Sojić Daniela V, Anderluh Vesna B, Orcić Dejan Z, Abramović Biljana F
Department of Chemistry, Faculty of Sciences, Novi Sad, Serbia.
J Hazard Mater. 2009 Aug 30;168(1):94-101. doi: 10.1016/j.jhazmat.2009.01.134. Epub 2009 Feb 10.
The work is concerned with the kinetics, identification of intermediates and reaction pathways of the photocatalytic degradation of the herbicide clopyralid (3,6-dichloropyridine-2-carboxylic acid) in UV illuminated aqueous suspensions of TiO(2) (Degussa P25). In the investigated concentration range (0.5-3.0 mM) the photocatalytic degradation kinetics of clopyralid in the first stage of the reaction follows approximately a pseudo-first kinetic order. The highest reaction rate was observed at 4 mg mL(-1)of catalyst concentration, the apparent activation energy of the reaction being 7.74 kJ mol(-1). The effect of the presence of hydrogen peroxide, potassium bromate, and ammonium persulfate, acting as electron acceptors along with molecular oxygen, were also studied. By studying the effect of ethanol as a hydroxyl radical scavenger it was shown that the heterogeneous catalysis takes place mainly via hydroxyl radicals. The reaction intermediates (3,6-dichloropyridin-2-ol, 3,6-dichloro hydroxypyridine-2-carboxylic acid, and 3,3',6,6'-tetrachloro-2,4'-bipyridine-2'-carboxylic acid) were identified and the kinetics of their appearance/disappearance was followed by LC-MS/MS (ESI+). Tentative photodegradation pathways were proposed and discussed.
该研究工作涉及在紫外光照射的TiO₂（德固赛P25）水悬浮液中，除草剂氯吡嘧磺隆（3,6 - 二氯吡啶 - 2 - 羧酸）的光催化降解动力学、中间体鉴定及反应途径。在研究的浓度范围（0.5 - 3.0 mM）内，氯吡嘧磺隆在反应第一阶段的光催化降解动力学大致遵循准一级动力学。在催化剂浓度为4 mg mL⁻¹时观察到最高反应速率，该反应的表观活化能为7.74 kJ mol⁻¹。还研究了过氧化氢、溴酸钾和过硫酸铵作为电子受体与分子氧共同存在时的影响。通过研究乙醇作为羟基自由基清除剂的作用表明，多相催化主要通过羟基自由基进行。鉴定了反应中间体（3,6 - 二氯吡啶 - 2 - 醇、3,6 - 二氯羟基吡啶 - 2 - 羧酸和3,3',6,6'-四氯 - 2,4'-联吡啶 - 2'-羧酸），并通过LC - MS/MS（ESI⁺）跟踪它们的出现/消失动力学。提出并讨论了初步的光降解途径。
