Ligand-Exchange Assisted Formation of Au/TiO₂ Schottky Contact for Visible-Light Photocatalysis

Abstract

Plasmonic noble metal nanoparticles have emerged as a promising material in sensitizing wide-bandgap semiconductors for visible-light photocatalysis. Conventional methods in constructing such heterocatalysts suffer from either poor control over the size of the metal nanoparticles or inefficient charge transfer through the metal/semiconductor interface, which limit their photocatalytic activity. To solve this problem, in this work we construct Au/TiO2 photocatalysts by depositing presynthesized colloidal Au nanoparticles with well-controlled sizes to TiO2 nanocrystals and then removing capping ligands on the Au surface through a delicately designed ligand-exchange method, which leads to close Au/TiO2 Schottky contact after a mild annealing process. Benefiting from this unique synthesis strategy, the obtained photocatalysts show superior activity to conventionally prepared photocatalysts in dye decomposition and water-reduction hydrogen production under visible-light illumination. This study not only opens up new opportunities in designing photoactive materials with high stability and enhanced performance for solar energy conversion but also provides a potential solution for the well-recognized challenge in cleaning capping ligands from the surface of colloidal catalyst nanoparticles.

Integration of Multiple Plasmonic and Co-Catalyst Nanostructures on TiO2 Nanosheets for Visible-Near-Infrared Photocatalytic Hydrogen Evolution

“…[ 33 ] With 3-mercaptopropionic acid (MPA) as an intermediate ligand, the original capping agent cetyltrimethylammounium bromide (CTAB) on the synthesized Au nanocubes can be replaced by the MPA due to the strong interaction of MPA with both Au and TiO 2 through its thiol and carboxylic groups, respectively. When the mixed aqueous suspension of Au nanocubes and TiO 2 nanosheets is sonicated with the MPA solution, the Au nanocubes can be deposited on TiO 2 nanosheets through the linkage of MPA, forming a hybrid structure (namely, Au cube-TiO 2 ) ( Figure 1 a).…”

“…The deposition was achieved through a ligand-exchange method, in which the CTAB on Au nanocubes was replaced by the intermediate ligand 3-MPA. [ 33 ] In brief, 20 mg of TiO 2 nanosheets were dispersed in 50 mL of an aqueous solution containing 50 µL of NH 3 ·H 2 O (28%) and 50 µL of MPA by sonication. Then 5 mL aqueous suspension (0.6 mg mL -1 ) of Au nanocubes was added under sonication for 10 min.…”

Solar-Powered Plasmon-Enhanced Heterogeneous Catalysis

“…Indeed, besides serving as a plasmonic carrier collector, the semiconductor has intrinsic physico-chemical surface properties (e.g., acidbase character, hydration extent) that influence both the selectivity and final reaction yield. In addition, important parameters usually considered in traditional catalysis such as metal loading and strong metal-support interaction ( Figure 5A) can be conveniently exploited to increase plasmonic field enhancement [103,104].…”

Metal oxide semiconducting interfacial layers for photovoltaic and photocatalytic applications

“…Au/TiO 2 photocatalysts prepared by depositing presynthesized colloidal Au nanoparticles onto TiO 2 nanocrystals of precisely controlled size and morphology through a delicately designed ligand-exchange method resulted in Au/TiO 2 Schottky contact with low energetic charge transfer barrier. The photocatalysts thus obtained by this strategy showed superior activity compared to conventionally prepared photocatalysts in dye decomposition under visible-light illumination [195]. Figure 18 shows that the rate of decomposition of the dye is significantly higher than that of the commercial/pure TiO 2 NPs.…”