Single-molecule and -particle probing crystal edge/corner as highly efficient photocatalytic sites on a single TiO ₂ particle

Abstract

The exposed active sites of semiconductor catalysts are essential to the photocatalytic energy conversion efficiency. However, it is difficult to directly observe such active sites and understand the photogenerated electron/hole pairs’ dynamics on a single catalyst particle. Here, we applied a quasi-total internal reflection fluorescence microscopy and laser-scanning confocal microscopy to identify the photocatalytic active sites at a single-molecule level and visualized the photogenerated hole–electron pair dynamics on a single TiO2 particle, the most widely used photocatalyst. The experimental results and density functional theory calculations reveal that holes and electrons tend to reach and react at the same surface sites, i.e., crystal edge/corner, within a single anatase TiO2 particle owing to the highly exposed (001) and (101) facets. The observation provides solid proof for the existence of the surface junction “edge or corner” on single TiO2 particles. These findings also offer insights into the nature of the photocatalytic active sites and imply an activity-based strategy for rationally engineering catalysts for improved photocatalysis, which can be also applied for other catalytic materials.

Well-defined Cu2O photocatalysts for solar fuels and chemicals

“…Singleparticle single-molecule uorescence photocatalysis could be a suitable tool for on-site observation of interfacial chemical reactions involving charge carriers and reactive oxygen species (ROS), such as singlet oxygen and the hydroxyl radicals, generated by the photoexcitation of semiconductor nanocrystals. 101,102 Such studies conrmed that the presence of anisotropic facets can be benecial to obtaining efficient spatial charge separation. Using the small sized Cu 2 O crystals with anisotropic facets remains a challenge.…”

Facet Junction Engineering for Photocatalysis: A Comprehensive Review on Elementary Knowledge, Facet‐Synergistic Mechanisms, Functional Modifications, and Future Perspectives

“…[68] Furthermore, the exposed active sites of decahedral TiO 2 are also essential to the photocatalytic performance. Recently, a quasi-total internal reflection fluorescence (TIRF) microscopy and laser-scanning confocal microscopy were applied to directly observe the active sites on a decahedral TiO 2 anatase co-enclosed with {001} and {101} facets, [17] which provides solid proof for the existence of the surface junction "edge or corner" on single decahedral TiO 2 particles. In this experiment, the researchers have first carried out the single particle spectroscopic measurements to the electron transfer and photoluminescence (PL) lifetime in a single decahedral TiO 2 particle, thus the PL lifetime mapping of a single decahedral TiO 2 particle can be obtained, in which the color change stand for different lifetimes of different locations in this individual particle.…”

“…Consequently, this should be considered in future studies within this field, and a good inspiration has been given in Ref. [17]. Anyhow, the development of diversified facet junctions is an exciting way to improve the photocatalytic performance of single-crystalline photocatalysts.…”

“…[7] Since then, semiconductorbased photocatalysis have emerged and been utilized because of the formation of photogenerated charge carriers (electron-hole pairs) for participating in photochemical redox reactions. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] A typical photocatalytic process involves three main steps. [26] Initially, photoinduced electrons are generated by exciting them from the valence band (VB) of a semiconductor photocatalyst to the conduction band (CB) when the solar energy absorbed is greater than the band gap (E g ).…”

Single‐Molecule Fluorescence Imaging of Nanocatalysis

“…[ 51 ] It is essential to clarify the mechanisms for the high‐photocatalytic activities of anatase TiO 2 particles, which would be crucial for rationally engineering other catalysts. Recently, by using the single‐particle confocal fluorescence and TIRF microscopes, Majima group [ 52 ] identified the distribution of active sites on single TiO 2 nanoparticles at single‐molecule level. First, single particle photoluminescence (PL) measurements were carried out to probe the electron transfer and PL lifetime in a single anatase TiO 2 with (001) and (101) facets.…”