Plasmonic metal-semiconductor heterostructures for hot-electron-driven photochemistry
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he conversion of renewable solar energy to chemical energy represents a promising strategy to reduce current reliance on fossil fuels. The efficient utilization of solar energy in chemical transformations requires photocatalysts to strongly absorb light in the visible region (which constitutes 42% of solar radiation).1 Plasmonic metal nanoparticles (NPs) (e.g., Au, Ag, and Cu) possess broad absorption across the whole visible region, a quality that attracts tremendous scientific interest in photochemistry.2–6 Such capability originates from the unique optical property called surface plasmon resonance (SPR),7 which can be understood as a coherent oscillation of conduction electrons induced by incident light when the frequency of the light matches the intrinsic resonant frequency of the plasmonic metal NPs.8,9 The SPR excitation consequently generates an intense localized electromagnetic (EM) field on plasmonic metal NPs, which in turn amplifies the absorption of light at the same frequency.8,9 Upon SPR excitation, the oscillation of conduction electrons quickly decays to generate hot electrons that play essential roles in prompting photochemical reactions.2,3 However, it is challenging for these hot electrons to directly drive chemical reactions on the surface of plasmonic metal NPs as there is a significant mismatch between the lifetimes of hot electrons (femtoseconds to nanoseconds) and the time scale of chemical
reactions (microseconds to seconds).2,3 In addition, the chemical inertness of plasmonic noble metals prevents them from facilitating a wider range of reactions.10 The development of plasmonic metal–semiconductor heterostructures offers a strategy for resolving these two limitations. In these heterostructures, Schottky barriers are formed at the plasmonic metal– semiconductor interface, which prolong the lifetime of hot electrons into the time scale of chemical reactions once they are transferred into semiconductors.11,12 Meanwhile, surface defects on semiconductors, such as oxygen vacancies, provide additional active sites to promote chemical reactions by simultaneously functioning as trapping sites for hot electrons and adsorption sites of reactant molecules.13,14 This article focuses on recent progress in using plasmonic metal–semiconductor heterostructures for hot-electron-driven photochemistry. We begin by summarizing the application of plasmonic heterostructures using oxides as substrates in photochemistry, including the most commonly used modification strategies for improving the performance of these heterostructures. Subsequent sections describe other types of semiconductors, such as two-dimensional (2D) materials and metal–organic frameworks (MOFs), as supports for plasmonic metal NPs. The article concludes with an outlook on potential directions in designing high-performing plasmonic metal–semiconductor heterostructures for hot-carrier-driven photochemistry.
Jiawei Huang, Department of Chemistry, University of Florida, USA; [email protected] Wenxiao Guo, Department of Chemistry, Universit
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