Kinetic Analysis of Catalytic Reduction of 4-Nitrophenol by Metallic Nanoparticles Immobilized in Spherical Polyelectrolyte Brushes
Kinetic Analysis of Catalytic Reduction of 4-Nitrophenol by Metallic Nanoparticles Immobilized in Spherical Polyelectrolyte Brushes
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DOI：
10.1021/jp101125j
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发表时间：
2010-05-20
影响因子：
3.7
通讯作者：
Ballauff, Matthias
中科院分区：
文献类型：
--
作者：
Wunder, Stefanie;Polzer, Frank;Ballauff, Matthias
研究了金属纳米粒子催化硼氢化钠还原对硝基苯酚的反应。纳米颗粒嵌入球形的聚苯乙烯刷中，该刷由聚苯乙烯核组成，在聚苯乙烯核上接枝有致密的阳离子聚苯乙烯刷层。纳米颗粒的平均尺寸约为2 nm。通过监测4-硝基苯酚的还原通过UV/VIS光谱得到的动力学数据可以解释的朗缪尔-欣谢尔伍德模型：硼氢化物离子转移的表面氢物种在一个可逆的方式到表面。伴随着4-硝基苯酚被吸附和速率决定步骤包括由表面氢物种的硝基苯酚的还原。因此，表观反应速率可以与纳米颗粒的总表面S、与速率决定步骤相关的动力学常数k以及分别与硝基苯酚和硼氢化物的吸附常数K-Nip和K-BH 4相关。在所有情况下，观察到诱导时间t（0）为分钟量级。由于1/（kt（0））与溶液中硝基苯酚的浓度之间存在线性关系，因此可以将诱导时间的倒数视为与表面反应动力学直接相关的反应速率。迄今为止获得的t（0）的所有数据以及与文献数据的比较表明，诱导时间与纳米颗粒的缓慢表面重构有关，其速率与表面反应直接相关。
We present a study on the catalytic reduction of 4-nitrophenol by sodium borohydride in the presence of metal nanoparticles. The nanoparticles are embedded in spherical polyelectrolyte brushes, which consist of a polystyrene core onto which a dense layer of cationic polyelectrolyte brushes are grafted. The average size of the nanoparticles is approximately 2 nm. The kinetic data obtained by monitoring the reduction of 4-nitrophenol by UV/vis-spectroscopy could be explained in terms of the Langmuir-Hinshelwood model: The borohydride ions transfer a surface-hydrogen species in a reversible manner to the surface. Concomitantly 4-nitrophenol is adsorbed and the rate-determining step consists of the reduction of nitrophenol by the surface-hydrogen species. The apparent reaction rate can therefore be related to the total surface S of the nanoparticles, to the kinetic constant k related to the rate-determining step, and to the adsorption constants K-Nip and K-BH4 of nitrophenol and of borohydride, respectively. In all cases, an induction time t(0) was observed of the order of minutes. The reciprocal induction time can be treated as a reaction rate that is directly related to the kinetics of the surface reaction because there is a linear relation between 1/(kt(0)) and the concentration of nitrophenol in the solution. All data obtained for t(0) so far and a comparison with data from literature indicate that the induction time is related to a slow surface reconstruction of the nanoparticles, the rate of which is directly related to the surface reaction.