Switching a Plasmon-Driven Reaction Mechanism from Charge Transfer to Adsorbate Electronic Excitation Using Surface Ligands
Switching a Plasmon-Driven Reaction Mechanism from Charge Transfer to Adsorbate Electronic Excitation Using Surface Ligands
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DOI：
10.1021/acs.jpcc.0c07479
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发表时间：
2020-10-15
影响因子：
3.7
通讯作者：
Habteyes, Terefe G.
中科院分区：
文献类型：
--
作者：
Kookhaee, Hamed;Tesema, Tefera E.;Habteyes, Terefe G.
了解在金属表面选择性产生所需产物的光催化反应条件是多相催化领域一个长期存在的研究问题。本文以等离子体增强的亚甲基蓝（MB） n-去甲基化反应为模型反应，研究人员发现，通过将机制从电荷转移（CT）转换为吸附电子激发（AEE），可以实现高度的产物选择性。当金纳米颗粒表面存在十六烷基三甲基溴化铵（CTAB）配体时，MB在与吸附质电子跃迁重叠的633 nm激发波长下选择性转化为硫氨酸。AEE机制涉及近场增强的MB吸附质的分子内电子激发，CTAB的存在有利于这一机制，CTAB通过分子偶极子沿驱动表面场定向增加吸附质的激发速率，并通过减缓吸附物到金属的能量转移延长激发态的寿命。另一方面，当MB直接吸附在纳米颗粒上时，其机制涉及电子转移，可能导致阴离子络合物的形成。原位表面增强拉曼散射光谱表明，该配合物在长激发波长（808和785 nm）下保持稳定，而在短波长（671,633和561 nm）下，它可能发生非选择性n -去甲基化，产生除硫氨酸外的部分去甲基化衍生物。这些实验结果强调了吸附条件在确定等离子体增强光催化反应机理中的重要性。
Understanding photocatalytic reaction conditions that selectively leads to a desired product on metal surfaces is a longstanding research problem in heterogeneous catalysis. Here, using plasmon-enhanced N-demethylation of methylene blue (MB) as model reaction, we show that a high degree of product selectivity can be achieved by switching the mechanism from charge transfer (CT) to adsorbate electronic excitation (AEE). In the presence of a cetyl trimethyl ammonium bromide (CTAB) surface ligand on gold nanoparticles, MB is selectively transformed to thionine at a 633 nm excitation wavelength that overlaps with the electronic transition of the adsorbate. The AEE mechanism involves near-field-enhanced intramolecular electronic excitation of the MB adsorbate, and this mechanism is favored by the presence of CTAB that appears to increase the rate of adsorbate excitation by orienting the molecular dipole along the driving surface field and to prolong the lifetime of the excited state by slowing down adsorbate-to-metal energy transfer. On the other hand, when MB is directly adsorbed on the nanoparticles, the mechanism involves electron transfer that may lead to the formation of an anionic complex. In situ surface-enhanced Raman scattering spectra suggest that the complex remains stable at long excitation wavelengths (808 and 785 nm), while at shorter wavelengths (671, 633, and 561 nm), it may undergo nonselective N-demethylation, yielding partially demethylated derivatives in addition to thionine. These experimental observations underscore the importance of adsorption condition in determining the mechanism of plasmon-enhanced photocatalytic reactions.