Regioselective chemisorption-induced separate deposition of two types of metal nanoparticles on TiO 2 .

The discovery of the excellent thermal catalytic activity of Au nanoparticles (NPs) for CO oxidation (Haruta et al., 1987 [1]) triggered intensive research on thermal and visible photo-catalysis based on these NPs (Ref. [2]). Recently, catalysts containing two types of metal NPs loaded onto a TiO2 support, i.e., NPs consisting of a separate Au photocatalyst (average size: 13 nm) and another noble metal, were developed as highly efficient visible photocatalysts for several important chemical reactions (Tanaka et al., 2013 [3]). Although the visible photocatalytic activities of Au NPs increase as their particle size decreases (Teranishi et al., 2016 [4]), small Au NPs with a narrow size distribution could not be deposited previously because these NPs underwent dissolution and redeposition (Tanaka et al., 2013 [3]). Additionally, little is known about the mechanism of separate deposition. Herein we report a new method involving the chemisorption and subsequent NaBH4 reduction of Au(III) complex ions on TiO2 -Pt. Our method enables the deposition of small Au NPs with a narrow size distribution (average size: 2.5 nm) on the TiO2 surface in TiO2 -Pt (Au/TiO2 -Pt). The separate deposition was rationalized in terms of the regioselective chemisorption of Au(III) complex ions on the surface of TiO2 by measuring the Au(III) complex ion adsorption. •The chemisorption and subsequent NaBH4 reduction of Au(III) complex ions on TiO2 -Pt led to the deposition of small Au NPs with a narrow size distribution on the TiO2 surface of TiO2 -Pt. These NPs differ from those obtained by using the existing CPH method, which produced Au NPs with a large particle size and a wide size distribution.•The separate deposition was rationalized in terms of the regioselective chemisorption of Au(III) complex ions on the TiO2 surface, although the mechanism of the CPH method was not disclosed.•Further application of the regioselective chemisorption-induced separate deposition may enable the development of new catalysts.