Creation of High‐Performance Heterogeneous Photocatalysts by Controlling Ligand Desorption and Particle Size of Gold Nanocluster

Abstract

Recently, the creation of new heterogeneous catalysts using the unique electronic/geometric structures of small metal nanoclusters (NCs) has received considerable attention. However, to achieve this, it is extremely important to establish methods to remove the ligands from ligand‐protected metal NCs while preventing the aggregation of metal NCs. In this study, the ligand‐desorption process during calcination was followed for metal‐oxide‐supported 2‐phenylethanethiolate‐protected gold (Au) 25‐atom metal NCs using five experimental techniques. The results clearly demonstrate that the ligand‐desorption process consists of ligand dissociation on the surface of the metal NCs, adsorption of the generated compounds on the support and desorption of the compounds from the support, and the temperatures at which these processes occurred were elucidated. Based on the obtained knowledge, we established a method to form a metal‐oxide layer on the surface of Au NCs while preventing their aggregation, thereby succeeding in creating a water‐splitting photocatalyst with high activity and stability.

Development and Functionalization of Visible-Light-Driven Water-Splitting Photocatalysts

“…Considering the mechanism of water-splitting photocatalysis ( Figure 3 ), researchers in the fields of catalytic chemistry, ceramic (semiconductor) materials chemistry, electrochemistry, metal NP/nanocluster (NC) chemistry [ 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 ], surface spectroscopy [ 69 , 70 , 71 ], and theoretical chemistry [ 72 ] must be employed to create highly functional Vis-light-driven water-splitting photocatalysts. Actually, we specialize in the chemical composition/structure control of metal NCs and have succeeded in enhancing the functionality of some UV-light-driven water-splitting photocatalysts by applying these techniques to water-splitting photocatalysts [ 73 , 74 , 75 , 76 , 77 , 78 , 79 ]. However, for researchers in metal NP/NC chemistry, surface spectroscopy, and theoretical chemistry, among other fields, to participate in this field, new reviews that summarize previous reports on water-splitting photocatalysis seem to be needed.…”

Glutathione Disulfide as a Reducing, Capping, and Mass-Separating Agent for the Synthesis and Enrichment of Gold Nanoclusters

“…For sensitive detection, additional strategies are often employed, such as lanthanide ion-induced enhancement [12], two-photon excited photoluminescence [13], and even enrichment of the nanoclusters [14]. In fact, enrichment is an indispensable step in the applications where high-concentration nanoclusters are needed, e.g., catalysis [15][16][17], therapy [18,19], and electronic and optical industries [20][21][22][23][24]. A number of concentration methods can potentially be used for this purpose, for instance, ultracentrifugation, ultrafiltration, reduced-pressure evaporation, chromatography, centrifugation, nanofluidic system,…”

Synthesis of active, robust and cationic Au25 cluster catalysts on double metal hydroxide by long-term oxidative aging of Au25(SR)18

“…22 The most conventional pretreatment is removal of the ligands by calcination in vacuum. 23–34 For example, thiolates (RS − ) are desorbed from Au x (SR) y by heating them at a temperature (>250 °C) higher than that required for the powder form of Au x (SR) y (∼200 °C). 27–34 The desorption processes and the structures of the resulting clusters have been studied intensively using a variety of methods including thermogravimetric analysis, mass spectrometry, transmission electron microscopy (TEM), theoretical calculation, and X-ray absorption spectroscopy (XAS).…”

“…23–34 For example, thiolates (RS − ) are desorbed from Au x (SR) y by heating them at a temperature (>250 °C) higher than that required for the powder form of Au x (SR) y (∼200 °C). 27–34 The desorption processes and the structures of the resulting clusters have been studied intensively using a variety of methods including thermogravimetric analysis, mass spectrometry, transmission electron microscopy (TEM), theoretical calculation, and X-ray absorption spectroscopy (XAS). One of the limitations of this approach is that the density of supported clusters has to be suppressed (<0.2 wt% loading and/or use of supports with high surface area) to avoid thermal-induced aggregation of the clusters (Scheme 1).…”