Atenas Gonzalo Montes, Mielczarski Ela, Mielczarski Jerzy A
Laboratoire Environnement et Mineralurgie, UMR 7569 CNRS, INPL-ENSG, B.P. 40, Vandoeuvre-les-Nancy, France.
J Colloid Interface Sci. 2005 Sep 1;289(1):171-83. doi: 10.1016/j.jcis.2005.03.042.
Although the decomposition of water pollutants in the presence of metallic iron is known, the reaction pathways and mechanisms of the decomposition of azo-dyes have been meagerly investigated. The interface phenomena taking place during orange I decomposition have been investigated with the use of infrared external reflection spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The studies presented in this paper establish that there are close relationships between the composition and structure of the iron surface oxidized layers and the kinetics and reaction pathway of orange decomposition. The influence of the molecular structure of azo-dye on the produced intermediates was also studied. There are remarkable differences in orange I decomposition between pH 3 and pH 5 at 30 degrees C. Decomposition at pH 3 is very fast with pseudo-first-order kinetics, whereas at pH 5 the reaction is slower with pseudo-zero-order kinetics. At pH 3, only one amine, namely 1-amino-4-naphthol, was identified as an intermediate that undergoes future decomposition. Sulfanilic acid, the second harmful reduction product, was not found in our studies. At pH 3, the iron surface is covered only by a very thin layer of polymeric Fe(OH)(2) mixed with FeO that ensures orange reduction by a combination of an electron transfer reaction and a catalytic hydrogenation reaction. At pH 5, the iron surface is covered up to a few micrometers thick, with a very spongy and porous layer of lepidocrocite enriched in Fe(2+) ions, which slows the electron transfer process. The fastest decomposition reaction was found at a potential near -300 mV (standard hydrogen electrode). An addition of Fe(2+) ions to solution, iron preoxidation in water, or an increase of temperature all result in an increasing decomposition rate. There is no single surface product that would inhibit the decomposition of orange. This information is crucial to perform efficient, clean and low cost waste water treatment. The findings presented here make the treatment of wastewater in the presence of metallic iron a very promising solution.
虽然在金属铁存在下水中污染物的分解是已知的，但对偶氮染料分解的反应途径和机制的研究却很少。利用红外外反射光谱、X射线光电子能谱和扫描电子显微镜研究了橙黄I分解过程中发生的界面现象。本文的研究表明，铁表面氧化层的组成和结构与橙黄分解的动力学和反应途径之间存在密切关系。还研究了偶氮染料分子结构对生成中间体的影响。在30℃时，pH值为3和pH值为5时橙黄I的分解存在显著差异。pH值为3时的分解非常快，具有准一级动力学，而在pH值为5时反应较慢，具有准零级动力学。在pH值为3时，仅鉴定出一种胺，即1-氨基-4-萘酚，作为后续分解的中间体。在我们的研究中未发现第二种有害还原产物磺胺酸。在pH值为3时，铁表面仅覆盖有一层非常薄的与FeO混合的聚合Fe(OH)₂层，该层通过电子转移反应和催化氢化反应的组合确保橙黄的还原。在pH值为5时，铁表面覆盖有高达几微米厚的非常海绵状和多孔的纤铁矿层，富含Fe(2+)离子，这减缓了电子转移过程。在接近 -300 mV（标准氢电极）的电位下发现了最快的分解反应。向溶液中添加Fe(2+)离子、铁在水中的预氧化或温度升高都会导致分解速率增加。没有单一的表面产物会抑制橙黄的分解。这些信息对于进行高效、清洁和低成本的废水处理至关重要。此处呈现的研究结果使在金属铁存在下处理废水成为一个非常有前景的解决方案。
