γ-Radiation synthesis of ultrasmall noble metal (Pd, Au, Pt) nanoparticles embedded on boron nitride nanosheets for high-performance catalysis

The large-scale synthesis and the stabilization of noble metal nanocatalysts with ultrasmall sizes are crucial to their practical application. Herein, Pd, Au, and Pt nanoparticles (NPs) are in situ embedded on boron nitride nanosheets (BNNSs) via the reduction of precursor salts induced by Co-60 gamma-irradiation, which is a mature technique widely used in industry. The reduction mechanism was elucidated by pulse radiolysis experiments. In comparison with other BN substrates like hexagonal BN (h-BN), BNNSs had not only large surface area of 263 m(2) g(-1), but also abundant hydroxyl groups produced during the sonicated exfoliation, resulting in ultrasmall sizes, large loading amounts, and uniform distribution of the anchored NPs. The particle sizes of the loaded Pd, Au, and Pt NPs were measured to be 2.9, 3.1, and 3.0 nm, respectively. As a consequence, in the model reaction of 2-nitroaniline reduction, the Pd-, Au- and Pt-BNNSs composite nanocatalysts showed much higher catalytic activities than those composites loading the corresponding NPs on other BN substrates. Particularly, most of the 2-nitroaniline could be reduced within merely 40 s when using Pd-BNNSs as catalysts, performing a rate constant of 1.1 x 10(-1) s(-1). The number of hydroxyl groups on BNNSs support as well as the catalytic performance of the corresponding NPs-loaded BNNSs composites could be improved by extending the sonicated exfoliation time, because more NPs were loaded and the hydroxyl groups were also proved to play an important role in enhancing the catalytic activity. Moreover, Pd-BNNSs catalysts still displayed prominent activity even after five cycles owing to the high stability of BNNSs and their strong affinity for PdNPs. This work not only demonstrates BNNSs as ideal supports to load noble metal NPs for catalysis, but also reveals the feasibility to synthesize and in situ embed ultrasmall noble metal NPs on BNNSs via gamma-irradiation.