物的降解程度从完全到非常差，但是，最近对新处理技术的研究表明，光催化氧化是从水中去除这些化合物的最有希望的处理技术之一。这项研究使用二氧化钛（TiO2）研究了四种药物的光催化氧化。随着pH值的升高，所有化合物在环境条件下对萘普生，布洛芬，次氯芬酸和双氯芬酸的吸附均降低。在pH 3时双氯芬酸，萘普生，布洛芬和氯纤维酸分别被100％，65％，50％和22％吸附，但在pH> 5时吸附降低到20％-5％。由于静电吸引和氢键作用。双氯芬酸显示出最高的吸附性，可能是由于羧基和胺孤对电子共同形成双齿络合物的结果。在pH 3、5、7和25°C的紫外线照射（λ> 300nm）TiO2悬浮液中研究了萘普生，布洛芬，克洛贝酸和双氯芬酸的光催化氧化，重点研究了动力学速率，中间反应产物和氧化途径。除双氯芬酸外，在pH 3处发生的速率更快，并且与TiO2上的较大吸附程度相符。双氯芬酸表现出相反的行为：尽管吸附减少，但氧化速率随pH的增加而增加。 pH值为5时的一级速率常数显示NP> IBN> CFA。 > DC，范围为0.098至0.026 min-1。动力学也遵循Langmuir-Hinshelwood动力学，并显示出相似的顺序。确定了两个pH依赖的氧化途径。电子从羧基转移到在pH 3下占主导地位的价带孔，从布洛芬和萘普生氧化产生酮和醇，从克洛贝酸氧化产生氯苯酚。在pH> 5时，羟自由基环氧化途径占主导地位，氯吡酸和双氯芬酸氧化产生Cl-离子。双氯芬酸仅通过具有羧基的芳环上的羟基自由基取代氧化，形成酚类中间体和Cl-离子。

著录项

  • 作者

    Thanasawasdi, Haruthai Tungudomwongsa.;

  • 作者单位

    Stanford University.;

  • 授予单位 Stanford University.;
  • 学科 Engineering Environmental.
  • 学位 Ph.D.
  • 年度 2007
  • 页码 118 p.
  • 总页数 118
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 环境污染及其防治;
  • 关键词

  • 入库时间 2022-08-17 11:40:33

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