Plasmon-generated hot holes for chemical reactions
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BSTRACT Plasmonic nanostructures have been widely used for photochemical conversions due to their unique and easy-tuning optical properties in visible and near-infrared range. Compared with the plasmon-generated hot electrons, the hot holes usually have a shorter lifetime, which makes them more difficult to drive redox reactions. This review focuses on the photochemistry driven by the plasmon-generated hot holes. First, we discuss the generation and energy distribution of the plasmon-generated hot carriers, especially hot holes. Then, the dynamics of the hot holes are discussed at the interface between plasmonic metal and semiconductor or adsorbed molecules. Afterwards, the utilization of these hot holes in redox reactions is reviewed on the plasmon-semiconductor heterostructures as well as on the surface of the molecule-adsorbed plasmonic metals. Finally, the remaining challenges and future perspectives in this field are presented. This review will be helpful for further improving the efficiency of the photochemical reactions involving the plasmon-generated hot holes and expanding the applications of these hot holes in varieties of chemical reactions, especially the ones with high conversion rate and selectivity.
KEYWORDS surface plasmon, hot hole, photochemistry, photocatalysis
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Introduction
Solar energy harvesting is one of the most important ways for solving the global problems of energy crisis and environment pollution [1–4]. Photochemical conversion is one of the effective pathways, which could produce not only energy but also chemical compounds that are useful in modern industry [5]. In nature, plants do this at any moment; however, it is still necessary to realize similar process in artificial photosynthesis. Fujishima and Honda first realized the water splitting under solar illumination by using titanium dioxide (TiO2) as photocatalyst [6]. Since then, many semiconductor-based photocatalysts have been developed for photochemical reactions [7, 8]. However, these semiconductor catalysts are usually limited by the large band gap (only ultraviolet and short wavelength visible light could be utilized) and the poor photo or chemical stability. In order to utilize the visible and near infrared light (which account for majority of the solar energy), it is promising to develop new photocatalysts or strategies for more efficient photosynthesis. Surface plasmons (SPs), the collective oscillation of free electrons occurred in nanostructures of metals or heavily doped semiconductors, have attracted much attention in the fields of medicine [9], biology [10, 11], and sensing [12, 13]. Due to the surface plasmon resonance, a molecule or nanoparticle in the vicinity of plasmonic metal experiences a much higher absorption coefficient in a large wavelength range, which could in principal introduce a much more efficient photochemical conversion. Moreover, when plasmonic metal forms a heterostructure with a semiconductor, the light absorption could be further broadened due to the synergistic effect between these Address cor
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