Department of Chemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
Nano Lett. 2016 May 11;16(5):3399-407. doi: 10.1021/acs.nanolett.6b01373. Epub 2016 Apr 15.
The activation energy of a catalytic reaction serves not only as a metric of the efficacy of a catalyst but also as a potential indicator of mechanistic differences between the catalytic and noncatalytic reaction. However, activation energies are quite underutilized in the field of photocatalysis. We characterize in detail the effect of visible light excitation on the activation enthalpy of an electron transfer reaction photocatalyzed by plasmonic Au nanoparticles. We find that in the presence of visible light photoexcitation, the activation enthalpy of the Au nanoparticle-catalyzed electron transfer reaction is significantly reduced. The reduction in the activation enthalpy depends on the excitation wavelength, the incident laser power, and the strength of a hole scavenger. On the basis of these results, we argue that the activation enthalpy reduction is directly related to the photoelectrochemical potential built-up on the Au nanoparticle under steady-state light excitation, analogous to electrochemical activation. Under optimum light excitation conditions, a potential as high as 240 mV is measured. The findings constitute more precise insights into the mechanistic role and energetic contribution of plasmonic excitation to chemical reactions catalyzed by transition metal nanoparticles.
催化反应的活化能不仅可以作为衡量催化剂效率的指标，还可以作为催化反应和非催化反应之间的机制差异的潜在指标。然而，在光催化领域，活化能的应用还相当有限。我们详细描述了等离子体 Au 纳米粒子光催化电子转移反应中可见光激发对活化焓的影响。我们发现，在可见光光激发的存在下，Au 纳米粒子催化的电子转移反应的活化焓显著降低。活化焓的降低取决于激发波长、入射激光功率和空穴清除剂的强度。基于这些结果，我们认为活化焓的降低与稳态光激发下 Au 纳米粒子上建立的光电化学势直接相关，类似于电化学活化。在最佳的光激发条件下，测量到高达 240 mV 的电势。这些发现为理解等离子体激发在过渡金属纳米粒子催化的化学反应中的机械作用和能量贡献提供了更精确的认识。
