Photocatalytic degradation of 4-chlorophenol in aerated aqueous titanium dioxide suspensions: A kinetic and mechanistic study
Photocatalytic degradation of 4-chlorophenol in aerated aqueous titanium dioxide suspensions: A kinetic and mechanistic study
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DOI：
10.1021/la960228t
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发表时间：
1996-12-25
期刊：
影响因子：
3.9
通讯作者：
Bahnemann, DW
中科院分区：
文献类型：
--
作者：
Theurich, J;Lindner, M;Bahnemann, DW
研究并比较了两种不同催化剂：Sachtleben Hombikat UV 100 和 Degussa P25 对二氧化钛水悬浮液中 4-氯苯酚 (4-CP) 的光催化降解作用。详细研究了 pH 值和初始 4-CP 浓度对反应速率和产物分布的影响。关于初始 4-CP 浓度，降解动力学可以用 Langmuir-Hinshelwood 表达式形式描述。虽然 4-CP 本身的降解几乎不受 pH 值的影响，但总体矿化速率（以总有机碳减少量衡量）变化很大，在 pH > 7 时急剧下降。使用 P25 作为光催化剂时，4-CP 的矿化速度比 Hombikat UV 100 稍快，但在后一种情况下检测到的中间体浓度和数量较小。在此光催化降解过程中观察到的大多数中间体与直接光解过程中鉴定的中间体相同。在酸性溶液（pH 3）中，当 Hombikat UV 100 为光催化剂时，氢醌和苯醌是唯一的中间体。使用 P25 作为光催化剂，另外七种中间体，即羟基氢醌、羟基苯醌、苯酚、4-氯儿茶酚、4-羟基苯基苯醌、2,5,4'-三羟基联苯和 5-氯-2,4'-二羟基联苯，发现对苯二酚（HQ）和苯醌（BQ）是光催化 4-CP 降解的主要中间体，可以证明 HQ/BQ 光系统充当电子继电器，有效地短路光催化剂，导致 4-CP 和最可能的其他芳香族化合物的降解效率降低。提出并讨论了 α-氯苯酚的降解机制，特别是考虑了 4-CP 降解的 pH 依赖性。
The photocatalytic degradation 4-chlorophenol (4-CP) in aqueous titanium dioxide suspensions has been studied and compared for two different catalysts: Sachtleben Hombikat UV 100 and Degussa P25. The influence of pH and initial 4-CP concentration on reaction rate and product distribution has been investigated in detail. Regarding the initial 4-CP concentration, the degradation kinetics formally can be discribed bg a Langmuir-Hinshelwood expression. While the degradation of 4-CP itself is hardly influenced by the pH, the overall mineralization rate (measured in terms of total organic carbon reduction changes considerably, decreasing strongly at pH > 7. With P25 used as the photocatalyst the mineralization of 4-CP is slightly faster than that with Hombikat UV 100, but smaller concentrations and. numbers oi intermediates are detected in the latter case. Most of the intermediates observed during this photocatalytic degradation process are identical with those identified during direct photolysis. In acidic solution (pH 3) hydroquinone and benzoquinone are the only intermediates when Hombikat UV 100 is the photocatalyst. Using P25 as a photocatalysts, seven additional intermediates, namely hydroxyhydroquinone, hydroxybenzoquinone, phenol, 4-chlorocatechol, 4-hydroxyphenylbenzoquinone, 2,5,4'-trihydroxybiphenyl, and 5-chloro-2,4'-dihydroxybiphenyl, were found. Hydroquinone (HQ) and benzoquinone (BQ) have bet li found to be the main intermediates of the photocatalytic 4-CP degradation. It could be shown that the HQ/BQ photosystem acts as an electron relay which effectively short circuits the photocatalyst resulting in a reduced efficiency of the degradation of 4-CP and most probably other aromatic compounds. An electron shuttle mechanism is proposed to explain Une highly efficient short circuiting of the photocatalyst in the presence of these compounds. A degradation mechanism for a-chlorophenol is proposed and discussed to account in particular for the pH dependence of the 4-CP degradation.