Humboldt-Universität zu Berlin , Department of Chemistry and School of Analytical Sciences Adlershof (SALSA) , Brook-Taylor-Straße 2 , 12489 Berlin , Germany.
BAM Federal Institute for Materials Research and Testing , Richard-Willstätter-Straße 11 , 12489 Berlin . Germany.
Anal Chem. 2018 Aug 7;90(15):9199-9205. doi: 10.1021/acs.analchem.8b01701. Epub 2018 Jul 13.
The characterization of a catalyst often occurs by averaging over large areas of the catalyst material. On the other hand, optical probing is easily achieved at a resolution at the micrometer scale, specifically in microspectroscopy. Here, using surface-enhanced Raman scattering (SERS) mapping of larger areas with micrometer-sized spots that contain tens to hundreds of supported gold nanoparticles each, the photoinduced dimerization of p-aminothiophenol (PATP) to 4,4'-dimercaptoazobenzene (DMAB) was monitored. The mapping data reveal an inhomogeneous distribution of catalytic activity in the plasmon-catalyzed reaction in spite of a very homogeneous plasmonic enhancement of the optical signals in SERS. The results lead to the conclusion that only a fraction of the nanostructures may be responsible for a high catalytic activity. The high spot-to-spot variation in catalytic activity is also demonstrated for DMAB formation by the plasmon-catalyzed reduction from p-nitrothiophenol (PNTP) and confirms that an improvement of the accuracy and reproducibility in the characterization of catalytic reactions can be achieved by microspectroscopic probing of many positions. Using SERS micromapping during the incubation of PATP, we demonstrate that the reaction occurs during the incubation process and is influenced by different parameters, leading to the conclusion of dimerization in a gold-catalyzed, nonphotochemical reaction as an alternative to the plasmon-catalyzed process. The results have implications for the future characterization of new catalyst materials as well as for optical sensing using plasmonic materials.
催化剂的特性通常是通过对催化剂材料的大面积进行平均来实现的。另一方面，光学探测很容易在微米级分辨率下实现，特别是在微光谱学中。在这里，我们使用表面增强拉曼散射（SERS）对具有微米大小斑点的较大区域进行映射，每个斑点包含数十到数百个负载的金纳米粒子，从而监测对氨基苯硫酚（PATP）光诱导二聚化为 4,4'-二巯基偶氮苯（DMAB）的过程。尽管 SERS 中光学信号的等离子体增强非常均匀，但映射数据显示在等离子体催化反应中存在催化活性的不均匀分布。结果得出的结论是，只有一小部分纳米结构可能对高催化活性负责。通过等离子体催化还原对硝基苯硫酚（PNTP）形成 DMAB 也证明了催化活性的高斑点间变化，并证实通过对许多位置进行微光谱探测，可以提高催化反应特性的准确性和重现性。在 PATP 的孵育过程中使用 SERS 微映射，我们证明反应发生在孵育过程中，并受到不同参数的影响，导致金催化的非光化学反应中的二聚化结论，作为等离子体催化过程的替代方法。这些结果对未来新型催化剂材料的特性以及使用等离子体材料进行光学传感具有重要意义。
