Local Photochemical Nanoscopy of Hot-Carrier-Driven Catalytic Reactions Using Plasmonic Nanosystems

Abstract

Nanoscale investigation of the reactivity of photocatalytic systems is crucial for their fundamental understanding and improving their design and applicability. Here, we present a photochemical nanoscopy technique that unlocks the local spatial detection of molecular products during plasmonic hot-carrier-driven photocatalytic reactions with nanometric precision. By applying the methodology to Au/TiO 2 plasmonic photocatalysts, we experimentally and theoretically determined that smaller and denser Au nanoparticle arrays present lower optical contribution with quantum efficiency in hot-hole-driven photocatalysis closely related to the population heterogeneity. As expected, the highest quantum yield from a redox probe oxidation is achieved at the plasmon peak. Investigating a single plasmonic nanodiode, we unravel the areas where oxidation and reduction products are evolved with subwavelength resolution (∼200 nm), illustrating the bipolar behavior of such nanosystems. These results open the way to quantitative investigations at the nanoscale to evaluate the photocatalytic reactivity of low-dimensional materials in a variety of chemical reactions.

Interfacial States in Au/Reduced TiO2 Plasmonic Photocatalysts Quench Hot-Carrier Photoactivity

“…(2) The hot electrons with sufficient energy to overcome the Schottky barrier (ϕ B ) forming at the metal–semiconductor interface are injected into the TiO 2 CB, while the corresponding hot holes accumulate in the Au NPs. The hot electrons are driven away thanks to the conductive underlayer (ITO) and react/relax either in TiO 2 /ITO DSs/doping centers or through bipolar electrochemical behavior. , (3) The hot holes with sufficient energy at the Au NPs–electrolyte interface oxidize the molecular species surrounding the Au NPs. (4) The UME detects the oxidized species by electrochemically reducing them back.…”

“…In order to gain insights into this behavior, we quantified the wavelength-dependent photooxidation efficiency of the different TiO 2 films by retrieving the EQE. This was possible by calculating the substrate current thanks to a diffusion model, which enables the calculation of the collection efficiency (ratio between tip and substrate currents) . The obtained EQE corresponds to the generation rate of the photogenerated holes reacting at the interface (TiO 2 –electrolyte).…”

“…Herein, we demonstrate, through scanning photoelectrochemical microscopy (SPECM), the possibility of studying the impact of induced defects generated via mild treatments over ultrathin films (∼30 nm) on the plasmon-driven photooxidation of chemicals from a model plasmonic photocatalyst; i.e., Au NP arrays on TiO 2 films (Figure a). We chose Au-TiO 2 photocatalysts because of their well-referenced plasmonic and photochemical properties. ,− We recently reported that SPECM, combined with other scanning probe microscopy techniques, enables the local spatial detection and quantification of molecular products during plasmonic hot-carrier-driven photocatalytic reactions . To do so, we investigated different ultrathin films of TiO 2 (pristine and reduced) by SPECM correlating the applied reduction process to the external quantum efficiency (EQE) under sub-band-gap excitation (2.72, 2.34, 1.88, 1.67, and 1.45 eV).…”

That Table of Contents Image Looks Really Interesting: *Click*!

“…Perusing the most recent issue (12, 2023) of ACS Nano , I chose three ToC images that are graphically interesting and scientifically clear (Figure ). − Even without the title and abstract, each of these images tells the key story and theme of the publication and makes very good first impression to a potential reader. The text is large enough to read even on a mobile device, and uses a clear Arial or Helvetica typeface to enable fast comprehension.…”

“…Three ToC images chosen from the most recent issue of ACS Nano that clearly and succinctly summarize the theme of the respective papers. Chosen from references , , and .…”