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 TiO(2) 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 NaBH(4) reduction of Au(III) complex ions on TiO(2)–Pt. Our method enables the deposition of small Au NPs with a narrow size distribution (average size: 2.5 nm) on the TiO(2) surface in TiO(2)–Pt (Au/TiO(2)–Pt). The separate deposition was rationalized in terms of the regioselective chemisorption of Au(III) complex ions on the surface of TiO(2) by measuring the Au(III) complex ion adsorption. • The chemisorption and subsequent NaBH(4) reduction of Au(III) complex ions on TiO(2)-Pt led to the deposition of small Au NPs with a narrow size distribution on the TiO(2) surface of TiO(2)-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 TiO(2) 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.